Hypobromous Acid, A Powerful Endogenous Electrophile: Experimental And Theoretical Studies.

Hypobromous acid (HOBr) is an inorganic acid produced by the oxidation of the bromide anion (Br(-)). The blood plasma level of Br(-) is more than 1,000-fold lower than that of chloride anion (Cl(-)). Consequently, the endogenous production of HOBr is also lower compared to hypochlorous acid (HOCl). Nevertheless, there is much evidence of the deleterious effects of HOBr. From these data, we hypothesized that the reactivity of HOBr could be better associated with its electrophilic strength. Our hypothesis was confirmed, since HOBr was significantly more reactive than HOCl when the oxidability of the studied compounds was not relevant. For instance: anisole (HOBr, k2=2.3×10(2)M(-1)s(-1), HOCl non-reactive); dansylglycine (HOBr, k2=7.3×10(6)M(-1)s(-1), HOCl, 5.2×10(2)M(-1)s(-1)); salicylic acid (HOBr, k2=4.0×10(4)M(-1)s(-1), non-reactive); 3-hydroxybenzoic acid (HOBr, k2=5.9×10(4)M(-1)s(-1), HOCl, k2=1.1×10(1)M(-1)s(-1)); uridine (HOBr, k2=1.3×10(3)M(-1)s(-1), HOCl non-reactive). The compounds 4-bromoanisole and 5-bromouridine were identified as the products of the reactions between HOBr and anisole or uridine, respectively, i.e. typical products of electrophilic substitutions. Together, these results show that, rather than an oxidant, HOBr is a powerful electrophilic reactant. This chemical property was theoretically confirmed by measuring the positive Mulliken and ChelpG charges upon bromine and chlorine. In conclusion, the high electrophilicity of HOBr could be behind its well-established deleterious effects. We propose that HOBr is the most powerful endogenous electrophile.

The Conformational Analysis Of 2-halocyclooctanones.

The establishment of the most stable structures of eight membered rings is a challenging task to the field of conformational analysis. In this work, a series of 2-halocyclooctanones were synthesized (including fluorine, chlorine, bromine and iodine derivatives) and submitted to conformational studies using a combination of theoretical calculation and infrared spectroscopy. For each compound, four conformations were identified as the most important ones. These conformations are derived from the chair-boat conformation of cyclooctanone. The pseudo-equatorial (with respect to the halogen) conformer is preferred in vacuum and in low polarity solvents for chlorine, bromine and iodine derivatives. For 2-fluorocyclooctanone, the preferred conformation in vacuum is pseudo-axial. In acetonitrile, the pseudo-axial conformer becomes the most stable for the chlorine derivative. According to NBO calculations, the conformational preference is not dictated by electron delocalization, but by classical electrostatic repulsions.

Um novo método para quantificar mercúrio orgânico (Hg orgânico) empregando a espectrometria de fluorescência atômica do vapor frio

In this work a simple and sensitive procedure to extract organic mercury from water and sediment samples, using methylene chloride in acidic media followed by CVAFS quantification has been developed. The method was evaluated for possible interferents, using different inorganic mercury species and humic acid, no effects being observed. The detection limit for organic mercury was 160 pg and 396 pg for water and sediment samples respectively. The accuracy of the method was evaluated using a certified reference material of methylmercury (BCR-580, estuarine sediment). Recovery tests using methylmercury as surrogate spiked with 1.0 up to 30.0 ng L-1 ranged from 90 up to 109% for water samples, whereas for sediments, recoveries ranged from 57 up to 97%.