Bond Activation and Hydrogen Evolution from Water through Reactions with M3S4 (M = Mo, W) and W3S3 Anionic Clusters

Transition metal sulfides (TMS) are being investigated with increased frequency because of their ability to efficiently catalyze the hydrogen evolution reaction. We have studied the trimetallic TMS cluster ions, Mo₃S₄^-, W₃S₄^-, and W₃S₃^-, and probed their efficiency for bond activation and hydrogen evolution from water. These clusters have geometries that are related to the edge sites on bulk MoS₂ surfaces that are known to play a role in hydrogen evolution. Using density functional theory, the electronic structures of these clusters and their chemical reactivity with water have been investigated. The reaction mechanism involves the initial formation of hydroxyl and thiol groups, hydrogen migration to form an intermediate with a metal hydride bond, and finally, combination of a hydride and a proton to eliminate H₂. Using this mechanism, free energy profiles of the reactions of the three metal clusters with water have been constructed. Unlike previous reactivity studies of other related cluster systems, there is no overall energy barrier in the reactions involving the M₃S₄ systems. The energy required for the rate-determining step of the reaction (the initial addition of the cluster by water) is lower than the separated reactants (-0.8 kcal/mol for Mo and -5.1 kcal/mol for W). They confirm the M₃S₄^- cluster's ability to efficiently activate the chemical bonds in water to release H_2. Though the W₃S₃^- cluster is not as efficient at bond activation, it provides insights into the factors that contribute to the success of the M₃S₄ anionic systems in hydrogen evolution.

Oxidant stress in pre-eclampsia and essential hypertension

BACKGROUND

Endothelial cell dysfunction may play a role in the pathobiology of pre-eclampsia and human essential hypertension. Vasodilators and platelet anti-aggregators such as prostacyclin and nitric oxide are produced by endothelial cells. The half-life of prostacyclin and nitric oxide are reduced by superoxide anion, whereas superoxide dismutase antagonizes its action.

OBJECTIVES

To estimate the plasma concentrations of nitric oxide and lipid peroxides and those of catalase and superoxide dismutase in patients with pre-eclampsia and essential hypertension.

METHODS

Patients of essential hypertension and pre-eclampsia were selected for the study. Nitric oxide and lipid peroxides were estimated in the plasma and anti-oxidants catalase and superoxide dismutase were estimated in the RBC membranes.

RESULTS

The ratio between lipid peroxides and nitric oxide was elevated and the activity of superoxide dismutase reduced in patients with pre-eclampsia and uncontrolled essential hypertension.

CONCLUSION

These results suggest that oxidants and anti-oxidants are altered in human essential hypertension and pre-eclampsia.

Quantitative structure activity relationship (QSAR) studies of some substituted benzenesulphonyl glutamines as tumour suppressors

As a part of a composite programme of rational drug design (RDD), we had synthesized some substituted benzenesulphonyl glutamines and evaluated their inhibitory activities against Ehrlich Ascites Carcinoma (EAC) cell line in Swiss albino mice. Quantitative structure activity relationship (QSAR) studies of these inhibitory activities using Fujita-Ban model as well as Modified Hansch-Fujita model gave excellent correlations (correlation coefficient r = 0.89 and 0.82 respectively). These results could be useful in designing 'lead' compound with potent inhibitory activity on DNA and RNA synthesis and tumour development.

Role of linkage specific 9-O-acetylated sialoglycoconjugates in activation of the alternate complement pathway in mammalian erythrocytes

Substitution of the -OH group at C-9 of sialic acid by an O-acetyl ester has been suggested to modify various biological phenomena that are regulated by sialic acids. Amongst them, enhancement of erythrocyte lysis by 9-O-acetylated sialic acid determinants through modulation of the alternate pathway of complement has been extensively studied on murine erythrocytes [1]. A variable expression of linkage specific 9-O-acetylated sialoglycoconjugates as defined by the lectinogenic epitope of Achatinin-H namely 9-O-acetylated sialic acid alpha2-->6Gal NAc was identified on rabbit, guinea pig, hamster, rat, mouse and human erythrocytes. This differential expression of linkage specific 9-O-acetylated sialoglycoconjugates strongly correlated with the susceptibility of mammalian erythrocytes to lysis by the alternate pathway of complement. Additionally, low levels of antibodies directed against O-acetylated sialic acids in these mammalian species suggested that these constitutively present determinants have low immunogenicity. Taken together, our results indicate that complement mediated hemolysis depends not simply upon the extent of surface 9-O-acetylated sialic acids present but more importantly upon the specific linkage.

Lipid peroxides, anti-oxidants and nitric oxide in patients with pre-eclampsia and essential hypertension

INTRODUCTION

The aim was to study the role of lipid peroxides, nitric oxide and anti-oxidants in pre-eclampsia and essential hypertension.

MATERIAL AND METHODS

The study was done in 28 patients with pre-eclampsia and 30 patients of essential hypertension. The plasma concentrations of lipid peroxides as a measure of pro-oxidant status, nitric oxide and RBC content of anti-oxidants were measured in these patients and compared with controls.

RESULTS

It was observed that in patients with pre-eclampsia the plasma concentrations of nitric oxide and lipid peroxides were elevated with a decrease in those of anti-oxidants such as catalase and superoxide dismutase and a concomitant increase in that of glutathione peroxidase. On the other hand, in patients with essential hypertension, the concentrations of nitric oxide and superoxide dismutase were found to be low where as that of lipid peroxides were high. When the lipid peroxides/nitric oxide (LP/NO) ratio was calculated a far more significant rise in the concentrations of lipid peroxides compared to NO levels was noted especially in patients with pre-eclampsia and patients with uncontrolled essential hypertension.

CONCLUSIONS

These results suggest that oxidants and anti-oxidants are altered in human essential hypertension and pre-eclampsia and that they may play a significant role in their pathophysiology.

Effect of melatonin on two stage skin carcinogenesis in Swiss mice

Melatonin, a hormone secreted by the pineal gland, is known to have anti-mutagenic and oncostatic actions. This beneficial action of melatonin has been explained in terms of its ability to scavenge free radicals and augment the activities of anti-oxidant enzymes. In the present study, we evaluated the effect of melatonin on benzo(a)pyrene-induced two stage skin carcinogenesis in mice and observed that it can not only decrease the number of animals bearing papillomas but also the number of papillomas per animal both in the initiation and promotion stages of skin carcinogenesis. It was also found that melatonin treated animals have low levels of lipid peroxides and that it can also prevent the binding of BP or its metabolites to DNA. In view of these evidence, it can be suggested that melatonin may function as an endogenous anti-mutagenic and oncostatic agent.

Group II nucleopolyhedrovirus subgroups revealed by phylogenetic analysis of polyhedrin and DNA polymerase gene sequences

Two major clades, designated Groups I and II, of nucleopolyhedroviruses (NPVs) from lepidopteran hosts have been previously identified. To reveal more detailed relationships, a series of DNA polymerase nucleotide sequences from the taxa MbMNPV, SeMNPV, HzSNPV, HearNPV, SpltNPV, BusuNPV, and OranNPV have been determined using a polymerase chain reaction (PCR)-based approach. This technique enabled gene sequence determination using microliter samples of NPV-infected insect cadavers. Polyhedrin genes from HearNPV, OranNPV, SeMNPV, and SpltNPV were also isolated and sequenced using a similar approach. These sequences, together with other database entries, were aligned for positional homology of peptide sequences. Phylogenetic analysis of DNA polymerase molecular sequence alignments supports LdMNPV as a taxon of Group II and three Group II subclades, designated A, B, and C. Comparison of DNA polymerase trees with those estimated from occlusion protein molecular sequences enabled identification of three subclades of Group II. These are Subgroup II-A [MbMNPV, LeseNPV, MacoNPV, PaflNPV, SeMNPV, SpltNPV (India isolate), SfMNPV]; Subgroup II-B [SpliNPV, SpltNPV (Japan isolate), SpltNPV (Queensland isolate), and possibly HzSNPV, HearNPV, and ManeNPV], and Subgroup II-C [OpSNPV, OranNPV (S-type), BusuNPV (S-type), and possibly EcobNPV (S-type)]. Notably, all Subgroup II-A taxa are from noctuid hosts. Correlations of virus and host evolution within Group II taxa are discussed. The methods and data developed in this study will allow rapid sequencing of NPV DNA polymerase genes.