Search PubMed⌕ Search

Biomedical subjects

A Domard

Publications and source records attributed to A Domard.

33 records · Page 2Linked to original sources
PubMed1996

Collagen and its interactions with chitosan, III some biological and mechanical properties.

Bovine atelocollagen and high molecular weight fully deacetylated chitosan, depending on the conditions, can form complexes whether by means of purely electrostatic interactions or by hydrogen bonding. In the first case the maximum proportion of chitosan in the complex is relatively low (approximately 10%) and then it is difficult to conclude whether chitosan prevents collagen digestion by collagenase or not. On the contrary, in the case of the second kind of complex, chitosan induces a strong protection toward the specific enzyme. If we consider the mechanical properties of polyanion/polycation complexes, chitosan brings softening rather than hardening to the system and the complex behaves like some polymer blends.

Animals↗
PubMed1995

Collagen and its interaction with chitosan. II. Influence of the physicochemical characteristics of collagen.

This work is a continuation of the study of the interactions which can occur when chitosan is in contact with bovine anticollagen. The major result of the first part was that under classical conditions, there exists a competition between collagen gelation and the formation of a pure polyanion-polycation complex with chitosan. In the present study, we have attempted to reach the 1:1 stoichiometry by two different methods. When collagen is denatured, the polyanion-polycation complex is improved, but the theoretical stoichiometry is not achieved. The presence of a large excess of chitosan gives rise to a second mechanism of interaction. Contrary to the case of the polyanion-polycation interaction, the latter seems to induce the denaturation of collagen. This behaviour is confirmed by infrared and circular dichroism spectrometries, as well as differential scanning calorimetry.

Animals↗
PubMed1993

Relation between the physicochemical characteristics of collagen and its interactions with chitosan: I.

The interaction between bovine atelocollagen and a high molecular weight fully deacetylated chitosan has been studied. Considering the apparent mass of an anionic equivalent of collagen and the results of various techniques (potentiometry, conductometry and IR spectroscopy), a purely electrostatic mechanism is demonstrated. The role of charge density and chain length of collagen chains is discussed, and although the interaction is weak and hindered by gel formation in collagen solutions, a polyanion-polycation complex is obtained. Circular dichroism spectroscopy experiments show an organization in the solid state of the complex which is quite different to those of collagen and chitosan.

Acetylation↗
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↗
PubMed1989

Glucosamine oligomers: 1. Preparation and characterization.

Hydrolysis of chitosan in hot concentrated HCl led to chito-oligosaccharides [beta-(1----4) linked 2-amino-2-deoxy-D-glucose]. The time dependence of the distribution was studied. A convenient choice of the conditions for steric exclusion chromatography of these hydrolysates allowed the separation of the first 15 oligomers and of fractions up to DP = 40.

Chitin↗
PubMedDate not supplied

Covalent immobilization of proteins onto (Maleic anhydride-alt-methyl vinyl ether) copolymers: enhanced immobilization of recombinant proteins.

Two genetically modified HIV-1 capsid p24 proteins, RH24 and RH24K, were covalently bound to maleic anhydride-alt-methyl vinyl ether (MAMVE) copolymer, under aqueous conditions. We demonstrated that the addition of a six lysine unit tag at the COOH-terminus of RH24K greatly improved the grafting reaction which could take place under many different experimental conditions. The course of the reaction was controlled by electrostatic attractive forces between the protein and the negatively charged polymer, as the chemical binding was more efficient at low ionic strength. The maximum loading capacity of the polymer depended on whether the protein bore the lysine tag (RH24K) or not (RH24). Twenty-four molecules of RH24 could be immobilized per polymer chain and 49 for RH24K. Such a difference could be explained by a difference of orientation of the protein on the polymer, side-on for RH24 and end-on for RH24K to account for the observed high packing density.

Adhesives↗