Degree of acetylation of heteropolysaccharides

Surface grafting of chitosan shell, polycaprolactone core fiber meshes to confer bioactivity

Electrospinning of polyesters (e.g. polycaprolactone) is an attractive approach for fabricating meshes with mechanical properties suitable for orthopedic tissue engineering applications. However, the resultant fused-fiber meshes are biologically inert, necessitating surface grafting of bioactive factors to stimulate cell adhesion. In this study, hydrophilic meshes displaying primary amine groups were prepared by coaxially electrospinning fibers with a chitosan/poly(ethylene oxide) shell and a polycaprolactone core. These chitosan–polycaprolactone fiber meshes were mechanically robust (Young’s modulus of 10.1 ± 1.6 MPa under aqueous conditions) with tensile properties comparable to polycaprolactone fiber meshes. Next, the integrin adhesion peptide arginine–glycine–aspartic acid was grafted to chitosan–polycaprolactone fiber meshes. Cell culture studies using bone marrow stromal cells indicated significantly better initial attachment and spreading on arginine–glycine–aspartic acid–conjugated fiber meshes. Specifically, metabolic activity, projected cell area, and cell aspect ratio were all elevated relative to cells seeded on polycaprolactone and unmodified chitosan–polycaprolactone meshes. These results demonstrate a flexible two-step process for creating bioactive electrospun fiber meshes.

Application of spectroscopic methods for structural analysis of chitin and chitosan

Chitin, the second most important natural polymer in the world, and its N-deacetylated derivative chitosan, have been identified as versatile biopolymers for a broad range of applications in medicine, agriculture and the food industry. Two of the main reasons for this are firstly the unique chemical, physicochemical and biological properties of chitin and chitosan, and secondly the unlimited supply of raw materials for their production. These polymers exhibit widely differing physicochemical properties depending on the chitin source and the conditions of chitosan production. The presence of reactive functional groups as well as the polysaccharide nature of these biopolymers enables them to undergo diverse chemical modifications. A complete chemical and physicochemical characterization of chitin, chitosan and their derivatives is not possible without using spectroscopic techniques. This review focuses on the application of spectroscopic methods for the structural analysis of these compounds.

Preparation and physical properties of chitin fatty acids esters

Trifluoroacetic anhydride is an effective promoter for the preparation of chitin single- and mixed-acid esters. Complete dissolution is achieved within 30 min when powdered chitin is heated at 70 degrees C in a mixed solution of carboxylic acid(s) and trifluoroacetic anhydride. Chitin esters prepared are chitin acetate, chitin butyrate, chitin hexanoate and chitin octanoate, chitin co-acetate/butyrate, chitin co-acetate/hexanoate, chitin co-acetate/octanoate, chitin co-acetate/palmitate, each from a solution of the respective reactants. The products have degrees of O-acyl substitution in a range of DS 1-2 depending on the nature of acyl group, as analyzed by gas-liquid and high-pressure liquid chromatography. Acetic acid as a mutual component for the mixed-acid esters increases the total degree of substitution, and the acetyl substitution is close to the relative distribution in the reaction mixture for chitin co-acetate/butyrate. It is favored over hexanoate, octanoate, and palmitate. The parent molecules, as calculated by the composition of the chitin esters and their molecular weights by light-scattering spectroscopy, are 30 kDa for the smallest and 150-151 kDa for the largest. Films of these chitin derivatives when cast from solution are strong and flexible with limited extensibility. By dynamic mechanical analysis of the ester film, it was found that both the glass transition temperature (T(g)) and the tensile modulus (E' at 25 degrees C) are highest for chitin acetate (218 degrees C and 5.8 GPa), and lowest for chitin octanoate (182 degrees C and 1.5 GPa). For the other esters, these values lie between the above-cited values, where the T(g) and the E' decrease with an increase in the chain length of the acyl constituent.

Derivatization in mass spectrometry--8. Soft ionization mass spectrometry of small molecules

This is the first of two reviews devoted to derivatization approaches for "soft" ionization mass spectrometry (FAB, MALDI, ESI, APCI) and deals, in particular, with small molecules. The principles of the main "soft" ionization mass spectrometric methods as well as the reasons for derivatizing small molecules are briefly described. Derivatization methods for modification of amines, carboxylic acids, amino acids, alcohols, carbonyl compounds, monosaccharides, thiols, unsaturated and aromatic compounds etc. to improve their ionizability and to enhance structure information content are discussed. The use of "fixed"-charge bearing derivatization reagents is especially emphasized. Chemical aspects of derivatization and "soft" ionization mass spectrometric properties of derivatives are considered.

Acid hydrolysis and quantitative determination of total hexosamines of an exopolysaccharide produced by Citrobacter sp

During the hydrolysis of an exopolysaccharide (EPS) produced by Citrobacter sp., the maximum liberation of hexosamine was obtained with 6 M HCl at 115 degrees C in an autoclave for 1 h. The glycosidic bond energy and degree of acetylation of the hexosamine in EPS were approximately 77 kJ mol(-1) and 61%, respectively. Thermal destruction of the hexosamines and the effect of salt on the hexosamine determination could be minimized under the optimized hydrolytic conditions. Using a modified Elson-Morgan method, maximum total hexosamine concentration was determined to be 3.2 g l(-1) (29% of crude EPS) after 96 h of fed-batch culture.

Extracellular polysaccharides of a bacterium associated with a fungal canker disease of Eucalyptus sp

Extracellular polysaccharides (EPSs) produced by an Erwinia sp associated with a fungal canker disease of Eucalyptus were fractionated into one polysaccharide that was identified with that produced by Erwinia chrysanthemi strains SR260, Ech1, and Ech9, and the other distinctively different from any other EPS produced by E. chrysanthemi strains so far studied. Their structures were determined using a combination of chemical and physical techniques including methylation analysis, low pressure gel-filtration, and anion-exchange chromatographies, high-pH anion-exchange chromatography, mass spectrometry and 1D and 2D 1H NMR spectroscopy. The new polysaccharide, identified as EPS Teranera, has the following structure: [structure: see text] The molecular weights of the polysaccharides range from 3.2-6.2 x 10(5) and their hydrodynamic properties are those of polydisperse, polyanionic biopolymers with pseudoplastic, non-thixotropic flow characteristics in aqueous solutions.

Mass spectra of copolymers

Recent and older literature (covering the last 12-13 years) in the field of mass spectra of random and block copolymers is reviewed. A detailed description is given of the information on copolymer properties that can be recovered from the analysis of the low-mass region of the spectrum (the region below 500 Da) and the high-mass region. The features of mass spectra of copolymers obtained by different synthetic routes are discussed, such as free radical, condensation, ring-chain equilibration, microbial synthesis, ring-opening, simple anionic, cationic, Ziegler-Natta, and/or metallocene catalysis, along with some random and block copolymers that occur in Nature. The emphasis is on copolymer composition and average molar mass determination, and on the benefits of coupling mass spectrometry (MS) with separation techniques such as size-exclusion chromatography (SEC) and high performance liquid chromatography (HPLC).

Pyruvated galactose and oligosaccharides from Erwinia chrysanthemi Ech6 extracellular polysaccharide

The acidic extracellular polysaccharide of Ech6 was depolymerized by fuming HCl. The pyruvated sugars were isolated and characterized by methods that included a combination of low-pressure gel-filtration and high-pH anion-exchange chromatographies, methylation linkage analyses, mass (GC-MS and MALDI-TOF MS) and 1H NMR (1D and 2D) spectroscopies. The following pyruvated sugars were obtained: 4,6-O-(1-carboxyethylidene)-D-Galp; 4,6-O-(1-carboxyethylidene)- alpha-D-Galp-(1-->4)-beta-D-GlcAp-(1-->3)-D-Galp; 4,6-O-(1-carboxyethylidene)-alpha-D-Galp-(1-->4)-alpha-D-GlcAp- (1-->3)-alpha-D-Galp-(1-->3)-L-Fucp; 4,6-O-(1-carboxyethylidene)-alpha-D-Galp-(1-->4)-beta-D-GlcAp-(1-->3) -alpha-D-Galp-(1-->3)-L-[beta-D-Glcp-(1-->4)]-Fucp. These oligosaccharides present potential haptenes for the development of specific antibodies and confirm the partial structure proposed previously for the extracellular polysaccharide from Erwinia chrysanthemi Ech6 [Yang, B. Y.; Gray, J. S. S.; Montgomery, R. Int. J. Biol. Macromol., 1994, 16, 306-312].