Redox-active Silver N-heterocyclic Carbene Complexes

Redox-active Silver N-heterocyclic Carbene Complexes
Author: Kotiba Malek
Publisher:
Total Pages: 55
Release: 2018
Genre: Antibacterial agents
ISBN:

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Bacterial resistance to current ß-lactam antibiotics necessitates new therapeutic approaches. Silver-based drugs offer a promising alternative because of their antibacterial properties and minimal bacterial resistance. However, many silver-based antibacterial drugs rapidly release silver ions, limiting the bioavailability of silver ions for a longer period of time. Recently, N-heterocyclic carbenes (NHC) containing silver complexes have become a popular subject of research due to their versatility and the slow release of silver ions under biological conditions. To further enhance the efficacy of silver-NHC drugs, we fused redox-active substituents such as naphthoquinone and ferrocenes to NHCs. Both naphthoquinone and ferrocenes have been shown to increase reactive oxygen species (ROS) under biological conditions that may augment the antibacterial action of redox-active silver-NHC complexes. Herein, we report synthesis and characterization of several redox-active silver-NHC complexes, 1-(ferrocenylmethyl)-3-mesityl-imidazol-2-ylidene silver chloride [(2)AgCl] (compound 6), 1,3-di (ferrocenylmethyl)imidazol-2-ylidene silver chloride [(3)AgCl] (compound 7), bis (1-benzyl-3-mesitylimidazol-2-ylidene) silver chloride [(1)2Ag][Cl], (compound 9), Bis (1-(ferrocenylmethyl)-3-mesityl-imidazol-2-ylidene) silver chloride [(2)2Ag][Cl] (compound 10), Bis (1,3 di(ferrocenylmethyl)imidazole-2-ylidene) silver chloride [(3)2Ag][Cl] (compound 11), and bis (1,3-dimesityl-4,5-naphthoquino-imidazol-2-ylidene) silver chloride [(4)2Ag][Cl] (compound 12). Complexes were identified and confirmed via various analytical techniques, including 1H NMR, 13C NMR, infrared spectroscopy, UV-vis spectroscopy, and single crystal X-ray crystallography.A series of cyclic and differential pulse voltammetry experiments were conducted on the complexes to investigate their electrochemical properties. Complexes [(2)AgCl], [(3)AgCl], [(2)2Ag][Cl], [(2)2Ag][Cl], [(3)2Ag][Cl], and [(4)2Ag][Cl] exhibited redox activity attributed to the presence of ferrocene and naphthoquinone moiety. Their antibacterial properties were tested against gram-negative bacterial strains (Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa) and showed excellent antibacterial properties that are comparable to previously reported silver-NHC complexes. All silver-NHC complexes detailed in this report exhibit MIC and MBC values in the range of 2-12.5 æg/mL. Further mechanistic studies are necessary to elucidate the manner in which these complexes affect bacterial cells.

The Great Potential of Redox Active Ligands

The Great Potential of Redox Active Ligands
Author: Meredith Miles
Publisher:
Total Pages: 60
Release: 2018
Genre: Biochemistry
ISBN:

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Metal N-heterocyclic carbene (NHC) complexes have recently gained much popularity due to their tunable, steric, and electronic properties. Applications for such versatile molecules include organocatalysis1 2 3, olefin metathesis4 5 6, sundry cyclization reactions7 8 9, and materials chemistry10 11. Redox active NHCs are of special interest due to their ability to alter the electronic properties of the metal centers they are ligated to.12 In the first chapter, Au(I)-NHC complexes were synthesized and tested for biological activity in human cancer cell lines. Increasing reactive oxygen species (ROS) in cellular systems has proven to be a successful pathway for treating cancer13 14 15. The redox active group in this case was naphthoquinone which contributed to the oxidative stress applied to the tumor cells. Three Au(I)-NHC complexes were synthesized and analyzed structurally utilizing 1H NMR, 13C NMR, and X-ray crystallography. Biological studies including IC50 cell culture lines and cell proliferation analyses were performed to determine the complexes' efficiency and success as a cancer treatment drug. The second chapter describes a theoretical approach to synthesize a redox active tetrathiafulvalene (TTF) fused with an iridium-NHC complex to serve as a redox switchable catalyst. The first compound in this synthetic route was successfully synthesized and analyzed structurally with 1H and 13C NMR, UV-Vis spectroscopy, and IR spectroscopy. The electrochemical properties were also investigated. Tetrathiafulvalene possesses the ability to undergo multiple one electron reversible redox transformations. This unique characteristic paired with the catalytic properties of iridium-NHC could produce a catalyst capable of accessing three or more catalytic species based upon the oxidation state of TTF.

Electrogenerated Chemiluminescence

Electrogenerated Chemiluminescence
Author: Allen J. Bard
Publisher: CRC Press
Total Pages: 707
Release: 2004-07-20
Genre: Science
ISBN: 1135535795

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The first source on this expanding analytical science, this reference explores advances in the instrumentation, design, and application of techniques with electrogenerated chemiluminescence (ECL), examining the use and impact of ECL-based assays in clinical diagnostics, life science research, environmental testing, food and water evaluation, and th

Silver(I) and Gold(I) N-heterocyclic Carbene Complexes

Silver(I) and Gold(I) N-heterocyclic Carbene Complexes
Author: Semih Durmus
Publisher:
Total Pages: 193
Release: 2006
Genre: Anti-infective agents
ISBN:

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"The introduction of N-heterocyclic carbenes (NHCs) to organometallic and inorganic chemistry was achieved by the synthesis and isolation of chromium and mercury NHC complexes by Öfele and Wanzlick in 1968. The synthesis and characterization of numerous carbene metal complexes by Lappert et al were a significant contribution to this area of chemistry. NHCs have become an important area of research after the isolation of the first stable carbene by Arduengo in 1991. In chapter 1, the synthesis and biological activities of NHCs and their silver(I) and gold(I) derivatives are discussed. In chapter 2, the synthesis and characterization of an imidazolium-linked cyclophane is discussed as well as its potential use as a medicinal agent. In chapter 3, the synthesis and characterization of a silver(I) NHC complex is reported. The antimicrobial activity of the silver(I) NHC complex is also reported against clinically important bacteria. In chapter 4, the synthesis of a variety of silver(I) NHC complexes and their carbene transfer reactions to gold(I) reagents are reported. The gold(I) NHC complexes are also investigated for their anticancer properties. In chapter 5, the use of urocanic acid as NHC precursor is reported. The synthesis and characterization of the first silver(I) NHC complex derived from biological molecule urocanic acid is discussed as well as its antimicrobial activity."--Abstract.

N-Heterocyclic Carbenes in Organocatalysis

N-Heterocyclic Carbenes in Organocatalysis
Author: Akkattu T. Biju
Publisher: John Wiley & Sons
Total Pages: 407
Release: 2019-01-07
Genre: Science
ISBN: 3527809058

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Summarizing the emerging field of N-heterocyclic carbenes used in organocatalysis, this is an excellent overview of the synthesis and applications of NHCs focusing on carbon-carbon and carbon-heteroatom bond formation. Alongside comprehensive coverage of the synthesis, characteristics and applications, this handbook and ready reference also includes chapters on NHCs for polymerization reactions and natural product synthesis.

N-Heterocyclic Carbenes

N-Heterocyclic Carbenes
Author: Steven P. Nolan
Publisher: Wiley-VCH
Total Pages: 0
Release: 2014-11-03
Genre: Science
ISBN: 9783527334902

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This comprehensive reference and handbook covers in depth all major aspects of the use of N-heterocyclic carbene-complexes in organic synthesis: from the theoretical background to characterization, and from cross-coupling reactions to olefin metathesis. Edited by a leader and experienced scientist in the field of homogeneous catalysis and use of NHCs, this is an essential tool for every academic and industrial synthetic chemist.

Synthesis, Characterization and Applications of Complexes Involving Redox-active Ligands

Synthesis, Characterization and Applications of Complexes Involving Redox-active Ligands
Author: Romain Kunert
Publisher:
Total Pages: 0
Release: 2022
Genre:
ISBN:

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We developed a new type of redox-active ligand, involving two N-heterocyclic carbenes and two phenolate units. The strong electron donating properties of the NHC moieties were utilized to stabilize complexes in high oxidation states while the phenolate groups were used as redox-active units. Group 10 metal complexes were developed. Their oxidation chemistry showed the formation of phenoxyl radicals, reaching up to two-electron oxidized, bis(phenoxyl) complexes. We also report the first Ni(III) complex with NHC donors. The ligand was also used to develop metal complexes with nitride ligands. The nitridomanganese complex proved to be unstable and degraded in successive intramolecular nitride-NHC reductive couplings. The degradation afforded a peculiar organic salt with three fused rings forming a central triazone pattern. Conversely, the chromium nitride complex could be isolated and thoroughly characterized. The one-electron oxidized product was generated reversibly at low temperature but readily evolved at room temperature. In a parallel work, we also developed new types of sterically hindered salen ligands to form distorted copper salen complexes as molecular models of galactose oxidase. The copper salen catalysts showed to be effective for the aerobic oxidation of non-activated alcohol substrates.

N-Heterocyclic Carbenes in Transition Metal Catalysis

N-Heterocyclic Carbenes in Transition Metal Catalysis
Author: Frank Glorius
Publisher: Springer
Total Pages: 240
Release: 2007-02-05
Genre: Science
ISBN: 3540369309

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In this book leading experts have surveyed major areas of application of NHC metal complexes in catalysis. The authors have placed a special focus on nickel- and palladium-catalyzed reactions, on applications in metathesis reactions, on oxidation reactions and on the use of chiral NHC-based catalysts. This compilation is rounded out by an introductory chapter and a chapter dealing with synthetic routes to NHC metal complexes.