The crystal structure of chitin and chitosan

Roentgenographic studies are performed to investigate the structural changes in chitin under pressure and shear during its solid-state processing using a twin-screw extruder and Bridgman anvils. The structure of chitosan synthesized by the solid-phase method is studied. Deformation under the conditions of dry extrusion grinding at room temperature reduces the crystallinity of the original chitin. Addition of water restores the crystallinity of the material up to the value characteristic of the original chitin. Extrusion processing of chitin at room temperature with addition of water virtually preserves the crystallinity and degree of ordering of the chitin crystal lattice, the same as ordinary dry grinding at an elevated (180°C) temperature. The maximum degree of amorphization of chitin is attained by its processing on Bridgman anvils. Solid-state synthesis of chitosan from chitin leads to a product with a more amorphous structure in comparison with chitosan produced by the suspension method.     

Fluorocarbon modified chitin and chitosan I. Synthesis and characterization of perfluorocarbonyl chitin

The esterification reaction of chitin with perflurocarboxylic acid was studied in methanic acid or perfluorocarboxylic acid as solvent. A series of substituted derivatives of trifluoroacyl. perfluorobutyric and perfluorooctanoyl chitin were synthesized. The properties of these chitin derivatives were investigated.     

Advancement of chitin and chitosan as promising biomaterials

Biopolymers like cellulose, polysaccharides, chitosan, starch, chitin, and alginates have sparked an increasing curiosity in creating natural replacements for synthetic polymers during the last several decades. Chitin is a major part of fungi’s cell walls, the crustaceans’ exoskeletons, like lobsters, crabs, and shrimps, cephalopod beaks, the radulae of mollusks, and fish and lissamphibians scales. Since the late 1970 s, biopolymer chitosan has gathered interest in basic science and applied research due to its incredible macromolecular framework, physicochemical properties, and biological activities, which differ from those of synthetic polymers. Chitin and derivatives thereof have practical usages in chemistry, the agriculture sector, medicine, cosmetics, as well as textile and paper industries. Chitosan has also received a lot of recent interest in the fields of dentistry, ophthalmology, veterinary science, biomedicine, the drink industry, hygiene and personal care, catalysis, chromatography, sewage treatment, and biotechnology. Numerous fundamental investigations have been conducted on chitin and chitosan. This article presents a short compact summary of research over the last two decades in an attempt to highlight the works on chitin and chitosan applications.     

甲壳素和壳聚糖在电化学分析中的应用进展

甲壳素和壳聚糖特有的吸附、螯合作用的性质使其在电化学分析领域中应用广泛,本文对此进行了综述,着重介绍了甲壳素和壳聚糖修饰电极的制备、特点及其在痕量物质的测定、生物传感器等方面的应用,并对其研究前景进行了展望。     

Hydrogenation catalytic behaviors of palladium complexes of chitin and chitosan

Palladium complexes of chitin and chitosan have been shown to have catalytic activities for hydrogenation at room temperature and under atmospheric pressure. They could catalyze not only reduction of olefines but also aromatic nitro-compounds and acrylic acid. And they are very active, stable and selective. They also show different catalytic behaviors in different pH solutions. It is noteworthy that the catalytic activities of the two polymer-supported metal complexes in the cycle of pH 11 → pH 2 → pH 11 are reversible.     

Elastic modulus of the crystalline regions of chitin and chitosan

The elastic moduli E_l of the crystalline regions of α‐chitin and chitosan in the direction parallel to the chain axis were measured by X‐ray diffraction. The E_l values were 41 GPa for α‐chitin, and 65 GPa for chitosan, respectively, at 20°C. The contracted skeletons of α‐chitin and chitosan are the key factor for the low E_l values compared with that (138 GPa) of cellulose I. The E_l value of α‐chitin was constant at 41 GPa both at −190°C and 150°C, which indicates that the molecular chain of α‐chitin is stable against heat within the temperature and stress range studied. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1191–1196, 1999     

Water sorption on and water diffusion in chitin and chitosan

The kinetics of the sorption of water vapor on powders of crab-shell chitin and chitosan are studied via the methods of static sorption, thermography, and X-ray structural analysis. Sorption isotherms are obtained in the range of humidity from 10 to 95%. S-Shaped water-sorption isotherms observed for all chitin and chitosan samples are approximated via superpositioning of Langmuir and Flory-Huggins isotherms. The water-polysaccharide interaction parameters and the maximum sorption capacities of water located in chitin and chitosan are determined. The cluster integral is calculated, and the moisture values corresponding to water-cluster formation are determined. The water-diffusion coefficients are determined, and the effective activation energies of water diffusion are estimated: 70 kJ/mol in chitosan and 60 kJ/mol in chitin. The data on the concentration dependences of the coefficients of diffusion of water in the powdered chitin and chitosan are summarized.     

Preparation and properties of chitin and chitosan from a hydroid polyp

The chemical composition of Obelia longissima hydroid polyp from mariculture system fouling community was examined. Conditions for chitin recovery and chitosan preparation thereof were developed. The initial raw material, chitin, and chitosan were characterized by electron microscopy, infrared spectroscopy, and X-ray diffraction analysis. Also, certain qualitative characteristics of these materials were determined.     

Thermomechanical properties of composite films of polyacrylonitrile with chitin and chitosan

Composite films were prepared from polyacrylonitrile synthesized by anionic and radical polymerization and combined with chitin or chitisan. The thermomechanical properties of the films were examined. The compatibility of polyacrylonitrile synthesized by radical polymerization with chitosan was studied by DSC over a wide temperature range 140–280°C.     

Release characteristics of cisplatin chitosan microspheres and effect of containing chitin

To increase cisplatin (CDDP) content, to suppress burst effect during the initial phase of drug release, and to improve the capacity of the system for sustained release, we prepared various types of CDDP chitosan microspheres incorporating chitin and investigated the content of CDDP and its in vitro release kinetics from these microspheres. The results of this study showed that the CDDP content increased with increasing chitosan concentration and that the incorporation of chitin in the carrier matrix produced a more pronounced increase in drug content. The addition of chitin also led to inhibition of the initial burst effect. The rate of CDDP release reduced with increasing concentration of chitosan: that is, the 50% CDDP release time was about 0.5 h with the microspheres prepared with 1.0% of chitosan and about 4.5 h with those prepared with 5.0% of chitosan, indicating about nine-fold prolongation. The addition of chitin further resulted in retardation of the rate of CDDP release. Meanwhile, our chitosan microspheres were shown to undergo enzymatic degradation by lysozymes.     

Depolymerization of chitin and chitosan in the course of base deacetylation

Depolymerization of chitin and chitosan in the course of deacetylation in an alkaline medium was studied, and the influence exerted on the process by the nature and concentration of the alkali (NaOH, KOH) and salts (NaCl, NaI, KI) was examined.     

Production of the low-molecular-weight chitin and chitosan forms in electron-beam plasma

The degradation of chitin and chitosans of different molecular weights stimulated by electronbeam plasmas of different gases has been experimentally studied. Biologically active water-soluble lowmolecular-weight chitooligosaccharides are formed as a result of plasma-beam treatment. It has been found that the degradation is a controlled process and products with a necessary molecular weight can be obtained by appropriately choosing plasma-beam treatment parameters (chemical composition of the plasma gas and treatment time and temperature).     

Comparative adsorption studies of indigo carmine dye on chitin and chitosan

The adsorption of indigo carmine dye onto chitin and chitosan from aqueous solutions was followed in a batch system. The ability of these materials to adsorb indigo carmine dye from aqueous solution was followed through a series of adsorption isotherms adjusted to a modified Langmuir equation. The maximum number of moles adsorbed was 1.24 +/- 0.16 x 10(-5) and 1.54 +/- 0.03 x 10(-4) mol g(-1) for chitin and chitosan, respectively. The same interactions were calorimetrically followed and the thermodynamic data showed exothermic enthalpic values of -40.12 +/- 3.52 and -29.25 +/- 1.93 kJ mol(-1) for chitin and chitosan, respectively. Gibbs free energies for the two adsorption processes of indigo carmine dye presented a positive value for chitin and a negative one for chitosan, reflecting that dye/surface interactions are thermodynamic favorable for chitosan and nonspontaneous for chitin at 298.15 K. The interaction processes were accompanied by an increase of entropy value for chitosan (90 +/- 6 J mol(-1)K(-1)) and a decrease for chitin (-145 +/- 13 J mol(-1)K(-1)). Thus, dye/chitosan interaction showed favorable enthalpic and entropic processes, reflecting thermodynamic stability of the formed complex, while dye/chitin interaction showed an exothermic enthalpic value and a highly nonfavorable entropic effect, resulting in a nonspontaneous thermodynamic system.     

Synthetic modifications of chitin and chitosan as multipurpose biopolymers: A review

Chitin and chitosan are well-thought-out multipurpose biopolymers. Chitosan which is deacetylated chitin is useful than chitin and is biomaterial of great interest. Regardless of its biodegradability, chemical modifications suggest due to the amino side reactivity, helps to impart it other great qualities. Herein, we discuss the preparative methods of synthetically modified derivatives, some are commercially available. This review shields the literature from last few decades.     

Adsorption and desorption of indomethacin on cellulose-like biopolymers: chitin and chitosan.

The adsorption-desorption effect of cellulose-like biopolymers such as chitin and chitosan, and microcrystalline cellulose on indomethacin was investigated. The adsorptive capacity was ranked in the order: chitosan greater than chitin greater than microcrystalline cellulose. All the adsorption isotherms were found to follow Langmuir and Freundlich equations. However, chitosan-acetate gel powders and chitosan powders with pre-added acetic acid and methanol did not follow these equations, due to gel formations that led to more adsorption of indomethacin on the interlayer space of the gel. The strong adsorption of chitosan might result in difficult desorption of indomethacin.     

The use of DSC curves to determine the acetylation degree of chitin/chitosan samples

The use of DSC curves is proposed as an alternative method to determine the degree of N-acetylation (DA) in chitin/chitosan samples, based in both peak area and height of the decomposition signal. Samples with DA from 74 to 16% were prepared from a chitin commercial sample and the DA was determined by ¹H NMR, ¹³C CP/MAS NMR and IR spectra. The effect of water content, heating rate, sample mass and gas flow on the DSC peaks were evaluated and optimized. Using optimized conditions a linear relationship between peak area and height with the DA could be achieved with linear correlation coefficients of −0.998 and −0.999 (n = 7), respectively. The calibration graphs were used to determine the DA of a commercial chitosan sample with relative errors ranging from 2 to 3% for both peak area and peak height, when compared with the DA determined by ¹H NMR method.     

Kinetics of base deacetylation of chitin and chitosan as influenced by their crystallinity

Structural properties of the initial and reprecipitated chitin and chitosan samples in dry and wet states were studied. Original Russian Text E.N. Chebotok, V.Yu. Novikov, I.N. Konovalova, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 10, pp. 1724–1729.     

Radiation resistance of chitin and chitosan applied in the chromatography of radioactive solutions

Chitin and chitosan were irradiated in acidic solutions containing a decontaminating soap. It has been shown that these powders suspended in aqueous media do not undergo radiolysis, as their I.R. spectra are not altered, and there is no radiolysis product in the solution, except for the case of nitric acid at lowpH where some chitosan is present in dissolved form. These polymers therefore exhibit very good radiation resistance, in spite of the fact that the monomers undergo very rapid radiolysis.⁶⁰Co radiations up to 50 000 krad were used. Under these conditions, chitosan does not lose its collection capacity for most of the metal ions of interest in the nuclear field, including cobalt, that can be collected from decontaminating soap solutions with a volume reduction of 10.     

Determination of the degree of acetylation of chitin and chitosan by thermal analysis

Several methods for the rapid determination of the degree of acetylation of chitin and related polymers have been evaluated, including the use of the infrared and the mass spectra. Chitin and chitosan have characteristic degradation temperatures and it is possible to determine the acetylation degree by the use of empirical correlations based on the weight losses associated with the main decomposition peaks.