Marguerite Rinaudo

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.

Hydrophobic derivatives of chitosan: Characterization and rheological behaviour

Chitosans which are substituted with alkyl chains having a minimum of six carbon atoms demonstrate hydrophobic interactions in solution. The chemical structure of synthetized polymers is determined from NMR spectroscopy and microanalysis and the distribution between the different types of substituted units is obtained. In relation to the rheological behaviour different parameters are studied such as the nature of the hydrophobic chain and the substitution degree, the polymer concentration, the temperature and the ionic content of the polymeric solution. All the observations tend to prove the hydrophobic nature of the interaction mechanism.

Terminology for biorelated polymers and applications (IUPAC Recommendations 2012)

Like most of the materials used by humans, polymeric materials are proposed in the literature and occasionally exploited clinically, as such, as devices or as part of devices, by surgeons, dentists, and pharmacists to treat traumata and diseases. Applications have in common the fact that polymers function in contact with animal and human cells, tissues, and/or organs. More recently, people have realized that polymers that are used as plastics in packaging, as colloidal suspension in paints, and under many other forms in the environment, are also in contact with living systems and raise problems related to sustainability, delivery of chemicals or pollutants, and elimination of wastes. These problems are basically comparable to those found in therapy. Last but not least, biotechnology and renewable resources are regarded as attractive sources of polymers. In all cases, water, ions, biopolymers, cells, and tissues are involved. Polymer scientists, therapists, biologists, and ecologists should thus use the same terminology to reflect similar properties, phenomena, and mechanisms. Of particular interest is the domain of the so-called “degradable or biodegradable polymers” that are aimed at providing materials with specific time-limited applications in medicine and in the environment where the respect of living systems, the elimination, and/or the bio-recycling are mandatory, at least ideally.

Water soluble derivatives obtained by controlled chemical modifications of chitosan

Abstract Chemical modifications of polysaccharides are increasingly studied as they have the potential of providing new applications for such abundant polymers. Water soluble chitosan derivatives (quaternized and N-carboxylated chitosans) are prepared, using techniques which allow homogeneous modifications without any sharp decrease in molecular weight, and characterized using NMR spectroscopy and viscometry. In addition a new method for nearly complete deacetylation of chitin is proposed and the role of the acid used for solubilizing chitosan derivatives is mentioned.

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.

Conformational investigation on the bacterial polysaccharide xanthan.

The conformation of xanthan has been investigated as a function of temperature, ionic strength, and polymer concentration. A reversible transition induced by temperature is demonstrated; the melting temperature (TM) is directly correlated to the total ionic-strength and is independent of the polymer concentration. Measurements of circular dichroism show that the polysaccharide exists in a combination of only two characteristic conformations (random and ordered), regardless of the temperature and the concentrations of salt and polymer. Hydrodynamic measurements show that the hydrodynamic volume of both conformations is almost constant over the range of temperature investigated. The mechanism proposed by Morris for melting is confirmed, and a multichain process is excluded. The birefringence stability of the concentrated solutions is discussed.

13C NMR structural investigation of scleroglucan

Abstract This paper concerns the 13 C NMR signal assignment in the DMSO of a neutral polysaccharide, scleroglucan. The previously proposed chemical structure is confirmed. The 13 C NMR spectrum shows that scleroglucan is a regular poly (A, B, C, D) type glucan. The relaxation times of the different series of carbon atoms demonstrate that a single, pendant glucose group is attached to each third monomer along the main chain of what is a β(1 → 3)-glucan. Partial acid hydrolysis gives a spectrum analogous to that of the β(1 → 3)- d -glucan, curdlan, and confirms the structure of the polymer backbone. In aqueous solution, no signal has been obtained due to the existence of a rigid, ordered conformation as demonstrated by optical rotation; in the presence of sodium hydroxide, a conformational transition is produced just as with curdlan. The conclusion is that the behaviour of scleroglucan in solution is similar to that of other β(1 → 3)- d -glucans even though it is more soluble.

Properties of xanthan gum in aqueous solutions: Role of the conformational transition

Abstract Xanthan is shown to exist in native (I) and denatured (II) forms, both of which are ordered by the criterion of optical activity, and both of which undergo a temperature-driven, conformational transition to a common, disordered form (III). Changes in optical activity and conductivity are identical for the transformations I → III and II → III. The denatured, ordered form II displays a considerably larger viscosity increment than the native, ordered form I under given conditions of added salt at temperatures below the transition temperature (Tm). Light-scattering measurements yield the same molecular weight for forms I and II; consequently, the observed difference in viscosity increment appears to reflect inherent differences in the chain extension and conformation of forms I and II. Measured persistence lengths for forms I and II are consistent with earlier reports of the persistence length of single-stranded, ordered xanthan in solution. In the present viscosity studies, the absence of any dependence of measured properties of the native form I and the denatured form II on the thermal and concentration history strongly suggests that forms I and II are not aggregated species. Similar comparisons of the chain extension of disordered form III with the ordered forms I and II are more difficult, owing to the absence of conditions under which ordered and disordered forms are simultaneously stable. It is possible, nevertheless, to conclude that the viscosity increment of form II exceeds that of form III, whereas those of forms I and III are similar. Measurements of the molecular weight of form III, needed to convert this observation reliably into information about chain extension, are lacking. These observations are interpreted in terms of a model for xanthan in which the native, single-stranded, ordered form I is stabilized by side chain-backbone interactions that are shown, by experiments reported here, to be strong. These strong interactions are disrupted upon temperature-induced conversion into the disordered form III above the Tm. On subsequent cooling, there is established an alternative pattern of side chain-backbone interactions, presumably dictated by kinetic rather than thermodynamic factors, which stabilizes a more-extended backbone conformation in the denatured, ordered form II. The assumption is made that these strong, side chain-backbone interactions can bridge some backbone breaks which can appear during partial degradation of forms I and II.

Physical properties of acetylated starch- based materials: relation with their molecular characteristics

Abstract In order to obtain thermoplastic starch-based materials with a reinforced hydrophobicity, amylose and amylopectin were acetylated following the pyridine-acetic anhydride procedure. An amylose-rich starch triacetate was saponified under controlled conditions to obtain products with different acetyl contents. The adsorption of water by these polymers equilibrated in a 98% r.h. atmosphere was studied using thermogravimetric analysis and differential scanning calorimetry. A slight increase of non-freezing water content is observed when the acetyl content increases up to DS ≈ 1.3–1.4. For higher acetyl contents, the hydrophobicity of the material is efficiently enhanced and no more freezing water is adsorbed. Tensile strength measurements were performed on films with different amylose acetate-amylopectin acetate ratios: no variation of the tensile modulus (2.5 ± 0.5 GPa) was observed when composition changed, but the elongation at break was strongly decreased when the amylopectin acetate content increased. The influence of acetyl content on thermal properties was also studied. The position of glass transition (∼150°C in the dried state) was unchanged when DS ranged from 1.7 to 3, and moved towards higher temperatures when the acetyl content decreased. This thermal characteristic when DS > 1.7 will allow easy processing of these materials.

The viscosity dependence on concentration, molecular weight and shear rate of xanthan solutions

SummaryThis paper concerns the viscosity dependence of Xanthan as a function of polymer concentration, shear rate and molecular weight in the ordered conformation. The different samples with various molecular weights are obtained by ultrasonication. A unique curve is obtained for the reduced specific viscosity (n