壳聚糖不饱和羧酸盐聚集行为的研究

以半干法制备了一系列壳聚糖不饱和羧酸盐--壳聚糖水杨酸盐(a1)、壳聚糖苯甲酸盐(a2)、壳聚糖肉桂酸盐(a3)壳聚糖丙烯酸盐(a4)和壳聚糖衣康酸盐(a5).用红外光谱和紫外光谱表征了该产品的结构,以凯氏定氮法测定了羧酸的结合量.结果表明壳聚糖和不饱和羧酸盐是通过壳聚糖上的氨基和羧酸中的羧基发生了成盐反应,羧酸的结合...     

Synthesis and characterization of a new conducting polymer composite

Organic conductive composite films have been synthesized by electropolymerization of pyrrole in the presence of chitosan and p-toluene sulfonic acid sodium salt. The obtained conductive polymer composite films have been characterized by Fourier Transform Infrared spectroscopy, dynamic mechanical analysis, scanning electron microscopy, X-ray diffraction and conductivity measurements. The prepared polymer composite films had the amorphous structure and exhibited the enhanced conductivity and mechanical properties due to the presence of chitosan in the composite films.     

Crystalline Transformation of Chitosan from Hydrated to Anhydrous Polymorph Via Chitosan Monocarboxylic Acid Salts

ABSTRACT

Spontaneous removal of monocarboxylic (formic, acetic, propionic or butyric) acids accompanying dehydration of the corresponding chitosan salts was observed from X-ray fiber diffraction diagrams obtained during the storage of these salts for a given period of time. The first three salts were prepared by immersing a tendon chitosan (a hydrated crystal) in an aqueous solution of respective monocarboxylic acid and 2-propanol. The salts showed similar fiber patterns not only to one another but also to the “Eight-fold” polymorph of the original chitosan, indicating that they are Type II salts, hydrated crystals, where the backbone chitosan molecule takes up an eight-fold helical conformation. The temperature required for the salt formation depended on the hydrophobicity of the acid, e.g., the chitosan formic acid salt could be prepared at room temperature, whereas, formation of the propionic acid salt was carried out at 4 °C. All the acids spontaneously evaporated accompanied by dehydration during storage of the salts, resulting in formation of anhydrous crystalline chitosan. Removal of the monocarboxylic acids was accelerated by increasing the hydrophobicity of the acid: at 100% relative humidity approximately 3 months for the formic, 1 month for the acetic and 3 weeks for the propionic acid salts. In the case of butyric acid the anhydrous polymorph of chitosan was obtained immediately after the reaction, suggesting that the water removing action of this acid was too fast to detect a Type II salt by the present X-ray method. The anhydrous crystals of chitosan were irreversibly prepared by annealing a hydrated crystal in water at a high temperature, such as 240 °C, leading to a little loss of orientation and to thermal decomposition of the sample specimen to some extent. But it was found that, through Type II salts of monocarboxylic acids, the hydrated crystals of chitosan can be dehydrated even at room temperature without any loss of orientation and decomposition of the chitosan specimen.     

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.     

Alternating bioactivity of multilayer thin films assembled from charged derivatives of chitosan

Charged derivatives of chitosan, N-sulfofurfuryl chitosan (SFC) and N-[(2-hydroxyl-3-trimethylammonium)propyl]chitosan chloride (HTACC) were prepared by reductive alkylation of amino groups of chitosan (CHI) using 5-formyl-2-furansulfonic acid, sodium salt (FFSA) as a reagent and ring opening of glycidyltrimethylammonium chloride (GTMAC) by amino groups of chitosan, respectively. The chemical structures of the charged derivatives were verified by (1)H NMR and FTIR analyses. Multilayer assembly of SFC, HTACC, CHI and the selected oppositely charged polyelectrolytes was monitored by a quartz crystal microbalance (QCM). Stratification of the multilayer film fabricated on plasma-treated poly(ethylene terephthalate) (treated PET) substrate was demonstrated by water contact angle data. The coverage of the assembled films was characterized by AFM and ATR-FTIR analyses. The bioactivity of the deposited multilayer film on the treated PET substrate was tested against selected proteins having a distinctive size and charge. This research strongly suggests that both SFC and HTACC are potential candidates for altering the surface bioactivity of materials.     

Synthesis of 2-(4,6-dimethoxy-1,3,5-triazin-2-yloxyimino) derivatives: application in solution peptide synthesis

A new class of 1,3,5-triazinyloxyimino derivatives were prepared, characterized and tested for reactivity in solution peptide synthesis. The new triazinyloxyimino derivatives failed to activate the carboxyl group during formation of peptide bonds, but gave the corresponding N-triazinyl amino acid derivatives as a major product. The oxyma (ethyl 2-cyano-2-(hydroxyimino)acetate) uronium salt was superior to other uronium salts in terms of racemization, while 2-chloro-4,6-dimethoxy-1,3,5-triazine (CDMT, 9) gave the best results.     

Cyclopolycondensation. XII. Polymerization mechanism of polybenzoxazinones in polyphosphoric acid medium

The polymerization mechanism of polyphosphoric acid (PPA) solution polymerization of an aromatic diaminodicarboxylic acid with aromatic dicarboxylic acid derivatives was studied. By means of NMR methods, the initiation process for the polymerization of polybenzoxazinone in PPA medium was elucidated. The NMR spectra of a series of compounds were taken, and the salt formation of amino groups of monomer with PPA and the equilibrium between the salt and the free amino group were determined. It was established that the polymerization proceeded through the formation of phosphorylated intermediates to give the salt of amino groups of monomer with PPA. In the second step, the amine–PPA salt dissociates into the free amino group and PPA at the polymerization temperature above 140°C. Polymerization proceeds through the attack of “free” amino on phosphorylated carbonyl compounds to form polyamide acid of high molecular weight, and on subsequently being heated in PPA at higher temperatures, it undergoes an intramolecular cyclodehydration along the polymer chain to form polybenzoxazinones.     

Modification of chitosan via grafting of glycolic acid followed by polycondensation during heat treatment

The modification of chitosan via grafting of glycolic acid and subsequent polycondensation during heat treatment have been studied. The formation of copolymers, the degree of amidization of amino groups, and the length of side polyglycolide chains are investigated by IR spectroscopy and gravimetry. The structural features and surface behavior of the films based on chitosan modified by poly(glycolic acid) are examined by X-ray diffraction and AFM. The grafting of side polyglycolide chains leads to marked changes in the chitosan structure. The study of the sorption behavior of the films based on the modified chitosan confirms the hydrophobization of chitosan via grafting of poly(glycolic acid).     

Effect of oleic acid plasticizer on chitosan-lithium acetate solid polymer electrolytes

Plasticized polymer electrolytes composed of chitosan as the host polymer, oleic acid (OA) as the plasticizer and lithium acetate (LiOAc) as the doping salt were prepared by the solution cast technique. These complexes with different amounts of salts and plasticizers were investigated as possible ionic conducting polymers. The highest ionic conductivity of the plasticized chitosan-LiOAc was ∼10⁻⁵ S cm⁻¹ for the film containing 40.0 wt.% LiOAc and 10.0 wt.% of OA. Conductivity for the plasticized LiOAc-doped chitosan polymer was also studied as a function of temperature between 300 and 363 K. The plot of ln(σT) versus 10³/T for each sample obeys Arrhenius rule indicating the conductivity to be thermally assisted. XRD and FTIR spectroscopy techniques have been used for the structural studies.     

巯基化壳聚糖/明胶的制备研究

仿生杂化构建可注射水凝胶支架是制备组织工程材料的一条有效途径,而天然聚合物的改性即成为其前提条件。本文以巯基乙酸和4-丁巯内酯为反应试剂采用均相反应法制备了巯基化天然聚合物衍生物。结果表明,利用壳聚糖和明胶上的氨基等活性基团,可采用不同途径对它们进行巯基化改性;在水溶性碳二亚胺的活化作用下巯基乙酸的羧基与壳聚糖的氨基形成酰胺键,从而将活性巯基引入到壳聚糖中,但大部分被氧化;随着贮存时间的延长,各改性物中的巯基含量逐渐降低,因此需将改性物保存于低温惰性环境中,以保持其反应活性。     

Spectral and thermal characterization of polyaniline–oxalic acid salt

Polyaniline–oxalic acid salts were prepared at 5 and 30°C by chemical polymerization of aniline using different concentration of oxalic acid. Polyaniline base was obtained from the corresponding polyaniline salt by dedoping using aqueous ammonium hydroxide solution. Conductivity measurements, elemental analysis, Infrared, electronic absorption, electron paramagnetic resonance spectral, and thermogravimetric analysis were performed on the polyaniline salts and bases. Composition and the extent of dopant in polyaniline salt systems where determined. The value of composition of polyaniline: oxalic acid is 4: 1.6 and the polymer yield is around 66%. The value of conductivity, polymer yield and composition of polyaniline–oxalic acid salt is independent of concentration of oxalic acid used and also the synthesis temperature. The results are compared with polyaniline–hydrochloride salt prepared by chemical polymerization. The conductivity of polyaniline–oxalic acid salt is three orders of magnitude lower than that of polyaniline-hydrocholoride salt. © 1995 John Wiley & Sons, Inc.     

Efficient synthesis of β-halogeno protected l-alanines and their β-phosphonium derivatives

Ring opening of oxazolines, prepared from l-serinates, with trimethylsilyl halides (TMSX) led to β-halogeno-N-benzoyl-α-amino esters in good to excellent yields. Quaternization of triphenylphosphine by the β-bromo or -iodo amino esters gave the corresponding β-phosphonium salts in overall yields of up to 93% and with e.e. >96%. Hydrolysis of the ester function afforded the phosphonium salt bearing an N-benzoyl-α-amino acid substituent, with partial racemization. However, the reaction of the TMSX with the carboxylic salt, prepared by saponification of the starting oxazoline ester, furnished the corresponding β-halogeno-N-benzoyl-α-amino acids in 70–95% yields. Quaternization of triphenylphosphine by the bromo or iodo derivatives led to the phosphonium salts bearing a free acid function in 95% yield, without racemization. The efficiency of this synthesis was demonstrated by the preparation of these phosphonium salts in excellent overall yields, by a one-pot procedure starting from the oxazoline.     

Natural and synthetic polymers as reagents. I. Diazonium salt derivatives of polycarboxylic resins (insoluble diazonium salt chromogens)

A method is described for the preparation of insoluble polymeric diazonium-salt chromogens which have a precise composition and well-defined specific reactivity and which are capable of undergoing coupling reactions to produce highly colored azo derivatives. The technique involves reaction of the acid chloride of an acrylic or methacrylic acid polymer crosslinked with divinylbenzene with an aromatic diamine, followed by diazotization of the free amino groups of the resultant aminoarylamido resin to give an insoluble diazonium salt. The aminoarylamido derivatives, the corresponding diazonium salts, and colors of the azo derivatives obtained in coupling reactions are tabulated.     

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.     

Nanocomposites based on modified chitosan and titanium oxide

The effect of primary amino groups and molecular mass of chitosan on the stability of suspensions based on nanoscale TiO₂ dispersions in acidic solutions of various concentrations at pH 2.5 was studied. In the case of chitosan prepared according to a commercialized process, the stability of TiO₂ suspensions was low and depended on the concentration of the polymer solution. Solutions of low-molecular-mass highly deacetylated chitosan prepared by solid-phase synthesis stabilized a dispersion of nanosized TiO₂ particles for a very long time. Nanocomposites based on a chitosan-PVA graft copolymer and TiO₂ were prepared, in which the initial filler dispersion is retained up to very high filling ratios. A potential use of these nanocomposites in photocatalytic processes is discussed. The results of this study can be used for refining engineering procedures and processes for the manufacture of new biocompatible, bioactive, and biodegradable functional composite materials based on chitosan and synthetic polymers.     

A biocompatible nanocomposite based on allyl chitosan and vinyltriethoxysilane for tissue engineering

The synthesis, structure, and electrophysical properties of a polymer-inorganic biocompatible composite based on unsaturated chitosan ether, namely, allyl chitosan, and vinyltriethoxysilane are studied. During composite synthesis, allyl chitosan forms an individual nanophase with vinyltriethoxysilane and its condensation products in the polymer matrix of allyl chitosan. The size of nanoparticles embedded in a polymer matrix increases from 50 to 1000 nm as the fraction of the added vinyltriethoxysilane grows. Under exposure to UV radiation, both homopolycondensation and heteropolycondensation occur in the composite films via crosslinking according to the radical mechanism and the composite becomes insoluble in water. It has been shown that the resulting composites feature ionic conductivity under application of both direct current and high-frequency electric fields to the sample. Conductivity is provided by a proton–electron ensemble that concentrates at the nanoparticle/polymer matrix interface.     

Synthesis of polyglutamine conjugates of lysine dendrimers in solution and polymer gel

The synthesis of polyglutamine conjugates of lysine dendrimers, in which carboxyl groups of polyglutamine chains are linked via one point to the amino groups of N-terminal lysine fragments of dendrimers, is studied. Lysine dendrimers of third, fourth, and fifth generations are preliminarily prepared via the solid-phase synthesis on a polymer support, crosslinked p-methylbenzohydrylaminopolystyrene. The first approach to the synthesis of polyglutamine conjugates of dendrimers consisted in that, after the synthesis of lysine dendrimers, their removal from the polymer support, their full unblocking, and their purification, γ-benzyl glutamate N-carboxyadhydride is involved in solution polymerization at the amino groups of lysine of the outer sphere of dendrimers. The second approach includes the polymerization of γ-benzyl glutamate N-carboxyadhydride on the amino groups of N-terminal lysine residues of lysine dendrimers performed before dendrimer removal from the polymer support. The structural study of star-shaped conjugate of lysine dendrimers makes it possible to for the first time estimate the similarities and differences in these two approaches to the synthesis of polyglutamine conjugates of lysine dendrimers.     

Preparation and structure of chitosan-silica organic-inorganic hybrid films

Organic-inorganic hybrid films are prepared via the hydrolysis and polycondensation of tetraethoxysilane in chitosan solutions. It is shown that the composition of reagents, the time of synthesis, the crosslinking of chitosan macromolecules via amino groups by glutaric aldehyde, and the conditions of drying affect structurization of the resulting films. With the use of optical polarization microscopy and atomic force microscopy, it is found that the films contain silica particles with a wide size distribution. The crosslinking of the chitosan matrix by glutaric aldehyde results in the predominant formation of inorganic nanoparticles in the films. A good sorption capacity of the films for copper ions in solutions is found. It increases by a factor of 1.7 as the content of the silica in the films increases to 30 wt %.     

New 2-pyrone-based hydrazones: Synthesis,spectral characterisation,UV–visible study and evaluation of the antiradicalar activity

The synthesis of new 2-pyrone-based hydrazones has been prepared by the coupling of 6-methyl-2H-furo[3,2-c]pyran-3,4-dione with diazonium salts, obtained by diazotization of aniline derivatives. The structure of all compounds was established by spectroscopic methods, and the structure of the more stable conformer was theoretically confirmed by the potential energy profile analysis. The prepared 2-pyrone-based hydrazone dyes were acetylated and both groups of compounds showed moderate to good radical scavenging activity.     

Diastereoselective solid-phase radical addition to oxime ether anchored to polymer support

Stereocontrol in radical reactions of oxime ether anchored to polymer support was studied. Highly diastereoselective solid-phase radical reaction was achieved by using triethylborane and diethylzinc as a radical initiator at low reaction temperature, providing a novel method for the synthesis of the alpha-amino acid derivatives with excellent diastereoselectivities.