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PubMed1990

Reactivity of ebselen and related selenoorganic compounds with 1,2-dichloroethane radical cations and halogenated peroxyl radicals.

The reactivity of ebselen, 2-phenyl-1,2-benzisoselenazol-3(2H)one, and structurally related analogues was studied by pulse radiolysis. The rate constant for the reaction of ebselen with trichloromethylperoxyl radicals was determined to be 2.9 X 10(8) M-1 s-1, while its sulfur analogue, 2-phenyl-1,2-benzisothiazol-3(2H)one, was oxidized at much lower rates, k less than or equal to 10(7) M-1 s-1. Among several derivatives studied, the only other compound that exhibited a high rate constant was 2-(methylseleno)-benzoic acid-N-phenylamide. Oxidation of ebselen by other halogenated peroxyl radicals was also carried out and revealed a direct relationship between rate constant and the degree of halogenation of the oxidant. The transient radicals generated during oxidation of ebselen and the analogues were characterized by optical absorption and conductivity measurements and were attributed to one-electron-oxidized radical cations. The oxidation potentials were determined by cyclic voltammetry. Comparative evaluation of the in vitro behavior during microsomal lipid peroxidation revealed ebselen to be the most potent antioxidant of the compounds investigated, 2-(Methylseleno)-benzoic acid-N-phenylamide, despite its high rate constant for oxidation by halogenated peroxyl radicals, was found to be a poor antioxidant. The rate constant of oxidation of ebselen by trichloromethylperoxyl radicals is comparable to that of alpha-tocopherol under similar conditions, underscoring the potential pharmacological interest of ebselen as an antioxidant.

Antioxidants↗
PubMed2004

Host nutritional status: the neglected virulence factor.

The emergence of new infectious diseases and old diseases with new pathogenic properties is a burgeoning worldwide problem. Severe acute respiratory syndrome (SARS) and acquired immune deficiency syndrome (AIDS) are just two of the most widely reported recent emerging infectious diseases. What are the factors that contribute to the rapid evolution of viral species? Various hypotheses have been proposed, all involving opportunities for virus spread (for example, agricultural practices, climate changes, rainforest clearing or air travel). However, the nutritional status of the host, until recently, has not been considered a contributing factor to the emergence of infectious disease. In this review, we show that host nutritional status can influence not only the host response to the pathogen, but can also influence the genetic make-up of the viral genome. This latter finding markedly changes our concept of host-pathogen interactions and creates a new paradigm for the study of such phenomena.

Animals↗
PubMed2000

Roles of Se and NO in apoptosis of hepatoma cells.

Mice inoculated with hepatoma cell (H22) suspension subcutaneously at their right axilla were administered orally with kappa-selenocarrageenan (Se) solution, the inoculated hepatoma's growth was suppressed. Different concentrations of Se solution added in human hepatoma cell line culture could inhibit proliferation and induce apoptosis in hepatoma cells. Meanwhile Se solution could increase the activity of glutathione peroxidase (GSH-Px) in the mice's plasma and the content of NO in the mice's sera and the hepatoma cell culture supernatant as well. Therefore, apoptosis in hepatoma cell induced by Se solution may be associated with the increase in antioxidative activity, the suppression free radical's intervention, and the excessive release of NO by stress.

Animals↗
PubMed2004

Application of the SO4(2-)/Se tracer technique to study SO2 oxidation in cloud and fog on a time scale of minutes.

We have demonstrated the use of Se as a tracer to quantitatively determine in situ SO4(2-) production from SO2 oxidation in clouds and fogs. Until now, it has not been possible to study the kinetics of SO2 oxidation because the aerosol sampling interval for Se determination was limited to 2 h or longer. Here we report results of 5-min aerosol measurements carried out at Lahore, Pakistan, during January 9-11, 2001, using new methodology for Se analysis coupled with hydride generation and ICP-MS detection. These improvements will enable the tracer technique to determine in situ SO4(2-) production in clouds and fogs on a time scale of several minutes and possibly 1 min. The method may prove useful for kinetic studies of in-cloud SO2 oxidation and in the study of other phenomena such as atmospheric mixing, cloud drop lifetimes, and aerosol formation that occur on the time scale of a few minutes.

Atmosphere↗
PubMed2000

A bis-cyclodextrin diselenide with glutathione peroxidase-like activity.

A diselenide, 2,2'-diseleno-bis-beta-cyclodextrin (2-SeCD), was synthesized to imitate the antioxidant enzyme glutathione peroxidase (GPX). The GPX mimic accepts a variety of hydroperoxides as substrates. The GPX activities, reduction of H(2)O(2), tert-butyl hydroperoxide and cumenyl hydroperoxide by glutathione, are 7.4, 4.5 and 10.2 U/micromol, respectively. In contrast to ebselen (PZ51), the diselenide displays high GPX-like activity. The reduction of hydroperoxide by glutathione in the presence of a radical trap shows that the mimic catalyzes the reaction via a non-radical mechanism. A ping-pong mechanism was observed in the steady-state kinetic studies of the 2-SeCD-catalyzed reaction.

Animals↗
PubMedDate not supplied

Role of aromacity, ring strain, and stereochemistry of selected disulfides and their congeners in the oxidative linkage of DNA strands at the major groove. A computational study.

Three aromatic disulfides and their two selected congeners were studied in order to see if they could be initiators or catalysts in a process that aims to tie together the two strands of a DNA double helix. Thermodynamic functions were calculated from first principle molecular computations on deoxyribose models and the disulfide congener. The gas reaction of one of the disulfides turned out to be the closest to the thermoneutral process. Solvation study caused a relatively minor energetic modification. The disulfides were subjected to docking studies, and the stabilities of the complexes obtained were further analyzed by molecular dynamics simulations. Only one of the two atropic disulfide enantiomers was the matching partner of the chiral DNA double helix, and therefore this remained in the major groove of the DNA. The other enantiomer dissociated from the major groove as it was incapable of forming a stable complex with the chiral double helix. A mechanistic scheme for the reaction has been investigated.

Catalysis↗
PubMed2006

A ratiometric CdSe/ZnS nanocrystal pH sensor.

The development of a reversible chemical sensor based on a CdSe/ZnS nanocrystal (NC) is described. Signal transduction is accomplished by fluorescence resonance energy transfer (FRET) between the NC and a fluorescent pH-sensitive squaraine dye attached to the surface of the NC. The efficiency of FRET, and consequently the relative intensity of NC and dye emissions, is modulated with the pH-dependent absorption cross section of the squaraine dye. The design of a NC sensor based on FRET results in a ratiometric sensor since the emission intensities of dye and NC may be referenced to the isosbestic point between NC and dye emissions. The ratiometric approach allows sensing to be performed, regardless of issues surrounding collection efficiency (scattering environment, light fluctuations, etc.) and dye:NC loadings.

Biosensing Techniques↗
PubMed2001

Bioactivation of chemopreventive selenocysteine Se-conjugates and related amino acids by amino acid oxidases novel route of metabolism of selenoamino acids.

Several selenocysteine Se-conjugates have been shown to possess potent chemopreventive activity in animal models for chemical carcinogenesis. As a mechanism of action, beta-elimination reactions to form chemopreventive selenols, ammonia, and pyruvate has been proposed. The enzymes involved in these beta-elimination reactions, however, have been partially elucidated. Next to cysteine conjugate beta-lyases, as yet unidentified non-pyridoxal-5'-phosphate-dependent enzymes also appear to be involved in cytosolic beta-elimination reactions. In the present study, it was investigated whether amino acid oxidases contribute to the bioactivation of selenocysteine Se-conjugates. Using purified L-amino acid oxidase from Crotalus adamanteus as a model enzyme, significant beta-elimination activities were indeed observed upon incubation with Se-methylselenocysteine (K(m), 195 microM; k(cat), 48 min(-1)), Se-allylselenocysteine (K(m), 608 microM; k(cat), 34 min(-1)), Se-phenylselenocysteine (K(m), 107 microM; k(cat), 57 min(-1)) and Se-benzylselenocysteine (K(m), 59 microM; k(cat), 13 min(-1)). For all selenocysteine Se-conjugates tested, the rate of pyruvate formation was comparable to that of hydrogen peroxide, one of the products of oxidative deamination. The fact that addition of catalase did not alter pyruvate formation indicated that the beta-elimination reaction observed was not mediated by selenoxidation/syn-elimination due to the hydrogen peroxide formed via the oxidative deamination pathway. Using D-amino acid oxidase from porcine kidney and D-SeCys conjugates similar results were obtained. To delineate whether mammalian L-amino acid oxidases are also able to catalyze beta-elimination of selenocysteine Se-conjugates, rat renal cytosol was fractionated and screened for beta-elimination and oxidative deamination activities. One of the fractions isolated displayed oxidative deamination activity with several amino acids and cysteine S-conjugates. With selenocysteine Se-conjugates as substrates, however, this fraction displayed both oxidative deamination and beta-elimination activities, when incubated in the presence of aminoxyacetic acid to block contribution of pyridoxal-5'-phosphate-dependent enzymes. The potential significance of this novel bioactivation route for the chemopreventive activity of selenocysteine Se-conjugates is discussed.

Amino Acid Oxidoreductases↗
PubMed2001

Novel small organo-P-S/Se heterocycles.

Oxidative addition of elemental sulfur and selenium to cyclomonocarbatetraphosphines (PhP)4CR2 (R = H, Me) afforded novel five- and four-membered heterocycles PhP(E)CH2PhP(E)E2(E = S, Se) and PhP(Se)CMe2-PhP(Se)Se.

Journal Article↗
PubMed2002

Selenocysteine-mediated backbone cyclization of unprotected peptides followed by alkylation, oxidative elimination or reduction of the selenol.

An unprotected 16 residue peptide containing a C-terminal thioester and an N-terminal selenocysteine residue efficiently cyclizes in the presence of thiophenol; subsequent reduction, elimination or alkylation of the selenol yields modified cyclic peptides with alanine, dehydroalanine or a non-natural amino acid at the site of ligation.

Alkylation↗
PubMed2005

Size and ligand effects on the electrochemical and spectroelectrochemical responses of CdSe nanocrystals.

The electrochemical properties of CdSe quantum dots with electrochemically inactive surface ligands (TOPO) have been investigated in comparison with the analogous nanocrystals containing electrochemically active oligoaniline ligands. The TOPO-capped nanocrystals have been studied in a wide size range (from 3 to 6.5 nm) with the goal to amplify the influence of the quantum confinement effect on the electrochemical response. The determined HOMO and LUMO levels have been found in good agreement with the ones obtained from photoluminescence studies and those predicted theoretically. Ligand exchange with aniline tetramer significantly influences the voltammetric peaks associated with the HOMO oxidation and the LUMO reduction of the quantum dots, which are shifted to higher and lower potentials, respectively. These shifts are interpreted in terms of the positive ligand charging which precedes the oxidation of the nanocrystals and the insulating nature of the ligand in the case of the nanocrystal reduction. The ligand-nanocrystal interactions have also been studied by UV-Vis-NIR and Raman spectroelectrochemistry in comparison with a specially prepared model compound which, apart from the anchoring function is identical to the grafted oligoaniline ligand. Both spectroelectrochemical techniques clearly indicate the same nature of the oxidation/reduction pathway for both the model compound and the grafted ligand. The influence of the grafting is manifested by a shift in the onset of the ligand oxidation as compared to the case of the "free" model compound. Since both components (ligands and nanocrystals) mutually influence their electrochemical and spectroelectrochemical properties, the newly developed system can be considered as a true molecular hybrid. Such hybrids are of interest because the potential zone of the ligand electroactivity is well separated from that of the nanocrystals and, as a result, the organic part can be electrochemically switched between the semiconducting and the conducting states with no change in the oxidation state of the nanocrystal. The newly developed system offers therefore the possibility of an electrical addressing of individual nanocrystals via the conducting ligands.

Aniline Compounds↗