New mixed amino acids complexes of iron(III) and zinc(II) with isonitrosoacetophenone: Synthesis, spectral characterization, DFT study and anticancer activity

New mixed Fe(III) and Zn(II) complexes with isonitrosoacetophenone (HINAP) and l-amino acids (such as l-histidine, l-phenylalanine and l-proline) have been synthesized and characterized by elemental analyses, UV-Vis, IR and ESR spectroscopy and thermal analyses. The values of molar conductance of the complexes in DMSO solution at 10^-3 M concentration indicate their non-electrolyte nature. IR spectroscopy has revealed the coordination of deprotonated ligands to metal through nitrogen and oxygen atoms in an N₂O₂ arrangement. Density functional theory (DFT) calculations were performed using the hybrid functional of Truhlar and Zhao (M06) with basis set of double zeta quality LANL2DZ to evaluate the cis and trans coordination modes and to ascertain dipole moment, HOMO-LUMO energy gap, chemical hardness, softness and electrophilicity. The magnetic moments and ESR measurements suggest that there is an admixture of S = 5/2 and S = 1/2 spins in Fe(III) complexes. UV-Visible spectra indicate a distorted octahedral geometry around the metal ions. Thermal analyses show the presence of hydrated and coordinated water. The antimicrobial activity was investigated against (G⁺ and G^-) bacteria (Staphylococcus aureus, bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa) and fungi (Candida albicans). The iron and zinc complexes were found to be more active against Gram-positive than Gram negative bacteria. They also show considerable growth inhibition against the fungi tested. In vitro antitumor activity assayed against cancer cell lines of the HEP2 type (cancer cells of the larynx) exhibited significant toxicity of the ligands and their mixed complexes.

Unidirectional growth of benzil crystal from solution by Sankaranarayanan-Ramasamy method and its characterization

Good quality <100> benzil single crystal with a diameter 18 mm and length 75 mm was successfully grown from solution by the unidirectional growth method of Sankaranarayanan-Ramasamy (SR) for the first time in the literature. The seed crystals have been harvested from conventional solution growth technique and subsequently used for unidirectional growth. The grown crystal was subjected to various characterization studies. The results of UV-vis spectral analysis, photoluminescence, etching and microhardness studies were compared with conventional solution grown crystal to that of SR method grown crystal. The quality of SR method grown benzil crystal is better than conventional solution grown crystal.

An efficient oxidation of benzoins to benzils by ACC/silica gel under ultrasound irradiation

The oxidation of benzoins to the corresponding benzils was carried out in CH2Cl2 by ACC/silica gel in excellent yields within short time under ultrasound irradiation.

Synthesis, spectroscopic and thermal studies of transition metal complexes derived from benzil and diethylenetriamine

A macrocyclic ligand, bdta (where bdta=3,6,9,12,15,18-hexaaza-1,2,10,11-tetraphenyl-2,9,11,18-tetraenecyclododecane) has been prepared by cyclocondensation of benzil with diethylenetriamine which efficiently encapsulates transition as well as pseudo-transition metal ions leading to the formation of M(bdta)Cl2 type complexes [where M=Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)]. The analytical, spectroscopic and magnetic moment data suggests an octahedral geometry for all the complexes. EPR spectra of Mn(II) and Cu(II) show considerable exchange interaction in the complex. They are non-conducting in DMSO. The TGA profile of the ligand and its complexes are identical and consists of two discreet stages. The voltammogram of Cu-complex exhibits a quasi-reversible one-electron transfer wave for Cu(II)/Cu(I) couple.

Inhibition of carboxylesterases by benzil (diphenylethane-1,2-dione) and heterocyclic analogues is dependent upon the aromaticity of the ring and the flexibility of the dione moiety

Benzil has been identified as a potent selective inhibitor of carboxylesterases (CEs). Essential components of the molecule required for inhibitory activity include the dione moiety and the benzene rings, and substitution within the rings affords increased selectivity toward CEs from different species. Replacement of the benzene rings with heterocyclic substituents increased the K(i) values for the compounds toward three mammalian CEs when using o-nitrophenyl acetate as a substrate. Logarithmic plots of the K(i) values versus the empirical resonance energy, the heat of union of formation energy, or the aromatic stabilization energy determined from molecular orbital calculations for the ring structures yielded linear relationships that allowed prediction of the efficacy of the diones toward CE inhibition. Using these data, we predicted that 2,2'-naphthil would be an excellent inhibitor of mammalian CEs. This was demonstrated to be correct with a K(i) value of 1 nM being observed for a rabbit liver CE. In addition, molecular simulations of the movement of the ring structures around the dione dihedral indicated that the ability of the compounds to inhibit CEs was due, in part, to rotational constraints enforced by the dione moiety. Overall, these studies identify subdomains within the aromatic ethane-1,2-diones, that are responsible for CE inhibition.

Identification and characterization of novel benzil (diphenylethane-1,2-dione) analogues as inhibitors of mammalian carboxylesterases

Carboxylesterases (CE) are ubiquitous enzymes responsible for the metabolism of xenobiotics. Because the structural and amino acid homology among esterases of different classes, the identification of selective inhibitors of these proteins has proved problematic. Using Telik's target-related affinity profiling (TRAP) technology, we have identified a class of compounds based on benzil (1,2-diphenylethane-1,2-dione) that are potent CE inhibitors, with K(i) values in the low nanomolar range. Benzil and 30 analogues demonstrated selective inhibition of CEs, with no inhibitory activity toward human acetylcholinesterase or butyrylcholinesterase. Analysis of structurally related compounds indicated that the ethane-1,2-dione moiety was essential for enzyme inhibition and that potency was dependent on the presence of, and substitution within, the benzene ring. 3D-QSAR analyses of these benzil analogues for three different mammalian CEs demonstrated excellent correlations of observed versus predicted K(i) (r(2) > 0.91), with cross-validation coefficients (q(2)) of 0.9. Overall, these results suggest that selective inhibitors of CEs with potential for use in clinical applications can be designed.

Synthesis and evaluation of 4-(3-methyl-2-butenoxy) isonitrosoacetophenone, a radiation-induced stress metabolite in Citrus

The time- and dose-dependent occurrence of 4-(3-methyl-2-butenoxy)isonitrosoacetophenone, a gamma-irradiation-induced stress metabolite was investigated. The chemical synthesis of the compound is reported. The compound exhibits antifungal activity, as well as antioxidant activity, as indicated by its ability to scavenge reactive oxygen radicals in a chemiluminescence assay.

Chemical properties of the anion transport inhibitory binding site of arginine-specific reagents in human red blood cell membranes

A series of arginine-specific reagents with different size and polarity have been synthesized and their inhibitory potency on sulfate exchange in resealed ghosts has been investigated. The synthesized phenylglyoxal derivatives p-nitro-, p-methyl-, p-hydroxy-, p-carboxy-, p-sulfo-, and p-azido-phenylglyoxal are found to be potent inhibitors of anion transport. The reaction between the cells and azidophenylglyoxal was performed in the dark. Exposure of the modified cells to the light was not followed by an increase in the inhibition. No cross-linking products were visible after gel electrophoresis. The rate of inactivation of sulfate flux with these reagents obeyed pseudo-first-order kinetics and increases with increasing reagents concentration and pH. Prolonged incubation of the cells with these reagents results in almost complete inhibition of the transport system. The positively charged phenylglyoxal derivative 4-(trimethylammonioacetylamido)phenylglyoxal was not able to inhibit the transport system. The hydrophobic character and the electronic properties of these reagents do not correlate with their inhibitory potency. Their electrostatic and steric effects seem to play the major role in their action.

p-Azidophenylglyoxal-epidermal growth factor: a photoactivatable affinity crosslinking reagent

A photoaffinity derivative of highly purified 125I-labelled epidermal growth factor (125-I-EGF) has been synthesized. The heterobifunctional crosslinking reagent p-azidophenylglyoxal (PAPG) was bound to arginine residues in 125I-EGF. PAPG-125 I-EGF bound to EGF receptors on rat fibroblasts and human A431 epidermoid carcinoma cells in culture. An apparent decreased affinity of PAPG-125I-EGF for the EGF receptor is in accord with at least one arginine being at or near the EGF receptor binding site. The PAPG-125I-EGF:EGF receptor complexes on rat cells were internalized to the same extent as control EGF:receptor complexes. A431 cells treated with PAPG-125I-EGF were irradiated with ultraviolet light and the labelled proteins were analyzed by SDS-polyacrylamide gel electrophoresis. The 3 major labelled proteins had apparent molecular weights ranging from 75,000 to 200,000. Only the labelling of the 200,000-Mr protein was prevented by the addition of excess unlabelled EGF with the PAPG-125I-EGF. This molecular weight is in agreement with the reported size of the EGF receptor plus EGF. A protein with apparent molecular weight of 100,000 was labelled by 125I-EGF by an unknown mechanism which was dependent on the dose of UV light and blocked by the addition of excess unlabelled EGF.

p-Azidophenylglyoxal. A heterobifunctional photoactivable cross-linking reagent selective for arginyl residues

1. The synthesis described is of p-azidophenylglyoxal (p-APG) by diazotization of p-aminoacetophenone to an intermediate which when reacted with sodium azide gives p-azidoacetophenone; oxidation of the latter with selenium dioxide gives rise to p-APG (corrected melting point, 103-105 degrees C). The phenylglyoxal moiety was designed to react with arginine residues, whereas the p-azidoaryl function generates a reactive nitrene when activated with UV light; p-APG reacts most selectively with arginine and to a lesser extent with cystine and histidine. 2. p-APG has absorption peaks at 205 and 280 nm which decrease on photolysis. 3. Bovine heart lactic dehydrogenase, egg white lysozyme, horse liver alcohol dehydrogenase, and yeast alcohol dehydrogenase, all enzymes having arginyl residues at their active sites, are inhibited by p-APG in the dark. 4. Gel electrophoresis of oligomeric enzymes having arginyl residues at their active sites and exposed to p-APG and to UV irradiation gave varying proportions of monomers and photocross-linked dimers, trimers, tetramers, and larger molecular weight aggregates.

4-Hydroxy-3-nitrophenylglyoxal. A chromophoric reagent for arginyl residues in proteins

The chromophoric reagent, 4-hydroxy-3-nitrophenylglyoxal, is highly selective for the modification of arginine in aqueous solution at pH 7--9. The reagent also inactivates creatine kinase (ATP:creatine N-phosphotransferase, EC 2.7.3.2) in a manner analogous to that reported with phenylglyoxal.