The pro-radical hydrogen peroxide as a stable hydroxyl radical distributor: lessons from pancreatic beta cells.

The toxic potential of H2O2 is limited, even if intracellular concentrations of H2O2 under conditions of oxidative stress increase to the micromolar concentration range. Its toxicity is mostly restricted to the oxidation of highly reactive thiol groups, some of which are functionally very important. Subsequently, the HO· radical is generated spontaneously from H2O2 in the Fenton reaction. The HO· radical is extremely toxic and destroys any biological structure. Due to the high reactivity, its action is limited to a locally restricted site of its generation. On the other hand, H2O2 with its stability and long half-life can reach virtually any site and distribute its toxic effect all over the cell. Thereby HO·, in spite of its ultra-short half-life (10-9 s), can execute its extraordinary toxic action at any target of the cell. In this oxidative stress scenario, H2O2 is the pro-radical, that spreads the toxic action of the HO· radical. It is the longevity of the H2O2 molecule allowing it to distribute its toxic action from the site of origin all over the cell and may even mediate intercellular communication. Thus, H2O2 acts as a spreader by transporting it to sites where the extremely short-lived toxic HO· radical can arise in the presence of "free iron". H2O2 and HO· act in concert due to their different complementary chemical properties. They are dependent upon each other while executing the toxic effects in oxidative stress under diabetic metabolic conditions in particular in the highly vulnerable pancreatic beta cell, which in contrast to many other cell types is so badly protected against oxidative stress due to its extremely low H2O2 inactivating enzyme capacity.

Voltammetric analysis of Pinus needles with physiological, phylogenetic, and forensic applications.

Polyphenolic compounds are electrochemically active components of vegetal matter which were targeted under simple experimental conditions to produce voltammetric profiles characterizing the metabolite composition. Application to bivariate and multivariate chemometric techniques permits to discriminate the species and age of plant leaves, illustrated here for the case of six Pinus species from two different subgenera. Such responses, associated with the electrochemical oxidation of polyphenolic compounds (quercetin, gallic acid, ellagic acid, among others), define a voltammetric profile which varies systematically with the age of the leaves for the different species. The application of this methodology for phylogenetic studies, plant physiology, forensic science, and chemoecology is discussed. Graphical Abstract Image of Pinus in a typical Mediterranean forest; Courtesy of the Botanic Garden of the University of Valencia.

The lipid composition determines the kinetics of adhesion and spreading of liposomes on mercury electrodes.

The dependence of membrane properties on their composition was studied by following the adhesion and spreading of unilamellar and multilamellar liposomes on static mercury electrodes with the help of chronoamperometry. The analysis of the peak-shaped signals allows determining the kinetic parameters of the three-step adhesion-spreading process. The presence of cholesterol in the membrane stabilizes the bilayer in the liquid-crystalline phase, and destabilizes the gel phase. The kinetic parameters also show the effect of superlattice formation in the DMPC-cholesterol system. The detergent triton X-100 is only incorporated in the liquid-crystalline DMPC membranes, and it is expelled to the solution when the membrane is transformed to the gel phase. In the liquid-crystalline membrane, it enhances the adhesion-spreading of liposomes on mercury. The lytic peptides mastoparan X and melittin affect the adhesion-spreading in a similar manner. For the rupture-spreading step, their effect is explained by pore formation. The results obtained with lecithins of different length suggest that the bilayer opening process has much in common with flip-flop translocations. For this process the activation energies were found to be independent of the chain length of the lecithin molecules, while the preexponential factor in the Arrhenius equation decreases drastically for longer chains.