Mohd. R. Razali

Dinuclear silver(I)-N-heterocyclic carbene complexes of N-allyl substituted (benz)imidazol-2-ylidenes with pyridine spacers: synthesis, crystal structures, nuclease and antibacterial studies

The synthesis, structures and antibacterial studies of silver complexes of N-heterocyclic carbene (NHC) ligands are reported. The NHC precursors, 2,6-bis(3-allylimidazol-1-ylmethyl) pyridine hexafluorophosphate (1) and 2,6-bis(3-allylbenzimidazol-1-ylmethyl)pyridine dibromide (2) were treated with Ag2O to yield 2,6-bis(3-allylimidazol-1-ylmethyl)pyridine disilver bis(hexafluorophosphate) (3) and 2,6-bis(3-allylbenzimidazolium-1-ylmethyl)pyridine disilver bis(hexafluorophosphate) (4). All four compounds were characterized by physico-chemical and spectroscopic techniques and by single-crystal X-ray diffraction. The compounds were screened for their antibacterial activities against Staphylococcus aureus (ATCC 12600) as a Gram-positive and Escherichia coli (ATCC 11303) as a Gram-negative bacteria. Compounds 1 and 2 showed no inhibition while 3 and 4 inhibited the growth of these bacteria. The nuclease activities of the compounds were evaluated by gel electrophoresis, and the results indicate that complexes 3 and 4 can degrade both DNA and RNA.

Synthesis and crystal structures of sterically tuned ether functionalized NHC–silver(I) complexes: antibacterial and nucleic acid interaction studies

A series of new imidazolium salts (1–4) as N-heterocyclic carbene (NHC) precursors have been synthesized by successive N-alkylation method. Reactions of these salts with Ag2O by varying the metal to salt ratio forms a series of new Ag(I)–NHC complexes (5–8). All compounds were characterized by physico-chemical and spectroscopic techniques. The molecular structures of 1 and 5 were characterized by single-crystal X-ray diffraction analysis. A comparative investigation of the bacterial growth inhibition potential of the salts and respective complexes indicates that 5–8 displayed good antibacterial activities on Staphylococcus aureus (ATCC 12600) and Escherichia coli (ATCC 11303) compared with the salts. Furthermore, it was observed that with increase in chain length at N-positions, the antibacterial activities also increased. Nuclease activity of the reported salts and Ag(I)–NHC complexes with nucleic acids (DNA and RNA) were also studied using agarose gel electrophoresis; the results show that the compounds do not have any apparent interaction with nucleic acids in the absence of hydrogen peroxide (H2O2). However, 5 and 8 were efficient in promoting the cleavage of nucleic acids in the presence of H2O2. Graphical Abstract

Sterically modulated silver(I) complexes of N-benzyl-substituted N-heterocyclic carbenes: synthesis, crystal structures and bioactivity

Abstract The reaction of non-symmetrically substituted N-benzyl benzimidazolium salts (1–3) with Ag2O gives Ag(I)–NHC complexes (4–6) of the type [NHC–Ag–NHC]PF6, (NHC: benzimidazol-2-ylidene). Structures of these compounds were elucidated by physico-chemical and spectroscopic techniques. The mononuclear structures of complexes 4 and 5 in the solid state were further confirmed by single-crystal X-ray diffraction studies. The effect of substitutions on antibacterial activities of compounds 1–6 by successive N-alkylation has been investigated. The compounds were screened for their antibacterial efficacy against Staphylococcus aureus (ATCC 12600) as a Gram-positive bacterium and Escherichia coli (ATCC 25922) as a Gram-negative bacterium. All the Ag(I)–NHC complexes, in general, showed good antibacterial activities while their corresponding salts were inactive against both strains of bacteria. The results of this investigation showed that E. coli and S. aureus appeared markedly inhibited. It was observed that the derivatives of the Ag(I)–NHC complexes with longer alkyl chains were more bioactive. In order to gain preliminary insights into their actual mode of action(s), circular plasmid pTS414 DNA was exposed to gel electrophoresis and it was found that all the complexes were efficient in promoting the cleavage or degradation of DNA in the absence of an oxidant.

Mononuclear and coordination polymer of silver(I) complexes: design, synthesis, and crystal structure analysis

A series of mononuclear structures and coordination polymers of silver(I) has been synthesized and characterized by IR spectroscopy, NMR spectroscopy, and single-crystal X-ray diffraction. Reaction of the silver(I) precursor [Ag(PPh3)2(OAc)] with 2,3-pyridinedicarboxylic acid (2,3-pyCOOH), 2,6-pyridinedicarboxylic acid (2,6-pyCOOH), 3-pyridinecarboxylic acid (3-pyCOOH), and 4-pyridinecarboxylic acid (4-pyCOOH) afforded mononuclear complexes [Ag(PPh3)2(2,3-COO)] (1), [Ag(PPh3)2(2,6-COO)]·EtOH·MeCN (2), [Ag(PPh3)2(3-COO)]·H2O (3), and [Ag(PPh3)2(4-COO)] (4), respectively. Coordination polymers [Ag(PPh3)(2,3-COO)]n (5), [Ag2(PPh3)2(3-pyCOO)2]n (6), and [Ag(PPh3)2(4-COO)]n·EtOH (7) were obtained from reaction of Ag(OAc), PPh3, and pyridinedicarboxylic acid or pyridinecarboxylic acid. Even though the formation of 5 can be achieved by hydrothermal reaction using similar reactants to those in formation of 1, the percentage yield and by-products of the final product prohibit further analysis of the compound. Complexes 5 and 6 are 1-D zigzag and ladder type structures, respectively, with argentophilic interactions, Ag⋯Ag, dominating the stability of 6. Complex 7 shows a 2-D layer structure with three-connected 4.82-fes topology.

Linear Trinuclear Copper(II) Complexes Derived from the Nucleophilic Addition Products of Dicyanonitrosomethanide [C(CN)2(NO)]–: Syntheses, Structures, and Magnetic Properties

Two novel trinuclear CuII complexes have been synthesised from the nucleophilic addition derivatives of the small cyano anion, dicyanonitrosomethanide (dcnm). The reaction of CuII with the water adduct ligand, carbamoylcyanonitrosomethanide (ccnm) and teaH3 (triethanolamine) in a basic MeOH/MeCN solution results in the formation of [Cu3(acnm)2(teaH2)2]·2MeOH (1) (acnm = amidocarbonyl(cyano)nitrosomethanide and teaH2– = singly deprotonated triethanolamine). The reaction of CuII with dicyanonitrosomethanide (dcnm) and m-xylenediamine in a basic MeOH/MeCN solution results in the formation of [Cu3(cimm)2(a3acnm)2]·6MeCN (2) (cimm = cyano(imido(methoxy)methyl)nitrosomethanide and a3acnm = {amino(3-aminomethylphenyl)methylimino}methyl(cyanonitrosomethanide)). Both complexes display linear trinuclear CuII metallic cores. Solid state DC magnetic susceptibility studies were performed on 1 and 2. Compound 1 revealed very strong antiferromagnetic interactions between central and terminal Cu atoms, while compound 2 displayed ferromagnetic interactions because of the orthogonal relationship of the terminal and the central ‘magnetic’ orbitals, which contrasts with these orbitals being coplanar in 1 thus providing strong superexchange pathways involving Cu-N-O-Cu moieties.

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

Abstract 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.

Synthesis, crystal structure, in vitro anticancer and in vivo acute oral toxicity studies of tetramethylene linked bis-benzimidazolium salts and their respective dinuclear Ag(I)–NHC complexes

Abstract The proligands of the series tetramethylenebis(N-n-alkylbenzimidazolium bromide) (where n = 3–10) (1–8) as N-heterocyclic carbene (NHC) precursors have been prepared by reacting the initially synthesized N-n-alkyl benzimidazole with 1,4-dibromobutane in 2 : 1 M ratio. A reaction of Ag2O with 1–8 resulted in the formation of Ag(I) complexes tetramethylenebis{(N-n-alkylylbenzimidazol-2-ylidene)silver(I)hexafluorophosphate} (9–16), respectively. All the synthesized compounds were characterized by FT-IR, 1H NMR, 13C NMR, atomic absorption and elemental analysis. Single-crystal X-ray diffraction study on tetramethylenebis{(N-n-octylbenzimidazol-2-ylidene)silver(I)hexafluorophosphate} (14) has revealed that the complex exists as a dinuclear compound. All compounds were assessed for their antiproliferation test on human colorectal cancer cell line (HCT 116). Interestingly, increasing the n-alkyl chain length from n = 3 to 10 of the proligands and their respective complexes showed trends in increased cytotoxicity against human colon cancer cell line. Cytotoxicity data showed that tetramethylene linked bis-benzimidazolium salts and their respective dinuclear Ag(I)–NHC complexes can be useful therapeutic agents against colon cancer.

Crystal structure of (E)-4-meth-oxy-2-{[(5-methyl-pyridin-2-yl)imino]-meth-yl}phenol.

The molecule of the title Schiff base compound, C14H14N2O2, displays an E conformation with respect the imine C=N double bond. The molecule is approximately planar, with the dihedral angle formed by the planes of the pyridine and benzene rings being 5.72 (6)°. There is an intramolecular hydrogen bond involving the phenolic H and imine N atoms.

Structure and magnetism of a mixed-valence octanuclear manganese(II/III) cluster derived from carbamoylcyanonitrosomethanide (ccnm)

A mixed-valence octanuclear manganese complex of formula [Mn(II)(4)Mn(III)(4)O(4)(ccnm)(12)]·4MeCN·7H(2)O (1·4MeCN·7H(2)O) (ccnm = carbamoylcyanonitrosomethanide) has been synthesized and characterized by single crystal X-ray diffraction, IR spectroscopy, elemental analysis and magnetic measurements. The metal core of 1 adopts a tetra-capped (with Mn(II) ions) distorted [Mn(III)(4)O(4)](4+) cubane topology, with a three-J magnetic analysis indicating that the cluster displays dominant antiferromagnetic interactions. Three equally possible fits were obtained, all leading to a spin ground state of S = 0 with S = 1, 2 and 3 close in energy. Comparisons of the magnetic analysis are made with that published for a related Mn(8) cluster and, more generally, with other Mn(III)Mn(III) and Mn(III)Mn(II) fragments in clusters of various types.

Temperature- and pressure-dependent utilising dimensionality cross-over of Silver(I) complex supported by short Ag···Ag Interactions

Abstract Two Ag(I)-based complexes, a mononuclear [Ag(PPh3)2(2tpCOO)]·EtOH (1) and a tetranuclear [Ag4(PPh3)4(2tpCOO)4] (2) have been prepared by a small tuning on the molar ratio of the reactants as well as the crystallisation method. A 1-D polymeric structure, [Ag2(PPh3)(2tpCOO)2]n (3) was obtained while the crystals of 2 were left under high temperature and autogenous pressure. The study suggests that the formation of 1-D polymeric structure is due to the removal along with the intramolecular and intermolecular reorganisation of the coordinated ligands that leads to dimensionality cross-over from 0-D to 1-D. The rearrangement of the ligands in 3 also resulted the metal centres moving closer together, being separated by 2.9626(3) Å in 3, compared to 3.215(8) Å in 2. The photoluminescence properties have been investigated showing that only complexes 2 and 3 exhibit this property at room temperature in solid state that is due to metal-to-ligand charge transfer.