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A Domard

Publications and source records attributed to A Domard.

8 recordsLinked to original sources
PubMed1992

Glucosamine oligomers: 4. Solid state-crystallization and sustained dissolution.

When glucosamine oligomers are stored in the solid state they undergo a process of crystallization. The extent to which this occurs depends on whether the samples are isolated in the -NH3+ or -NH2 form, on the storage time, and on the degree of polymerization of the isolated oligomer. The allomorph obtained by this process seems to correspond to the so-called 'tendon-chitosan'. Dissolution of such aged oligomer samples gives rise to a process of dissociation of the associated chains in the crystal, leading to the establishment of a pseudo-equilibrium between single and associated oligomer chains and hence the simultaneous presence of the 'monomeric', 'dimeric', 'trimeric', etc., forms of the oligomer. The phenomenon cannot be attributed to a process of aggregation in solution. The effects of various parameters on this behaviour have been investigated.

Chromatography↗
PubMed1992

Single crystals of alpha-chitin.

Single crystals of alpha-chitin were grown by the addition of precipitants to dilute solutions of low molecular weight chitin fractions dissolved in aqueous LiSCN. At temperatures around 200 degrees C, bundles of thin needle-shaped crystals were obtained. Each of these needles was an alpha-chitin single crystal, characterized by a spot electron diffraction pattern which could be indexed along the hk0 reciprocal net corresponding to the Minke and Blackwell unit cell [a = 0.474 nm, b = 1.88 nm, c (fibre axis) = 1.032 nm, space group P2(1)2(1)2(1)]. In a crystal, the a* parameter was along the crystal axis and the b* perpendicular to it.

Chitin↗
PubMed1991

Non-specificity of a colorimetric method for the estimation of N-acetyl-D-glucosamine.

The colorimetric method of Reissig et al. for the estimation of N-acetylamino sugars, is often used as a specific method for the quantification of the N-acetyl-D-glucosamine. Although this assay is more sensitive to the monomer, it recognizes all soluble N-acetyl-D-glucosamine oligomers. This result is very important because this method is extensively used in biology for the estimation of chitinolytic activity.

Acetylglucosamine↗
PubMed1991

Glucosamine oligomers: 2. N.m.r. studies on a DP3.

This paper concerns the characterization of the chemical structure of a DP3 glucosamine oligomer. The assignments of nearly all protons are reported. Variations of 1H chemical shifts with pD and temperature are correlated to the pKa of amino groups, and not with substantial conformational changes.

Carbohydrate Conformation↗
PubMed1990

Single crystals of chitosan.

Lamellar single crystals of chitosan were prepared at 125 degrees C by adding ammonia to a low DP fraction of chitosan dissolved in water. The crystals gave sharp electron diffraction diagrams which could be indexed in an orthorhombic P2(1)2(1)2(1) unit cell with a = 8.07 A, b = 8.44 A, c = 10.34 A. The unit cell contained two anti-parallel chitosan chains and no water molecules. It was found that cellulose microfibrils from Valonia ventricosa could act as nuclei for inducing the crystallization of chitosan on cellulose. This produced a shish-kebab morphology.

Chitin↗