Synthesis and characterization of N-aryl chitosan derivatives

Selective N-arylation of chitosan was performed via a Schiff bases formed by the reaction between the 2-amino group of glucosamine residue of chitosan with an aromatic aldehyde under acidic condition followed by reduction of the Schiff base intermediate with sodium cyanoborohydride (Borch reduction). Aromatic aldehydes bearing either an electron donating or electron withdrawing substituent were used. The chemical structures and thermal properties of the N-aryl chitosans were characterized by FT-IR, (1)H NMR, (13)C NMR, TGA, and DSC. The extent of N-substitution (ES) was influenced by the molar ratio of the aldehyde to the glucosamine residue of chitosan, the reaction time and the substituent on the aromatic ring. Lower ESs resulted from N-arylation using an aldehyde with an electron donating substituent. A linear relationship between the targeted ES and the ES obtained was observed when aldehydes bearing electron withdrawing substituents were employed.     

Synthesis of dehydroabietic acid-modified chitosan and its drug release behavior

A new type of chitosan derivative, dehydroabietic acid-modified chitosan (DAMC), was synthesized by the acylation reaction of chitosan with dehydroabietic acid chloride (DHAC) under microwave irradiation. The resulting product (DAMC) was characterized by FT-IR, UV, ¹H NMR, X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), and elemental analysis. The degree of substitution (DS) of DAMC was 16.5%. And chitosan and DAMC were used as carriers of fenoprofen calcium (FC), and their controlled release behavior in artificial intestinal juice was studied. The results showed that the controlled release of FC from the carrier of DAMC is better than that from original chitosan.     

Synthesis and characterization of water-soluble glucosyloxyethyl acrylate modified chitosan

A novel water-soluble chitosan derivative, glucosyloxyethyl acrylated chitosan was successfully synthesized by Michael addition reaction of chitosan with glucosyloxyethyl acrylate (GEA), and the obtained glyco-chitosan derivative was characterized by FT-IR, (1)H NMR, elemental analysis, XRD, TG, DSC and SEM. The FT-IR and (1)H NMR results showed that GEA residues were grafted onto the amino group of chitosan. The degree of substitution (DS) was calculated by elemental analysis. XRD data revealed that the introduced saccharide moieties decreased the crystalline structure of chitosan. TG and DSC results demonstrated that the glucosyloxyethyl acrylated chitosan was less thermal stable than chitosan. This efficient synthetic method provided an approach of preparing water-soluble glyco-chitosan derivatives. The obtained derivatives would show stronger specific affinity of lectin than chitosan thus would have potential applications in biomaterials.     

Preparation of soluble p-aminobenzoyl chitosan ester by Schiff's base and antibacterial activity of the derivatives

Schiff's base of chitosan (BCTS) was obtained by the reaction of chitosan (CTS) and benzaldehyde. Then BCTS reacted with acyl chloride which was synthesized by p-aminobenzoic acid and thionyl chloride to get N-benzoyl-O-aminobenzoyl chitosan ester (BABCTSE), removing the groups of amino protection of BABCTSE to get the final product (ABCTSE). The structures of the derivatives were characterized by FT-IR, (1)H NMR, (13)C NMR and elemental analysis. The elemental analysis results indicated that the degrees of substitution (DS) of the products were 16.8% and 40.4%. The synthesized compounds exhibited an excellent solubility in organic solvents. TG and DTG results showed that thermal stability of the derivatives was lower than that of chitosan. In addition, the existence of two different amido in the molecular structures contributed to forming more -NH(3)(+) in the acid solution which could make the derivatives have a greater advantage in the field of bacteriostasis.     

Synthesize and characterization of organic-soluble acylated chitosan

Acylated chitosan was synthesized by reaction of chitosan and stearoyl chloride. The chemical structures and physical properties of the prepared compounds were confirmed by Fourier transform infrared (FT-IR), ¹H Nuclear Magnetic Resonance (¹H NMR) spectroscopy, X-ray diffraction (XRD) and Thermogravimetric (TG) techniques. The degree of substitution (DS) was calculated by ¹H NMR and ranged from 1.8 to 3.8. The synthesized compounds exhibited an excellent solubility in organic solvents. XRD analysis showed that they had high crystalline structure. TG results demonstrated that thermal stability of the prepared compounds was lower than that of chitosan, the weight loss decreased with increase of DS. This procedure could be a facile method to prepare organic-soluble chitosan derivatives.     

Photo-polymeriable chitosan derivative prepared by Michael reaction of chitosan and polyethylene glycol diacrylate (PEGDA)

N-Alkyled photo-polymeriable chitosan derivative (PEGDA-CS) was synthesized by Michael reaction of chitosan and polyethylene glycol diacrylate (PEGDA) under mild reaction conditions. The chemical structure and physical properties of PEGDA-CS were characterized by FT-IR, ¹H NMR, XRD and TG techniques. The degree of substitution (DS) of PEGDA-CS could be calculated from ¹H NMR. PEGDA-CS exhibited good solubility in distilled water. XRD analysis showed that PEGDA-CS was amorphous. TG results demonstrated that thermal stability of the derivate was lower than that of chitosan. Antimicrobial test showed that PEGDA-CS had the antimicrobial activity on Escherichia coli. It could photopolymerize under ultraviolet light with 2959 as initiator.     

N,N,N-三甲基壳聚糖甲基硫酸盐的合成及理化性质的测定

壳聚糖与甲醛、甲酸反应得到N,N-二甲基壳聚糖,然后以硫酸二甲酯为季铵化试剂反应得到N,N,N-三甲基壳聚糖甲基硫酸盐(TMCMS),用IR1、H NMR和元素分析对其结构进行了表征。元素分析结果表明其季铵化度为74.6%,差示扫描量热法和热重分析法结果表明其热稳定性比壳聚糖差,但其水溶性明显优于壳聚糖,25℃时在水中的溶解度可达20 mg/mL,浓度为2 mg/mL时在pH 3～12范围内无沉淀产生。     

Selective carboxypropionylation of chitosan: synthesis, characterization, blood compatibility, and degradation

Two water-soluble chitosan (WSC) derivatives of N-succinyl-chitosan (NSCS) and N,O-succinyl-chitosan (NOSCS) with a degree of substitution (DS) that ranged form 0.28 to 0.61 were selectively synthesized by varying the molar ration of succinic anhydride and chitosan. The chemical structure and physical properties of the chitosan derivatives were characterized by FT-IR, ¹H NMR, and XRD. XRD analysis showed that the derivatives were amorphous. The lysozyme enzymatic degradation results revealed that the NSCS was of higher susceptibility to lysozyme. The degradation rate and the solubility of the chitosan derivatives were strongly determined by the degree of substitution and the position of the substitution. The results of antithrombotic properties, hemolytic properties and anticoagulant properties of WSCs indicated that the blood compatibility was dramatically improved, and the carboxyl group introduced on the C-6 or C-2 hydroxyl group appeared to impact anticoagulant activity in different ways.     

Synthesis of novel quaternary chitosan derivatives via N-Chloroacyl-6-O-triphenylmethylchitosans

Various quaternary chitosan derivative structures were synthesized by reacting N-chloroacyl-6-O-triphenylmethylchitosans with tertiary amines. Full substitutions were obtained from the quaternization reactions and the obtained water-soluble quaternary chitosan derivatives were thoroughly characterized with (1)H NMR, (13)C NMR, (1)H-(13)C HSQC NMR, and FT-IR.     

Novel water soluble phosphonium chitosan derivatives: synthesis, characterization and cytotoxicity studies

Novel water soluble phosphonium chitosan derivatives (WSPCSs) with two different degrees of substitution (3.6% and 4.2%) of quaternary phosphonium were synthesized in a homogeneous system at 25°C. The chemical structures of the WSPCS were characterized by (31)P NMR (nuclear magnetic resonance), (1)H NMR, FT-IR (Fourier-transformed infrared) spectroscopy and WAXD (wide-angle X-ray diffraction). Their solubility in water and several organic solvents and cytotoxicity to L929 cells were also evaluated. The degree of substitution (DS) of WSPCS was calculated by (1)H NMR. WAXD analysis showed that the derivatives had low crystallinity. The derivatives could be easily dissolved in water. MTT (methyl thiazolyl tetrazolium) assay indicated that they had low cytotoxicity to L929 cells.     

Preparation and spectroscopic characterization of methoxy poly(ethylene glycol)-grafted water-soluble chitosan

The object of this study was to test the solubility of a methoxy poly(ethylene glycol) (MPEG)-grafted chitosan copolymer in organic solvents and aqueous solution. Water-soluble chitosan with low molecular weight (LMWSC) was used in a PEG-graft copolymerization. The MPEG was conjugated to chitosan using 4-dicyclohexylcarbodimide (DCC), and N-hydroxysuccimide (NHS). Introduction of PEG was confirmed by (1)H and (13)C NMR spectroscopy and FT-IR spectroscopy. The degree of substitution (DS) of MPEG into chitosan was calculated from (1)H NMR data and also by estimating the molecular weight (MW) using gel permeation chromatography (GPC). The DS values obtained from (1)H NMR spectroscopy and GPC were similar, indicating that MPEG-grafted LMWSC was synthesized and properly characterized. Furthermore, the introduction of PEG into chitosan increases the solubility in aqueous solutions over a range of pH values (4.0-11.0) and organic solvents such as DMF, DMSO, ethanol, and acetone.     

A new chitosan-thymine conjugate: synthesis, characterization and biological activity

Conjugation of chitosan with nucleobases is expected to expand its not only antimicrobial activity but also anti-cancer activity. Here, we report the synthesis of a novel chitosan-thymine conjugate by the reaction between chitosan and thymine-1-yl-acetic acid followed by acylation. The synthesized conjugate was characterized by FTIR, XRD, (1)H NMR, TGA and SEM. The microbiological screening results demonstrated the antimicrobial activity of the conjugate against bacteria viz., Escherichia coli, Staphylococcus aureus, and fungi viz., Aspergillus niger. The chitosan-thymine conjugate also inhibited (p<0.05) the proliferation of human liver cancer cells (HepG2) in a dose-dependent manner but had no cellular toxicity in non-cancerous mouse embryonal fibroblast cells (NIH 3T3). Thus, the chitosan-nucleobase conjugate may open a new perspective in biomedical applications.     

A short synthesis of highly soluble chemoselective chitosan derivatives via "click chemistry"

A short synthesis of chemoselective chitosan derivatives was achieved by copper-catalyzed Huisgen cycloaddition, which is an ideal reaction for click chemistry, by using N-(4-azidophthaloyl)-chitosan. N-(4-azidophthaloyl)-chitosan was prepared through chemoselective N-bromophthaloylation of chitosan in acidic water and subsequent azidation. The obtained N-(4-bromopthaloyl)-chitosan had higher solubility in common solvents than conventional phthaloyl chitosan. N-(4-azidophthaloyl)-chitosan was successfully converted with ethynyl derivatives having functional groups (hydroxymethyl, phenyl, and methyl ester) in the presence of copper(II) sulfate, sodium ascorbate and/or trimethylamine. FT-IR spectra, elemental analyses, and (1)H and (13)C NMR spectra supported that the desired chitosan derivatives were chemoselectively transferred by these groups with a 1,4-triazole linker.     

Physicochemical characterisation of residual hemicelluloses isolated with cyanamide-activated hydrogen peroxide from organosolv pre-treated wheat straw

Seven residual hemicellulosic preparations (19.6-45.0% of the original hemicelluloses) were extracted from wheat straw pre-treated with various organic solvents using 1.8% H2O2-0.18% cyanamide at 50 degrees C and pH 10.0 for 4 h. Their chemical compositions and physicochemical properties were determined using GC, HPLC, GPC, FT-IR and 13NMR spectroscopy. The results indicated that all the residual hemicellulosic preparations were heteropolysaccharides containing xylose, glucose, arabinose, galactose, mannose, rhamnose and 4-O-methyl-alpha-D-glucopyranosyluronic acid. The predominant monosaccharide was xylose, ranging between 67.7% and 81.9% of the total neutral sugars, composed mainly of L-arabino-(4-O-methyl-D-glucurono)-D-xylan. The content of contaminant lignin in the isolated residual hemicelluloses was 2.89-5.31%. The Mw values of the two residual hemicellulosic preparations H6 and H7 (42,710 and 44,080 g mol-1, respectively) obtained from the aqueous-alcohol pre-treated straw were much higher than those of H1-H5 (12,980-15,950 g mol-1) extracted from the organic acid pre-treated straw.     

A new method of controlled grafting modification of chitosan via nitroxide-mediated polymerization using chitosan-TEMPO macroinitiator

The controlled graft modification of chitosan has first been achieved by nitroxide-mediated polymerization using chitosan-TEMPO macroinitiator. Chitosan-TEMPO macroinitiator was obtained from the (60)Co gamma-ray irradiation of N-phthaloylchitosan and 4-hydroxy-TEMPO in DMF under argon atmosphere. The graft copolymers were characterized by (1)H nuclear magnetic resonance ((1)H NMR), Fourier transform infrared spectrometer (FT-IR), X-ray powder diffractometer (XRD) and high performance particle sizer (HPPS). The results indicate that the graft copolymers were successfully synthesized and that the graft polymerization was well controlled by the nitroxide-mediated process. The size distribution of chitosan-g-polystyrene in benzene is very narrow, which may be associated with the "well-defined" polystyrene (PSt) onto chitosan from nitroxide-mediated polymerization. This work provides a new method to prepare chitosan grafting copolymers with controlled molecular weights and "well-defined" structures.     

Preparation of N-vanillyl chitosan and 4-hydroxybenzyl chitosan and their physico-mechanical, optical, barrier, and antimicrobial properties

Chitosan derivatives such as N-vanillyl chitosan and 4-hydroxybenzyl chitosan were prepared by reacting chitosan with 4-hydroxy-3-methoxybenzaldehyde (vanillin) and 4-hydroxybenzaldehyde. Amino groups on chitosan reacts with these aldehydes to form a Schiff base intermediate, which is later on converted into N-alkyl chitosans by reduction with sodium cyanoborohydride. The chemical reaction was monitored by ¹H NMR spectroscopy and the absence of aldehydic proton at 9.83 ppm in NMR spectra was observed for both the modified chitosan derivatives confirming the reaction. Modified chitosan films were later prepared by solution casting method and their physico-mechanical, barrier, optical and thermal properties were studied. The results clearly indicated significant change in tensile strength, water vapour transmission rate, and haze properties of modified chitosans. Modified chitosan films were also studied for their antimicrobial activity against Aspergillus flavus. The results showed a marked reduction of aflatoxins produced by the fungus in the presence of the N-vanillyl chitosan and 4-hydroxybenzyl chitosan film discs to 98.9% and non-detectable levels, respectively.     

Isolation and structural characterization of a neutral polysaccharide from the stems of Dendrobium densiflorum

A novel neutral heteropolysaccharide (DDP-1-D) was purified from hot water extracts of dried stem of Dendrobium densiflorum by DEAE-52 and Sephacryl S-200 High-Resolution Chromatography. The heteropolysaccharide had an average molecular weight about 9440 Da. It was composed mainly of glucose and mannose in the ratio of 3.01:1. Structural features of DDP-1-D were elucidated by a combination of chemical and instrumental techniques, including FT-IR, GC-MS, periodate oxidation-Smith degradation, (1)H and (13)C NMR spectroscopies (including COSY, TOCSY, HSQC, and HMBC spectra). The results indicated that DDP-1-D is a mannoglucan and has a backbone consisting of (1→4)-linked α-D-Glcp, (1→6)-linked α-D-Glcp, (1→2)-linked α-D-Manp and (1→4)-linked β-Manp. This is the first study to provide clear evidence for the structure of the polysaccharide in D. densiflorum.     

Sequential nuclear magnetic resonance assignment of beta-1,2-linked mannooligosaccharides isolated from the phosphomannan of the pathogenic yeast Candida albicans NIH B-792 strain.

The H-1 and H-2 signals of beta-1,2-linked mannooligosaccharides isolated from the phosphomannan of Candida albicans NIH B-792 strain by mild acid hydrolysis were assigned by a sequential NMR assignment method that combines two-dimensional 1H-1H correlated spectroscopy (COSY) and two-dimensional nuclear Overhauser enhancement and exchange spectroscopy (NOESY). The results indicated that the H-1 and H-2 of each beta-1,2-linked mannopyranose unit show largely different signals compared with those of the alpha-linked ones and that the correlation between linkages and signals could not be explained by a conventional additivity rule. Furthermore, a regular proportional downfield shift of the H-1 signal was observed in the order of the mannose unit from the reducing terminal except those of the reducing and nonreducing terminal positions. Although the 1H NMR spectra of these oligosaccharides were complicated due to the presence of a large portion of the beta-anomer from the reducing terminal mannose unit, reduction of the oligosaccharides with NaBH4 to the corresponding alcohols gave simple and more readily interpretable 1H NMR spectra. Unexpectedly, however, a shift of H-1 signals by this reduction occurred not only on the second mannose unit but also on the third and fourth mannose units from the modified reducing terminal group of each oligosaccharide alcohol. This result indicates that the reducing terminal mannose unit is able to affect up to the fourth mannose unit from the reducing terminal. The presence of a long-distance interresidue NOE also suggests that the beta-1,2-linked mannooligosaccharides have a compactly folded conformation in solution.     

Synthesis and characterisation of chitosan-graft-poly(OEGMA) copolymers prepared by ATRP

Two synthetic routes, “grafting-from” and “grafting-to” the chitosan backbone, were investigated to prepare chitosan-graft-poly(OEGMA) copolymers by ATRP. The copolymers were characterised by ¹H NMR and FT-IR spectroscopy, elemental analyses and GPC. Estimates of the degree of grafting were quantitatively found from integration of the ¹H NMR spectra. The GPC data indicated that the hydrodynamic volumes of the polymers were significantly altered by the incorporation of poly(OEGMA). A comparison of the two synthetic methods showed differences in the ratio of synthetic and natural polymers present in the resulting combs. The “grafting-to” synthetic route was preferable as the polymers were of higher purity and more defined.     

New exopolysaccharides produced by Aureobasidium pullulans grown on glucosamine

The polysaccharides produced by Aureobasidium pullulans, grown using glucosamine as the carbon source, were investigated by means of methylation analysis, affinity chromatography and NMR spectroscopy. The results indicated that, besides a small amount of pullulan, this micro-organism was capable of producing-in low yields-mixtures of at least two different complex polysaccharides containing mainly mannose and galactose. (1)H NMR spectra of two fractions obtained by lectin affinity chromatography indicated that one polymer was constituted exclusively of mannose residues while the other contained both galactofuranosyl and mannopyranosyl residues.