HK1099288A - Metal complexes of n-heterocyclic carbenes as radiopharmaceuticals and antibiotics - Google Patents

Description

Statement regarding federally sponsored research or development of metal complexes of N-heterocyclic carbenes for use as radiopharmaceuticals and antibiotics

no marking

[0001] The invention is carried out under the support of government fund withdrawal, and the fund number is NIH R15 CA 96739-01; and fund No. NSF CHE-0116041. The government may have certain rights in the invention.

Background

[0002] The present invention relates to metal-containing, therapeutic, antimicrobial and antifungal compounds. More particularly, the present invention relates to metal complexes of N-heterocyclic carbenes and their use as antimicrobial, antifungal and radiopharmaceutical compositions.

[0003] Silver has long been used for its antimicrobial properties. This use is earlier than scientific or medical understanding of its mechanism. For example, ancient greeks and romans use silver coins to maintain the purity of water. Silver is still used today by the national space and aviation administration (NASA) in its space shuttle for the same purpose. Silver nitrate was used to treat many medical conditions before 1800 years. Today, 1% silver nitrate solutions are still widely used to prevent gonococcal ophthalmia (gonorrheal opthalmia) after birth of infants. Since at least the late 19 th century, silver has been administered in many different forms to treat and prevent many types of bacterial related ailments.

[0004] Other treatments, such as applying silver foil to post-operative wounds to prevent infection, have remained as a medical practice in europe for the 80's of the 20 th century, and silver nitrate has still been used as a topical antimicrobial. In the 60's of the 20 th century, a very successful silver complex for burn treatment, silver sulfadiazine (silver sulfadiazine), was developed and is shown in formula 1 below. Known commercially as Silvadene ® Cream 1%, this complex has been one of the most effective treatments for preventing second and third degree burn infections. Silver sulfadiazine has been shown to have excellent antimicrobial properties against many gram-positive and gram-negative bacteria. It is believed that the slow release of silver in the wound area of the epidermis is responsible for the healing process. Studies on surgically injured mice have shown the effectiveness of silver nitrate and silver sulfadiazine to aid in the healing process. Although the complete mechanism of these phenomena is not yet understood, inflammation and granulation of the wound is reduced by the use of these common silver antimicrobials.

1 Sulfadiazine silver

[0005] The recently developed silver coating technology has led to the creation of burn dressings known as Acticoat. The purpose of this dressing is to avoid sticking to the wound while providing an anti-infective barrier. Some clinical trials have also demonstrated that the dressing can be easily removed compared to conventional wound dressings treated with silver nitrate. Acticoat has been shown to increase antimicrobial function over silver nitrate and sulfadiazine silver. Acticoat consists of nanocrystalline silver particles. Antibiotic resistant strains have developed resistance to silver nitrate and sulfadiazine silver, but not to nanocrystalline silver. The broader range of activity of nanocrystalline silver is apparently due to the release of silver cations and uncharged silver species. Due to the emergence of antibiotic resistant strains of infectious agents (infectious agents), there is a need for new antibiotics.

[0006] In other therapeutic applications, metal compounds also play an important role. Examples of the usefulness of metals can be seen in the field of radiopharmaceuticals. The use of radiation therapy to destroy tumor cells is well known, but tumors can be reproduced after treatment. Hypoxic cells (hypoxiccell) within a tumor are 2.5 to 3 times more resistant to X-ray radiation than other tumor cells. Therefore, these cells are more likely to survive radiation therapy or chemotherapy and cause the tumor to reappear. Targeting radionuclides to hypoxic cells would serve as a means of making them visible.

[0007]Gamma-ray emitters, e.g.⁹⁹Tc complexes are particularly useful as imaging agents, and therapeutic radiopharmaceuticals such as 89^Sr、¹⁵³Sm、¹⁸⁶Re and¹⁶⁶ho is important in the treatment of bone tumors. Rh-105 emits 319keV (19%) gamma rays that allow for tracking in vivo and dosimetry calculations. By using the entire periodic table, many more radioactive nuclei can be utilized to construct diagnostic or therapeutic agents.

[0008] The effectiveness of the complex of the radiometal is highly dependent on the nature of the chelating ligand. Successful metallodrugs must both target specific tissues or organs and be rapidly cleared from other tissues. In addition, for imaging and tumor therapy, the target organ or tissue must have optimal exposure to the radiopharmaceutical. Thus, there is a need for new ligand systems designed for binding radioactive metals.

Summary of The Invention

[0009] Although some N-heterocyclic carbene metal complexes (metal complex of N-heterocyclic carbene complexes) have been previously known, the use of N-heterocyclic carbene silver complexes as antimicrobial agents has not been recognized. Also, it has not been recognized that complexes of N-heterocyclic carbenes and radiometals can be used as radiopharmaceuticals. Strong chelating ligands, such as the chelated N-heterocyclic carbenes described herein, may provide an alternative, more advantageous route for producing radiopharmaceutical complexes.

[0010] Accordingly, it is an aspect of the present invention to provide a method of inhibiting the growth of a microorganism. Microbial growth is inhibited by exposing the microorganism to a silver complex of an N-heterocyclic carbene (silver complex of an N-heterocyclic carbene).

[0011] It is also an aspect of the present invention to provide a method of treating cancer cells. Cancer cells are treated by exposing the cancer cells to a complex of an N-heterocyclic carbene and a radioactive metal. It is therefore also an aspect of the present invention to provide novel N-heterocyclic carbenes which are useful as antimicrobial agents when complexed with silver, and as radiopharmaceuticals when complexed with radioactive metals.

[0012] It is a further aspect of the present invention to provide a method of synthesizing a radiopharmaceutical. It is also an aspect of the present invention to provide a method of synthesizing antimicrobial compounds.

[0013] At least one or more of the above aspects and advantages thereof over known techniques related to the treatment of infections, which will be apparent from the description that follows, are achieved by the invention described and claimed herein.

[0014] In general, the present invention provides a method for inhibiting microbial or fungal growth comprising the step of administering an effective amount of a silver complex of an N-heterocyclic carbene.

[0015] The present invention also provides an N-heterocyclic carbene represented by the formula:

wherein Z is a heterocyclic group; r₁And R₂The method comprises the following steps: independently or in combination hydrogen or C₁-C₁₂Organic radical, C₁-C₁₂The organic group is selected from the group consisting of alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl, arylalkyl (arylalkyl), alkylaryl (alkylaryl), heterocycle, alkoxy, and substituted derivatives thereof.

[0016] The present invention also provides a method for synthesizing a radiopharmaceutical compound, comprising the steps of: reacting an imidazolium salt (imidazolium salt) with a transition metal complex or base to form an N-heterocyclic carbene; and reacting the N-heterocyclic carbene with a metal to form a metal complex.

[0017] The present invention also provides a method for synthesizing an antibiotic compound, comprising: reacting the imidazolium salt with a transition metal or base to form an N-heterocyclic carbene; and reacting the N-heterocyclic carbene with a silver compound to form a silver complex having the N-heterocyclic carbene.

[0018] The invention also provides a method for treating cancer cells comprising the step of administering an effective amount of a complex of an N-heterocyclic carbene and a radiometal.

[0019] The invention also provides a method of generating an image of one or more tissues in a patient comprising the step of administering an effective amount of a complex of an N-heterocyclic carbene and a radioactive metal.

[0020] The present invention also provides a nanofiber comprising: fiber-forming materials (fiber-forming materials); and metal complexes of N-heterocyclic carbenes.

[0021] The invention also provides radiopharmaceutical compounds comprising radiometal complexes of N-heterocyclic carbenes.

[0022] The present invention also provides a method for treating a cancerous tumor comprising the steps of: administering an effective amount of a radiometal complex of an N-heterocyclic carbene.

[0023] The invention also provides a method as claimed in claim 28, wherein the radioactive metal is an element selected from the group consisting of transition metals, lanthanides and actinides.

Detailed Description

[0024] In this specification and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0025]The present invention includes metal complexes of N-heterocyclic carbenes, methods of production and methods of use thereof. Several general types of N-heterocyclic carbene ligands may be used as ligands for metals such as silver. These include monodentate carbenes such as those represented by formula 2, bidentate carbenes such as those represented by formulae 3-5, and bidentate macrocyclic carbenes such as those represented by formulae 6 and 7. In addition to monodentate carbenes, each of these ligand types has as its basic constituent two N-heterocyclic carbene units which are bridged either by a methylene group as in formula 3, a dimethylpyridyl group as in formula 4 and a dimethylpyrrolyl group as in formula 5, or are part of a ring as in formulae 6 and 7. Can be prepared by reacting at R₁And R₂The changes in (a) modify the water solubility, stability, charge and lipophilicity of these N-heterocyclic carbene silver complexes. Each R₁And R₂May, separately or in combination, be selected from hydrogen, C₁-C₁₂Alkyl radical, C₁-C₁₂Substituted alkyl, C₁-C₁₂Cycloalkyl radical, C₁-C₁₂Substituted cycloalkyl, C₁-C₁₂Alkenyl radical, C₁-C₁₂Cycloalkenyl radical, C₁-C₁₂Substituted cycloalkenyl radical, C₁-C₁₂Alkynyl, C₁-C₁₂Aryl radical, C₁-C₁₂Substituted aryl, C₁-C₁₂Arylalkyl radical, C₁-C₁₂Alkylaryl group, C₁-C₁₂Heterocyclic group, C₁-C₁₂Substituted heterocyclyl and C₁-C₁₂An alkoxy group. For at least some pharmaceutical applications, it is particularly desirable to select R₁And R₂So that the metal/N-heterocyclic carbene complexes formed are soluble and stable in aqueous solution.

[0026]In one embodiment, the N-heterocyclic carbene is a bidentate carbene represented by formula 4 or 5, wherein R is₁Is a C₁-C₆Alkyl or C₁-C₆Hydroxyalkyl radical, R₂Is a hydrogen atom. In one embodiment, the N-heterocyclic carbene is represented by formula 4 or 5, wherein R is₁Is a C₂-C₃Hydroxyalkyl radical, R₂Is a hydrogen atom. In another embodiment, the N-heterocyclic carbene is represented by formula 4, each adjacent R₁And R₂Together form a substituted alkyl group.

[0027] As described above, the present invention also provides a novel N-heterocyclic carbene represented by the following formula:

wherein Z is a heterocyclic group, R₁And R₂Is, independently or in combination, hydrogen or C₁-C₁₂An organic radical, the C₁-C₁₂The organic group is selected from the group consisting of alkyl, substituted alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl, alkynyl, aryl, substituted aryl, arylalkyl, alkylaryl, heterocyclic, substituted heterocyclic, and alkoxy. In one embodiment, Z is pyridine or pyrrole. In another embodiment, Z is lutidine or dimethylpyrrole.

[0028] Typically, imidazolium salts are direct precursors of N-heterocyclic carbenes (immedicapresser). Several steps can be used to convert the imidazolium salts to the corresponding N-heterocyclic carbenes. N-heterocyclic carbenes can be generated from imidazolium salts by deprotonation with bases such as KOtBu, KH and NaH in solvents such as THF and liquid ammonia. The dissociable N-heterocyclic carbenes can replace the two electron donors on many transition metal complexes (e.g., tetrahydrofuran, carbon monoxide, nitriles, phosphines, and pyridines) to form N-heterocyclic carbene transition metal complexes. However, detaching the carbene is not always feasible.

[0029]N-heterocyclic carbene complexes may also be obtained by in situ generation of N-heterocyclic carbenes by deprotonation of the corresponding imidazolium salts in the presence of suitable transition metal complexes. Basic ligands on the metal complex, such as hydrides, alkoxides or acetates, can deprotonate the imidazolium salt to form an N-heterocyclic carbene that readily binds to an empty coordination site on the metal. For example, Pd (OAc) has been shown₂Reaction with a number of imidazolium salts (imidazolium salt) forms palladium-carbene complexes.

[0030]Carbenes can also be formed by treating imidazolium salts with inorganic or organic bases. The reaction of imidazolium salts with metals containing basic substituents has been shown to be very helpful for the synthesis of transition metal complexes of carbenes. Basic oxide Ag₂The combination of O with imidazolium salts can be used to generate silver-carbene complexes. The use of silver-carbene complexes as carbene transferrerents has been used to provide carbene complexes of gold (I) and palladium (II). Silver-carbene complexes have been used in this manner to provide complexes having Pd-carbene and Cu-carbene bonds. The formation of transition metal-carbene bonds using carbene transferants is advantageous in many cases, since these reactions are carried out under mild conditions and without the use of strong bases.

[0031]For example, the condensation of 2 equivalents of n-butylimidazole or methylimidazole and 1 equivalent of diiodomethane in refluxing THF provides the imidazolium salt shown in formula 8a or 8b in high yield. Reacting a substance represented by the formula 8a or 8b with Ag in water₂O combines to form water-soluble silver dimers 9a and 9b, respectively.

The thermal ellipsoid plots (thermal ellipsoid plots) of the cationic portions of 9a and 9b are shown below.

[0032] Two equivalents of 1-iodoethanol (formula 12) are combined with bisimidazole (formula 11) in refluxing butanol to produce a water-soluble diol as shown in formula 13. The compound has been characterized by NMR and X-ray crystallography.

[0033] A similar reaction has been carried out using 1, 2-dibromoethane (formula 14) and bisimidazole to form a carbene represented by formula 15. The alcohol group of compound 13 and the bromide of compound 15 provide functional sites for the introduction of solubilizing moieties (solvabilizing moieties).

[0034]The chelate ligand (piner ligand) dihalogenated 2, 6-bis- (N-butylimidazolium methyl) pyridine (2, 6-bis- (N-butylimidazolium methyl) pyridine dihalide) (compounds 16a and 16b) can be easily obtained by reacting N-butylimidazole with 2, 6-bis (halomethyl) pyridine in a molar ratio of 2: 1, respectively. In CH₂Cl₂Middle ligand 16a and Ag₂O reacts readily to produce the silver carbene complex 17. The complex 17 is stable in air and light.

[0035]The synthesis of the chelate-like N-heterocyclic carbene together with pyridine as a bridging unit is summarized below. Two equivalents of potassium imidazolide were reacted with 2, 6-bis (bromomethyl) pyridine to give compound 19 in 70% yield. The compound represented by formula 18 is combined with 2-bromoethanol or 3-bromopropanol to give 19a and 19b, respectively. 19a or 19b with an equimolar amount of Ag₂O binds to produce silver dicarbene polymers 20a and 20b, respectively. Compound 20a has been characterized crystallographically. The bromide salts represented by 20a and 20b are easily soluble and slowly decomposed in water, and either one of them is containedSilver mirrors were generated on the flask walls of the compounds. 20a and its propanol analog 20b are effective bactericides. Derivatives of these complexes may be synthesized using histidine as an exemplary precursor, as described below, to improve their antimicrobial properties.

[0036] The antimicrobial activity of water-soluble silver (I) N-heterocyclic carbenes 20a was studied on yeasts and fungi (Candida albicans, Aspergillus niger, Mucor, saccharomyces cerevisiae) using LB broth dilution technique with reference to silver nitrate, and on clinically important bacteria (escherichia coli, staphylococcus aureus, p. Sensitivity tests of silver compounds using the Kirby-Bauer agar diffusion (filter paper) procedure, performed by measuring growth inhibition zones, showed that silver (I) N-heterocyclic carbenes exhibit antimicrobial activity on all bacteria as effective as silver nitrate, using filter paper impregnated with a silver compound solution, placed on a lawn of organisms on an agar plate. The growth of overnight cultures containing various silver compound concentrations and bacteria or fungi was examined. For each organism, a tube containing the Minimum Inhibitory Concentration (MIC) of each silver compound was used to inoculate agar plates to confirm that there were no viable organisms in the culture. Compound 20a was effective against bacteria and fungi at lower concentrations and had a longer silver active period during the 7 day test period compared to silver nitrate. Toxicity testing in rats showed that the precursors of ligands 19a, 20a and the material formed upon degradation of 20a were of low toxicity and were cleared by the kidney within two days as determined by mass spectrometry of urine.

[0037] Two equivalents of potassium imidazolide (formula 21) are combined with 2, 5-bis (trimethylaminomethyl) pyrrole diiodide (2, 5-bis (trimethylammoniomethyl) iodide (formula 22) in THF to give compound 23. Compound 23 has been crystallographically characterized and its thermal ellipsoid plot is shown below. To compound 23, di-equivalent butyl bromide was added to produce compound 24 in high yield.

[0038] Histamine dihydrochloride (formula 25) was reacted with carbonyldiimidazole in DMF to give 5, 6, 7, 8-tetrahydro-5-oxoimidazo [1, 5-c ] pyrimidine (formula 26) in 40% yield. The compound of formula 26 has been crystallographically characterized (see thermal ellipsoid plots below). Two equivalents of compound 26 combined with one equivalent of 2, 6-bis (bromomethyl) pyridine in acetonitrile resulted in the formation of compound 27 in very high yield.

[0039]Methylated histamine and histidine (histadine) are also expected to have low toxicity because they occur naturally in the body. Reaction of L-histidine methyl dihydrochloride 28 with carbonyldiimidazole in DMF yielded 29. Three equivalents of methyl iodide were combined with 29 in refluxing acetonitrile to yield 30. The iodide salt of 30 (iodide salt) was reacted with methanol in the presence of N, N-diisopropylethylamine at reflux for 3 days to give 1-methyl-L-histidine 31. Three equivalents of methyl iodide were combined with compound 31 in refluxing acetonitrile to yield 1, 3-dimethyl-L-histidine 32. 32 and Ag₂O binds in DMSO to form a silver carbene complex 33. By the Kirby-Bauer technique, it has been shown that compound 33b has significant antimicrobial activity against Staphylococcus aureus (Staphylococcus aureus), Escherichia coli (Escherichia coli) and Pseudomonas aeruginosa (Pseudomonas aeruginosa).

[0040]Macrocyclic N-heterocyclic carbenes can be synthesized according to the following procedure. Two equivalents of potassium imidazolide and 26-bis (bromomethyl) pyridine (formula 34) to produce the compound of formula 35 in 70% yield. Compound 35 was combined with compound 34 in DMSO to give compound of formula 36 in 80% yield. PF of Compound 36₆ ^-Salt with equimolar amount of Ag₂O binds to produce silver bis-carbene dimer (formula 37) in nearly quantitative yield. Compounds 36 and 37 have been crystallographically characterized. The bromide salt of compound 37 (X ═ Br) is soluble and stable in water. Under similar reaction conditions, compound 36 was reacted with 4 equivalents of Ag₂O binds to form a tetrasilver bis-carbene dimer (not shown, but see formula 38). Compound 36(X ═ Br) and Ag₂The O combines in water to directly form the brominated salt of compound 37. The halide salt of compound 37 can be synthesized in water and is water soluble. Both the brominated and chlorinated salts of compound 37 are effective antimicrobial agents.

Compound 36[ PF₆ ^-]₂TEP of the divalent cation moiety of (a)

Compound 37[ PF₆ ^-]₂TEP of the divalent cation moiety of (a)

Compound 38[ PF₆ ^-]₄TEP of the tetravalent cationic moiety of

[0041]Pyrrole represented by formula 22(R ═ H or Me) and 3+1 condensation of pyridine represented by formula 18 to give productTo form a compound of formula 39(R ═ H or Me). 39a and NH₄ ⁺PF₆ ^-To produce compound 39 b. 39b (X ═ PF)₆ ^-R ═ Me) with four equivalents of Ag₂O binding to form tetrasilver dicarbene dimer, compound 40(X ═ PF)₆ ^-R ═ Me), the thermal ellipsoid diagram of which is shown below.

Compound 39b (X ═ PF)₆TEP of R ═ H)

Compound 40[ PF₆ ^-]₄TEP of the tetravalent cationic moiety of

[0042]One equivalent of compound 22 is added to compound 23 to produce bisimidazolium porphyrin 34 in high yield and on a large scale. Compound 34 has been crystallographically characterized and the thermal ellipsoid plot of the divalent cation ring of 34 is shown below. Compounds 39(R ═ H) and 41 with 4 equivalents of Ag₂O binds to form a tetrasilver bis-carbene dimer similar to compounds 38 and 40.

TEP of 41 (anion not shown)

[0043] Compound 18 binds to bis (bromomethyl) phenanthroline (bis (bromomethyl) phenathroline)42 to form an expanded macrocycle 43 which is a dibromide salt.

TEP of Compound 43

[0044]Monodentate N-heterocyclic carbene silver complexes, such as those represented by formula 48, may be synthesized by interaction of imidazolium salt precursor 44 with silver oxide. As mentioned above, the side chain R may be chosen so as to modify the water solubility, lipophilicity and other properties of the complex. For example, R may be hydrogen or C selected from alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl, arylalkyl, alkylaryl, heterocycle and alkoxy and substituted derivatives thereof₁-C₁₂An organic group. Silver complexes such as those represented by formulas 46 and 47, synthesized from histamine and histidine, respectively, can be synthesized and used as antimicrobial compounds. Because histamine and histidine are present in the body, derivatives thereof are expected to cause minimal skin irritation when used as topical antimicrobial agents, and are expected to pose very limited problems as internal antimicrobial agents with excellent toxicological properties.

[0045]The synthesis of a chelate-like N-heterocyclic carbene with a methylene (methene) or methylene (methyl ene) group bridging two N-heterocyclic carbenes (see formula 3) and having additional substituents is provided below. Substituents may be selected to provide sufficient solubility, lipophilicity, or other properties to the overall complex. In the steps discussed below, the pyridine ring and imidazole act as basic building blocks. Based on the synthesis of compounds 8a and 8b above, two equivalents of compound 58 will combine with diiodomethane to form compound 59. Reaction of Compound 59 with HClRing-forming compound 60. Because the primary amine is more reactive than the imidazole nitrogen, one equivalent of alkyl halide will readily add to the primary amine of compound 60 to form compound 61. The second alkyl halide will add to the second imidazolium nitrogen of compound 61 to form the bis-imidazolium salt cation, as shown in compound 62. The bisimidazolium salt cation 62 may be reacted with Ag₂O combine to form a silver complex represented by formula 63, similar to compounds 9a and 9b described above.

[0046] Compound 27 can be treated with HCl to form compound 64, and then compound 64 contacted with a solubilizing substituent-containing derivatized alkyl halide to form compound 65. Compound 64 can also be derivatized with a carboxylic acid and Dicyclohexylcarbodiimide (DCC) to form an amide bond. Compound 65, in combination with a derivatized alkyl halide similarly containing solubilizing substituents at higher temperatures, will generate an imidazolium salt dication as shown in formula 66, which can be further complexed with a metal such as rhodium.

[0047]Silver-carbene complexes may also be used as carbene transferrerents to produce other carbene complexes. The use of carbene transferants is advantageous in many cases for the formation of transition metal-carbene bonds, since the reaction is carried out under mild conditions and without the use of strong bases. For example, 8b and Pd (OAc)₂Binding in DMF followed by treatment with NaI in acetonitrile leads to the formation of the compound of formula 8 c. The thermal ellipsoid diagram of this compound is shown below. Similarly, 8b with PtCl₂And sodium acetate in DMSO to produce the compound represented by formula 8d in 50% yield. An X-ray thermal ellipsoid plot of compound 8d is shown below.

[0048]Imidazolium salts represented by formula 8a with [ (1, 5-cyclooctadiene) RhCl]₂Rhodium carbene 8e was generated in 80% yield by combining in the presence of NaOAc and KI in refluxing MeCN. Has passed through¹H and¹³the compound was characterized by C NMR and X-ray crystallography. The rhodium complex is water stable over an extended period of time. The relevant chelated bis-carbene rhodium complexes have been synthesized and have been shown to be sufficiently stable to be used in catalytic processes.

[0049]Silver complexes of N-heterocyclic carbenes represented by formula 17 can be used as carbene transfer agents. Complex 17 with (PhCN)₂PdCl₂In CH₂Cl₂To give a palladium carbene complex represented by formula 67 and two equivalents of AgCl in almost quantitative yield.

[0050]Similarly, the complex represented by formula 20a with (PhCN)₂PdCl₂In CH₂Cl₂To yield a palladium carbene complex represented by formula 68.

[0051] From the compound represented by formula 19a, a compound represented by formula 69 can be synthesized using a similar synthetic route.

[0052] For the synthesis of pyrrole-bridged, chelated N-heterocyclic carbenes, 2, 5-bisdimethylpyrroles having a leaving group on the methyl group are particularly useful in the synthesis method of the present invention. Dimethylammonium chloride undergoes a Mannich reaction with pyrrole in aqueous formaldehyde to produce 2, 5-bisdimethylaminomethylpyrrole represented by formula 70. Diiodomethane is added to pyrrole 70 in TNF to form 2, 5-bis (trimethylaminomethyl) pyrrole diiodide (2, 5-bis (trimethylammoniomethyl) pyrolodide) (formula 71).

[0053] Molecules containing 2-nitroimidazolyl are believed to be targeted to hypoxic cells. These compounds are reduced at the nitroimidazolyl group and are trapped inside the cell with a hypoxic environment. The 2-nitroimidazolyl group is bonded to the chelate N-heterocyclic carbene to form the compound represented by formula 73, and the formation can be performed as follows. It is desirable that the compound represented by formula 72 is condensed with bisimidazole in a ratio of 2: 1 to produce a compound represented by formula 73. Similarly, other derivatives of 2-nitroimidazole with various linker fragments can be synthesized. The class of linker groups, including polyethylene oxide (PEO), will allow for flexibility in positioning the chelator relative to the targeting group, as well as for changes in the octanol/water partition coefficient of the compound, which correlates with clearance through the kidney. The formation of rhodium complexes like 73 is also conceivable. Similar procedures can be used to synthesize 75 and 76 derivatives containing nitroimidazole and solubilizing substituents.

[0054]May be used as shown hereinAs a component of an N-heterocyclic carbene complex to form a radiopharmaceutical. For example, it is possible to use¹⁰⁵Rh was substituted for Rh.¹⁰⁵Rh has a convenient half-life of 1.5 days and also emits relatively low levels of gamma radiation. Such isotopes of rhodium are decomposed by beta-emission into¹⁰⁵Pd, a stable naturally occurring isotope of palladium. Other available isotopes may be selected from transition metals, elements from the lanthanide series and elements from the actinide series. Preferred isotopes are Ag, Rh, Ga and Tc.

[0055] As noted above, the present invention includes metal N-heterocyclic carbene complexes, which may be prepared from several N-heterocyclic carbene precursors, imidazolium salts. Imidazolium salts derived from biological analogs such as purine bases, including xanthines, hypoxanthine, adenine, guanine and derivatives thereof, can be readily reacted with silver (I) oxide in suitable solvents to obtain silver-N-heterocyclic carbene complexes. Imidazolium salt cations (imidazolium cations) can be readily classified as mono-imidazolium salt cations, such as those represented by formulas 77-81, bis-imidazolium salt cations, such as those represented.

[0056] Preferred mono-imidazolium salt cations include those represented by formulas 48-52:

which can be used to form preferred monodentate N-heterocyclic carbene silver complexes, such as those having the formulas 53-57, respectively. Carbene silver complexes shown in formulas 53-57 can be synthesized by the interaction of imidazolium salt precursors (imidazolium precursors) 48-52, respectively, with silver oxide.

[0057] Also, the poly-imidazolium salt cations according to the present invention include those represented by formulas 82-90:

[0058]the bridged bis-imidazolium salt cation may be represented by Z. Wherein Z can be methylene, heterocyclic (heterocyclic group), dimethylheterocyclic, dimethylcycloalkyl, dimethyl-substituted heterocyclic, aryl, dimethyl-substituted aryl. The bis-imidazolium salt cation may be replaced by Z₁And Z₂To form a ring (cyclophane), wherein Z₁And Z₂Each independently or in combination, selected from the group consisting of heterocycle, C₁-C₁₂Substituted heterocycles, aryls, C₁-C₁₂Substituted aryl, C₃-C₁₂Substituted ketones and C₁-C₁₂An alkenyl group. Each R group; r₁、R₂、R₃And R₄The functionality and counter anion (counter anion) X of the imidazolium salt can be modified to improve the lipophilicity of the compound. X^-The counter anion may be from the group consisting of halides, carbonates, acetates, phosphates, hexafluorophosphates (hexafluoro phosphates), tetrafluoroborates, nitrates, dimethyl sulfates, hydroxides and sulfates. Each R group (R)₁，R₂，R₃And R₄) Can be independently or combined selected from hydrogen and C₁-C₁₂Alkyl radical, C₁-C₁₂Substituted alkyl, C₁-C₁₂Alkoxy radical, C₁-C₁₂Cycloalkyl radical, C₁-C₁₂Substituted C₁-C₁₂Cycloalkyl radical, C₁-C₁₂Alkenyl radical, C₁-C₁₂Cycloalkenyl radical, C₁-C₁₂Substituted cycloalkenyl radical, C₁-C₁₂Alkynyl, C₁-C₁₂Aryl radical, C₁-C₁₂Substituted aryl, C₁-C₁₂Arylalkyl radical, C₁-C₁₂Alkylamine, C₁-C₁₂Substituted alkylamines, C₁-C₁₂Alkyl pentose phosphate (C)₁-C₁₂Phenols and C₁-C₁₂And (3) an ester. In some of its pharmaceutical applications, to R₁、R₂、R₃And R₄The choice of functionality is desirable.

[0059] Purines were also studied as silver-carrying carbene precursors. Of particular interest is guanine, which is one of the nucleobases (nucleoases) in DNA. Guanine 91 has a ring system similar to caffeine 95. Since guanine is non-toxic, it seems reasonable that 7, 9-dimethylguanine has low toxicity. This makes the dimethylguanine ligand very attractive for cystic fibrosis studies, as we are looking for non-toxic and small ligands that can be used as carriers of silver cations.

[0060]The dimethylation of guanine 91 with dimethyl sulfate followed by treatment with ammonium hydroxide yields water-insoluble 7, 9-dimethylguanine zwitterions 92. HBr is added to the zwitterion 92 to form the bromide salt 93. The bromide salt was dissolved in water and precipitated out using THF. Ag was prepared by suspending bromide salt in DMSO₂O is added to the solution and heated at 60-80 c for about 6 hours to form a silver complex.

[0061] Xanthine has been used for many years as a bronchodilator (bronchodilator) for the treatment of airway obstruction (airwayobstruction) in patients with cystic fibrosis. Since xanthines contain imidazole rings, we hypothesize that it should be possible to alkylate them to form imidazolium salts and eventually silver carbene complexes. Because they are useful as bronchodilators, we also assume that their methylated derivatives will be relatively non-toxic. Probably the best known xanthine is caffeine 95. We have investigated the alkylation of caffeine to form methylated caffeine and the formation of silver carbene complexes using caffeine as a carbene precursor. Methylated caffeine has been shown to be less toxic than caffeine.

[0062]The methyl sulfate of methylated caffeine, 1, 3, 7, 9-tetramethylxanthine salt (1, 3, 7, 9-tetramethylxanthonium), 96a, is produced by the reaction of caffeine 95 with dimethyl sulfate in nitrobenzene. Use of NH in water₄PF₆The anion exchange of (a) yields 96 b.

[0063]Ligand 96a is water soluble and reacts with Ag in water₂The reaction of O produces complex 97 a. 97a was stable in water for 5 days. C-¹⁰⁷Ag and C-¹⁰⁹The lack of Ag linkers is described in¹³The C NMR time scale showed a stereo-variable behaviour (fluorogenic behavior) as observed for many silver (I) complexes. Similarly, 96b with Ag₂O reacts in DMSO to form 97b, which has been structurally characterized by X-ray crystallography. Thermal Ellipsoids (TEP) of the cationic portions of 96b and 97b are shown below.

[0064]Caffeine 1, 3, 7-trimethyl xanthine is a xanthine derivative,xanthine derivatives are commonly used in medicine as diuretics, central nervous system stimulants, and inhibitors of cyclic adenosine monophosphate (c-AMP) phosphodiesterase. 1, 3, 7, 9-tetramethylxanthinium iodide (1, 3, 7, 9-tetramethylxanthinium iodide) (methylated caffeine) was synthesized using a modified literature procedure, as an imidazolium salt, and by¹H，¹³C NMR, mass spectrometry and X-ray crystallography.

[0065] Two equivalents of 1, 3, 7, 9-tetramethylxanthium iodide were reacted with three equivalents of silver (I) oxide in methanol at room temperature to give compound 99.

[0066]99 was crystallized from a mixture of methanol and ethyl acetate to yield compound 100 as colorless crystals, soluble in water and air stable. By passing¹H，¹³C NMR and mass spectrometry characterized compounds 99 and 100. X-ray crystallography is used to determine the molecular structure of 100, whose thermal ellipsoid plots are shown above. The antimicrobial performance of 100 was evaluated using the filter disk test and standard MIC technique. Compound 100 has been found to have potent antimicrobial activity against staphylococcus aureus (s. aureus), pseudomonas aeruginosa (p. aeruginosa) and escherichia coli (e.coli). Dose-response effect (dose-response effect) on compound 98 was evaluated to determine the toxicity of the compound to mice. Toxicity studies are standard protocols for determining the amount of lethal (LD 50) required to kill half of the animals (mice). The LD 50 evaluation for Compound 98 was 2.37g per Kg of mouse. The protocol used in this study was approved by Institutional Animal Care and Use Committee (IACUC), University of Akron.

[0067] The method of administration of an effective amount of a transition metal complex of an N-heterocyclic carbene for in-vitro and in-vivo medical applications consists of aerosols, biodegradable polymers, polymeric micelles, hydrogel-type materials, dendrimers and modified C-60fullerenes (C-60 fullerenes).

[0068] To demonstrate the practice of the present invention, two N-heterocyclic carbenes 101 and 102 were synthesized and tested for antimicrobial properties as described below. These compounds can be represented by formula 4.

Wherein R is₁Is hydroxyethyl or hydroxypropyl, R₂Is a hydrogen atom. These carbenes 101 and 102 are synthesized by reacting 2, 6-bis- (imidazolylmethyl) pyridine with 2-iodoethanol or 3-bromopropanol to provide compounds of formulas 101 and 102.

[0069]The IR spectrum of these compounds was 3325cm^-1The O-H stretching band vibration is shown. The FAB-MS spectrum obtained from these compounds in a nitrobenzyl matrix (nitrobenzyl matrix) shows at m/z 456 [51][I]⁺(C₁₇H₂₃N₅O₂I) Display at m/z 436 [52 ]][I]⁺(C₁₉H₂₇N₅O₂Br). These compounds can be readily reacted with Ag₂O, to form silver-bis (carbene) pincer complexes (silver-bis (carbene) complexes) 103 and 104 in high yield.

[0070]In the presence of these compounds¹Loss of imidazolium salt protons (imidazolium proton) at 9.13ppm, 9.36ppm in the H NMR spectrumAnd in the preparation of these compounds¹³The appearance of a resonance at 181ppm in C NMR confirms the formation of compounds 103 and 104. Further evidence for compound 103 formation and structure is provided by X-ray crystallography.

[0071] By slowly evaporating the methanol solution of compound 103, colorless crystals of compound 103 are obtained. Interestingly, compound 103 underwent complete anion exchange in aqueous methanol, replacing the iodide ion with hydroxide ion. In the solid state, compound 103 exists as a one-dimensional linear polymer, as shown in fig. 1. Fig. 1 is a thermal ellipsoid plot of compound 103, whose thermal ellipsoid is plotted at a probability level (probability level) of 30%. For clarity, the hydrogen atoms are omitted from FIG. 1.

[0072] The geometry at the silver atom is nearly linear with bond angles of C5-Ag1-C15 of 174.7(4) ° and bond lengths of Ag1-C5 and Ag1-C15 of 2.108(11) Å and 2.060(13) Å, respectively. Mass spectrometry showed that compound 103 was present as a monomer in solution and in the gas phase, while X-ray crystallography showed that compound 103 was polymerized in the crystals.

[0073] The anion exchange reaction of compound 103 with aqueous ammonium hexafluorophosphate solution results in the formation of compound 105. In the solid state, compound 105 exists as a dimer, as shown in figure 2. Figure 2 is a thermal ellipsoid plot of compound 105, whose thermal ellipsoid is plotted at a 30% probability level. For clarity, the hydrogen atoms are omitted from fig. 2. The geometry of the silver atoms is nearly linear, with bond angles: C32-Ag1-C5(175.7(4) °), C22-Ag2-C17(174.6(3) °), bond length: ag1-C32(2.070(9) Å), Ag1-C5(2.091(9) Å), Ag2-C22(2.064(9) Å) and Ag2-C17(2.074(8) Å). The nature of the anion is important to the structural changes of compound 103 versus compound 105, and the choice of anion has a significant impact on the solubility of these compounds. For example, compound 103 is soluble in aqueous media, while compound 105 is not. A summary of the crystal data for these two compounds is given in table 1.

TABLE 1

Empirical formula	103，C17H22N5O3Ag	105，C34H42N10O4AgP2F12
			Molecular weight	434.0735	868.1481
Temperature (K)	100	100
			Wavelength (Å)	0.71073	0.71073
Crystal system, space group, Z	Orthogonal, P2(1)2(1), 4	Monoclinic, P2(1)/c, 8
			Unit cell size
a(Å)	4.5586(17)	10.9448(14)
			b(Å)	14.900(6)	22.885(3)
c(Å)	29.923(12)	17.729(2)
			α(°)	90	90
β(°)	90	92.196(2)

γ(°)	90	90
			V(Å3)	2032.5(14)	4437.4(10)
Dcalc(Mg/m3)	1.422	1.737
			Absorption coefficient (mm)-1)	1.010	1.055
Theta range (°) of data collection	1.36 to 24.99	1.45 to 25.00
			Collected reflectance/singleness (reflactionated/unique)	6300/3506[R(int)＝0.0650]	20811/7757[R(int)＝0.0437]
At F2Goodness of fit of (3)	1.034	1.058
			Final R index [ I > 2 sigma (I)]	0.0655	0.0956
R index (all data)	0.1410	0.2491
			Maximum difference peak and hole (e Å)-3)	0.954 and-0.875	2.069 and-1.230

[0074] Compounds 103 and 105 were evaluated for effectiveness as antimicrobial agents. Sensitivity data as shown in table 2 were obtained using the standard agar plate overlay (agar plates overlay) method. In this test, a 6mm diameter disc of filter paper is impregnated with 20. mu.l of a known concentration of silver compound and placed on a lawn of microorganisms on an agar plate. After overnight incubation, the diameter of the area where the growth of the microorganism was inhibited by the test solution was measured as a measure of the relative antimicrobial activity of the silver compound. The microorganisms tested were Escherichia coli (Escherichia coli), Staphylococcus aureus (Staphylococcus aureus) and Pseudomonas aeruginosa (Pseudomonas aeruginosa). Silver nitrate was used as the reference standard, while compounds 101 and 102 served as negative controls.

Table 2.

Antimicrobial activity of silver compounds

			Diameter of inhibition zone (mm)
						Test compounds	Ag+(ug/ml)		Escherichia coli	Staphylococcus aureus	Pseudomonas aeruginosa
						AgNO3	3176		11.38	10.88	11
0.5％(w/v)
103	3130		11.5	11	12

1.31％
105	3195		11.58	10.67	10.25
						1.42％
						103	1195		10.13	10	11.13
0.50％
105	1125		10	9	12
						0.50％
						101			6	6	6
0.50％
102			6	6	6
						0.50％

[0075] The data demonstrate that compounds 103 and 105 have antimicrobial properties at levels comparable to silver nitrate as shown in table 2. Chelate (pincer ligand) compounds 101 and 102 were found to have no antimicrobial activity.

[0076] Silver compounds were also tested according to the Minimum Inhibitory Concentration (MIC) assay. MIC is a standard microbiological technique used to evaluate the bacteriostatic activity of an antimicrobial agent. In this case, the MIC is based on the total amount of silver available, not on the concentration of silver ions. A0.5% (w/v) solution of each silver compound 103 and 105 was tested. When the silver complex was dissolved in the medium (LB broth), AgCl precipitation was observed in all samples. The supernatant fraction of the silver complex solution was evaluated for activity in a dilution series in which a constant volume of newly grown microorganisms (20. mu.l) was added daily. Escherichia coli (Escherichia coli), Staphylococcus aureus (Staphylococcus aureus) and Pseudomonas aeruginosa (Pseudomonas aeruginosa) were again used as the test microorganisms. The MIC was obtained by visual inspection of the culture for growth (+) or no growth (-), as reported in table 3. In table 3, DF is the dilution factor. From the results, it can be concluded that compounds 103 and 105 are less prone to bind chloride ions (chloridion) than silver nitrate, due to the stability of the Ag — C donor coordinate bond. Thus, compounds 103 and 105 showed better antimicrobial activity than silver nitrate. This is a desirable property of compounds 103 and 105 when considering silver compounds for in vivo applications. It may be noted that although an equal weight of silver compound was used, the amount of silver ions released by compounds 103 and 105 was about 2.7 times lower than the amount of silver ions released by silver nitrate.

TABLE 3

MIC results of supernatants of silver compounds (less silver chloride)

Testing of Ag Compounds	Ag(ul/ml)	Escherichia coli		Staphylococcus aureus		Pseudomonas aeruginosa
								Day one	The next day	Day one	The next day	Day one	The next day
		103×1DF×2DF×3DF×4DF105×1DF×2DF×3DF×4DFAgNO3×1DF×2DF×3DF×4DF	118611253176	---++---++-++++	-++-+++	---++---++-++++	--+-+++							--+++--++++++++	-+-+

[0077] While not wishing to be bound by any particular theory of patentability, it is believed that the activity and stability of compounds 103 and 105, as well as their solubility in water, may be attributed to the relatively slow decomposition of the Ag — C donor coordination bond into silver metal and silver ions over time.

[0078] When the MIC test was repeated as described above, the activity of the silver compound was enhanced except for the presence of insoluble silver chloride, which performs better with silver nitrate as shown in table 4. It has been previously reported that the presence of chloride contributes to the toxicity of silver in sensitive strains of microorganisms.

Table 4.

Effect of chloride (e.g., silver chloride) on the bacteriostatic Activity of silver Compounds

Testing Ag Compound (% w/v)	Escherichia coli (days)						Pseudomonas aeruginosa (days)						Staphylococcus aureus (days)
																			1	2	3	4	5	6	1	2	3	4	5	6	1	2	3	4	5	6
	1030.500.250.120.060.031050.500.250.120.060.03AgNO30.500.250.120.060.03	---------------	---------------	----+----+-----	------------+	------------	------------	---------------	---------------	----+----+----+	------------	------------	------------	---------------	----+----+-----	------------+	------------	------------																			------------

[0079] The minimum lethal concentration was determined to evaluate the bactericidal properties of the compounds represented by formulas 103 and 105. The clear (no growth) portion of the medium with the lowest concentration of Ag compound was used, and 0.01ml of the solution was streaked on an agar plate by using a sterilizing ring, followed by incubation at 37 ℃ for 24-48 hours. Colonies were counted visually, with the end point of Minimum Bactericidal Concentration (MBC) being seen as no growth on agar plates. Up to day seven of culture and MBC testing, the test compounds showed improved bactericidal effect compared to silver nitrate, for which no growth was observed after day ten of culture and testing. In spite of the fact that the newly growing microorganisms are added daily to the silver compound-containing medium throughout the entire cultivation period. The bactericidal and bacteriostatic properties of 103 and 105 are believed to be due to the slow decomposition of the Ag-C donor (carbene) coordinate bond over time to silver metal, silver ions, AgCl, and their solubility in water.

[0080] The alkanol N-functionalized silver carbene complexes 103 and 105 are soluble in aqueous media.

In addition, they have proven to be useful antimicrobial agents, and their solubility in water makes them excellent silver compounds that can be used for in vivo applications. The solubility and stability of silver complexes in chloride solutions has become a key factor limiting the use of silver complexes for in vivo applications.

[0081]In accordance with another aspect of the present invention, a silver (I) imidazole cycloarylgem-diol complex (silver (I) imidazole cyclophane gel diol complex)106[ Ag₂C₃₆N₁₀O₄]²⁺2(x)^-Wherein x ═ OH^-，CO₃ ^2-. MIC testing showed that 106 in aqueous solution with approximately equal amounts of silver had antimicrobial activity compared to 0.5% AgNO₃Is 2 times smaller (fold). When 106 is encapsulated by electrospinning (technique) into Tecophilic ® to obtain a layer (mat) made of nanofibres, the antimicrobial activity of 106 is enhanced. The fibrous layer (fiber mat) releases aggregates of silver nanoparticles and maintains the antimicrobial activity of the fibrous layer for a long period of time. By encapsulation, the rate of bactericidal activity of 106 is greatly improved and the amount of silver used is much reduced. The fibrous layer with 75% (106/tecophilic) 106 contained 2mg of silver, which was compared to 16mg (0.5%) of AgNO₃8 times lower than 1% sulfadiazine silver ointment (10 mg). The fibrous layer has been found to be compatible with 0.5% AgNO₃Staphylococcus aureus (s. aureus) was killed at the same rate with zero colonies on the agar plate and approximately 6 hours faster than the sulfadiazine silver paste. The inocula tested and found to be effective on the above were e.coli (e.coli), p.aeruginosa, s.aureus (s.aureus), candida albicans (c.albicans), a. niger (a. niger) and s.cerevisiae (s.cerevisiae). Using transmission electron microscopes and scanning electron microscopesThe fibrous layer was characterized by examination. The acute toxicity of the ligand, an imidazolium dichloride cycloarylgem-diol (imidazolium chloride gem diol), was evaluated by intravenous administration to mice, with an LD 50 of 100mg/Kg mice.

[0082] The electrospun fiber (electrospun fiber) of the present invention can encapsulate the silver (I) N-heterocyclic carbene complex. The antibacterial activity of water-soluble silver (I) carbene complex 107, silver (I) hydroxide-N-chelated 2, 6-bis (hydroxyethylimidazolylmethyl) pyridine (silver (I) -N-piner 2, 6-bis (hydroxyethylimidazolidone) pyridine hydroxide) on some clinically important bacteria is described above. Compound 107 is an example of a compound that is sparingly soluble in pure ethanol, but completely soluble in methanol. By varying the functional group coupled to the nucleophilic end group of the bis (imidazolylmethyl) pyridine compound, the solubility of the silver (I) carbene complex type 1 in ethanol is improved. Although an embodiment is shown in equation 1 where m-2 and m-3, m may be any positive integer of at least 1, preferably m is a value in the range of about 1 to about 4. Furthermore, the above-described alternative starting materials or precursors may be used to form the desired silver (I) carbene complexes without departing from the scope of the invention. The specific embodiments illustrated and described below are provided to illustrate the present invention.

Equation 1

[0083] Electrospinning (Electrospinning) is a common method used to elongate and solidify by creating an electrostatically charged spray of polymer solution or polymer melt, producing fibers with diameters from a few nanometers to greater than a micron. The formed fibers can be used in filter materials, coated templates, protective clothing, biomedical applications, wound dressings, drug delivery, solar sailboats (solar sails), solar cells, catalyst supports, and reinforcing agents for composites.

[0084] Imidazolium salts (NHC) cycloarylgem-diol salts 108 can be prepared by reacting 2, 6-bis (imidazolylmethyl) pyridine with 1, 3-dichloroacetone. As shown in equation 2 below. It is undesirable for the salt 108 with the electron withdrawing group to be formed as a gem-diol (gem-diol) in preference to the carbonyl form. Without being bound by theory, it is believed that the formation of salt 108 as a gem-diol proceeds by an acid catalyzed process with a slightly acidic solution observed to have a pH range of 5-6.

Equation 2

[0085]¹H NMR spectrum showed the presence of gem-O-H as a broad peak at 7.65ppm¹³No C ═ O was observed in salt 108 in both the CNMR and the infrared spectra. At 3387cm^-1Here, O-H stretching vibration was observed to be 1171cm^-1C-O stretching vibration was observed, and 91ppm vibration was observed¹³C NMR chemical shift. X-ray crystallography provides further evidence that the structure of 108 is shown in the following figure:

TEP of salt 108, thermal ellipsoid plot was plotted at 50% probability level.

The counter anion is omitted for clarity.

[0086]According to the reaction scheme illustrated in equation 3, silver (I) oxide is combined with salt 108 in methanol to form complex 106 in high yield as an air and light stable yellow solid by reaction in¹The loss of imidazolium salt proton at 9.35ppm of the H NMR spectrum was confirmed. Proton NMR of complex 106 shows a broad signal with a complex peak that is not easily identified. Also, andwithout being bound by theory, this may be attributed to the sterically variable behaviour of the compound on the NMR timescale (fluorogenic behavior).

Equation 3

[0087]Resonance signals of fenamidocarbon (NCN) from 138ppm to 184 and 186ppm¹³The shift in the low magnetic field (down field) of the C NMR spectrum indicates a rare coupling of the Ag-C bonds. Observed large Ag-C coupling constant value (J)_AgC211Hz) with those reported¹⁰⁹The 204Hz-220Hz range of Ag core coupling is consistent. It is generally observed that¹⁰⁹Ag coupling due to coupling with¹⁰⁷Compared with Ag, it has higher sensitivity. X-ray crystallography confirms the structure of complex 106, which is shown in formula II, where the bond is long: ag1-C15 ═ 2.085(5) Å, Ag1-C31 ═ 2.077(5) Å, Ag2-C5 ═ 2.073(5) Å and Ag2-C21 ═ 2.072 Å. Weak Ag1 … Ag2 interactions were observed with bond lengths of 3.3751(10) Å, longer than the commonly reported Ag … Ag bond in the 2.853-3.290 Å range, but shorter than the Ag … Ag van der waals radius of 3.44 Å. In silver metal, Ag … is known to have a bond length of 2.888 Å Ag. The bond angle of C-Ag-C is almost linear, wherein the bond angle of C15-Ag1-C31 is 175.20(18) °, and the bond angle of C21-Ag2-C5 is 170.56(18) °.

Formula II

The thermal ellipsoid plot of the complex 106, which is plotted at a 50% probability level.

The counter anion is omitted for clarity.

[0088] Electrospun fibers derived from Tecophilic ® and silver complexes were characterized by Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). In the as-spun fiber, no significant phase separation was observed, as shown in fig. 3, which indicates that Tecophilic ® and the silver complex were uniformly mixed overall. The thickness of the fibrous layers with pure Tecophilic ® (100 microns), 25: 75 silver complex 106/Tecophilic ® (30 microns) and 75: 25 complex 106/Tecophilic ® (60 microns) were measured by Scanning Electron Microscopy (SEM), respectively. Encapsulation of the complex 106 by the polymer prevents rapid decomposition of the silver complex into silver ions or silver particles in an aqueous medium. The formation of nano-sized silver particles has been observed in the polymer matrix when electrospun fibers are exposed to water. Transmission electron microscopy studies show that activation of nano-silver particles in the fiber is a process that occurs gradually over time. By exposing the as-spun fibers to water, the complex 106 decomposes and releases silver ions, which are agglomerated into nano-sized silver particles. The formation of silver particle aggregates has been observed within 30 minutes of exposure to water vapor (as shown in fig. 4). Aggregation of silver ions with aggregates adsorbed on the fiber surface in the presence of water is considered to be a simplified mechanism by which the fiber layer releases the active form of silver to achieve its antimicrobial activity. The fibers of the compound 106 are stable in light and air for months, but are sensitive to high humidity environments.

FIG. 3

Electrospun fibers prepared from 106 and Tecophilic ® in a weight ratio of 25 to 75.

(a) As-spun fibers (b) silver particles formed by exposing the as-spun fibers to water.

FIG. 4

TEM image: shows the release of silver particles by exposing the fibres of complex 106 and Tecophilic ® (50: 50 by weight) to a water vapour environment; (a) spinning fiber, and (b) steaming

Fiber in a gas atmosphere for 65 hours.

Sterilizing effect

[0089] Using a modified Kirby Bauer technique, electrospun Tecophilic ® fiber layers encapsulating complex 106 and pure electrospun Tecophilic ® fibers as a control were placed on the lawn of the microorganism in agar plates and incubated overnight at 35 ℃. The inocula used were gram-positive and gram-negative prokaryotes of clinical interest (escherichia coli, Pseudomonas aeruginosa) and Staphylococcus aureus (Staphylococcus aureus). The fungi used are Candida albicans (Candida albicans), Aspergillus niger (Aspergillus niger) and Saccharomyces cerevisiae (Saccharomyces cerevisiae). After overnight incubation of the agar plates at 35 ℃, the bactericidal activity showed clear zones of inhibition (clearance zones of inhibition) around and within the fibrous layer. After 48 hours of incubation at 25 ℃, fungicidal activity (fungal activity) was observed. The pure Tecophilic ® fiber layer as a control showed no growth inhibition (see fig. 5). When the composition of the fibrous layer changed from 75% complex 106 and 25% Tecophilic ® to 25% complex 106 and 75% Tecophilic ®, no significant difference in the diameter of the transparent inhibition zone around the fibrous layer was observed. The diameter of the zone of inhibition of the 75 (conjugate 106/tecophilic ®) fibrous layer was 4.00mm, while the diameter of the zone of inhibition of the 25% (conjugate 106/tecophilic ®) fibrous layer was 2.00 mm. The difference in the diameter of the zone of inhibition between the two types of fibrous layers has no linear relationship with the amount of silver (3: 1 ratio) present in the two fibrous layers. These results further show that the Kirby Bauer technique has limitations as a quantitative tool for determining the antimicrobial activity of a drug. The diffusion capacity of silver ions may have been limited by the formation of secondary silver compounds. It is known that ionized silver undergoes ligand exchange reactions with biological ligands such as nucleic acids, proteins and cell membranes.

FIG. 5

Susceptibility testing of the fiber layer encapsulating the complex 106 compared to the bactericidal activity of the pure Tecophilic ® fiber layer. (a) Complex 106/Tecophicic ® (25: 75) (b) pure Tecophicic ® (c)

Complex 106/Tecophilic ® (75: 25)

[0090] When one fiber layer was placed in 5ml of distilled water and exposed to light for 4 days, some precipitation of silver particles was observed at the bottom of the test tube. Leaching of silver particles from the surface of the fiber layer into the solution occurs gradually over time. The release of nanosilver particles from the as-spun layer of the conjugate 106 into an aqueous medium resulted in an investigation of the kinetics of killing (bactericidal activity) of the as-spun fiber layer of the conjugate 106 with respect to time, by comparing the as-spun fiber layer of the conjugate 106 with silver nitrate and silver sulfadiazine 1% paste or Silver Sulfadiazine (SSD), which is a widely used clinical drug. Both types of fiber layer compositions 75: 25(Ag content: 424 μ g/mL) and 25: 75(Ag content: 140 μ g/mL) used in this study showed faster kill rates than SSD (Ag content: 3020 μ g/mL). Silver nitrate (0.5%) with 3176 μ g/mL Ag showed about the same kill rate as complex 106/tecophilic 75: 25 at a concentration 8 times lower than it (Ag 424 μ g/mL) (see fig. 6). The bactericidal activity of the silver compound against pseudomonas aeruginosa (p. aeruginosa) is faster than that of staphylococcus aureus (s. aureus). The fibrous layer kills bacteria faster than silver sulfadiazine.

FIG. 6

CFU (colony Forming Unit) of silver Compound on Staphylococcus aureus

The kinetics of bactericidal activity for each silver compound tested is expressed in a plot of time (hours).

[0091]The time dependence of the bacteriostatic and bactericidal activity of the as-spun fiber layer of complex 106 as a function of the volume of the inoculated organism was investigated. The fibrous layer of complex 106 showed potent bactericidal activity against pseudomonas aeruginosa (p. aeruginosa), escherichia coli (e. coli) and staphylococcus aureus (s. aureus) inoculated daily (25 μ L) with new growth organisms over a period of more than one week. This indicates that the as-spun fiber layer remains constantly releasing the active silver species for a long period of time. The pure Tecophilic ® layer used as a control showed no antimicrobial activity within 24 hours of inoculation. In use, 200 μ L (2X 10)⁷) After inoculation of a large number of new growth organisms, the as-spun fibrous layer with 75% complex 106/tecophilic composition of complex 106 showed better bactericidal effect on pseudomonas aeruginosa (p. aeruginosa) than 25% complex 106/tecophilic over a period of more than 2 weeks. Bacteriostatic activity against staphylococcus aureus (s. aureus) and escherichia coli (e.coli) was observed after 10 days of streaking with LB broth solution daily on agar plates. Visual inspection of the cultured solution showed no growth of organisms.

[0092]108, Complex 106 and AgNO were studied using a Minimum Inhibitory Concentration (MIC) assay₃Bactericidal activity in aqueous LB broth. After 24 hours of incubation, in complex 106 and AgNO₃There was generally no difference in bactericidal activity and MIC as shown in table 5. However, after 48 hours of incubation, silver nitrate showed better antimicrobial activity at a 2-fold lower concentration (838. mu.g/mL) than compound 106.

Comparative AgNO₃And 106, the two compounds have about the same silver content.

Sample name	Sample concentration (wt/V%)	Sample concentration (μ g/mL)	Bacterial volume (μ L)	Escherichia coli (Tian)		Pseudomonas aeruginosa (Tian)		Staphylococcus aureus (Tian)
										1	2	1	2	1	2
				AgNO3106108	0.501DF2DF3DF4DF1.381DF2DF3DF4DF0.5	3462.351731.18865.59432.79216.403341.481675.74837.87418.94209.47	10010025	----------+	----+---++							----------+	--------++	----------+	----+---++

TABLE 5 comparison of AgNO with about the same silver content₃And MIC results of the activity of complex 106. DF is the dilution factor (1 mL). Growth, and no growth. The silver content per mL (μ g) of each compound was calculated as (molecular weight of Ag/molecular weight of compound) × wt%.

[0093]The MIC value of silver sulfadiazine was not determined because the solution was cloudy and the concentration of 108 used showed no antimicrobial activity. In the MIC assay, complexes 106 (209. mu.g/mL) and AgNO were observed with minimal concentrations₃Dilutions (216. mu.g/mL) showed the same number of Staphylococcus aureus (S.aureus) colony growth on agar plates after 24 hours incubation. The 25% complex 106/tecophilic fiber layer had a minimum concentration of silver of 140 μ g/mL (see table 6) and sustained release of bioavailable silver species over several days. No growth of organisms was observed on the inoculum with daily increase in volume.

Sample name	Weight of silver Compound used (mg)	Volume of LB Broth (ml)	Silver content (mg) in the sample	Mu g/ml of Ag
					SSDAgNO3AgNO3106/tecophilic(25∶75)106/tecophilic(75∶25)	20.0012.8025.0011.3011.40	5.005.005.005.005.00	6.058.1315.900.732.21	1210.001626.003176.00146.00441.00

Table 6 details of silver compounds used for kinetic studies are shown.

SSD: sulfadiazine silver 1% ointment

[0094]Thus, by encapsulation in suitable polymer fibers, the antimicrobial activity of the complex 106 is enhanced at very low Ag particle concentrations over a longer period of time. Bactericidal Activity of fibrous layer 75% (Complex 106/tecophilic) containing 424. mu.g/mL silver compared to AgNO at silver concentration₃(3176. mu.g/mL) was 8 times lower, which not only showed as fast a kill rate as silver nitrate, but also maintained the original color of the LB broth, a clear yellow solution, unlike silver nitrate, which stained the LB broth color and made it dark brown. Sulfadiazine silver paste is not readily soluble in aqueous LB broth, thus affecting the rate of its bactericidal activity.

[0095]The antimicrobial activity of the fibrous layer encapsulating the complex 106 can be considered a combination of active silver species, which can include AgCl₂ ^-Ions, Ag⁺Ion clusters, AgCl and free Ag⁺Ions. Theoretically, the slow release of active silver particles in solution results in the rapid formation of silver chloride. The presence of more chloride ions as the primary counterion will further result in a negative charge [ Ag_yCl_x]^n-Formation of an ionic species (where y is 1, 2, 3 …, etc.; x is 2, 3 … (y + 1); n is x-1). Has formed [ AgI₃]^2-、[Ag₂I₄]^2-、[Ag₄I₈]^4-And [ Ag₄I₆]^2-Anionic silver complexes of the type (I). Formation of anionic silver chloride species may not be limited to leaching aggregation of silver particles in solutionBulk (leached aggregate) may also be found on the surface of the fibrous layer, as shown in the SEM image of fig. 8. The anion silver dichloride (silver dichloride) is known to be soluble in aqueous media and therefore bioavailable. Anionic silver halides are reported to be toxic to both sensitive and resistant strains. The active silver species adsorbed on the network of fibers in the layer is advantageous because the fibrous layer has to increase the surface area of the active silver species compared to conventional use of hydrated silver ions. This mechanism may indicate that the fibrous layer has effective bactericidal activity in aqueous media, even at very low silver concentrations compared to the unencapsulated form of complex 106. Although complex 106 is not readily soluble in water, it has been observed that it undergoes rapid decomposition in aqueous media. Thus, the bactericidal activity of the complex 106 is reduced due to the poor availability of active silver species in the LB broth, possibly due to the formation of secondary silver compounds (AgCl), in particular.

FIG. 8 electrospun fibers of Complex 106 and Tecophilic ® (75: 25) after two weeks of antimicrobial activity in LB broth. (a) A perspective view of a fiber segment; (b) large aggregates (400nm) of silver particles encapsulated in Tecophilic fibers ®; (c) silver aggregates (200 to 300nm in diameter) and silver particles (10 to 20nm in diameter) in a Tecophilic ® matrix; (d) top view of a fibrous layer having an aggregation of silver particles.

Acute toxicity evaluation

[0096] LD 50 evaluation was performed by intravenous administration of 108, 108 dissolved in buffered saline and administered via the tail of the mice. Adult mice with an average weight of 500g were used. A0.3 ml dose (5mg, 50mg) was administered stepwise weekly. Mice were carefully examined for dose response effects (doseseponse effect). Death occurred 10 minutes after 50mg108 administration when 50% of the mice showed a vigorous twitch before death. Autopsy reports indicated lung bleeding, and bleeding was found in the brains of dead mice and diagnosed as stroke (stoke). Weight loss, a significant decrease in diet, and low urine output were observed in surviving mice. The evaluation value of LD 50 was found to be 100mg/Kg mouse.

[0097] The synthesis of 108 with a functional group helps to make the silver (I) imidazole cycloarylgem-diol suitable for encapsulation into nanofibers. The fibrous layer has been shown to have improved antimicrobial activity of silver (I) -n-heterocyclic carbene complexes on inoculum, which has a faster kill rate than silver sulfadiazine at 8-fold lower concentrations than silver sulfadiazine in LB broth. Encapsulation of the silver (I) -n-heterocyclic carbene complexes increases the bioavailability of the active silver species and reduces the amount of silver used. Encapsulated silver (I) carbene complexes in nanofibers have proven to be promising substances for sustained and efficient transport of silver ions over a longer period of time, with maximal bactericidal activity, compared to providing silver in hydrated form. Unencapsulated forms often involve an amount of silver in 0.5% silver nitrate, as compared to which the amount of silver required for antimicrobial activity is reduced using this encapsulation technique. Furthermore, the ability of the fibrous layer to retain the original color of the LB broth is a major shaping benefit. Evaluation of acute toxicity of the ligand on mice showed an LD 50 of 100mg/Kg in mice, a value considered moderately toxic.

[0098] In addition to useful antimicrobial or antibacterial properties, it is believed that the present invention may inhibit fungal growth, as well as viral growth. The compositions of matter and methods of the present invention also contemplate delivery of silver to a site via any known carrier, including but not limited to inhalation through the lungs, direct administration of a liquid to the eye, or any other type of topical application.

General test

[0099]Silver (I) oxide, silver sulfadiazine and 1, 3-dichloroacetone were purchased from Aldrich. Acetone, acetonitrile, methanol, ethanol, ammonium hexafluorophosphate, and biomass; saccharomyces cerevisiae (ATCC2601), candida albicans (c. albicans) (ATCC 10231), aspergillus niger (a. niger) (ATCC 16404)) Escherichia coli (e.coli) (ATCC 8739), pseudomonas aeruginosa (p.aeruginosa) (ATCC 9027), staphylococcus aureus (s.aureus) (ATCC6538) were purchased from Fisher. All reagents were used without purification. The infrared spectra were recorded on a Nicolet Nexus 870FT-IR spectrometer.¹H and¹³the C NMR data were recorded on a varian gemini 300MHz instrument and the spectra obtained were referenced to a deuterated solvent. Mass spectrometry data were recorded on ESI-QIT Esquire-LC with cationic polarity. TEM images were recorded on an FEI TE CNAI-12 Transmission Electron Microscope (TEM) at 120 KV.

Synthesis of imidazolium dichloride cycloarylgem-diol (imidazolium cyclophane gem-dioldichloride)

[0100]A solution of 0.24g (1.0 mmol) 2, 6-bis (imidazolylmethyl) pyridine and 0.254g (2.0 mmol) 1, 3-dichloroacetone in 60ml acetonitrile was stirred at 75 ℃ for 8 hours and filtered to give 108 as a brown solid. Yield: 0.9 mmol, 89.6%. PF of 108 obtained by slow evaporation from acetonitrile/water₆Colorless crystals of the salt. And Mp: 175 ℃ and 178 ℃.¹HNMR(300MHz，DMSO-d₆)：δ4.68(s，4H，CH₂C(OH)₂CH₂)，5.67(s，4H，CH₂)，7.40(s，2H，NC(H)CH)，7.47(d，2H，J＝7.8Hz，m-pyr)，7.65(s，2H，C(OH)₂)，7.89(s，2H，NCHC(H))，7.94(t，1H，J＝7.8Hz，p-pyr)，9.34(s，2H，NC(H)N)。¹³C NMR(75MHz，DMSO-d₆)：δ51.8，55.2，91.1，120.5，122.0，123.9，138.0，138.8，152.6。ESI-MS m/z：384[M²⁺2Cl^-]，348[M²⁺Cl^-]。FT IR(Nujol，cm^-1): 3387, 3105, 1597, 1564, 1439, 1346, 1171, 1085, 996, 755. And (3) analysis and calculation: c, 48.54; h, 4.41; n, 16.94; cl, 17.13. And (3) observation: c, 48.33; h, 4.32; n, 16.7; cl, 16.76. Synthesis of binuclear silver hydroxide cycloarylgem-diol (dimetlear silver carbene cycloarene-diol hydroxide)

[0101]0.232g (1.0 mmol) of silver (I) oxide and 0.366g (0.9 mmol) of 108 in 70ml of formazan at room temperatureThe composition in alcohol was stirred for 50 minutes. The filtrate was concentrated to give complex 106 as a yellow solid. By slow diffusion, a single crystal of complex 106, comprising needle-shaped carbonates (a spike of carbonate), is obtained from ethanol. Yield: 0.618g, 0.738 mmol, 82%. And Mp: 202 ℃ and 204 ℃. ESI-MS m/z: 400[0.5M ]²⁺]，801[2M⁺]，837[2M⁺2OH^-]。FTIR(Nujol，cm^-1)：3415，3105，1596，1564，1439，1344，1169，1084，1028，996，758。¹³C NMR(75MHz，DMSO-d₆): δ 48.6, 51.1, 53.8, 92.1, 119.9(J ═ 1.4Hz), 121.6, 128.6, 137.8(J ═ 2.4Hz), 154.2, 184.9(J carbene-Ag ═ 211 Hz). And (3) analysis and calculation: ag, 24.54; c, 43.79; h, 4.20; and N, 15.24. And (3) observation: c, 43.15; h, 4.22; n, 14.89.

Electrospinning fibre (electrospun fiber)

[0102] Tecophilic ® was dissolved in a mixture of ethanol and tetrahydrofuran in a ratio of 9 to 1. The pre-prepared Tecophilic ® solution was mixed with the ethanol solution of complex 106. Solutions were prepared with different weight ratios between the complex 106 and Tecophilic ®. Ratios are 0/100, 25/75 and 75/25. A solution of conjugate 106 and Tecophilic ® was placed in a pipette. A potential difference of 15KV was applied between the surface of the solution drop and the grounded collector, at a distance of about 20 cm. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) were used to characterize as-spun fibers and fibers exposed to water.

Antimicrobial testing

[0103] Sterilized LB broth (5mL) was measured in a sterile tube. The microorganisms cultured in the stable phase of the bacterial ring volume (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus) were introduced into tubes containing LB broth solution. The mixture was incubated overnight at 35 ℃ in a shaking incubator. The same procedure was carried out for stationary phase cultures of fungi (Candida albicans, Saccharomyces cerevisiae, Aspergillus niger) and cultured at room temperature for 72 hours without shaking.

Fiber layer test

[0104] A constant volume (25. mu.l) of the newly grown organism was placed on LB agar plates and allowed to grow to obtain a lawn of the organism. The complex 106 and a fibrous layer of pure tecophilic (2.0 cm. times.2.0 cm) were placed on a bacterial lawn of LB agar plate (E.coli, Pseudomonas aeruginosa, Staphylococcus aureus) and cultured overnight at 35 ℃. The bactericidal activity was observed by visual inspection of growth and absence of growth in and around the fibrous layer area. The fibrous layers of approximately the same size were placed on the lawn of fungi (candida albicans, saccharomyces cerevisiae, aspergillus niger) and incubated at room temperature for 48 hours. The diameter of the clear zone (clear zone) was measured.

Minimum Inhibitory Concentration (MIC) assay

[0105] Serial dilutions were made to obtain a range of concentrations by transferring 1mL of a freshly prepared stock solution of the silver compound (with the same amount of silver particles) into sterile culture tubes containing 2mL of LB broth, labeled a. 1mL of the mixed solution of A was transferred to a culture tube B containing LB broth. The same procedure was repeated to obtain diluted solutions of tubes C, D and E. MIC was determined by visual inspection of the growth/absence of growth of the silver compounds labeled A-E at the concentrations described above inoculated with 25. mu.l of organism. After overnight culture at 35 ℃ without growth of the organisms, the next day, an additional 80. mu.l of freshly grown organisms were added to each culture and cultured at the same temperature.

Kinetic testing of bactericidal Activity

[0106] The same volume (5mL) of LB broth was measured, placed in a sterile culture tube, and inoculated with 100. mu.l of Staphylococcus aureus into each tube containing a fibrous layer of silver nitrate (12.8mg, 25mg), silver sulfadiazine (20mg), 11.3mg of complex 106/tecophilic (25: 75), and 11.4mg of complex 106/tecophilic (75: 25). The mixtures were incubated at 35 ℃ and the bactericidal activity was checked over time by streaking a loopful of each mixture onto an agar plate. The agar plates were then incubated overnight at 37 ℃ and the number of colonies of organisms formed was counted. The same procedure was repeated using 100. mu.l of Pseudomonas aeruginosa.

Animal research

[0107] Male Sprague Dawley (Harlen Sprague Dawley, Indianapolis, IN) adult mice (weighing 400-. The temperature and humidity were kept constant, with a light/dark cycle of 6.00am-6.00 pm: light, 6.00pm-6.00 am: dark. Food (Lab diet 5P00, Prolab, PMI nutrition, intl., Bretwood, Mo.) and water were provided ad libitum. Animals were anesthetized with ether for the purpose of injecting the compound into the tail vein using a 27 gauge syringe needle in a volume of 0.3ml of sterile saline. The doses of ligand were 5mg and 50 mg. At the final dose of the experiment, animals were sacrificed and liver, lung, kidney and heart tissues were removed and frozen at-70 ℃. Urine samples were collected daily for later examination of compound distribution. These studies were approved by the University of Akron Institutional Animal Care and Use Committee (IACUC).

X-ray crystal structure determination

[0108] Crystal data and structure refinement parameters (structure refinement parameters) are included in the supportive information. The crystals of 108 and complex 106 were both coated with paraffin oil, mounted on a kyro ring, and placed on an goniometer under a nitrogen stream. X-ray data were collected using Mo K α radiation (λ ═ 0.71073 Å) on a Brucker Apex CCD diffractometer at a temperature of 100K. Intensity data were integrated using SAINT software and empirical absorption correction was performed using SADABS. The structures of 108 and the complex 106 were resolved by a direct method, and the structures of 108 and the complex 106 were perfected using a full-matrix least squares method (full-matrix least squares). All non-hydrogen atoms were refined by anisotropic displacement (anistropic displacement).

[0109] It is clear that the present invention is very effective in providing a method of inhibiting the growth of microorganisms by applying an N-functionalized silver carbene complex. It is therefore to be understood that any variations which fall clearly within the scope of the claimed invention, and the selection of specific component elements therefore, may be ascertained without departing from the spirit of the invention disclosed and described herein.

Claims (33)

1. A method for inhibiting at least one of microbial, fungal and viral growth comprising the step of administering an effective amount of a silver complex of an N-heterocyclic carbene.

2. The method of claim 1, wherein the N-heterocyclic carbene is selected from the group consisting of compounds represented by the following formulae:

wherein R is₁And R₂Is, independently or in combination, hydrogen or C₁-C₁₂An organic group, said C₁-C₁₂The organic group is selected from the group consisting of alkyl, substituted alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl, alkynyl, aryl, substituted aryl, arylalkyl, alkylaryl, pyrrole, pyridine, thiophene, and alkoxy.

3. The method of claim 1, wherein the silver complex of an N-heterocyclic carbene is selected from compounds represented by the following formulae:

wherein R is selected from the group consisting of hydrogen, alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl, arylalkyl, alkylaryl, heterocycle, and alkoxy, and substituted derivatives thereof, and X is an anion.

4. The method of claim 1, wherein the silver complex of an N-heterocyclic carbene is selected from compounds represented by the following formulae:

an N-heterocyclic carbene represented by the formula:

wherein Z is a heterocyclic group, and R₁And R₂Is, independently or in combination, hydrogen or C₁-C₁₂An organic group, said C₁-C₁₂The organic group is selected from the group consisting of alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl, arylalkyl, alkylaryl, heterocycle, alkoxy, and substituted derivatives thereof.

6. According to the rightThe N-heterocyclic carbene of claim 5, wherein the Z is dimethylpyridyl, each R₁Independently is C₁-C₆Hydroxyalkyl, and R₂Is hydrogen.

7. The N-heterocyclic carbene of claim 5, wherein the Z is dimethylpyridyl, each R₁Independently is C₂-C₃Hydroxyalkyl, and R₂Is hydrogen.

8. An N-heterocyclic carbene according to claim 5, wherein Z is dimethylpyridyl, and both R are₁Together form a dimethylphenhenanthrolinyl group, and R₂Is hydrogen.

9. An N-heterocyclic carbene according to claim 5, wherein the Z is dimethylpyridyl, each adjacent R being₁And R₂Together form a substituted alkyl group.

10. The N-heterocyclic carbene of claim 9, wherein the N-heterocyclic carbene is represented by formula 26.

11. An N-heterocyclic carbene according to claim 5, wherein Z is dimethylpyridyl, and both R are₁Form a monoaryl group, and R₂Is hydrogen.

12. An N-heterocyclic carbene according to claim 11, wherein the aryl group is dimethyl phenanthroline.

13. The N-heterocyclic carbene of claim 5, wherein the Z is dimethylpyridyl, and R₂Is a substituted alkyl group.

14. The N-heterocyclic carbene of claim 5, wherein Z is dimethylpyridyl, R₁Is C₁-C₆Alkyl, and R₂Is C₁-C₆An aminoalkyl group.

15. The N-heterocyclic carbene of claim 5, wherein Z is dimethylpyrrolyl, each R₁Independently is C₁-C₆Alkyl, and R₂Is hydrogen.

16. An N-heterocyclic carbene according to claim 5, further complexed with silver.

17. An N-heterocyclic carbene according to claim 5, in turn complexed with a radioactive metal.

18. A method for synthesizing a radiopharmaceutical compound, comprising the steps of:

reacting the imidazolium salt with a transition metal complex or base to form an N-heterocyclic carbene; and

reacting the N-heterocyclic carbene with a metal to form a metal complex.

19. A method for synthesizing an antibiotic compound, comprising:

reacting the imidazolium salt with a transition metal complex or base to form an N-heterocyclic carbene; and

reacting the N-heterocyclic carbene with a silver compound to form a silver complex having an N-heterocyclic carbene.

20. A method for treating cancer cells comprising the step of administering an effective amount of a complex of an N-heterocyclic carbene with a radioactive metal.

21. A method of generating an image of one or more tissues in a patient comprising the step of administering an effective amount of a complex of an N-heterocyclic carbene with a radioactive metal.

22. A nanofiber, comprising:

a fiber-forming material; and

metal complexes of N-heterocyclic carbenes.

23. The nanofiber recited in claim 22, wherein the metal is silver or a radioactive metal selected from the group consisting of transition metals, lanthanides, and actinides.

24. A method for producing the nanofiber recited in claim 22, comprising the steps of: electrospinning an electrospun solution comprising a fiber-forming material and a metal complex of an N-heterocyclic carbene.

25. A wound dressing comprising the nanofiber of claim 22.

26. A radiopharmaceutical compound which comprises a radiometal complex of an N-heterocyclic carbene.

27. The radiopharmaceutical of claim 26 wherein the N-heterocyclic carbene has a peptide moiety, a polyamine moiety, or a combination thereof.

28. A method for treating a cancer tumor comprising the steps of: administering an effective amount of a radiometal complex of an N-heterocyclic carbene.

29. The method of claim 28, wherein the N-heterocyclic carbene has a peptide moiety, a polyamine moiety, or a combination thereof.

30. The method of claim 28, wherein the radioactive metal is an element selected from the group consisting of transition metals, lanthanides and actinides.

31. The method of claim 28, wherein the metal is Ag, Rh, Ga, or Tc.

32. A method for the synthesis of a drug or radiopharmaceutical comprising the step of carrying out a carbene transfer reaction (carbene transfer reaction) on a metal complex of an N-heterocyclic carbene.

33. The method of claim 32, wherein the silver complex of an N-heterocyclic carbene is a carbene transfer agent.