Synthesis and characterization of oxidized cellulose

Samples of oxidized cellulose (OC) with various carboxyl contents and degrees of crystallinity were obtained by the oxidation of native and mercerized cellulose with a solution of nitrogen(IV) oxide in CCl₄. A detailed characterization of these OC samples was performed. The effect of oxidation conditions (concentration of N₂O₄ in the solution and oxidation time) and starting cellulose material on OC characteristics (carboxyl, carbonyl and nitrogen content, degree of crystallinity and polymerization, surface area and swelling, and acidic properties) was investigated. Reactivity in the oxidation process was higher in mercerized cellulose than in native cellulose. The action of dilute solutions (10–15%) of N₂O₄ did not affect the degree of crystallinity of cellulose samples. Under these conditions, the oxidation took place mainly in amorphous regions and on the surface of crystallites. Oxidation in a concentrated (40%) N₂O₄ solution led to the destruction of crystallites, which increased the surface area and swelling of cellulose in water. The surface area and the swelling of OC samples increased with a decrease in the index of crystallinity. The acidic properties of OC were shown to increase with an increase of swelling in water. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4785–4791, 2004     

Properties of Monocarboxy Cellulose Containing Sorbed Fe(III), Al(III), and Cr(III) Cations

Sorption of Fe(III), Al(III), and Cr(III) on monocarboxy cellulose at various pH, concentrations of metal chloride or sulfate in solution, and time was studied. The effect of type and amount of the cation sorbed on the physicomechanical properties, swelling, and stability in phosphate buffer of monocarboxy cellulose fibers was considered.     

Synthesis, structure, and physicochemical properties of gel-forming dextran phosphates

Dextran phosphates with the degree of substitution of 0.29–1.09 with phosphoric acid groups and of 0.14–0.83 with carbamate groups were prepared in the orthophosphoric acid-urea system. The effect of the component ratio in the esterifying mixture, temperature, and pressure in the reaction zone on the structure and physicochemical properties of dextran phosphate hydrogels and on the gel fraction yield was examined.     

Characterization of H3PO4/HNO3–NANO2 oxidized bacterial cellulose and its usage as a carrier for the controlled release of cephalexin

Biocompatibility, biodegradation, good sorption characteristics, and unique structure of highly oxidized bacterial cellulose (OBC) are of great interest for the development of new drug delivery systems. In this study, OBC with 9.6, 13.0 and 19.5% carboxyl groups for 5, 20, and 48 h of synthesis, respectively, was successfully obtained using the HNO₃/H₃PO₄–NaNO₂. The results of morphological analysis showed that with an increase in the number of carboxyl groups, OBC fibers become thicker and rougher. Fourier-transform infrared spectroscopy showed the formation of carboxyl groups in the OBC after the oxidation reaction. The crystallinity of the samples according to X-Ray diffraction analysis decreased with increasing reaction time. The immobilization of cephalexin in the polymer matrix was studied in detail, it took 120 min to achieve balance in the solution with a concentration of 1 mg/ml, and the maximum amount of a sorbed antibiotic reached 43 mg/g. The drug release in vitro at 37 °C in PBS with pH 7.4 and 2.0 was prolonged. Various models were used to describe the release mechanism, the best of which was Ritger-Peppas with a diffusion exponent value ranging from 0.743 to 0.830, which explains the drug release mainly through non-Fickian diffusional release. The cephalexin-loaded OBC showed high antimicrobial activity against Gram-negative bacteria Escherichia coli and Gram-positive bacteria Staphylococcus aureus. The structure and properties of the resulting highly oxidized cellulose make it an excellent candidate as a drug delivery carrier with prolonged antimicrobial drug release characteristics.

     

Multilayer adsorption of amino acids on oxidized cellulose

The adsorption of amino acids (AA) (glycine, L-alanine, L-proline) on oxidized cellulose (OC) with various carboxyl contents and degrees of crystallinity from aqueous and water/ethanol solutions was studied. It was found that multilayer adsorption occurs in concentrated solutions of AA. It proceeds according to successive mechanisms via adsorption of AA zwitterions onto carboxyls of already adsorbed AA. This leads to formation of chain AA associates in the OC phase. A sharp increase in swelling accompanies multilayer adsorption. It was established that structural characteristics and degree of polymerization of OC are the main factors that affect multilayer adsorption. The distribution of carboxyls in the OC phase also plays an important role. Multilayer adsorption does not proceed in water/ethanol solutions and in the case of the cationic form of AA.     

Sorption of aliphatic amines by monocarboxycellulose from aqueous and water-ethanol solutions

The features of the sorption of hydrochlorides of lower aliphatic amines by monocarboxycellulose (MCC) from aqueous and water-ethanol solutions are studied. The ion exchange character of the sorption is shown by IR spectroscopy and potentiometry. It is found that the sorption of all studied salts of aliphatic amines by MCC from dilute aqueous and water-ethanol solutions is thermodynamically advantageous due to the great contribution of Coulomb interactions between cations and polyanions. The selectivity of sorption is predetermined by solvophobic (hydrophobic) interactions, which are thermodynamically disadvantageous at any compositions of the binary solvent due to the formation of dimeric associates of carboxyl groups in the phase of MCC, which hinder the contacts of hydrocarbon radicals of aliphatic amines with hydrophobic sites of the cellulose adsorbent matrix. At high concentrations of aliphatic amines in aqueous and water-ethanol solutions, the process of nonexchange sorption proceeds intensely through the hydrogen bonding between nitrogen atoms and hydroxyl groups of MCC.     

Influence of the properties of modified dextran hydrogel polymer network on the kinetics of the release of prospidin antitumor agent

The influence exerted by the conditions of the synthesis of dextran phosphate hydrogels in the orthophosphoric acid–urea system on their functional composition and swellability in water was studied. The main parameters of the polymer network, namely, the mean molecular mass of segments between cross-linking points, the pore size, and the cross-linking density, were determined. Samples of prospidin immobilized on dextran phosphate hydrogels were prepared, and the kinetics of the cytostatic release into phosphate buffer solution (pH 7.4) was studied in relation to the functional composition and parameters of the polymer network of the support. The prospidin release from dextran phosphate hydrogels is due both to diffusion processes and to breakdown of the polymer network of the hydrogel.     

Preparation and flocculating properties of highly substituted cationic starches of different vegetable origins

Kinetic regularities of flocculation of model kaolin suspensions by highly substituted cationic flocculants synthesized from different starches (corn, waxy corn, potato, and tapioca starches) have been studied as depending on the doses and vegetable origins of the flocculants. The rate of kaolin suspension flocculation has been found to increase with the dose of the cationic starches of all types. It has been shown that, irrespective of the dose, the highest rate of kaolin sedimentation in the model systems is observed in the presence of cationic potato starch. It has been demonstrated that cationic potato starch flocculates kaolin suspensions with concentrations of 0.1, 0.5, and 1.0% with the same efficiency. In this case, the suspensions are almost completely clarified within 2–5 min. Moreover, the dependence of the flocculating efficiency for a 0.1% model suspension on the dose of cationic starch has been found to pass through a maximum at a starch content of 1.0–5.0 mg/g of kaolin depending on the type of starch.     

Kinetics of Starch Oxidation in the System Nitrogen(IV) Oxide-Tetrachloromethane

Kinetics of potato starch oxidation by dinitrogen tetroxide in CCl₄ was studied as influenced by the oxidant concentration, temperature, and starch to N₂O₄ ratio. The starch oxidation products were analyzed by IR spectroscopy.     

Complexation of Chromium,Aluminum, and Iron Ions with Monocarboxy Cellulose

Complexation of iron(III), aluminum(III), and chromium(III) cations with monocarboxy cellulose was studied by potentiometric titration and IR spectroscopy. The composition and stability constants of the complexes were determined.