CHEMICAL EVOLUTION OF THE GALACTIC BULGE: SINGLE AND DOUBLE INFALL MODELS

Recent work, has produced a wealth of data concerning the chemical evolution of the Galactic bulge, both for stars and nebulae. Present theoretical models generally adopt it limited range of such constraints, frequenfly using it single chemical element (usually iron), which is not enough to describe it unambiguously. In this work, we take into account contraints involving,9 Many chemical elements as possible, basically obtained from bulge nebulae and stars. Our main goal is to show that different scenarios can describe, at least partially the abundance distribution and several dishuice-independent correlations for these objects . Three classes of models were developed. The first is it one-zone, single-infall model, the. Second is it one-zone, double-infall model and the third is a multizone, double-infall model. We show that a one-zone model with it single infall episode is able to reproduce some of the observational data, but the best results tire achieved using it multizone, double-infall model.

Sample stacking in CZE using dynamic thermal junctions II: Analytes with high dpK(a)/dT crossing a single thermal junction in a BGE with low dpH/dT

In a previous work [M. Mandaji, et al., this issue] a sample stacking method was theoretically modeled and experimentally demonstrated for analytes with low dpK(a)/dT (analytes carrying carboxylic groups) and BGEs with high dpH/dT (high pH-temperature-coefficients). In that work, buffer pH was modulated with temperature, inducing electrophoretic mobility changes in the analytes. In the present work, the opposite conditions are studied and tested, i.e. analytes with high dpK(a)/dT and BGEs that exhibit low dpH/dT. It is well known that organic bases such as amines, imidazoles, and benzimidazoles exhibit high dpK(a)/dT. Temperature variations induce instantaneous changes on the basicity of these and other basic groups. Therefore, the electrophoretic velocity of some analytes changes abruptly when temperature variations are applied along the capillary. This is true only if BGE pH remains constant or if it changes in the opposite direction of pK(a) of the analyte. The presence of hot and cold sections along the capillary also affects local viscosity, conductivity, and electric field strength. The effect of these variables on electrophoretic velocity and band stacking efficacy was also taken into account in the theoretical model presented. Finally, this stacking method is demonstrated for lysine partially derivatized with naphthalene-2,3-dicarboxaldehyde. In this case, the amino group of the lateral chain was left underivatized and only the alpha amino group was derivatized. Therefore, the basicity of the lateral amino group, and consequently the electrophoretic mobility, was modulated with temperature while the pH of the buffer used remained unchanged.