Is the C=O frequency shift a reliable indicator of coumarin binding to metal ions through the carbonyl oxygen?

The coumarin ligand, 4-hydroxy-3-nitro-2H-chromen-2-one (Hhnc) and its Cu(II) and Ag(I) complexes were studied by DFT calculations at B3LYP/B1 and PW91/B1 levels. MEP of the deprotonated ligand, hnc-, and energy calculations of model metal complexes predicted the ligand binding to the metal ion through the hydroxyl and the nitro oxygens in agreement with experiment. Based on precisely selected Cu/Ag model complexes with hnc-, a relation between the vibrational behaviour of the ligand donor groups and the ligand binding modes in the complexes was deduced. The observed carbonyl m(C=O) downshift (50–90 cm-1) is attributed to intermolecular H-bonding formed between the C@O group and lattice water molecules or due to the C@O binding to the metal ion in case of bridging coumarin ligand (in Aghnc). Much larger m(C=O) downshift (~220–240 cm-1) is predicted in case of monodentate or bidentate (with the nitro group) bonding of the carbonyl C=O group to the metal ion

Copper(II) complexes of coumarin-derived Schiff bases and their anti-Candida activity.

The condensation of 7-amino-4-methyl-coumarin (1) with a number of substituted salicylaldehydes yielded a series of Schiff bases (2a–2k) in good yields. Subsequent reaction of these ligands with copper( II) acetate yielded Cu(II) complexes (3a–3k) and some were characterised using X-ray crystallography. All of the free ligands and their metal complexes were tested for their anti-Candida activity. A number of the ligands and complexes exhibited anti-Candida activity comparable to that of the commercially available antifungal drugs, ketoconazole and Amphotericin B

Mechanism of action of coumarin and silver(I)- coumarin complexes against the pathogenic yeast Candida albicans

The anti-fungal activity and mode of action of a range of silver(I)- coumarin complexes was examined. The most potent silver(I)- coumarin complexes, namely 7-hydroxycoumarin-3-carboxylatosilver(I), 6-hydroxycoumarin-3-carboxylatosilver(I) and 4-oxy-3-nitrocoumarinbis(1,10-phenanthroline)silver(I), had MIC80 values of between 69.1 and 4.6 M against the pathogenic yeast Candida albicans. These compounds also reduced respiration, lowered the ergosterol content of cells and increased the trans-membrane leakage of amino acids. A number of the complexes disrupted cytochrome synthesis in the cell and induced the appearance of morphological features consistent with cell death by apoptosis. These compounds appear to act by disrupting the synthesis of cytochromes which directly aVects the cell's ability to respire. A reduction in respiration leads to a depletion in ergosterol biosynthesis and a consequent disruption of the integrity of the cell membrane. Disruption of cytochrome biosynthesis may induce the onset of apoptosis which has been shown previously to be triggered by alteration in the location of cytochrome c. Silver(I)- coumarin complexes demonstrate good anti-fungal activity and manifest a mode of action distinct to that of the conventional azole and polyene drugs thus raising the possibility of their use when resistance to conventional drug has emerged or in combination with such drugs

Copper(II) Complexes of Coumarin-Derived Schiff Bases and their anti-Candida Activity

The condensation of 7-amino-4-methyl-coumarin (1) with a number of substituted salicylaldehydes yielded a series of Schiff bases (2a–2k) in good yields. Subsequent reaction of these ligands with copper( II) acetate yielded Cu(II) complexes (3a–3k) and some were characterised using X-ray crystallography. All of the free ligands and their metal complexes were tested for their anti-Candida activity

Anticancer and Antifungal Activity of Copper(II) Complexes of Quinolin-2(1H)-one-Derived Schiff Bases

The condensation of substituted aromatic aldehydes with 7-amino-4-methyl-quinolin-2(1H)-one (1) has lead to the isolation of quinolin-2(1H)-one derived Schiff bases (2–14). The copper(II) complexes (2a–14a) of the ligands were also prepared, and together with their corresponding free ligands were fully characterised by elemental analyses, spectral methods (IR, 1H and 13C NMR, AAS, UV–Vis), magnetic and conductance measurements. The bidentate ligands coordinated to the copper(II) ion through the deprotonated phenolic oxygen and the azomethine nitrogen of the ligands in almost all cases. X-ray crystal structures of two of the complexes, 5a and 8a, confirmed the bidentate coordination mode. All of the compounds were investigated for their antimicrobial activities against the fungus, Candida albicans, and against Gram-positive and Gram-negative bacteria. The compounds were found to have excellent anti-Candida activity but were inactive against Staphylococcus aureus and Escherichia coli. Selected compounds (2–8 and 2a–8a) were also screened for their in vitro anticancer potential using the human hepatic carcinoma cell line, Hep-G2. Several derivatives were shown to be active comparable to that of cisplatin

Anticancer and antifungal activity of copper(II) complexes of quinolin-2(1H)-one-derived Schiff bases

The condensation of substituted aromatic aldehydes with 7-amino-4-methyl-quinolin-2(1H)-one (1) has lead to the isolation of quinolin-2(1H)-one derived Schiff bases (2–14). The copper(II) complexes (2a–14a) of the ligands were also prepared, and together with their corresponding free ligands were fully characterised by elemental analyses, spectral methods (IR, 1H and 13C NMR, AAS, UV–Vis), magnetic and conductance measurements. The bidentate ligands coordinated to the copper(II) ion through the deprotonated phenolic oxygen and the azomethine nitrogen of the ligands in almost all cases. X-ray crystal structures of two of the complexes, 5a and 8a, confirmed the bidentate coordination mode. All of the compounds were investigated for their antimicrobial activities against the fungus, Candida albicans, and against Gram-positive and Gram-negative bacteria. The compounds were found to have excellent anti-Candida activity but were inactive against Staphylococcus aureus and Escherichia coli. Selected compounds (2–8 and 2a–8a) were also screened for their in vitro anticancer potential using the human hepatic carcinoma cell line, Hep-G2. Several derivatives were shown to be active comparable to that of cisplatin

Role of cell cycle events and apoptosis in mediating the anti-cancer activity of a silver(I) complex of 4-hydroxy-3-nitro-coumarin-bis(phenanthroline) in human malignant cancer cells.

The central objective of the current study was to investigate the potential in vitro anti-proliferative effect of 4-hydroxy-3-nitro-coumarin (hncH), and the mixed-ligand silver (I) complex of 4-oxy-3-nitro-coumarin-bis (phenanthroline), [Ag(hnc)(phen)2] using four human-derived model cell lines. In addition, selected mechanistic studies were carried out using the most sensitive of the four cell lines. Results obtained show that the complex could decrease the proliferation of all four cell lines including neoplastic renal and hepatic, namely A-498 and HepG2 cells, respectively, along with two non-neoplastic renal and hepatic cell lines, HK-2 and Chang, respectively. Furthermore, non-neoplastic hepatic cells (Chang) appeared to be less sensitive to the effect of the complex, but this effect was not replicated in the non-neoplastic renal (HK-2) cells. Based on IC50 values [Ag(hnc)(phen)2] was shown to be almost four times more potent than cisplatin, using HepG2 cells. In addition, the observed anti-proliferative effect was shown to be both dose- and time-dependent. Furthermore, the complex was shown to decrease DNA synthesis, but did not intercalate with it. Moreover, there was no evidence that P-glycoprotein-mediated multi-drug resistance was likely to decrease antiproliferative activity. Cytological stains, analysis of genomic DNA, and biochemical assays [caspase-3 and -9 and cleaved poly(ADP-ribose)-polymerase protein] showed that cell death appeared to result from apoptosis, with the possibility of secondary necrosis. Additionally, flow cytometric analysis showed that the complex functioned through an alteration in cell cycle progression. Taken together, [Ag(hnc)(phen)2] has been shown to be a more potent anti-proliferative agent than cisplatin, capable of altering key biochemical events leading to cell death. Additional mechanistic studies are underway to probe more fully its mechanism of action

Silver(I) complexes of 9-anthracenecarboxylic acid and imidazoles: synthesis, structure and antimicrobial activity

[Ag2(9-aca)2] (1) (9-acaH = 9-anthracenecarboxylic acid) reacts with a series of imidazoles to give [Ag(imidH)2.3(CH3CN)0.7](9-aca) (3), [Ag6(imidH)4(9-aca)6(MeOH)2] (4), {[Ag(1-Me-imid)2]2[Ag4(9- aca)6]} (5), {[Ag(1-Bu-imid)2]2[Ag4(9-aca)6]} (6) and [Ag(apim)](9-aca)·H2O (7) (imidH = imidazole; 1-Me-imid = 1-methylimidazole; 1-Bu-imid = 1-butylimidazole; apim = 1-(3-aminopropyl)imidazole). The mononuclear complex 3, hexanuclear 4–6, and polymeric 7, were all characterised using X-ray crystallography. While many of the complexes possess excellent in vitro antifungal and antibacterial activities they are, unanimously, more effective against fungal cells. The insect, Galleria mellonella, can survive high doses of the Ag(I) complexes administered in vivo, and a number of the complexes offer significant protection to larvae infected with a lethal dose of pathogenic Candida albicans cells

Interaction of anticancer reduced Schiff base coumarin derivatives with human serum albumin investigated by fluorescence quenching and molecular modeling

The specific binding of five reduced Schiff base derived 7-amino-coumarin compounds with antitumor activity to human serum albumin, the principal binding protein of blood, was studied by fluorescence spectroscopy. Their conditional binding constants were computed and the reversible binding at the Sudlow’s site I was found to be strong (KD ~ 0.03-2.09 M). Based on the data albumin can provide a depot for the compounds and is responsible for their biodistribution and transport processes. The experimental data is complemented by protein– ligand docking calculations for two representatives which support the observations. The proton dissociation constants of the compounds were also determined by UV-Vis spectrophotometric and fluorometric titrations to obtain the actual charges and distribution of the species in the various protonation states at physiological pH

Novel Coumarin-Thiadiazole Hybrids and Their Cu(II) and Zn(II) Complexes as Potential Antimicrobial Agents and Acetylcholinesterase Inhibitors

A series of coumarin-thiadiazole hybrids and their corresponding Cu(II) and Zn(II) complexes were synthesized and characterized with the use of spectroscopic techniques. The results obtained indicate that all the coumarin-thiadiazole hybrids act as bidentate chelators of Cu(II) and Zn(II) ions. The complexes isolated differ in their ligand:metal ratio depending on the central metal. In most cases, the Zn(II) complexes are characteristic of a 1:1 ligand:metal ratio, while in the Cu(II) complexes the ligand:metal ratio is 2:1. All compounds were tested as potential antibacterial agents against Gram-positive (Staphylococcus aureus, Staphylococcus epidermidis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacterial strains demonstrating activities notably lower than commercially available antibiotics. The more promising results were obtained from the assessment of antineurodegenerative potency as all compounds showed moderate acetylcholinesterase (AChE) inhibition activity