Silver (I) N-Heterocyclic Carbene Complexes: A Winning and Broad Spectrum of Antimicrobial Properties

Abstract

The evolution of antibacterial resistance has arisen as the main downside in fighting bacterial infections pushing researchers to develop novel, more potent and multimodal alternative drugs.Silver and its complexes have long been used as antimicrobial agents in medicine due to the lack of silver resistance and the effectiveness at low concentration as well as to their low toxicities compared to the most commonly used antibiotics. N-Heterocyclic Carbenes (NHCs) have been extensively employed to coordinate transition metals mainly for catalytic chemistry. However, more recently, NHC ligands have been applied as carrier molecules for metals in anticancer applications. In the present study we selected from literature two NHC-carbene based on acridinescaffoldand detailed nonclassicalpyrazole derived mono NHC-Ag neutral and bis NHC-Ag cationic complexes. Their inhibitor effect on bacterial strains Gram-negative and positivewas evaluated. Imidazolium NHC silver complex containing the acridine chromophore showed effectiveness at extremely low MIC values. Although pyrazole NHC silver complexes are less active than the acridine NHC-silver, they represent the first example of this class of compounds with antimicrobial properties. Moreover all complexesare not toxic and they show not significant activity againstmammalian cells (Hek lines) after 4 and 24 h. Based on our experimental evidence, we are confident that this promising class of complexes could represent a valuable starting point for developing candidates for the treatment of bacterial infections, delivering great effectiveness and avoiding the development of resistance mechanisms.

Chemical Composition and Biological Activities of Prangos ferulacea Essential Oils

“…The microdilution method established by the Clinical and Laboratory Standards Institute (CLSI) was used to evaluate of minimal inhibitory concentrations (MICs) of P. ferulacea essential oil against the Gram-positive and Gram-negative strains. In addition, ~5 × 10 5 CFU/mL was added to 95 µL of Mueller–Hinton broth (CAM-HB; Difco) with or without P. ferulacea essential oil at different concentrations (1–200 µg/mL) [ 49 ]. After overnight incubation at 37 °C, MIC 100 values were determined as the lowest concentration responsible for the absence of visible bacterial growth.…”

A Fluoroponytailed NHC–Silver Complex Formed from Vinylimidazolium/AgNO3 under Aqueous–Ammoniacal Conditions

“…While it was difficult to assess the success of the reaction via FT-IR owing to strong C-F vibrations that dominate the educt as well as the product spectrum (Figure S5), the 1 H NMR spectrum proves the formation of a singular carbene species, as evidenced by the complete disappearance of the C2 proton and shifts in the heterocyclic resonances (Figure S2). Additionally conducted 13 C (Figure S1), 19 F (Figure S3) and 19 F- 13 C HSQC NMR experiments (Figure S4) showed six peaks for the perfluorohexyl moieties, revealing that the complex sustains a chemically equivalent conformation and thus exists as Ag + (FNHC) 2 in solution.…”

“…Molecules 2022, 27, 4137 2 of 9 NHC derivatives) exhibit good biocompatibility and have opened new horizons in life sciences [16][17][18]. In particular, they garnered enormous attention in biological as well as pharmaceutical research, for example, as antimicrobial [19][20][21][22] and cytostatic agents [23][24][25][26][27]. The profiles of bioactivity depend on either lipophilicity [28] or fluorophilicity [29], which in turn are primarily contingent on the chain length of the nitrogen substituents.…”

Dihydrophenanthrenes from a Sicilian Accession of Himantoglossum robertianum (Loisel.) P. Delforge Showed Antioxidant, Antimicrobial, and Antiproliferative Activities

“…Each experiment was performed in triplicate, and the reported result was an average of three independent experiments (p value was <0.05). Subsequently to determine the minimal inhibitory concentration values, assays were performed as previously described elsewhere [72]. Briefly, bacteria were grown to a midlogarithmic phase at 37 • C and then diluted to 1 × 10 6 CFU/mL in Difco 0.5× Nutrient Broth (Becton-Dickenson, Franklin Lakes, NJ, USA) containing increasing amounts of loroglossol and hircinol.…”