Faruk Nome

GPx-Like Activity of Selenides and Selenoxides: Experimental Evidence for the Involvement of Hydroxy Perhydroxy Selenane as the Active Species

The reaction mechanism of the GPx-like oxidation of PhSH with H(2)O(2) catalyzed by selenoxides proceeds via formation of the hydroxy perhydroxy selenane, which is a stronger oxidizing agent than selenoxide. A hydroxy perhydroxy selenane intermediate was observed by electrospray ionization mass spectrometry and (77)Se NMR spectroscopy in reactions of selenoxide 8 with H(2)O(2).The initial velocity of oxidation of PhSH by H(2)O(2) with selenoxide 8 is 4 orders of magnitude higher than that of 8 without peroxide. Selenoxide 8 is not reduced to selenide 6 by PhSH in the presence of H(2)O(2). While electronic substituent effects have minimal impact on the catalytic performance of selenoxides, chelating groups increase the rate of catalysis.

Synthesis of a new zwitterionic surfactant containing an imidazolium ring. Evaluating the chameleon-like behavior of zwitterionic micelles.

Synthesis of a new zwitterionic surfactant containing the imidazolium ring 3-(1-tetradecyl-3-imidazolio)propanesulfonate (ImS3-14) is described. The solubility of ImS3-14 is very low but increases on addition of a salt which helps to stabilize the micellized surfactant. Fluorescence quenching and electrophoretic evidence for ImS3-14 shows that the micellar aggregation number is only slightly sensitive to added salts, as is the critical micelle concentration, but NaClO(4) markedly increases zeta potentials of ImS3-14 in a similar way as in N-tetradecyl-N,N-dimethylammonio-1-propanesulfonate (SB3-14) micelles. The rate of specific hydrogen ion catalyzed hydrolysis of 2-(p-heptoxyphenyl)-1,3-dioxolane and equilibrium protonation of 1-hydroxy-2-naphthoate ion in zwitterionic micelles of ImS3-14 and SB3-14 are increased markedly by NaClO(4) which induces anionoid character and uptake of H(3)O(+), but NaCl is much less effective in this respect. Comparison of ImS3-14 with SB3-14 is based on experimental evidence, and computational calculations indicate similarities and differences in structures of both compounds.

Imidazolium-based zwitterionic surfactant: a new amphiphilic Pd nanoparticle stabilizing agent.

Palladium nanoparticles (NPs) with an average size of 3.4 nm were prepared in water using imidazolium-based surfactant 3-(1-dodecyl-3-imidazolio)propanesulfonate (ImS3-12) as a stabilizer. The Pd NPs are highly dispersible in water and chloroform and were characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy, powder X-ray diffraction, and dynamic light scattering. The results indicate that in water the NP surface is covered with a double layer of ImS3-12 molecules. The NPs were effective in the aqueous biphasic hydrogenation of cyclohexene, with easy recycling and no loss of catalytic activity after four successive runs.

Estratégias utilizadas no combate a resistência bacteriana

This article provides an overview on the recent achievements to combat Gram-positive bacteria and the mechanisms related to antimicrobial activity and bacterial resistance. Selected synthetic methodologies to access structurally diverse bioactive compounds are presented in order to emphasize the most important substances currently developed to overcome multiresistant strains. The main properties of vancomycin and related glycopeptide antibiotics are also discussed as a background to understanding the design of new chemotherapeutic agents.

Suicide Nucleophilic Attack: Reactions of Benzohydroxamate Anion with Bis(2,4-dinitrophenyl) Phosphate

The reaction between the benzohydroxamate anion (BHO(-)) and bis(2,4-dinitrophenyl)phosphate (BDNPP) has been examined kinetically, and the products were characterized by mass and NMR spectroscopy. The nucleophilic attack of BHO(-) follows two reaction paths: (i) at phosphorus, giving an unstable intermediate that undergoes a Lossen rearrangement to phenyl isocyanate, aniline, diphenylurea, and O-phenylcarbamyl benzohydroxamate; and (ii) on the aromatic carbon, giving an intermediate that was detected but slowly decomposes to aniline and 2,4-dinitrophenol. Thus, the benzohydroxamate anion can be considered a self-destructive molecular scissor since it reacts and loses its nucleophilic ability.

Intramolecular Catalysis of Phosphodiester Hydrolysis by Two Imidazoles

Two imidazole groups act together to catalyze the hydrolysis of the phosphodiester bis(2-(1-methyl-1H-imidazolyl)phenyl) phosphate (BMIPP). A full investigation involving searching computational and electrospray ionization (ESI-MS-/MS) and ultra mass spectrometry (LTQ-FT) experiments made possible a choice between two kinetically equivalent mechanisms. The preferred pathway, involving intramolecular nucleophilic catalysis by imidazole, assisted by intramolecular general acid catalysis by the imidazolium group, offers the first simple model for the mechanism used by the extensive phospholipase D superfamily.

The chameleon-like nature of zwitterionic micelles: the intrinsic relationship of anion and cation binding in sulfobetaine micelles.

The rate of specific hydrogen ion-catalyzed hydrolysis of 2-( p-heptoxyphenyl)-1,3-dioxolane and acid-base equilibrium of 4-carboxy-1-n-dodecylpyridinium in zwitterionic micelles of SB3-14, C14H29NMe2+(CH2)3SO3(-) are controlled by NaClO4, which induces anionic character and uptake of H3O+ in the micelles. Other salts, e.g., NaF, NaCl, NaBr, NaNO3, NaI, NaBF4, have similar, but smaller, effects on the uptake of H3O+. Salt effects upon zeta potentials of SB3-14 micelles, estimated by capillary electrophoresis, are anion specific, and the anion order is similar to that of the rates of acid hydrolysis and of acid-base equilibria. Fluorescence quenching shows that the micellar aggregation number is not very sensitive to added salts, consistent with electrophoretic evidence. These specific anion effects follow the Hofmeister series and are related to anion hydration free energies.

Phosphorylimidazole derivatives: potentially biosignaling molecules.

The phosphorylation of imidazole by two activated phosphate diesters and a triester gives phosphorylimidazole derivatives that are stable enough in aqueous solution to be observed and identified by ESI-MS/MS and NMR. Half-lives ranging from hours to days (in the case of the monoethyl ester) show that it is possible to design molecules with variable half-lives with potential to be used for biological intervention experiments as possible inhibitors of biosignaling processes or as haptens for the generation of antibodies.

Anion-specific binding to n-hexadecyl phosphorylcholine micelles.

Hexadecyl phosphorylcholine (HPC) micelles incorporate anions rather than cations in the interfacial region, giving an anionoid micelle with a negative zeta potential. Hydronium ion incorporation in the micellar pseudophase parallels the increase in the negative zeta potential, and salts increase the rate of A1 hydrolysis of 2-(p-heptyloxyphenyl)-1,3-dioxolane in micellized HPC and inhibit the reaction of OH(-) with naphthoic anhydride. The kinetic effects are larger with NaClO(4) than with NaCl. The increased micellar negative charge with added salts increases the repulsion between headgroups and decreases the aggregation number. These observations are relevant to understanding the behaviors of biological phosphorylcholine amphiphiles.

Determination of environmentally important metal ions by fluorescence quenching in anionic micellar solution

This work describes the effect of a variety of metal ions as quenchers of the fluorescence of naphthalene, in aqueous micellar solutions of sodium dodecyl sulfate (SDS). The quenching by the metal ions can be adequately described by the Stern-Volmer equation and the best signal to noise ratios are obtained with low micellized detergent concentrations. Apparent Stern-Volmer constants decrease in the order: Fe3+ > Cu2+ > Pb2+ > Cr3+ > Ni2+ and directly reflect the relative sensitivity of the method for these ions. Detection limits (defined as three times the standard deviation of the blank for n= 10) for the fluorescence quenching of naphthalene by the metal ions in aqueous micellar SDS are in the range of 1.0 x 10(-6) to 1.0 x 10(-5) mol dm(-3). The proposed fluorescence quenching method shows good repeatibility for a variety of added quencher metal ions, indicating that anionic micelle-enhanced fluorescence quenching by metal ions constitutes an analytical method of rather general application.