The mechanism of N2O formation via the (NO)(2) dimer: A density functional theory study

Catalytic formation of N2O via a (NO)(2) intermediate was studied employing density functional theory with generalized gradient approximations. Dimer formation was not favored on Pt(111), in agreement with previous reports. On Pt(211) a variety of dimer structures were studied, including trans-(NO)(2) and cis-(NO)(2) configurations. A possible pathway involving (NO)(2) formation at the terrace near to a Pt step is identified as the possible mechanism for low-temperature N2O formation. The dimer is stabilized by bond formation between one O atom of the dimer and two Pt step atoms. The overall mechanism has a low barrier of approximately 0.32 eV. The mechanism is also put into the context of the overall NO+H-2 reaction. A consideration of the step-wise hydrogenation of O-(ads) from the step is also presented. Removal of O-(ads) from the step is significantly different from O-(ads) hydrogenation on Pt(111). The energetically favored structure at the transition state for OH(ads) formation has an activation energy of 0.63 eV. Further hydrogenation of OH(ads) has an activation energy of 0.80 eV. (C) 2004 American Institute of Physics.

Combined inhibition of FLIP and XIAP induces Bax-independent apoptosis in type II colorectal cancer cells.

Death receptors can directly (type I cells) or indirectly induce apoptosis by activating mitochondrial-regulated apoptosis (type II cells). The level of caspase 8 activation is thought to determine whether a cell is type I or II, with type II cells less efficient at activating this caspase following death receptor activation. FLICE-inhibitory protein (FLIP) blocks death receptor-mediated apoptosis by inhibiting caspase 8 activation; therefore, we assessed whether silencing FLIP could convert type II cells into type I. FLIP silencing-induced caspase 8 activation in Bax wild-type and null HCT116 colorectal cancer cells; however, complete caspase 3 processing and apoptosis were only observed in Bax wild-type cells. Bax-null cells were also more resistant to chemotherapy and tumor necrosis factor-related apoptosis inducing ligand and, unlike the Bax wild-type cells, were not sensitized to these agents by FLIP silencing. Further analyses indicated that release of second mitochondrial activator of caspases from mitochondria and subsequent inhibition of X-linked inhibitor of apoptosis protein (XIAP) was required to induce full caspase 3 processing and apoptosis following FLIP silencing. These results indicate that silencing FLIP does not necessarily bypass the requirement for mitochondrial involvement in type II cells. Furthermore, targeting FLIP and XIAP may represent a therapeutic strategy for the treatment of colorectal tumors with defects in mitochondrial-regulated apoptosis.

Prediction of the formation and stabilities of energetic salts and ionic liquids based on ab initio electronic structure calculations

A computational approach to predict the thermodynamics for forming a variety of imidazolium-based salts and ionic liquids from typical starting materials is described. The gas-phase proton and methyl cation acidities of several protonating and methylating agents, as well as the proton and methyl cation affinities of many important methyl-, nitro-, and cyano- substituted imidazoles, have been calculated reliably by using the computationally feasible DFT (B3LYP) and MP2 (extrapolated to the complete basis set limit) methods. These accurately calculated proton and methyl cation affinities of neutrals and anions are used in conjunction with an empirical approach based on molecular volumes to estimate the lattice enthalpies and entropies of ionic liquids, organic solids, and organic liquids. These quantities were used to construct a thermodynamic cycle for salt formation to reliably predict the ability to synthesize a variety of salts including ones with potentially high energetic densities. An adjustment of the gas phase thermodynamic cycle to account for solid- and liquid-phase chemistries provides the best overall assessment of salt formation and stability. This has been applied to imidazoles (the cation to be formed) with alkyl, nitro, and cyano substituents. The proton and methyl cation donors studied were as follows: HCl, HBr, HI, (HO)(2)SO2, HSO3CF3 (TfOH), and HSO3(C6H4)CH3 (TsOH); CH3Cl, CH3Br, CH3I, (CH3O)(2)SO2, CH3SO3CF3 (TfOCH3) and CH3SO3(C6H4)CH3 (TsOCH3). As substitution of the cation with electron-withdrawing groups increases, the triflate reagents appear to be the best overall choice as protonating and methylating agents. Even stronger alkylating agents should be considered to enhance the chances of synthetic success. When using the enthalpies of reaction for the gas-phase reactants (eq 6) to form a salt, a cutoff value of - 13 kcal mol(-1) or lower (more negative) should be used as the minimum value for predicting whether a salt can be synthesized.

Inhibition of cytochrome P450-mediated metabolism enhances ex vivo susceptibility of Fasciola hepatica to triclabendazole

A study has been carried out to investigate whether the action of triclabendazole (TCBZ) against Fasciola hepatica is altered by inhibition of drug metabolism. The cytochrome P450 (CYP P450) system was inhibited using piperonyl butoxide (PB). The Oberon TCBZ-resistant and Cullompton TCBZ-susceptible isolates were used for these experiments. The CYP P450 system was inhibited by a 2 h pre-incubation in PB (100 mu M). Flukes were then incubated for a further 22 h in NCTC medium containing either PB; PB + nicotinamide adenine dinucleotide phosphate (NADPH) (1 nM); PB + NADPH + TCBZ (15 mu g/ml); or PB + NADPH + TCBZ.SO (15 mu g/ml). Morphological changes resulting from drug treatment and following metabolic inhibition were assessed using scanning electron microscopy. After treatment with either TCBZ or TCBZ.SO alone, there was greater disruption to the TCBZ-susceptible than the resistant isolate. However, co-incubation with PB and TCBZ/TCBZ.SO lead to more severe surface changes to the TCBZ-resistant Oberon isolate than with each drug on its own. With the TCBZ-susceptible Cullompton isolate, there was limited potentiation of drug action, and only with TCBZ.SO. The results support the concept of altered drug metabolism in TCBZ-resistant flukes and this process may play a role in the development of drug resistance.

MEASUREMENT OF SUPEROXIDE FORMATION BY MITOCHONDRIAL COMPLEX I OF YARROWIA LIPOLYTICA

Complex I (NADH: ubiquinone oxidoreductase) is generally regarded as one of the major sources of mitochondrial reactive oxygen species (ROS). Mitochondrial membranes from the obligate aerobic yeast Yarrowia lipolytica, as well as the purified and reconstituted enzyme, can be used to measure complex I-dependent generation of superoxide (O-2(center dot-)). The use of isolated complex I excludes interference with other respiratory chain complexes and matrix enzymes during superoxide dismutase-sensitive reduction of acetylated cytochrome c. Alternately. hydrogen peroxide formation can be measured by the Amplex Red/horseradish peroxidase assay. Both methods allow the determination of complex I-generated ROS, depending on substrates (NADH, artificial ubiquinones), membrane potential, and active/deactive transition. ROS production by Yorrowia complex I in the

Modulation of gel formation and drug-release characteristics of lidocaine-loaded poly(vinyl alcohol)-tetraborate hydrogel systems using scavenger polyol sugars

Polyol sugars, displaying a plurality Of hydroxyl groups, were shown to modulate tetra hydroxyborate (borate) cross-linking in lidocaine hydrochloride containing poly(vinyl alcohol) scini-solid hydrogels. Without polyol, demixing of borate cross-linked PVA hydrogels into two distinct phases was noticeable upon lidocaine hydrochloride addition, preventing further use as a topical System. D-Mannitol incorporation was found to be particularly suitable in cicumventing network constriction induced by ionic and pH effects upon adding the hydrochloride salt of lidocaine. A test formulation (4% w/v lidocaine HCl, 2% W/V D-mannitol, 10% w/v PVA and 2.5%, w/v THB) was shown to constitute an effective delivery system, which was characterised by an initial burst release and a drug release mechanism dependent on temperature, changing from a diffusion-controlled system to one with the properties of a reservoir system. The novel flow properties and innocuous adhesion of PVA-tetrahydroxyborate hydrogels Support their application for drug delivery to exposed epithelial surfaces, Such as lacerated wounds. Furthermore, addition of a polyol, such as mannitol, allows incorporation of soluble salt forms of active therapeutic agents by modulation of cross-linking density. (C) 2008 Elsevier B.V. All rights reserved.

Binding and degradation of fibrinogen by Bacteroides fragilis and characterization of a 54 kDa fibrinogen-binding protein

Bacteroides fragilis is a bacterium that resides in the normal human gastro-intestinal tract; however, it is also the most commonly isolated Gram-negative obligate anaerobe from human clinical infections, such as intra-abdominal abscesses, and the most common cause of anaerobic bacteraemia. Abscess formation is important in bacterial containment, limiting dissemination of infection and bacteraemia. In this study, we investigated B. fragilis binding and degradation of human fibrinogen, the major structural component involved in fibrin abscess formation. We have shown that B. fragilis NCTC9343 binds human fibrinogen. A putative Bacteroides fragilis fibrinogen-binding protein, designated BF-FBP, identified in the genome sequence of NCTC9343, was cloned and expressed in Escherichia coli. The purified recombinant BF-FBP bound primarily to the human fibrinogen Bß-chain. In addition, we have identified fibrinogenolytic activity in B. fragilis exponential phase culture supernatants, associated with fibrinogenolytic metalloproteases in NCTC9343 and 638R, and cysteine protease activity in YCH46. All nine clinical isolates of B. fragilis examined degraded human fibrinogen; with eight isolates, initial A-chain degradation was observed, with varying Bß-chain and -chain degradation. With one blood culture isolate, Bß-chain and -chain degradation occurred first, followed by subsequent A-chain degradation. Our data raise the possibility that the fibrinogen-binding protein of B. fragilis, along with a variety of fibrinogenolytic proteases, may be an important virulence factor that facilitates dissemination of infection via reduction or inhibition of abscess formation.