Rubens Bernardes Filho

Estudo de métodos de aumento de resolução de espectros de FTIR para análise de estruturas secundárias de proteínas

The FTIR spectroscopy has been used to quantify the secondary structures of proteins, using amide I band (1600 - 1700 cm-1). The resolution enhancement methods have been used to resolve the individual components of this band that correlate to the secondary structure. In this paper we discuss the methods of derivative, Fourier deconvolution and fitting with simulated spectra. The results shows that they have serious problems and can be used only as a qualitative or semiquatitative method.

pH effect in aquatic fulvic acid from a Brazilian river

Studies of the morphological behavior of fulvic acids were carried out using the Atomic Force Microscopy technique together with zeta Potential techniques and fluorescence spectroscopy. Results showed that the aquatic fulvic acid (AFA) of a Brazilian River changed its morphology when the AFA aqueous solution had its pH changed. In acid pH the morphology is granular forming 10-55 nm high agglomerates. In alkaline pH values were 2.5-4.0 nm, and the morphology forms non granular structures. These results suggest that for pH 3.0 electrostatic interactions are weak and hydrogen bonding is responsible for the aggregates formation; while at pH 9.0 electrostatic interactions are strong due to the increase in phenolic groups ionization and low hydrogen interaction forming open structures. Fluorescence spectroscopy results confirmed the AFM, that is, a change in the AFA in tropical river in alkaline pH compared to the structure in acid pH.

Measuring bacterial cells size with AFM

Atomic Force Microscopy (AFM) can be used to obtain high-resolution topographical images of bacteria revealing surface details and cell integrity. During scanning however, the interactions between the AFM probe and the membrane results in distortion of the images. Such distortions or artifacts are the result of geometrical effects related to bacterial cell height, specimen curvature and the AFM probe geometry. The most common artifact in imaging is surface broadening, what can lead to errors in bacterial sizing. Several methods of correction have been proposed to compensate for these artifacts and in this study we describe a simple geometric model for the interaction between the tip (a pyramidal shaped AFM probe) and the bacterium (Escherichia coli JM-109 strain) to minimize the enlarging effect. Approaches to bacteria immobilization and examples of AFM images analysis are also described.

Quantification of protein secondary structure by 13 C solid-state NMR

High-resolution 13C solid-state NMR stands out as one of the most promising techniques to solve the structure of insoluble proteins featuring biological and technological importance. The simplest nuclear magnetic resonance (NMR) spectroscopy method to quantify the secondary structure of proteins uses the areas of carbonyl and alpha carbon peaks. The quantification obtained by fitting procedures depends on the assignment of the peaks to the structure, type of line shape, number of peaks to be used, and other parameters that are set by the operator. In this paper, we demonstrate that the analysis of 13C NMR spectra by a pattern recognition method—based on the singular value decomposition (SVD) regression, which does not depend on the operator—shows higher correlation coefficients for α-helix and β-sheet (0.96 and 0.91, respectively) than Fourier transform infrared spectroscopy (FTIR) method. Therefore, the use of 13C solid-state NMR spectra and SVD is a simple and reliable method for quantifying the secondary structures of insoluble proteins in solid-state.

Desenvolvimento de filmes poliméricos ultrafinos e reticulados para aplicações em sensores

Este trabalho propoe um novo metodo de producao de filmes estaveis para aplicacoes em sensores baseado na deposicao pela tecnica de automontagem de poli(o-etoxianilina) alternada com fenol-formaldeido (POEA/PF) seguida por cura termica. O processo de reticulacao foi caracterizado por espectroscopias no infravermelho por transformada de Fourier e no ultravioleta-visivel, microscopia de forca atomica e estudos de dessorcao; a capacidade sensorial destes filmes foi avaliada atraves de medidas em sensores. Os resultados mostram que a resina PF serviu como agente de cura e alternante formando uma rede semi-interpenetrante, por conseguinte, filmes mais estaveis foram produzidos. Embora tenha ocorrido uma diminuicao da sensibilidade dos sensores com o reticulacao, tais filmes sao bastante estaveis e podem ser potencialmente usados em sensores, especialmente onde uma maior estabilidade se faz necessaria.