Reduction of sulfoxides catalyzed by oxo-complexes

This work reports the catalytic activity of the oxo-complexes HReO₄, MoO₂(acac)₂, WO₂Cl₂, and VO(acac)₂ in the reduction of sulfoxides with PhSiH₃ or HBcat. The results obtained showed that the catalyst systems PhSiH₃/HReO₄ (5 mol %) and HBcat/HReO₄ (5 mol %) are highly efficient for the deoxygenation of sulfoxides. The complex MoO₂(acac)₂ was also efficient, but the reactions required more time and heating. Finally, the complexes WO₂Cl₂ and VO(acac)₂ showed a moderate activity.     

Screening nucleotide binding to amino acid-coated supports by surface plasmon resonance and nuclear magnetic resonance

Here, we describe a rapid and efficient screening method using surface plasmon resonance (SPR) and saturation transfer difference–nuclear magnetic resonance (STD-NMR) spectroscopy to yield information regarding the residues involved in nucleotide binding to amino acid-coated supports. The aim of this work was to explore the use of these spectroscopic techniques to study amino acid–nucleotide interactions in order to improve the binding specificity of the amino acid ligands used to purify plasmid DNA. For SPR, we present a strategy that immobilizes arginine and lysine on a surface as model supports, and we analyze binding responses when synthetic homo-deoxyoligonucleotides are injected over the amino acid surface. The binding responses are detectable and reproducible despite the small size of the immobilized amino acids. Using STD-NMR, we performed epitope mapping of homo-deoxyoligonucleotides bound to l-arginine–bisoxyran–Sepharose and l-lysine–Sepharose supports. Polynucleotide binding preferences differed; for example, polyC interacted preferentially through its backbone with the two supports, whereas polyT bound the supports through its thymine moiety. STD-NMR combined with SPR measurements was successfully used to screen amino acid–nucleotide interactions and determine the binding affinities of the complexes.     

Analysis of nucleotides binding to chromatography supports provided by nuclear magnetic resonance spectroscopy

The epitope mapping of nucleotides bound to three chromatography supports is accomplished using saturation transfer difference (STD)-NMR spectroscopy. This experiment involves subtracting a spectrum in which the support was selectively saturated from one recorded without support saturation. In the difference spectrum only the signals of the ligands that bind to the support and received saturation transfer remain. The nucleotide protons in closer contact with the support have more intense signals due to a more efficient transfer of saturation. We investigate the effects on the binding to the nucleotides by the introduction of a spacer arm between l-histidine and Sepharose. Our NMR experiments evidence a clear contribution of the spacer to the interaction with all the nucleotides, increasing the mobility of the amino acid and giving different STD responses. This enhanced mobility originates the reinforcement of the interactions with the sugar moiety and phosphate group of 5'-CMP and 5'-TMP or the base of 5'-GMP and 5'-UMP. Hence, with this study we show that by using STD NMR technique on chromatographic systems it is possible to provide a fast, robust and efficient way of screening the atoms involved in the binding to the supports.     

The Plasticity of the Carbohydrate Recognition Domain Dictates the Exquisite Mechanism of Binding of Human Macrophage Galactose-Type Lectin

The human macrophage galactose-type lectin (MGL), expressed on macrophages and dendritic cells (DCs), modulates distinct immune cell responses by recognizing N-acetylgalactosamine (GalNAc) containing structures present on pathogens, self-glycoproteins, and tumor cells. Herein, NMR spectroscopy and molecular dynamics (MD) simulations were used to investigate the structural preferences of MGL against different GalNAc-containing structures derived from the blood group A antigen, the Forssman antigen, and the GM2 glycolipid. NMR spectroscopic analysis of the MGL carbohydrate recognition domain (MGL-CRD, C181-H316) in the absence and presence of methyl α-GalNAc (α-MeGalNAc), a simple monosaccharide, shows that the MGL-CRD is highly dynamic and its structure is strongly altered upon ligand binding. This plasticity of the MGL-CRD structure explains the ability of MGL to accommodate different GalNAc-containing molecules. However, key differences are observed in the recognition process depending on whether the GalNAc is part of the blood group A antigen, the Forssman antigen, or GM2-derived structures. These results are in accordance with molecular dynamics simulations that suggest the existence of a distinct MGL binding mechanism depending on the context of GalNAc moiety presentation. These results afford new perspectives for the rational design of GalNAc modifications that fine tune MGL immune responses in distinct biological contexts, especially in malignancy.     

Impact of malolactic fermentation on low molecular weight phenolic compounds

A reversed phase liquid chromatography-DAD method is proposed for analysis of major non-flavonoid phenolic compounds in wines. The method employed a mixture of acetic acid, water and methanol as eluents and was used to evaluate the impact of malolactic fermentation in low molecular phenolic compounds.

The wines analyzed underwent different treatments, like the addition of a pectolytic enzyme or lysozyme, and the way malolactic fermentation was carried out—spontaneously or with the inoculation of two different commercial lactic bacteria.

The main result observed was the disappearance of hydroxycinnamoyltartaric acids and the increase of resultant free forms, regardless the way malolactic fermentation was carried out.     

Rapid distinction of intracellular and extracellular proteins using NMR diffusion measurements

In-cell NMR spectroscopy offers a unique opportunity to begin to investigate the structures, dynamics, and interactions of molecules within their functional environments. An essential aspect of this technique is to define whether observed signals are attributable to intracellular species rather than to components of the extracellular medium. We report here the results of NMR measurements of the diffusion behavior of proteins expressed within bacterial cells, and find that these experiments provide a rapid and nondestructive probe of localization within cells and can be used to determine the size of the confining compartment. We show that diffusion can also be exploited as an editing method to eliminate extracellular species from high-resolution multidimensional spectra, and should be applicable to a wide range of problems. This approach is demonstrated here for a number of protein systems, using both (15)N and (13)C (methyl-TROSY) based acquisition.     

High-valent oxo-molybdenum and oxo-rhenium complexes as efficient catalysts for X-H (X = Si, B, P and H) bond activation and for organic reductions

High-valent oxo-complexes have recently emerged as powerful catalysts for the activation of X-H (X = Si, B, P and H) bonds and for the reduction of several functional groups. This new reactivity represents a complete reversal from the traditional role of these complexes as oxidation catalysts and opened a new research area for high-valent oxo-complexes. This tutorial review highlights the work developed using high-valent oxo-molybdenum and oxo-rhenium complexes as excellent catalysts for X-H (X = Si, B, P and H) bond activation and for organic reductions.