Interplay between Structure and Dynamics in Chitosan Films Investigated with Solid-State NMR, Dynamic Mechanical Analysis, and X-ray Diffraction

Modern solid-state NMR techniques, combined with X-ray diffraction, revealed the molecular origin of the difference in mechanical properties of self-associated chitosan films. Films cast from acidic aqueous solutions were compared before and after neutralization, and the role of the counterion (acetate vs Cl⁻) was investigated. There is a competition between local structure and long-range order. Hydrogen bonding gives good mechanical strength to neutralized films, which lack long-range organization. The long-range structure is better defined in films cast from acidic solutions in which strong electrostatic interactions cause rotational distortion around the chitosan chains. Plasticization by acetate counterions enhances long-range molecular organization and film flexibility. In contrast, Cl⁻ counterions act as a defect and impair the long-range organization by immobilizing hydration water. Molecular motion and proton exchange are restricted, resulting in brittle films despite the high moisture content

DNA Fingerprinting of Pearls to Determine Their Origins

We report the first successful extraction of oyster DNA from a pearl and use it to identify the source oyster species for the three major pearl-producing oyster species Pinctada margaritifera, P. maxima and P. radiata. Both mitochondrial and nuclear gene fragments could be PCR-amplified and sequenced. A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay in the internal transcribed spacer (ITS) region was developed and used to identify 18 pearls of unknown origin. A micro-drilling technique was developed to obtain small amounts of DNA while maintaining the commercial value of the pearls. This DNA fingerprinting method could be used to document the source of historic pearls and will provide more transparency for traders and consumers within the pearl industry

The behaviour of chitin towards anhydrous hydrogen fluoride. Preparation of β-(1→4)-linked 2-acetamido-2-deoxy-D-glucopyranosyl oligosaccharides

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Polymeric gels. NMR study of elementary chain swelling. Effect of trapped topological constraints

This work aims at studying the progressive swelling process of three polydimethylsiloxane covalent gels, synthetized at several volume fractions, νc ; two good solvents (chloroform and heptane) and a theta-solvent (bromocyclohexane) were used as swelling agents. i) The macroscopic swelling was found to obey a simple addition law of volumes of solvent and polymer. ii) The transverse magnetic relaxation process of protons linked to PDMS chains is shown to reflect a progressive swelling process of elementary chains occurring according to two well defined steps. The first one (1 qd) and an excluded volume effect arises ; this is fully observed on gels at equilibrium with a liquid solvent. Superposition properties are interpreted from a basic formula describing the transfer of localization of NMR properties from a local space-scale to a semi-local one.L'objectif de ce travail est d'étudier le gonflement progressif de trois gels covalents, de polydiméthylsiloxane, synthétisés à des concentrations, vc, différentes ; deux bons solvants (chloroforme et heptane) et un solvant-thêta (bromocyclohexane) étaient utilisés comme agents de gonflement. i) Le gonflement observé à l'échelle macroscopique obéit à une simple loi d'addition des volumes de solvant et de polymère. ii) La relaxation de l'aimantation transversale des protons liés aux chaînes est analysée pour proposer un processus de gonflement progressif des chaînes élémentaires en deux étapes bien séparées; dans la première (1 qd) laissant apparaître un effet de volume exclu qui est complet au gonflement maximum. Les lois de superposition sont interprétées à partir d'une formule de base décrivant le transfert de localisation des propriétés RMN d'une échelle locale à une échelle semi-locale

Pyrolysis patterns of 5 close Corynebacterium species analyzed by artificial neural networks

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Evaluation of chitosans and Pichia guillermondii as growth inhibitors of Penicillium digitatum

International audienceChitosans were obtained by room-temperature-homogeneous-deacetylation (RTHD) and freeze-pump-out-thaw-heterogeneous-deacetylation (FPT) from chitins purified from fermentations. Commercial chitosan was deacetylated by three-FPT-cycles. Chitosans and Pichia guillermondii were evaluated on the growth of Penicillium digitatum. Medium molecular weight (M(W)) chitosans displayed higher inhibitory activity against the yeast than low M(W) biopolymers. Chitosans with low degree of acetylation (DA) were inhibitory for yeast and mould. Therefore, a low M(W) and high DA chitosan was selected for use against moulds combined with yeasts. Biopolymer and yeasts presented an additive effect, since chitosans were effective to delay spore germination, whereas yeast decreased apical fungal growth