A. Cosani

Structural differences between chitin polymorphs and their precipitates from solutions—evidence from CP-MAS 13C-NMR, FT-IR and FT-Raman spectroscopy

Abstract Structural differences between α-chitin from shrimp ( Crangon crangon ) and β-chitin from squid (Loligo), as well as between their precipitated products from N,N-dimethylacetamide-LiCl solutions, are indicated by the CP-MAS 13 C-NMR, FT-IR, FT-Raman spectra and the X-ray diffractograms. The 13 C-NMR spectra in the solid state of α-chitin consisting of eight major resonances suggest a high degree of structural homogeneity. In the spectrum of β-chitin, the C-3 and C-5 signals merged in a single resonance. The bands contour of deconvoluted and curve-fit FT-IR and FT-Raman spectra shows a more detailed structure of α-chitin in the region of OH, NH and CO stretching regions; in particular the Amide I band is split, whereas a single broad band dominates in the corresponding β-form. Precipitation treatments induce a general disorder in α-chitin, while the metastable structure of β-chitin tends toward a more ordered architecture. All the present spectroscopic data of chitin samples are consistent with the corresponding X-ray diffraction patterns.

Molecular parameters of chitosans depolymerized with the aid of papain

Abstract The profiles and positions of the GPC curves are progressively altered during the course of the papain-promoted hydrolysis of chitosan. The chitosan fractions having the highest degrees of polymerization are depolymerized and Mw, [η] and R G values are lowered. Viscometric measurements confirm that the immobilized papain depolymerizes chitosan with high initial velocity, the more acetylated chitosan [0.42] being more susceptible to papain than chitosan [0.22] and chitosan [0.15]. This holds true for chemically reacetylated chitosan [0.49] as well. The behavior of papain in this respect is different from that of lysozyme which is more active on chitosan [0.22] than on more acetylated chitosans. The data suggest that papain acts on the link between glucosamine and N -acetylglucosamine units.

Solution studies of the chitin-lithium chloride-N,N-di-methylacetamide system

Abstract Light scattering and viscosity measurements on dilute or moderately concentrated solutions of chitin in N,N -dimethylacetamide (DMAc) containing 5% or 8% of LiCl are reported. Chitins with d.p. lower than that of commercial samples were obtained by treatment of these solutions with ultrasound. The curve c/H o vs. c exhibits a maximum at c values inversely related to the molecular weight of the polymer and is consistent with a model in which, at relatively low concentration, the polysaccharide chains intertwine whereas at high concentration they become hyper-entangled, eventually resulting in an inhomogeneous network. Light scattering measurements on the dilute solutions containing 5% of LiCl allowed an evaluation of the molecular weight, second virial coefficient, and radius of gyration. The values of the Mark-Houwink parameters a and K and the relationship between radius of gyration and molecular weight were obtained. An evaluation of the linear expansion factor, α s , using the interpenetration function, gives values close to unity. This fact, together with the observed high values of the second virial coefficient, implies that the chitin molecules are rather stiff in this solvent system. The persistence length was evaluated by means of the Yamakawa-Fujii and Benoit-Doty theories for worm-like chains. Derivatives of chitin prepared in DMAc-5% LiCl in a homogeneous phase under mild conditions had high degrees of substitution without main-chain degradation.

Chitosan : chain rigidity and mesophase formation

Abstract Light-scattering measurements on samples of chitosan with degrees of acetylation (d.a.) of 42 and 15% have been performed in 0.1 m acetic acid-0.2 m sodium chloride. From the values of R G °, a persistence length q t ° of ∼ 220 A has been deduced, which is lower than that (∼ 350 A) of chitin and indicates a decrease of rigidity with decrease in d.a. The existence of a cholesteric mesophase above a critical value of [polymer] has been demonstrated.

6-Oxychitins, novel hyaluronan-like regiospecifically carboxylated chitins

Abstract Crustacean chitins and fungal chitin–glucan complexes are subjected to regiospecific oxidation at C-6 with NaOCl in the presence of Tempo® and NaBr at 25°C in aqueous solution. The resulting products have anionic character and are fully soluble over the entire pH range; they lend themselves to metal chelation, polyelectrolyte complex formation with a number of biopolymers including chitosan, and to microsphere and bead formation. 6-Oxychitin coagulates papain, lysozyme and other hydrolases active on chitosans. 6-Oxychitins of fungal and animal origins, in the form of free acids, salts and esters, might find use as surrogates of hyaluronans and of bacterial antigens in medical and health care products.

Chitosans from Euphausia superba. 2: Characterization of solid state structure

Abstract Chitosans from Euphausia superba of different degrees of acetylation (42%, 28% and The X-ray powder patterns indicated a decrease of order with decreasing the degree of acetylation as well as after regeneration and acid treatments. Similarly, the CP-MAS 13C-NMR and FTIR spectra exhibited a general broadening of signals suggesting the occurrence of new conformations for chitosans after regeneration. Furthermore, samples treated with hydrochloric acid showed some structural modifications which accounted for their behaviour in solution as reported in the first part of this study.

Chitosans from Euphausia superba. 1: Solution properties

Abstract A technological development of chitosan (copolymer of N -acetylglucosamine and glucosamine) is based on the knowledge of parameters such as composition. types of sequence, chain length and distribution. In addition to the sample source, these factors are related to preparation and purification methods. In this connection the authors examined chitosan samples having the same origin ( Euphausia superba ), but different degrees of acetylation, as well as materials which were subjected to regeneration and beating processes. In addition, the authors prepared chitosan samples of different degrees of polymerization by hydrolysis of commercial chitosan of high degree of acetylation under different pH and temperature conditions. The samples were characterized in 0·1 n CH 3 COOH (HAc) - 0·2 m NaCl by intrinsic viscosity ([η]) and light scattering techniques. The viscometric behaviour of the starting chitosans and of all depolymerization products follows an expected pattern. On the other hand, light scattering shows important differences among samples having identical [η], but obtained under different hydrolysis conditions. A tentative explanation is suggested for the discrepant responses.

Structural properties of hyaluronic acid in moderately concentrated solutions.

The solution properties of hyaluronic acid having various d.p. values have been examined at physiological pH and ionic strength by light-scattering techniques at various concentrations. The angular dependence of Kc/R0 was linear at low concentrations, whereas substantial curvature was present at small angles on increasing the concentration. This phenomenon was affected by the conditions of centrifugation. Moreover, the function Kc/R0 exhibited a maximum value at concentrations of polymer inversely related to the molecular weight. The maximum concentration was always higher than the critical concentration. Ageing, molecular-weight distribution, and polymer purity influenced the light-scattering response. A model is proposed in which the polysaccharide chains intertwine at relatively low concentrations of polymer and become entangled at high concentration, eventually leading to a non-homogeneous polymer network.

Regenerated and graft copolymer fibers from steam‐exploded wheat straw: Characterization and properties

Steam explosion treatment has been proven to effectively induce such marked modifications to the chemical and supramolecular structure of wheat straw cellulose as to make this cellulose a suitable raw for dissolving processes. Regenerated and poly(acrylonitrile) (PAN) and poly(methyl methacrylate) (PMMA) grafted wheat straw fibers obtained on the laboratory scale were characterized by various techniques (X-ray diffraction, cross polarization-magic angle spinning (CP-MAS) 13C nuclear mag-netic resonance and vibrational spectroscopy, scanning electron microscopy, differential scanning calorimetry), and the relationships between the morphological–structural features and physicomechanical and end-use properties have been evidenced.

High-performance gel-permeation chromatography of chitosan samples

Abstract The conformational properties of chitosan, a copolymer of 2-acetamido-2-deoxy- d -glucose and 2-amino-2-deoxy- d -glucose, have been examined both in solution and in the solid state. Little has been reported previously on the determination of molecular weight using high-performance gel-permeation chromatography (HPGPC) and no attempt has been devoted to an examination of molecular weight distribution. An HPGPC method for evaluating the above-mentioned parameters for chitosan samples having different molecular weights and different degrees of acetylation was therefore developed. Calibration using sodium polystyrene sulfonate commercial standards of narrow molecular weight distribution could not be carried out in the solvent system used for chitosan. Calibration was therefore performed by means of chitosan samples obtained by depolymerization.