A. Domard

Preparation and characterization of fully deacetylated chitosan

A new method for N-deacetylation of chitosan is proposed in which a polymer free of N-acetyl groups is obtained without much decrease in molecular weight. Different methods for determining the degree of acetylation were used, mainly i.r. spectroscopy and conductimetry. Average molecular weights were determined by membrane osmometry and light scattering; a polydispersity <2 was found. This well defined amino-polymer can be used for investigation of chelating properties.

pH and c.d. measurements on a fully deacetylated chitosan: application to CuII—polymer interactions

Abstract Potentiometric properties of a fully deacetylated chitosan have been investigated using pH and c.d. measurements. The same studies have also been performed in the presence of copper II ions in order to determine the mode of interaction and to deduce the stoichiometry of the complex formed under these conditions.

New method for the quaternization of chitosan

Abstract Trimethyl chitosan ammonium iodide was obtained by reaction of a low acetyl content chitosan with methyl iodide and sodium hydroxide under controlled conditions. The role of sodium iodide as an electrostatic charges screening salt is discussed. The reaction was performed in several steps to obtain derivatives of chitosan at various degrees of quaternization with a limit value near 64%. For a degree of quaternization greater than 25%, these polymers are soluble in water, whatever the pH.

Study of molybdate ion sorption on chitosan gel beads by different spectrometric analyses

Molybdate ion uptake both by raw chitosan and by glutaraldehyde cross-linked chitosan beads was investigated. This study focused on the identification of sorption mechanisms by means of several analytical procedures such as infra-red and reflectance spectrophotometries and CP-MAS 13C NMR analyses. Although the amine functions of glucosamine residues remain the major sites of interaction with the metal species, other functional groups can also be involved. It is certainly the case with carbonyl functions provided by the glutaraldehyde structure in cross-linked sorbents. Due to the large size of the polynuclear hydrolysed molybdate species, the sorption may involve several monomer units, resulting in additional linkages between the polymer chains. This behaviour can be confirmed by the chemical shifts of the carbon atoms observed by CP-MAS 13C NMR on raw chitosan beads, showing that the carbon atoms supporting the amino sites are not the only atoms affected by molybdate ion sorption. Moreover, cross-linking promotes a partial reduction of molybdenum species in the presence of some unreacted aldehyde groups.

13C and 1H n.m.r. spectroscopy of chitosan and N-trimethyl chloride derivatives

Abstract This paper concerns the chemical structure characterization of chitosan and N-trimethyl chloride derivatives at various degrees of quaternization. The assignment of the different signals obtained by n.m.r. spectroscopy is proposed. The values of degrees of quaternization determined by 13C and 1H n.m.r. are compared with those obtained by potentiometry. Methylation of the -OH groups is demonstrated.

Determination of N-acetyl content in chitosan samples by c.d. measurements

A glucosamine residue, in the ammonium form, does not give a c.d. signal in the 200–250 nm range whereas an N-acetyl glucosamine residue gives an n-π∗ transition with a c.d. band located near 211 nm. Thus circular dichroism allows one to deduce the N-acetyl content of chitosans with relatively great accuracy. The c.d. results are compared with three i.r. determinations in the literature.

Interaction between chitosan and uranyl ions: Part 1. Role of physicochemical parameters

This work is devoted to the comprehension of the sorption mechanism of uranyl ions on chitosan particle dispersions. The uranyl concentration measurements were obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES) and we considered the role of various physicochemical parameters (pH; nature and concentration of added salts; degree of acetylation, DA). The use of appropriate calculation software allowed us to determine the chemical nature of uranyl species in solution in relation to these different parameters. The optimal pH of fixation has been found to be within 6.5-7.5 and can be related to the necessity of having both deprotonated amino groups and no carbonate ions, which are a strong complexant of uranyl ions, thus inhibiting their interaction with chitosan. The decrease of metal uptake with an increase of DA and the lack of influence of ionic strength, confirm the results obtained with pH and allowed us to suppose the formation of a complex with chitosan amino groups rather than interactions of an electrostatic nature.

Interaction between chitosan and uranyl ions. Part 2. Mechanism of interaction.

In this part of the study--understanding the mechanism of interaction between chitosan and uranyl ions, we confirmed the restrictive role of polymer crystallinity on uranyl sorption capacity. The saturation of the polymer by uranyl ions showed that approximately 1 mol of uranyl ions was sorbed for 2 mol of amino groups contained in the amorphous domain. This result can be related to the intrinsic properties of chitosan. Desorption experiments are in favour of strong interaction, in fact, no desorption was observed whatever the experimental conditions. Spectroscopic characterization was performed on complexes in solution and in the solid state. U.V.-visible spectrophotometric experiments showed that a unique type of complex was formed. FT-IR spectroscopy allowed us to observe the appearance of a new band at 1525 cm of amide II type and led us to conclude the formation of a unique complex by the coordination with chitosan amino groups.

Circular dichroism study on N-acetylglucosamine oligomers

Abstract A series of N-acetylglucosamine oligomers with DP 1 to 10 has been studied by circular dichroism. The anomeric α-β equilibrium composition is determined for the monomer. The influence of the degree of polymerization and of several other parameters on the local conformation is tested.

Covalent immobilization of biological molecules to maleic anhydride and methyl vinyl ether copolymers—A physico‐chemical approach

The covalent grafting of biological molecules to copolymers of maleic anhydride and methyl vinyl ether (MAMVE) has been used in various applications in diagnostics. To tentatively elucidate the phenomena involved in the control of the immobilization of oligodeoxynucleotides and proteins, the physico-chemical properties of MAMVE copolymers were investigated. Because the grafting mixture contains water, to allow dissolution of the biomolecules without loss of biological properties, the anhydride-based copolymer evolves from a neutral to a negatively charged macromolecule due to hydrolysis of the anhydride moities. The properties of both hydrolyzed and nonhydrolyzed polymers were investigated. As demonstrated by light-scattering measurements in batch, the copolymers showed some level of aggregation in DMF, DMSO, and aqueous DMSO. The presence of aggregates was confirmed by size-exclusion chromatography in DMF. However, partial deaggregation occurred for the lowest molecular weight sample, on adding 1% w/v of LiBr. The nonhydrolyzed copolymers exhibited a rigid conformation in a 5% water/DMSO mixture, as well as their hydrolyzed counterpart at a low ionization degree. The rate of the hydrolysis reaction was shown to be dependent on the pH of the reaction medium and on temperature. The activation energy of the hydrolysis reaction was 14 kJ/mol, and the rate constant in the order of 10 -4 s -1 . On the basis of these data, the effect on the grafting reaction of biomolecules of different parameters such as ionic strength and the nature of the solvent, along with some other results were interpreted in terms of interactions between the synthetic and bioactive macromolecules.