Counterion-induced modulation in biochemical properties of nitrile functionalized silver(I)-N-heterocyclic carbene complexes

Synthesis, Characterization, Antimicrobial Properties, and Antioxidant Activities of Silver-N-Heterocyclic Carbene Complexes

The emergence of antimicrobial resistance has become a major handicap in the fight against bacterial infections, prompting researchers to develop new, more effective, and multimodal alternatives. Silver and its complexes have long been used as antimicrobial agents in medicine because of their lack of resistance to silver, their low potency at low concentrations, and their low toxicity compared to most commonly used antibiotics. N-Heterocyclic carbenes (NHCs) are widely used for coordination of transition metals, mainly in catalytic chemistry. In this study, several N-alkylated benzimidazolium salts 2a-j were synthesized. Then, the N-heterocyclic carbene (NHC) precursor was treated with Ag₂O to give silver (I) NHC complexes (3a-j) at room temperature in dichloromethane for 48 h. Ten new silver-NHC complexes were fully characterized by nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), elemental analysis, and LC-MSMS (for complexes) techniques. The antibacterial and antioxidant activities of salt 2 and its silver complex 3 were evaluated. All of these complexes were more effective against bacterial strains than comparable ligands. With MIC values ranging from 6.25 to 100 g/ml, the Ag-NHC complex effectively showed strong antibacterial activity. Antioxidant activity was also tested using conventional techniques, such as 2, 2-diphenyl-1-picrylhydrazine (DPPH) and hydrogen peroxide scavenging assays. In DPPH and ABTS experiments, compounds 3a, 3b, 3c, 3e, 3g, and 3i showed significant clearance.

Palladium (II), platinum (II) and silver (I) complexes with oxazolines: Their synthesis, characterization, DFT calculation, molecular docking and antitumour effects

Six new Pd(II), Pt(II) and Ag(I) complexes, (1);{Pd (L₁)]2C₆H₄}₂Cl₄} (2); Pt(L₂)(DMSO)Cl; 3; {PtL₅]₂C₆H₄}₂·PhCOO^-⋅11NO₃^-; 4; {[Pt(L₄)]₂C₆H₄}; the binuclear cyclometalated complex the polymer chain (5); {[PtL₅]C₆H₄}·NO₃^-}; and the polymeric silver species (6); Zn(L₆)₂·AgNO₃·CHCl₃ were synthesized and thoroughly characterized using X-ray diffraction and spectroscopic techniques (L₁=(S,S)-1,4-i-PrOx]₂C₆H₄}₂Cl₄, L₂=Di(2,2-bis(4R-isopropyl-4,5-dihydro-oxazol-2-yl)acetonitrile) zinc (II) (B_R1);L₃= 1,4-bis(4R-benzyl-4,5-dihydro-oxazol-2-yl)benzene (A_R2); L₄= 1,4-bis(4R-benzyl-4,5-dihydro-oxazol-2-yl)benzene，L₅=1,4-bis(4R-benzyl-4,5-dihydro-oxazol-2-yl)-benzene，L₆=Di(2,2-bis(4S-isopropyl-4,5-dihydrooxazol-2-yl)acetonitrile) zinc (II). Complexes 1-6 showed cytotoxic effects against human tumour cell lines, including a multidrug-resistant subline. Oxazoline and Pd complex 1 induced apoptosis in A549 cells. DFT calculations were also performed to exhibit the excellent bioactivity of complex 1 against A549, MDA-MB-231, and KB cells. Complex 1, with the best docking score and a stable interaction network within the binding site of the G-quadruplex, could stably interact with the G-quadruplex. Additionally, complex 1 was further used in the animal experiment of human lung adenocarcinoma cells in nude mice. By comparing with the model control group, the tumour volume, relative tumour volume and relative tumour proliferation rate T/C decreased significantly in the cisplatin group and compound 1 (complex 1) group.

A focus on the biological targets for coinage metal-NHCs as potential anticancer complexes

Metal complexes of N-heterocyclic carbene (NHC) ligands are the object of increasing attention for therapeutic purposes. Among the different metal centres, interest on Au-based compounds started with the application as anti-arthritis drugs. On the other hand, Ag(I) antimicrobial properties have been known for a long time. For Au(I)/Au(III)-NHC and Ag(I)-NHC anti-tumour and anti-proliferative properties have been quite recently demonstrated. In addition to these and as for Group 11, copper is a much less investigated metal centre, but a few papers underline its pharmacological potential. This review wants to focus on the different biological targets for these metal-based compounds. It is divided into chapters which are respectively devoted on: i) mitochondria and thiol oxidoreductase systems; ii) other relevant enzymes; iii) nucleic acids. Examples of representative coinage NHCs for each of the targets are provided together with significant references on recent advances on the topic. Moreover, a final comment summarises the aspects enlightened by each chapter and provides some hints to better understand the metal-NHCs mechanistic behaviour based on structure-activity relationships.

A Novel Ag-N-Heterocyclic Carbene Complex Bearing the Hydroxyethyl Ligand: Synthesis, Characterization, Crystal and Spectral Structures and Bioactivity Properties

In this study, a novel silver N-heterocyclic carbene (Ag-NHC) complex bearing hydroxyethyl substituent has been synthesized from the hydroxyethyl-substituted benzimidazolium salt and silver oxide by using in-situ deprotonation method. A structure of the Ag-NHC complex was characterized by using UV-Vis, FTIR, 1H-NMR and 13C-NMR spectroscopies and elemental analysis techniques. Also, the crystal structure of the novel complex was determined by single-crystal X-ray diffraction method. In this paper, compound 1 showed excellent inhibitory effects against some metabolic enzymes. This complex had Ki of 1.14 0.26 µM against human carbonic anhydrase I (hCA I), 1.88±0.20 µM against human carbonic anhydrase II (hCA I), and 10.75±2.47 µM against α-glycosidase, respectively. On the other hand, the Ki value was found as 25.32±3.76 µM against acetylcholinesterase (AChE) and 41.31±7.42 µM against butyrylcholinesterase (BChE), respectively. These results showed that the complex had drug potency against some diseases related to using metabolic enzymes.

Green synthesis of selenium-N-heterocyclic carbene compounds: Evaluation of antimicrobial and anticancer potential

Three benzimidazolium salts (III-V) and respective selenium adducts (VI-VIII) were designed, synthesized and characterized by various analytical techniques (FT-IR and NMR ¹H, ¹³C). Selected salts and respective selenium N-Heterocyclic carbenes (selenium-NHC) adducts were tested in vitro against Cervical Cancer Cell line (Hela), Breast Adenocarcinoma cell line (MCF-7), Retinal Ganglion Cell line (RGC-5) and Mouse Melanoma Cell line (B16F10) using MTT assay and the results were compared with standard drug 5-Fluorouracil. Se-NHC compounds and azolium salts showed significant anticancer potential. Molecular docking studies of compounds (VI, VII and VIII) showed strong binding energies and ligand affinity toward following angiogenic factors: VEGF-A (vascular endothelial growth factor A), EGF (human epidermal growth factor), HIF (Hypoxia-inducible factor) and COX-1 (Cyclooxygenase-1) suggesting that the anticancer activity of adducts (VI, VII and VIII) may be due to their strong anti-angiogenic effect. In addition, compounds III-VIII were screened for their antibacterial and antifungal potential. Adduct VI was found to be potent anti-fungal agent against A. Niger with zone of inhibition (ZI) value 27.01 ± 0.251 mm which is better than standard drug Clotrimazole tested in parallel.

A comparative insight into the bioactivity of mono- and binuclear silver(I)-N-heterocyclic carbene complexes: synthesis, lipophilicity and substituent effect

Silver(I)-N-heterocyclic carbene (Ag(I)-NHC) complexes of mononuclear and binuclear species, synthesised by our group and others in recent years, offer a fascinating outlook on their bioactivity. These complexes advance a range of adaptable structural patterns, leading to intra-specific variation in anticancer and antimicrobial activities. This study therefore reviews the synthesis, structural analysis and bioactivity of Ag complexes derived from mononuclear-NHC complexes either with coordinating or non-coordinating anions and binuclear NHC complexes. Specifically, the effect of stability, chain lengths and lipophilicity on the biological activity of recently reported Ag(I)-NHC complexes is reviewed. These complexes can be further explored as novel antibacterial and anticancer drugs in the nearest future.