The first detailed structural model for the hevein-chitin complex is presented on the basis of the analysis of NMR data. The resulting model, in combination with ITC and analytical ultracentrifugation data, conclusively shows that recognition of chitin by hevein domains is a dynamic process, which is not exclusively restricted to the binding of the nonreducing end of the polymer as previously thought. This allows chitin to bind with high affinity to a variable number of protein molecules, depending on the polysaccharide chain length. The biological process is multivalent.

Polysaccharides are the most abundant organic materials in nature, yet correlations between their three-dimensional structure and macroscopic properties have not been established. Automated glycan assembly enables the preparation of well-defined oligo- and polysaccharides resembling natural as well as unnatural structures. These synthetic glycans are ideal probes for the fundamental study of polysaccharides. According to molecular modeling simulations and NMR analysis, different classes of polysaccharides adopt fundamentally different conformations that are drastically altered by single-site substitutions. Larger synthetic polysaccharides are obtained via a "LEGO"-like approach as a first step toward the production of tailor-made carbohydrate-based materials.

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Hybrid organic-inorganic solids represent an important class of engineering materials, usually prepared by sol-gel processes by cross-reaction between organic and inorganic precursors. The choice of the two components and control of the reaction conditions (especially pH value) allow the synthesis of hybrid materials with novel properties and functionalities. 3-Glycidoxypropyltrimethoxysilane (GPTMS) is one of the most commonly used organic silanes for hybrid-material fabrication. Herein, the reactivity of GPTMS in water at different pH values (pH 2-11) was deeply investigated for the first time by solution-state multinuclear NMR spectroscopic and mass spectrometric analysis. The extent of the different and competing reactions that take place as a function of the pH value was elucidated. The NMR spectroscopic and mass spectrometric data clearly indicate that the pH value determines the kinetics of epoxide hydrolysis versus silicon condensation. Under slighly acidic conditions, the epoxy-ring hydrolysis is kinetically more favourable than the formation of the silica network. In contrast, under basic conditions, silicon condensation is the main reaction that takes place. Full characterisation of the formed intermediates was carried out by using NMR spectroscopic and mass spectrometric analysis. These results indicate that strict control of the pH values allows tuning of the reactivity of the organic and inorganic moities, thus laying the foundations for the design and synthesis of sol-gel hybrid biomaterials with tuneable properties.

The transgalactosylation activity of Kluyveromyces lactis cells was studied in detail. Cells were permeabilized with ethanol and further lyophilized to facilitate the transit of substrates and products. The resulting biocatalyst was assayed for the synthesis of galacto-oligosaccharides (GOS) and compared with two soluble β-galactosidases from K. lactis (Lactozym 3000 L HP G and Maxilact LGX 5000). Using 400 g/L lactose, the maximum GOS yield, measured by HPAEC-PAD analysis, was 177 g/L (44% w/w of total carbohydrates). The major products synthesized were the disaccharides 6-galactobiose [Gal-β(1→6)-Gal] and allolactose [Gal-β(1→6)-Glc], as well as the trisaccharide 6-galactosyl-lactose [Gal-β(1→6)-Gal-β(1→4)-Glc], which was characterized by MS and 2D NMR. Structural characterization of another synthesized disaccharide, Gal-β(1→3)-Glc, was carried out. GOS yield obtained with soluble β-galactosidases was slightly lower (160 g/L for Lactozym 3000 L HP G and 154 g/L for Maxilact LGX 5000); however, the typical profile with a maximum GOS concentration followed by partial hydrolysis of the newly formed oligosaccharides was not observed with the soluble enzymes. Results were correlated with the higher stability of β-galactosidase when permeabilized whole cells were used.

Abstract:We report the synthesis of a series of aglucosyl derivatives of resveratrol (3,5,4'-trihydroxy-A C H T U N G T R E N N U N G stilbene) by a transglycosylation reaction catalyzed by the enzyme cyclodextrin glucanotransferase (CGTase) using starch as glucosyl donor. Several reaction parameters (temperature, solvent composition, enzyme concentration and starch/resveratrol ratio) were optimized. The yield of a-glucosylated products reached 50% in 24 h. The structures of the derivatives were determined by a combination of amyloglucosidase-hydrolysis tests, MS and 2D-NMR. Three families of products were obtained: glucosylated at 3-OH, at 4'-OH and at both 3-OH and 4'-OH. The bonds between glucoses were basically aA C H T U N G T R E N N U N G (1!4). Interestingly, the water solubilities of the a-glucosylated derivatives were at least 65-and 5-fold higher than those of resveratrol and the natural b-glucosylated derivative (piceid), respectively. In contrast with piceid, the synthesized a-glucosylated compounds exhibited surfactant activity, with critical micelle concentration (CMC) values in the range 0.5-3.6 mM. Although the incorporation of a glucosyl moiety caused a loss of antioxidant activity (more pronounced in the position 3-OH compared with 4'-OH), the fact that the glycosides need to be converted into the aglycones before they are absorbed minimizes such an effect. In contrast, the modification of physicochemical properties such as solubility and partition coefficient by glycosylation could exert a positive influence on the bioavailability of resveratrol.

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