Investigation on the micro-mechanisms of Al(3+) interfering the reactivities of aspartic acid and its biological processes with Mg(2+).

Density functional theory (DFT) has been applied to study the micro-mechanisms of Al3+ interfering the reactivities of aspartic acid (H2asp) and its biological processes with Mg2+. All the 46 stable conformers of Hasp- and 3 of asp2- have been determined at the B3LYP/6-311++G** level, showing that the 7 most stable conformers of Hasp- all present a very strong and linear O-H...O H-bond between carboxyl and carboxylic acid groups with the bond energy high up to 162 kJ mol(-1). The reaction thermodynamics and micro-mechanism between Al3+ and Hasp- (or asp2-) in aqueous phase have been investigated by the combined application of supramolecular model and polarizable continuum IEFPCM solvent model, firstly revealing Al3+ interfering in the biological processes of aspartic acid. The substitution thermodynamics and mechanisms of Mg2+ by Al3+ in the biological processes between the species of aspartic acid and Mg2+ in aqueous phase were probed, revealing the facile displacement of Mg2+ by Al3+. These results may provide a reasonable mechanism of Al3+ biological toxicity at the microscopic level.

Theoretical insight into the influences of alpha-substituents in aliphatic aldehydes on the enantioselectivities of aldol reactions.

Density functional theory has been applied to study the influences of alpha-substituents in aliphatic aldehydes on the enantioselectivities of the (S)-proline-catalyzed direct aldol reactions. Reaction scenarios of three kinds of aliphatic aldehydes were investigated. Four transition states associated with the stereocontrolling step of each reaction have been obtained. They are corresponding to the syn and anti arrangements of enamine intermediates and the si and re attacks to the carbonyl group of an aldehyde. The solvent effect of DMSO was investigated using self-consistent reaction field method based on the polarizable continuum model. The computed energies of transition states explain the origin of the catalysis and enantioselectivities for these (S)-proline-catalyzed aldol reactions and reveal the influences of alpha-substituents in aliphatic aldehydes on the enantioselectivities of these reactions.