Mario Branca

In vitro interaction of mutagenic chromium(VI) with red blood cells

Glutathione; Chromium; ESR; (Red blood cell)

Plasmodium falciparum glutathione metabolism and growth are independent of glutathione system of host erythrocyte.

Plasmodium falciparum parasites grew normally in glutathione (GSH)‐depleted normal and G6PD‐deficient (Mediterranean variant) erythrocytes (RBC). Growth inhibition was observed only at less than approximately 6–12% residual GSH. Parasites studied separately with the Sendai virus technique synthesized GSH de novo and regenerated reduced GSH 10–20 times faster than non‐parasitized RBC. Electron spin resonance measurement of Tempol reduction indicated that the ability to reduce free radicals was restricted to the parasite. The marked efflux of oxidized GSH was mainly derived from the parasite. In conclusion, parasites are endowed with powerful and host‐independent mechanisms which de novo synthesize or regenerate GSH and allow undisturbed parasite development in GSH‐depleted RBC.

Reduction of chromium(VI) by D-galacturonic acid and formation of stable chromium(V) intermediates

Abstract The interaction of dichromate with D-galacturonic acid in aqueous solution, as a function of pH, is described. The reaction involves the reduction of Cr(VI) to Cr(III), but the reaction rate is remarkably dependent on pH. In fact, the reduction of Cr(VI) to Cr(III) proceeds rather quickly in strongly acidic solutions, while it is slow in neutral or moderately acidic media. In all cases, according to the ESR evidence, Cr(V) species are found as intermediates. The stability of the Cr(V) species increases with increasing pH, so that it may be suggested that the overall reaction rate is controlled by the Cr(V) to Cr(III) conversion.

Optically active aldehydes via hydroformylation of 1,3-dienes with chiral diphosphinerhodium complexes

Abstract Optically active aldehydes have been obtained by hydroformylation of simple aliphatic conjugated dienes under standard oxo conditions (90 atm (CO/H 2  1/1) and 95°C), using HRh(CO)(PPh 3 ) 3 /()DIOP as catalyst. The highest optical yield (32%) was achieved in the preparation of 3-methylpentanal from isoprene.

Reduction of chromate ions by glutathione tripeptide in the presence of sugar ligands

Polarographic and ESR data obtained for the reduction of chromate in the presence of the tripeptide glutathione (GSH) and sugars are presented. The results indicate that in the binary GSH-Cr(VI) system, glutathione binds chromate forming a thioester species which can be reduced efficiently by free tripeptide molecules. In the systems containing chromate, sugars and glutathione, chromium(VI) interacts with the sugar ligand (or with both sugar and GSH) yielding esters which are easily reduced by GSH. The formed Cr(V) ions are then stabilized by the coordination to the sugar ligands. The sugars having pairs of cis hydroxyl groups available for binding to metal are the most effective in the formation, first, of Cr(VI) esters and then, of Cr(V) complexes.

Oxovanadium(IV) complex formation by simple sugars in aqueous solution

The binding of oxovanadium(IV) to simple sugars in neutral or basic aqueous solution, as studied by EPR and electronic absorption spectroscopy, is reported. The complexation is favored in basic media and involves the coordination of the metal ion to couples of adjacent deprotonated hydroxyls of the sugar molecule. However, only the ligands provided with cis couples can adopt this chelating ligand behavior. The ability of the cis hydroxyl couples to yield chelated complexes has been related to the structural rearrangement (decrease of the O-C-C-O torsion angle in the five-membered chelated ring) needed to permit the oxovanadium(IV) coordination by the sugar molecule.

The binding of bilirubin to albumin a study using spin-labelled bilirubin

Binding between human serum albumin and a spin-labelled derivative of bilirubin was investigated by circular dichroism, fluorescence quenching, electron spin resonance and visible spectroscopy. The orders of magnitude of the binding constants obtained by flurorescence quenching and electron spin resonance spectroscopies were 10(7) and 10(3) 1 . mol-1, respectively. These data suggest that most spin-labelled bilirubin interacts with human serum albumin at the side not holding the spin-labelled side-arm. CD measurements showed the presence of at least two sites, associated with opposite Cotton effects. It is worthy of note that the Cotton sign of the first site is inverted with respect to the corresponding one of bilirubin. CD measurements on mixed systems (spin-labelled bilirubin/human serum albumin/bilirubin) were also performed. The decomposition of the ternary curves shows that the rotatory power of bilirubin bound to human serum albumin is higher in the ternary system than in the binary (bilirubin/human serum albumin). The corresponding CD measurements for the binding between spin-labelled bilirubin and bovine serum albumin are also reported and discussed.

Evidence of a chaotic transient in a closed unstirred cerium catalyzed Belousov-Zhabotinsky system

Abstract Aperiodic oscillations in a cerium catalyzed Belousov-Zhabotinsky reaction were experimentally observed in a closed system. This phenomenon was noted by a simple spectrophotometric measure which enabled us to prove the dependence of the initial conditions as being the major signature of chaos.

Hydroformylation of phenyl-substituted olefins with cobalt catalysts

Abstract A study of the hydroformylation of styrene, α-methylstyrene, allylbenzene and trans -propenylbenzene catalysed by octacarbonyldicobalt has shown that use of pyridine as a catalyst activator has a marked influence on the selectivity of the reaction and that the isomeric composition of the aldehydes is strongly dependent upon the temperature. Deuterium scrambling was observed in the hydrogenation and hydroformylation products concurrently formed from 2-phenylpropene-1 d 2 -3 d 3 even at p (CO)  100 atm.

Potentiometric and spectroscopic studies on oxovanadium(IV) complexes of salicylic acid and catechol and some derivatives

The interaction of oxovanadium(IV) with ligands containing phenolate and carboxylate donors, such as salicylic acid, catechol, 2,x-dihydroxybenzoic acids (x= 3–6), and 3,4-dihydroxybenzoic acid has been studied in aqueous solution by means of potentiometric and spectroscopic (electronic absorption, e.s.r., and electron nuclear double resonance) techniques. Over the low pH range the salicyclic acid-type mode of co-ordination predominates, while the catechol type is preferred in basic media. A mixture of these donor sets is observed in the ternary oxovanadium(IV)–salicylic acid-catechol and binary oxovanadium(IV)-2,3-dihydroxybenzoic acid systems. Besides monomeric complexes, dinuclear species are also formed by the potentially ambidentate dihydroxybenzoic acid derivatives over the intermediate pH range. In the latter complexes both CO2– and O– groups take part in metal bridging.