Biblioteca Digital

The Raman spectra of serine [[alpha]-amino-[beta]-hydroxypropionic acid; HOCH2CH(NH3)+COO-] and 3,3-dideutero-serine [HOCD2CH(NH3)+COO-] in aqueous solution were studied in the range 4000-300 cm-1. The data obtained for the deuterated compound are novel and provide compelling evidence that previously reported assignments for the undeuterated amino acid should be revised.; http://www.sciencedirect.com/science/article/B6THW-4KNMB16-1/1/19da7b30f32b5efeacb053228a66c4a4

As propriedades estruturais, energéticas e vibracionais da L- e DL-Ser e dos seus isotopólogos deuterados nas formas neutra e zwiteriónica, em diferentes ambientes químicos e bioquímicos, foram investigadas por espectroscopia de IR e Raman e métodos teóricos. A investigação da Superfície de Energia Potencial da serina na forma neutra foi realizada recorrendo aos métodos DFT e MP2. As estruturas e os espectros vibracionais dos confórmeros mais estáveis da serina foram calculados usando ambos os níveis de teoria e utilizados na interpretação dos resultados espectroscópicos obtidos para o composto isolado em matrizes de árgon a baixa temperatura. Os efeitos da entropia no equílibrio conformacional da serina foram também investigados. Além disso, foi efectuada irradiação in situ dos compostos isolados e realizados estudos de variação de temperatura da matriz. Os espectros de IV das amostras policristalinas puras da L- e DL-Ser e das espécies isotopicamente substítuidas foram investigados. Um método experimental assente na conjugação do uso de dopagem isotópica e de temperaturas baixas foi usado, conjuntamente com correlações empíricas, para estimar as energias e os comprimentos das diferentes ligações-de-hidrogénio presentes em ambos os cristais. Adicionalmente...

A systematic investigation of the conformational potential energy surface of neutral serine [HOCH2CHNH2COOH] and 3,3-dideutero-serine [HOCD2CHNH2COOH] was undertaken, revealing the existence of 61 different minima. The structures and vibrational spectra of the most stable conformers, which were estimated to have relative energies within 7 kJ mol-1 and account for ca. 93% of the total conformational population at room temperature, were calculated at both the MP2 and DFT/BLYP levels of theory with the 6-311++G(d,p) basis-set and used to interpret the spectroscopic data obtained for the compounds isolated in low-temperature inert matrixes. The assignment of the main spectral infrared features observed in the range 4000−400 cm-1 to the most stable conformers of serine was undertaken. In addition, UV irradiation (λ > 200 nm) of the matrix-isolated compounds was also performed, leading to decarboxylation, which was found to be strongly dependent on the conformation assumed by the reactant molecule.

Sulbactam is a mechanism-based inhibitor of β-lactamase enzymes used in clinical practice. It undergoes a complex series of chemical reactions in the active site that have been studied extensively in the past three decades. However, the actual species that gives rise to inhibition in a clinical setting has not been established. Recent studies by our group, using Raman microscopy and X-ray crystallography, have found that large quantities of enamine-based acyl-enzyme species are present within minutes in single crystals of SHV-1 β-lactamases which can lead to significant inhibition. The enamines are formed by break down of the cyclic beta-lactam structures with further transformations leading to imine formation and subsequent isomerization to cis and/or trans enamines. Another favored form of inhibition arises from attack on the imine by a second nucleophilic amino acid side chain, e.g. from serine 130, to form a cross linked species in the active site that can degrade to an acrylate-like species irreversibly bound to the enzyme. Thus, the imine is at a branch point on the reaction pathway. Using sulbactam and 6,6-dideuterated sulbactam we follow these alternate paths in WT and E166A SHV-1 β-lactamase by means of Raman microscopic studies on single enzyme crystals. For the unlabeled sulbactam...