This article provides an overview on the recent achievements to combat Gram-positive bacteria and the mechanisms related to antimicrobial activity and bacterial resistance. Selected synthetic methodologies to access structurally diverse bioactive compounds are presented in order to emphasize the most important substances currently developed to overcome multiresistant strains. The main properties of vancomycin and related glycopeptide antibiotics are also discussed as a background to understanding the design of new chemotherapeutic agents.

O estudo da sorção e dessorção de Cd(II) na interface de vários sorventes e soluções aquosas mostrou que a capacidade de troca depende do tipo de sorvente, do pH e do sistema tampão. Tampões como succinato e citrato, os quais são bons complexantes de Cd(II) suprimem completamente a incorporação dentro dos diferentes sorventes. Na presença do tampão Tris, a capacidade de troca observada decresce na seguinte ordem, gama-alumina > montmorilonita > caolinita <FONT FACE=Symbol>»</FONT> sílica. A precipitação de Cd(II) torna-se importante na presença de bicarbonato aquoso na faixa de pH 5,5-7. As isotermas observadas para as diferentes argilas mostram saturação em concentração bastante altas de Cd(II). Isto sugere que em águas naturais, a sorção e distribuição de Cd(II) entre as fases geoquímicas dos sedimentos deve seguir uma relação linear. A cinética de dessorção de Cd(II) da superfície da montmorilonita, na presença do íon citrato, mostra que este é um ligante orgânico eficiente para remover o Cd(II) ligado em sítios facilmente acessíveis. O processo ocorre em duas etapas, com liberação inicial de aproximadamente 70% do Cd(II), seguido pela liberação lenta do metal de sítios com acesso controlado pela difusão.

The sorption and desorption of Cd(II) that occurs at the interface between several sorbents and aqueous solutions has been investigated and it is shown that the observed exchange capacity depends on the type of sorbent, the pH and the buffering system. Buffers such as succinate and citrate, which are good complexants of Cd(II) completely supress its incorporation into the different sorbents. In the presence of Tris buffer the observed exchange capacity decreases in the order gamma-alumina > montmorillonite > kaolinite <FONT FACE=Symbol>»</FONT> silica, while precipitation is important in the presence of aqueous bicarbonate in the pH range 5.5-7. The sorption data fit with general purpose isotherms well, and the sorption isotherm shows saturation at rather high concentrations of Cd(II) in both clays. This suggests that under many experimental conditions in natural waters, the sorption and distribution of Cd(II) between geochemical phases of sediments should follow a linear relationship. The kinetics of desorption from montmorillonite, in the presence of citrate ion, is particularly important, showing that this efficient organic ligand removes all the Cd(II) bound to readily accessible sites in a fast step, while removal of Cd(II) from sites with diffusion-restricted access is much slower.

A broad picture of the graduate programs in chemistry in Brazil is analyzed from the data collected during the period 1996/1997 for evaluation by CAPES. The results are compared with those from previous evaluations, indicating significant quantitative and qualitative progresses.

This review gives a critical idea on the importance of intramolecular reactions as models for enzymatic catalysis. Intramolecular lactonizations, ester and amide hydrolysis studies result in theories which try to explain the difference between intermolecular, intramolecular and enzyme reactions and rationalize the enhancement promoted by these biological catalyst.