IR study on chitosan oxidation with sodium chlorite

Oxidation of chitosan with sodium chlorite was studied by IR spectroscopy. The process was shown to involve oxidation of the primary hydroxy group on C⁶ to carboxy group and subsequent oxidative decomposition of the polysaccharide. The degree of carboxylation of the oxidized chitosan was determined by potentiometric titration. The possibility for formation of a covalent bond between the amino nitrogen atom and carbon atom of the carboxy group in the oxidized chitosan was considered.     

Water-soluble polyplexes of modified chitosan

The alkylation of primary amino groups of chitosan with glycidyltrimethylammonium chloride yields the modified cationic polysaccharide that carries, in practically every deacetylated unit, a secondary amino group and a quaternized amino group that provide the solubility of the polymer over the whole range of pH values. The mixing of solutions of modified chitosan and nucleic acid in neutral solutions at various ratios gives soluble DNA-containing polyelectrolyte complexes (polyplexes) that preserve stability under physiological conditions. The effects of the pH, ionic strength, and charge-to-charge ratio of polymer components on the boundaries of existence of soluble polyplexes both negatively and positively charged are elucidated. The collected experimental data may serve as a basis for designing biocompatible and biodegradable means for the delivery of genetic material and drugs to living cells.     

Water-soluble nonstoichiometric polyelectrolyte complexes of modified chitosan

A modified polysaccharide that, in each deacetylated unit, carries a functional secondary amino group and a quaternized amino group that provides a positive charge and solubility to the polymer throughout the pH range is prepared by the alkylation of primary amino groups of chitosan with glycidyltrimethylammonium chloride. The mixing of modified chitosan solutions with solutions of polystyrenesulfonate or polymethacrylate anions in neutral solutions gives rise to negatively charged nonstoichiometric polyelectrolyte complexes soluble and stable under physiological conditions. The effects of pH, ionic strength, the degree of polymerization, the nature of the lyophilizing polyanion, and the charge-to-charge ratio of components on the boundaries of existence of soluble complexes are ascertained. The collected experimental data may serve as a basis for designing biocompatible and biodegradable means useful for the delivery of genetic material and drugs to living cells.     

Synthesis and characterization of water-soluble O-succinyl-chitosan

The efficient procedure to prepare novel water-soluble O-succinyl-chitosan was established by using one three-step reaction. Phthaloyl group was firstly chosen as the protection group for the amino group of chitosan, and O-succinylation was then completed. Protection group was removed finally by using hydrazine hydrate. The chemical structure of the modified chitosan was characterized by FTIR, ¹H-NMR, ¹³C-NMR and elemental analysis. Some physical properties were analyzed by X-ray diffraction, differential scanning calorimetry (DSC), thermogravimetry (TG) and solubility test. It indicates that after O-succinylation, the modified chitosan shows much better solubility in water. The study of enzymatic degradation showed that the O-succinyl-chitosan was of low susceptibility to lysozyme. O-succinylation-chitosan is a useful intermediate, which permits further chemical modification for amino group and may be have potential applications in biomedical system.     

Imidazole-containing chitosan derivative: a new synthetic approach and sorption properties

A novel method for the synthesis of a hetaryl-containing chelate amino polymer, namely, N-(4(5)-imidazolylmethyl)chitosan (IMC), with a degree of substitution up to 0.3 was proposed. The “synthesis in gel” approach involves direct substitution of the hydroxyl group in 4(5)-imidazolylmethanol. The structures of these polymers were confirmed by ¹H NMR data. For sorption studies, IMC samples were crosslinked with epichlorohydrin and diglycidyl ethers of ethylene glycol and diethylene glycol. The degrees of swelling and sorption properties of the polymers largely depend on the crosslinking agent and the degree of crosslinking. The sorption capacities of IMC for Au^III, Pt^IV, and Pd^II ions are higher than those of the nonmodified polymer. The extraction of noble metal ions from chloride solutions becomes more selective with increasing degree of crosslinking. The sorption capacity of IMC for Co^II and Ni^II ions is higher than those of chitosan and its known N-heterocyclic derivatives.     

Double Schiff bases derivatives of chitosan by selective C-6 and C-2 oxidation mediated by 5-fluorosalicylaldehyde aniline by TG-GC-MS and TG-FTIR analysis

Abstract

This enhancement in the activity may be efficient on the basis that ligands mainly possess CH=N bond. The use of a structure-based drug design approach (SBDD) provides a way for investigation as well as to understand the molecular basis of the target protein and ligand molecule interactions at the atomic level. Structure-based drug design is the design and optimization of a chemical structure to identify a compound suitable for clinical testing the drug candidates. Chitosan is a polysaccharide with recognized biological activities for improving the functionality of polysaccharide 5-Fluorosalicylaldehyde aniline system. The used for selectively oxidized chitosan to produce tailored derivatives. C-2-5-Fluorosalicylaldehyde-C-6 aniline double Schiff base derivatives of chitosan were synthesized. The structure and properties of the newly synthesized product were characterized by FT-IR, ¹H-NMR, ¹³C-NMR, GC-Mass spectroscopy, and thermal analysis (DSC/TGA). An exothermic process discusses a DSC and TGA analysis of thermal behavior of this polymer was shown to be a possible thermal polymerization of the double bonds in the polymer chains and thermo-oxidation of the polymer.     

Ordering in Bio-Polyelectrolyte Chitosan Solutions

The scaling of the polyelectrolyte scattering peak in chitosan solutions, as deduced from the relation q_max∼c_p^α was studied by synchrotron SAXS as a function of the charge density of the polymer. We observe a variation in the α exponent corresponding to the limit of the ionic condensation, by varying the degree of acetylation of the polymer. The nature of the solution medium also affects the polyelectrolyte peak, and it is shown that in alcoholic/water mixtures, the lower dissociation of the acid induces a lower charge density, thus influencing the polyelectrolyte ordering.     

Properties and adsorptive capacity of amino acids modified chitosans for copper ion removal

This work presents the results of the modification of lateral groups of chitosan (2-amino-2-desoxy-β-D-glucose) by the reaction with different amino acids (glycine, L-lysine, -glutamic acid and L-isoleucine) under acid catalysis. The Cu²⁺ adsorption capacity of pure chitosan and of the chemically modified chitosans were also evaluated. The modification reaction favored the amide formation of the C-2 carbon of the glycoside ring under the adopted reaction conditions: reaction time and temperature and using sulfuric acid as a catalyst. The Cu²⁺ adsorption kinetics and equilibrium response using pure chitosan and the chemically modified chitosans as adsorbents showes that the adsorption capacity of equilibrium depended on the initial ion concentration. The response of each adsorbent gave good correlation with Langmuir's isotherm model. The following maximum adsorption capacity constants were obtained: 172.4 mg/g for chitosan and 69.9, 34.4, and 26.7 mg/g for modified chitosan with glycine, L-glutamic acid, and L-lysine, respectively. The adsorptive capacity seems to be dependent on the length and complexity of the added group.     

Soluble–insoluble polyelectrolyte complex of quaternized chitosan with DIVEMA (pyran copolymer)

To endow chitosan with solubility in the whole pH-range without loss of functionality of the amino groups, the cationic polysaccharide was exhaustively alkylated yielding N-[(2-hydroxy-3-trimethylammonium) propyl]chitosan chloride (QCht). Each alkylated unit of QCht contained both quaternary amino group and secondary amino group. Recently we demonstrated that QCht forms with nucleic acids of soluble polyelectrolyte complexes stable at physiological conditions and capable of cell transfection in vitro. In the current work, the anionic counterpart of QCht was hydrolyzed copolymer of divinyl ether and maleic anhydride (DIVEMA) which is known to possess some anti-tumor and immune stimulating activity and use as a drug carrier in anti-tumor drug delivery systems. According to the potentiometry data and ζ-potential measurements, almost all carboxylic groups of DIVEMA were able to form ion pairs with QCht. In aqueous and water–salt solutions, formation of either soluble or insoluble complexes was controlled by pH, ionic strength, a ratio of the oppositely charged groups, and degree of polymerization of the chains following general rules revealed on studying polyelectrolyte complexes of polycarboxylic acids. These findings evidence plausible advantages of the complex formation as the non-covalent modification that imparts to both polyelectrolytes of the ability for reversible soluble–insoluble transformation under enzyme-friendly conditions.     

SYNTHESIS OF CONDENSATION POLYMERS OF SALICYLIC ACID, FORMALDEHYDE AND ALKYL PRIMARY AMINES AND ITS APPLICATION AS A CATALYST FOR THE HYDROLYSIS OF p-NITROPHENYL ACETATE (PNPA) IN AQUEOUS SOLUTION

As a model of serine hydrolase, the condensation polymers of salicylic acid, formaldehyde and methyl amine, n-propyl amine, n-hexyl amine or n-lauryl amine were prepared by polycondensation catalyzed by sulfuric acid. It was confirmed by potentiometric titration and infrared spectrum that the polymers containing tertiary amino group possess the structure which resembles the internal salt of amino acid in weak basic and weak acidic solution:     

Determination of the surface charge of lignocellulosic fiber by a derived spectroscopic technique

This paper proposed a derived spectroscopic technique for determining the surface charge of lignocellulosic fiber. In this method, chitosan quaternary ammonium iodide with higher molecule weight was selected to minimize its interaction with the negative charge inside of fiber pores. It was based on spectroscopically measuring the UV absorbance of I^? (the counter ion) in the filtrates from a set of solutions that containing the fixed amount of fibers and the different amount of cationic polymer (from under- to over-saturation). By plotting the derived absorbance at 245 nm versus the volume of chitosan addition, a transition point is determined, from which the fiber surface charge can be calculated. The results showed that the present method has a good measurement precision (RSD?<?3.24%) and accuracy (relative differences?<?3.11%, when compared with the conductivity titration method). It is suitable to be used for determining the surface charge of lignocellulosic fibers.

     

Vitamin A and vitamin E interaction behavior on chitosan microspheres

Chitosan is a biodegradable natural polymer with great potential for pharmaceutical applications due to its biocompatibility, high charge density, and non-toxicity. In this study, chitosan microspheres were successfully prepared by an adapted method of coagulation/dispersion. The degree of deacetylation of chitosan powder was obtained by NMR ¹H and FTIR techniques. Chitosan powder and chitosan microspheres were characterized by BET surface area and scanning electron microscopy (SEM). The interactions among the chitosan microspheres and the vitamins A and E were characterized by FTIR. In order to evaluate the ability of interaction of vitamin A and vitamin E with the chitosan microspheres, the thermodynamic parameters were followed by calorimetric titration. Different experimental approaches were applied, such as adsorption isotherms, kinetics and thermodynamics studies. The obtained results showed that the interactions of chitosan microspheres with the vitamins were spontaneous, enthalpically and entropically favorable, indicating that the chitosan microspheres can be used with success in the controlled release of these vitamins.     

Friedel-Crafts Polymers. 6. Friedel-Crafts Polycondensation of p-Xylylerte Dibromide with Salicylic Acid and β-Resorcyiic Acid

Polymers were prepared by condensing p-xylylene dibromide separately with salicylic acid and β-resorcylic acid in the presence of anhydrous ferric chloride in dioxane. The polymer samples_were characterized by elemental analysis, by IR spectral study, by M determined by vapor pressure osmometry, by nonaqueous conducto-metric titration in pyridine, by TGA in air, and by viscosity measurements of polymer solutions in DMF. Polymeric metal chelates of Cu²⁺, Co²⁺, Zn²⁺, Ni²⁺, and Fe³⁺ with polymer samples were prepared and characterized by elemental analysis, by IR spectral study, and by TGA in air. The chelation ion-exchange properties of the polymer samples were studied by employing the batch equilibration method.     

Preparation of a sorbent for metal ions based on N-(5-methylimidazol-4-ylmethyl) chitosan with medium degree of substitution

A procedure was developed for preparing a heterocycle-containing chelating amino polymer, N-(5-methylimidazol-4-ylmethyl) chitosan, by polymer-analogous transformations of chitosan in reaction with 4-chloromethyl-5-methylimidazole. The procedure allows synthesis of the polymer with the degree of substitution of up to 0.8, with simultaneous formation of the cross-linked structure. The structure of the polymers prepared was proved by IR and ¹³C NMR spectroscopy. The ability of N-(5-methylimidazol-4-ylmethyl) chitosan with the degree of substitution of 0.54 to sorb Cu²⁺ and Ni²⁺ ions was evaluated. According to the sorption isotherms, the sorption capacity of this derivative exceeds that of the unmodifi ed polymer by a factor of 5.     

A comparative study on the chitosan membranes prepared from acetic acid and glycine hydrochloride for removal of copper

Application of chitosan-based materials as adsorbents in wastewater treatment has received considerable attention in recent years. This study is concerned with the influence of various parameters of the reaction medium with a metal and a biosorbant on the kinetics of copper biosorption from synthetic solutions. Initially, we prepared pure chitosan-based membranes and those modified in two different ways: chitosan membrane prepared from traditional acetic acid and the membrane prepared from glycine hydrochloride, chitosan membranes modified such as chitosan/polyvinyl alcohol (PVA) blends membrane with different compositions (100/0, 80/20, 50/50, 20/80 and 0/100%) and chitosan membranes cross-linked with glutaraldehyde. The membranes were characterized by FTIR spectroscopy, DSC, and rheological measurements. Then, we studied the kinetics of copper biosorption by the membranes. The results suggest that adding PVA to a chitosan membrane can greatly improve the flexibility and wettability of chitosan membranes. The values attained in equilibrium for the chitosan membranes prepared from glycine hydrochloride (95.5 mg g^?1 for chitosan/PVA 50/50%) exceed those for chitosan membranes prepared from acetic acid (61.5 mg/g for chitosan/PVA 50/50%).     

Interaction behaviour of a PDMS–calixarene system and polar analytes characterised by microcalorimetry and spectroscopic methods

Spectroscopic techniques and microcalorimetry were applied to investigate a polymer–(polydimethylsiloxane; PDMS) calixarene system during interaction with propylamine and n-propanol as analyte molecules. This was done to understand the sensitivity and selectivity of this system. By these means the interesting binding site of the calixarene selector was identified and dependencies on specific properties of the polymer and the functional groups were determined. Reflectometric interference spectroscopy (RIfS) was used to characterize the kinetics whereas isothermal titration calorimetry (ITC) yielded thermodynamic data. Infrared (IR) and ¹H NMR spectroscopy allowed identification of the sensing process as an interaction between the selective group of the PDMS–calixarene system and the amino group of propylamine, and measurement of the effects on hydrogen bonds. The combination of the different spectroscopic methods and the microcalorimetric measurements broadened the understanding of this system, regarded as a model system. Thus, future tailoring of functional groups designed for improved and more selective analyte detection is possible.     

Electrorheology of chitosan polysaccharide suspensions in soybean oil

Chitosan, a biodegradable polysaccharide composed of primarily d -glucosamine repeating units, was adopted as a dry-base electrorheological fluid using soybean oil as a suspending medium. The electrorheological properties were examined under various applied electric field strengths. We found that natural organic polymers such as chitosan possessing amino polar groups induce electrorheological behavior, and the yield stress, τ_y, of chitosan increases with the electric field strength, E , according to a power-law form, τ_y∝ E ^α, which is consistent with the conduction model.     

Characterization of ethylene–propylene block copolymers by proton magnetic resonance

A high-resolution proton magnetic resonance compositional analysis has been developed for propylene polymers containing 0–40 wt.-% ethylene as either homopolymer or copolymer blocks. The test is independent of tacticity and provides qualitative information on copolymer sequencing and propylene chain structure. The analysis was developed using a series of standard reference polymers synthesized to contain various ratios of C¹⁴-tagged ethylene and propylene. The compositional standards were established by radiotracer analysis for C¹⁴ and by preparing weighed physical mixtures of homopolymers. Spectra were obtained at 200 ± 10°C. by placing externally heated polymer solutions into a conventional probe of a Varian A-60 proton spectrometer. All measurements were made on ± 10% polymer solutions in diphenyl ether. Analyses are accurate to about ± 10% at higher ethylene concentrations. The method is sensitive, with less precision, to below 1% for ethylene either as blocks or homopolymer.     

Physicochemical properties of aqueous solutions of L-aspartic acid containing chitosan

Physicochemical properties of aqueous solutions of L-aspartic acid with and without addition of chitosan have been studied by conductometry, potentiometry, refractometry, tensiometry, and viscosimetry. It has been shown that aspartic acid molecules take a cyclic configuration stabilized by hydrogen bonds in aqueous solution at c > 0.04 g/dL (298 K). The interaction of chitosan with aspartic acid results in the formation of the polymeric salt that dissociates in aqueous solution to give chitosan polycation [~(NH₃)⁺] and aspartate counterions. The addition of chitosan to solutions of L-aspartic acid results in progressive increase in the surface tension, absorbance, and refractive index as well as the change in hydrodynamic properties of the macromolecules. The polymeric salt exhibits polyelectrolyte properties in dilute aqueous solutions. The increase in temperature impairs the thermodynamic quality of the solvent for chitosan leading to the shrinkage of the polymer coils and, hence, to the decrease in the intrinsic viscosity of the system.     

Ionic conductivity and tensile properties of hydroxyethyl and hydroxypropyl chitosan membranes

Hydroxyethyl chitosan and hydroxypropyl chitosan were prepared through the reaction of alkali‐chitosan with 2‐chloroethanol and propylene epoxide, respectively. Fourier transform infrared and ¹³C NMR measurements were made to examine the substitution on the chitosan unit. According to a comparison of the peak areas between the modified chitosan and unmodified chitosan and the integration of peak areas of ¹H NMR spectra, for both modified chitosans, the maximum degree of substitution was less than 25%. The ionic conductivity and mechanical properties of modified chitosan membranes were investigated. In comparison with the unmodified chitosan membrane, hydrated hydroxyethyl and hydroxypropyl chitosan membranes with a higher degree of substitution showed an increase in ionic conductivity of about one order of magnitude; moreover, the crystallinity of hydroxyethyl and hydroxypropyl chitosan membranes was remarkably reduced, and their swelling indices increased significantly. However, these modified membranes did not exhibit significant changes in their tensile strength and breaking elongation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1379–1397, 2004