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.     

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.     

Water-soluble modified chitosan and its interaction with a polystyrenesulfonate anion

The selective alkylation of primary amino groups of polysaccharide is conducted through the interaction of chitosan with glycidyltrimethylammonium chloride with introduction of the quaternized amino group into every alkylated unit, thereby ensuring a positive charge and solubility of the polymer over the entire pH range. The structure of the modified chitosan is studied via FTIR spectroscopy and ¹³C and ¹H NMR measurements. On the basis of the potentiometric titration of solutions of the parent polysaccharide, its modified derivative, and their mixtures with the polystyrenesulfonate anion, as well as ζ-potential measurements and turbidimetric titration of polymer mixtures, it is demonstrated that the secondary amino group of the complexed modified chitosan can be protonated in weakly acidic solutions. This behavior is of particular importance for the design of biocompatible and biodegradable vehicles suitable for the delivery of genetic material and drugs to cells.     

Preparation and characterization of nanoparticles formed by chitosan-caseinate interactions

Intermacromolecular complexation between chitosan and sodium caseinate in aqueous solutions was studied as a function of pH (3–6.5), using absorbance measurements (at 600 nm), dynamic light scattering (DLS), and transmission electron microscopy (TEM). The chitosan–caseinate complexes formed were stable and soluble in the pH range 4.8–6.0. In this pH range, the biopolymers had opposite charges. At higher concentrations of chitosan (0.15 wt%), the soluble complexes associated to form larger particles. DLS data showed that, between pH 4.8 and 6.0, the particles formed by the complexation of chitosan and caseinate had sizes between 250 and 350 nm and these nanoparticles were visualized using negative staining TEM. Above pH 6.0, the nanoparticles associated to form larger particles, causing phase separation. Addition of NaCl increased the particle size. The pH dependence of the zeta potential of the mixture solutions was appreciably different from that of the pure protein and pure chitosan solutions.     

Nonstoichiometric polyelectrolyte complexes of chitosan soluble in neutral solutions

The technique of preparing nonstoichiometric polyelectrolyte complexes of chitosan soluble in neutral solutions is developed. Chitosan complexes soluble in neutral solutions and meeting the behavioral criteria of water-soluble nonstoichiometric polyelectrolyte complexes are prepared via mixing of strongly acidic solutions of chitosan and polystyrenesulfonate anions taken in a nonequimolar charge-charge ratio and subsequent neutralization of the products by a solution of alkali. Thus, the region of existence of soluble complexes narrows with a decrease in the length of the host polyanion up to its full degeneration in the case of oligomeric anions. The critical concentration of a salt that brings about phase separation decreases with an increase in the relative content of the guest chitosan in a mixture and depends on the ratio of chain lengths of polymer components.     

Studies of the association of chitosan and alkylated chitosan with oppositely charged sodium dodecyl sulfate

Cationic biopolymer chitosan has many applications in food, cosmetic and pharmaceutical industries. Grafting alkylated chains on its backbone can hydrophobically modify this water-soluble polymer.This paper concerns unmodified chitosan, alkylated chitosan and their interactions with a model anionic surfactant, sodium dodecyl sulfate (SDS). The solvent is pH 4 acetic acid solution. The purpose of this study is to highlight the hydrophobicity brought by the alkylated chains by comparing surface tension measurements and rheological properties of hydrophobically modified polymer (HMP) and chitosan solutions at 25 °C.Interactions of chitosan and HMP with surfactant have also been investigated giving information about surface activity and electrical conductivity of such systems. It results that alkylated chitosan/SDS system is more surface active than chitosan/SDS and it offers new potential applications in pharmaceutical and cosmetic fields because of the formation of amphiphilic complexes.     

A spectrophotometric study of the ionic complexation between chitosan and anionic dyes

Formation conditions and composition of ionic complexes in dilute mixed solutions of chitosan and anionic dyes containing two or more sulfo groups were studied. Immediately after mixing the components, only one sulfo group of the dye interacts with chitosan to form a soluble complex of stoichiometric composition. With time, the other sulfo groups of the dye also become involved in the interaction, which results in the formation of an insoluble complex in which the dye behaves as cross-linking polyvalent anion.     

Interactions between chitosan-modified particles and mucin-coated surfaces

Lipid-based particles (Cubosome particles) were surface-modified by chitosan and the ratio between particles and chitosan was optimized to minimize the free chitosan concentration in the dispersion. The modified particles were characterized by electrophoretic measurements and the pH dependence of the zeta potential could be directly related to the protonation of chitosan. Interaction between the modified particles and mucin-coated silica surfaces were subsequently investigated in situ by ellipsometry to assess the mucoadhesive properties at physiologically relevant conditions. The result showed that a substantial amount of modified particles was adsorbed to mucin-coated silica surfaces at both pH 4 and pH 6, probably due to electrostatic interactions between amino groups in chitosan and negatively charged groups in mucin. Furthermore, the amount of bound particles decreased by less than 15% upon rinsing indicating relatively strong interactions. This investigation demonstrates that ellipsometry is a useful tool to study mucoadhesive properties of particles in the submicrometer range. Moreover, the novel chitosan-modified particles may be of interest for mucosal drug delivery applications.     

Soluble polyelectrolyte complexes of biopolymers

This review analyzes the papers reflecting the state of the art and achievements in the field of experimental investigations of solutions of polyelectrolyte complexes containing biopolymers, specifically oligomeric enzymes, cationic polysaccharide chitosan, or DNA. The analysis shows that the use of soluble complexes is promising for solving urgent practical problems. The development of methods for suppressing thermal aggregation of globular proteins without any substantial loss in functional activity, for imparting chitosan the ability to dissolve under physiological conditions and to form polyelectrolyte complexes, and for creating dual-action dendrimer carriers that can simultaneously deliver genetic material and drugs to cells are among the most significant directions.     

壳聚糖基聚电解质复合物在生物医学领域的应用

近年来,国内外对壳聚糖在生物医学领域的应用研究十分活跃。壳聚糖在低pH时带正电荷,在溶液中可与带负电荷的聚离子形成聚电解质复合物。壳聚糖基聚电解质复合物除了具有壳聚糖的生物相容性,还表现出良好的物理化学性质,在药物控制释放体系、蛋白质分离、生物酶以及细胞固定化等领域具有广泛应用。本文重点介绍壳聚糖与几种天然的或合成的聚阴离子形成的聚电解质复合物及其在生物医学领域的应用。     

去质子化调控的肝素/壳聚糖抗凝血多层膜

本文研究了环境pH值变化对多层膜表面性能的影响, 并且评价了组装pH值与测试pH值的差异对多层膜血液相容性的影响.     

Liquid crystalline dispersions of complexes formed by chitosan with double-stranded nucleic acids

Double-stranded molecules of nucleic acids (NAs) were shown to interact with chitosans to form under certain conditions (chitosan molecular mass, content of amino groups, distance between amino groups, pH of solution, etc.) multiple types of liquid crystalline dispersions. The dispersions formed are different in their spatial structures, and hence in the sense and magnitude of the abnormal optical activity. The physicochemical properties of these dispersions were investigated. Time- and temperature-stabilization of dispersions that possess abnormal optical activity were achieved by chemical crosslinking of chitosan molecules in the liquid crystalline dispersions formed from NA–chitosan complexes. The accessibility of these ‘NA–liquid crystalline elastomers' with respect to enzyme and drug action was tested. The multiplicity of liquid crystalline forms of DNA–chitosan complexes was possibly explained by the influence of the character of the dipole distribution over the surface DNA molecules on the sense of the spatial twist of the cholesteric liquid crystalline dispersions resulting from these complexes.     

微过氧化物酶-11在壳聚糖修饰玻碳电极上的电化学

采用物理吸附法, 将微过氧化物酶-11(MP-11)固定在载体壳聚糖修饰的玻碳电极表面. 运用循环伏安法对MP-11在该修饰电极上的直接电化学行为及对氧(O2)和过氧化氢(H2O2)的电催化行为进行了表征. 研究结果表明, 在pH=7.12的磷酸盐缓冲溶液中, 壳聚糖修饰电极上的MP-11发生了准可逆的氧化还原反应, 而且在反应过程中包含质子的传递过程, 完全实现了MP-11在该修饰电极上的直接电化学. 该修饰电极也可以对O2和H2O2进行电催化还原, 并且两个反应的电催化还原过程都是受表面控制的电化学过程, 对H2O2催化还原产生的响应电流与H2O2的浓度呈线性关系.     

pH-potentiometirc study of polyion complexes between chitosan and poly(vinyl sulfate) or dodecylbenzene sulfonate

Polyion complexes of three chitosans with poly(vinyl sulfate) (PVS) and dodecylbenzene sulfonate (DBS) were examined by a potentiometric study that was to separately measure the pH of sample solutions individually prepared. Apparent formation constants (Ki) of ion association between the protonated amines of chitosan and the sulfates of PVS or the sulfonates of DBS were determined. The effects of pH, coexistent salt concentration, and molecular weight on the values of Ki were investigated in order to reveal the properties of the complexation. The values of Ki for chitosan-PVS were quite larger than that for chitosan-DBS. The deducing effect of the coexistent salt was strong against chitosan-PVS, but was weak against chitosan-DBS. Thus, chitosan-PVS complexes possessed a strong electrostatic binding, and chitosan-DBS complexes included a hydrophobic interaction. For chitosan-PVS complexes the effect of the coexistent salt was weaker for a high molecular weight of chitosan than for a low molecular weight.     

Investigation of vanadocene(IV) alpha-amino acid complexes: synthesis, structure, and behavior in physiological solutions, human plasma, and blood

This work is focused on investigating the interaction of antitumor active metallocene vanadocene dichloride (Cp2VCl2) and amino acids in aqueous solution at physiological pH. Sixteen vanadocene amino acid complexes [Cp2V(aa)][X] (aa = gly, ala, val, leu, ile, phe, his, and trp; X = Cl, PF6) were prepared and characterized on the basis of spectral measurements (EPR, MS, IR, Raman). Amino acids are coordinated to the vanadocene fragment through the oxygen atom of the carboxylic group and the nitrogen of the amino group, resulting in a five-membered chelate ring. Complexes [Cp2V(val)][PF6] and [Cp2V(ile)][PF6] have been characterized by X-ray structure analyses. It was evidenced that all prepared complexes are stable in both aqueous solutions with physiological pH and in therapeutic NaCl solutions. EPR spectra of vanadocene amino acid complexes in Krebs-Ringer solution in human blood plasma and in whole blood showed that these complexes react with the hydrogen carbonate anion present forming complex Cp2V(O2CO).     

水溶性壳聚糖降血脂作用的化学机理(Ⅰ)──水溶性壳聚糖及其衍生物对胆酸盐的结合能力研究

通过壳聚糖氧化裂解,制备了分子量为8000的水溶性壳聚糖,并通过烷基化反应合成了二乙氨乙基壳聚糖、二甲氨基(1-甲基)乙基壳聚糖及二乙基甲基铵乙基壳聚糖.在体外测定了水溶性壳聚糖及其衍生物对胆酸盐(牛磺胆酸钠和甘氨胆酸钠)的结合能力及其影响因素.结果表明,水溶性壳聚糖结合胆酸盐的能力主要取决于其阳离子化程度.修饰后的壳聚糖结合胆酸盐的能力增强,说明引入更多的胺基或铵基有利于对胆酸盐的结合.     

Synthesis and Characterization of a Novel Soluble Diethoxy Phosphoryl Chitosan

A simple and efficient method for the preparation of a novel soluble chitosan derivative, diethoxy phosphoryl chitosan (PH‐chitosan), has been developed. Ph‐chitosan was characterized by elemental analysis, FT‐IR, NMR, ICP, XRD, TG and SEM, respectively. The chemical identity of PH‐chitosan was determined by FT‐IR and confirmed by NMR, and those results unequivocally demonstrated that diethoxy phosphoryl groups were grafted onto the amino and hydroxyl groups of chitosan. The results of XRD indicated that the crystalline structure of chitosan was destroyed due to the incorporation of diethoxy phosphoryl group resulting in loss of hydrogen bond. The analysis of TG demonstrated that PH‐chitosan was less thermal stable than chitosan. This simple synthetic method provided a new and available approach to prepare a soluble high molecule weight chitosan derivative.     

Mechanisms and kinetics of humic acid adsorption onto chitosan-coated granules

Chitosan, a naturally abundant biopolymer, has widely been studied for metal adsorption from various aqueous solutions, but the extension of chitosan as an adsorbent to remove humic substances from water has seldom been explored. In this study, chitosan was coated on the surface of polyethyleneterephthalate (PET) granules through a dip and phase inversion process and was examined for humic acid removal in a series of batch adsorption experiments. Scanning electron microscopic (SEM) images showed that the PET granules were uniformly covered with a layer of chitosan and the chitosan layer possessed numerous open pores on the surface. Zeta potential study indicated that the chitosan-coated granules had positive zeta potentials at pH < 6.6 and negative zeta potentials at pH > 6.6. Adsorption of humic acid onto the chitosan-coated granules was found to be strongly pH-dependent. Significant amounts of humic acid were adsorbed under acidic and neutral pH conditions, but the adsorption capacity was reduced remarkably with increasing solution pH values. The adsorption isothermal data under various initial humic acid concentrations (at the same solution pH value) can be adequately modeled by the Langmuir and Freundlich models. X-ray photoelectron spectroscopy (XPS) revealed that the amino groups of the chitosan layer were protonated due to humic acid adsorption, suggesting the formation of organic complex between the protonated amino groups and humic acid. Kinetic study indicated that the adsorption process was transport-limited at low solution pH values, but became both transport- and attachment-limited at high solution pH values.     

pH-Dependent Release from Monoolein Cubic Phase Containing Hydrophobically Modified Chitosan

Monoolein (MO) cubic phase incorporating hydrophobically modified chosan (Hm chitosan) was prepared to obtain a pH-dependent release. Following calorimetric study, Hm chitosan had little effect on the crystal structure of MO cubic phase under acidic condition where Hm chitosan is readily soluble. At a higher pH (e.g., pH 9.0), however, the crystal structure of MO cubic phase was disturbed, possibly due to the insolubilization of Hm chitosan at the alkali condition. Whether the dye included in the cubic phase is anionic (amaranth) or cationic (methylene blue), the release from the cubic phase was suppressed as the pH of release medium increased. The structural change of cubic phase caused by the insolubilization of Hm chitosan, or the blockage of the water channel of the cubic phase by precipitated Hm chitosan would be responsible for the suppressed released.     

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.