Quinone cross-linked polysaccharide hybrid fiber

The present article describes the synthesis of the N-(Lys-Gly-Tyr-Gly)-chitosan using the water-soluble active ester method, the preparation of the N-(Lys-Gly-Tyr-Gly)-chitosan-gellan hybrid fibers, and the reinforcement of the hybrid fibers by enzymatic cross-linking between the N-grafted peptides chains of chitosan. The cationic polysaccharide chitosan was treated with Boc-Lys(Z)-Gly-Tyr(Bzl)-Gly (4-hydroxyphenyl)dimethylsulfonium methyl sulfate ester in DMF-0.15 M acetic acid to incorporate the peptides into the side chain amino groups of chitosan followed by the acidic removals of the Z and Bzl groups. The degrees of N substitution were estimated to be 2.0 and 10 molar % by changing the molar ratios of the amino groups of the parent chitosan and the active ester. The resulting cationic N-(Lys-Gly-Tyr-Gly)-chitosan was spun into the hybrid fibers with the anionic polysaccharide gellan in water. The tensile strengths of the N-(Lys-Gly-Tyr-Gly)-chitosan hybrid fibers were superior to those of the original chitosan-gellan fibers. The mechanical strengths of the hybrid fibers further increased upon enzymatic oxidation using tyrosinase. Based on these results, we concluded that the covalent cross-linking due to the enzyme oxidation between the grafted peptides significantly contributed to reinforcement of the polysaccharide hybrid fibers. The present results afford a new methodology for the reinforcement achieved by the polymer modification inspired by a biological process.     

tert-Butyldimethylsilyl O-protected chitosan and chitooligosaccharides: useful precursors for N-modifications in common organic solvents

An efficient and chemoselective procedure for preparing highly organosoluble 3,6-di-O-tert-butyldimethylsilyl (TBDMS)-chitosan and chitooligosaccharides is reported. The selective modification of the chitooligosaccharides with 0.50 degree of N-acetylation was achieved by using TBDMSCl as the reagent in combination with DMF/imidazole. These protocols yielded partly TBDMS-substituted chitooligosaccharides that were subsequently reacted with TBDMSOTf in dichloromethane in order to silylate the remaining, more sterically hindered hydroxyl groups. In the case of the chitosan polymer, a mesylate salt of chitosan was silylated using TBDMSCl in DMSO, yielding full silylation of the hydroxyl groups without using N-protection groups. The silyl-protected polymers displayed excellent solubility in a number of common organic solvents. The 3,6-di-O-TBDMS-chitosan and chitooligosaccharides were reacted with acetic anhydride, and deprotected to obtain the corresponding N-acetyl derivatives (chitin and chitinoligosaccharide). Our results show that the readily prepared 3,6-di-O-TBDMS-chitosan and chitooligosaccharides are useful precursors for selective N-modifications in common organic solvents.     

Synthesis and antifungal properties of sulfanilamide derivatives of chitosan

Sulfanilamide derivatives of chitosan (2-(4-acetamido-2-sulfanimide)-chitosan (HSACS, LSACS), 2-(4-acetamido-2-sulfanimide)-6-sulfo-chitosan (HSACSS, LSACSS) and 2-(4-acetamido-2-sulfanimide)-6-carboxymethyl-chitosan (HSACMCS, LSACMCS)) were prepared using different molecular weights of chitosan (CS), carboxymethyl chitosan (CMCS) and chitosan sulfates (CSS) reacted with 4-acetamidobenzene sulfonyl chloride in dimethylsulfoxide solution. The structures of the derivatives were characterized by FT-IR spectroscopy and elemental analysis, which showed that the substitution degree of sulfanilamide group of HSACS, HSACSS, HSACMCS, LSACS, LSACSS and LSACMCS were 0.623, 0.492, 0.515, 0.576, 0.463 and 0.477, respectively. The solubility of the derivatives (pH<7.5) was higher than that of chitosan (pH<6.5). The antifungal activities of the derivatives against Aiternaria solani and Phomopsis asparagi were evaluated based on the method of Jasso et al. in the experiment. The results indicated that all the prepared sulfanilamide derivatives had a significant inhibiting effect on the investigated fungi in the polymer concentration range from 50 to 500 microg mL(-1). The antifungal activities of the derivatives increased with increasing the molecular weight, concentration or the substitution degree. The sulfanilamide derivatives of CS, CMCS and CSS show stronger antifungal activities than CS, CMCS and CSS.     

Synthesis of organosoluble chitosan derivatives with polyphenolic side chains

A one-pot synthesis was used to produce chitosan derivatives with polyphenolic side chains via a regioselective phenolic coupling reaction. Under Mannich reaction conditions, treatment of chitosan with formaldehyde and methyl 2,4-dihydroxybenzoate gave N-(2,6-dihydroxy-3-methoxycarbonylphenyl)methylated chitosan in good yield (87%). Formation of a CC bond occurred regioselectively at the C(3) position of methyl 2,4-dihydroxybenzoate. Chitosan derivatives having various phenolic compounds as a side chain were easily synthesized in a similar manner. The chitosan derivatives showed good biodegradability and improved their solubility in methanol (9.8mgmL(-1)) and 2-methoxyethanol (> 10mgmL(-1)). The UV protection provided by the derivatives with phenolic benzophenone side chain was evaluated using UV spectra of polyethylene terephthalate and poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) films coated with the derivatives and the derivatives absorbed effectively in the UV-A region (<60%). Self-aggregation of the chitosan derivatives with the phenolic side chain was observed by using a fluorescent probe in aqueous solution.     

N-2′-Acetoxybenzoyl derivatives of chitosan, N-desulphated heparin and 2-amino-2-deoxy-d-glucose

N-2′-Acetoxybenzoyl (aspirin) derivatives (degree of substitution 0·35–1·00) of chitosan, N-desulphated heparin and 2-amino-2-deoxy-d-glucose were prepared by methods that gave yields in the range 65–86%. The salicylate of chitosan was isolated with a 98% yeild. Aspirin or salicylic acid was released much more slowly from N-(2′-acetoxybenzoyl)-chitosan than from the salicylate of chitosan, and much faster at 37°C in 0·1 m NaOH solution than in 2% aqueous acetic acid solution. Salicylic acid was isolated from the dialysate (0·1 m NaOH solution) of N-(2′-acetoxybenzoyl)-chitosan.     

Optimum conditions for lipase immobilization on chitosan-coated Fe3O4 nanoparticles

Magnetic Fe₃O₄-chitosan nanoparticles are prepared by the coagulation of an aqueous solution of chitosan with Fe₃O₄ nanoparticles. The characterization of Fe₃O₄-chitosan is analyzed by FTIR, FESEM, and SQUID magnetometry. The Fe₃O₄-chitosan nanoparticles are used for the covalent immobilization of lipase from Candida rugosa using N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) as coupling agents. The response surface methodology (RSM) was employed to search the optimal immobilization conditions and understand the significance of the factors affecting the immobilized lipase activity. Based on the ridge max analysis, the optimum immobilization conditions were immobilization time 2.14 h, pH 6.37, and enzyme/support ratio 0.73 (w/w); the highest activity obtained was 20 U/g Fe₃O₄-chitosan. After twenty repeated uses, the immobilized lipase retains over 83% of its original activity. The immobilized lipase shows better operational stability, including wider thermal and pH ranges, and remains stable after 13 days of storage at 25 °C.     

Palladium adsorbing properties of UV-curable chitosan derivatives and surface analysis of chitosan-containing paint

The results of X-ray photoelectron spectroscopy (XPS) analyses indicated that palladium chloride was adsorbed on a plastic surface coated with a chitosan-containing paint (C-Paint), and was completely reduced to Pd(0) after reduction with dimethylamine-borane. To improve the stability and hardening properties of C-Paint, UV-curable chitosan derivatives, such as N-[3-methoxy-4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]methylated chitosan and N-(3-methoxy-4-methacryloyloxyphenyl)methylated chitosan, were synthesized. The derivatives showed better affinity for organic solvents. After UV irradiation for 20s, an acidic solution of these derivatives was transformed to a gel, and the dried films exhibited good palladium(II) adsorption at pH 1.1.     

Comparison in antioxidant action between α-chitosan and β-chitosan at a wide range of molecular weight and chitosan concentration

Antioxidant activity in α- and β-chitosan at a wide range of molecular weight (Mw) and chitosan concentration (CS) was determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, reducing ability, chelating ability, and hydroxyl radical scavenging activity. The form of chitosan (FC) had significant (P <0.05) effect on all measurements except DPPH radical scavenging activity, and antioxidant activity was dependent on Mw and CS. High Mw (280–300 kDa) of β-chitosan had extremely lower half maximal effective concentrations (EC₅₀) than α-chitosan in DPPH radical scavenging activity and reducing ability. The 22–30 kDa of α- and β-chitosan showed significantly (P <0.05) higher activities in DPPH radical scavenging, reducing ability, and hydroxyl radical scavenging than samples at other Mw, while chelating ability was the highest in 4–5 kDa chitosan. CS had significant effect on all measurements and the effect was related to Mw. The antioxidant activity of 280–300 kDa chitosan was affected by coil-overlap concentrations (C¹) in the CS range of 4–10 mg/mL, forming entanglements. Reducing ability and hydroxyl radical scavenging activity were more predominant action in antioxidant activity of chitosan as shown by the lower EC₅₀ values than those in other antioxidant measurements.     

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.     

N-(2-Carboxyethyl)chitosans: regioselective synthesis,characterisation and protolytic equilibria

N-(2-Carboxyethyl)chitosans were obtained by reaction of low molecular weight chitosan with a low degree of acetylation and 3-halopropionic acids under mild alkaline media (pH 8-9, NaHCO3) at 60 degrees C. The chemical structure of the derivatives obtained was determined by 1H and 13C NMR spectroscopies. It was found that alkylation of chitosan by 3-halopropionic acids proceeds exclusively at the amino groups. The products obtained are described in terms of their degrees of carboxyethylation and ratio of mono-, di-substitution and free amine content. The protonation constants of amino and carboxylate groups of a series of N-(2-carboxyethyl)chitosans were determined by pH-titration at ionic strength 0.1 M KNO3 and 25 degrees C.     

Enterovirus 71 adsorption on metal ion-composite chitosan beads

In this study, we developed composite chitosan beads combining various metal ions, including Ni(2+), Cu(2+), Zn(2+), and Fe(2+), for direct adsorption of enterovirus 71 (EV71). The metal-ion species had significant effects on the adsorption capacity of beads. Among these metal ion-composite chitosan beads, Ni(2+)-chitosan beads exhibited the best adsorption capacity of EV71. Using a concentration of 0.01-M Ni(2+) was found to best provide for bead formation and EV71 adsorption. The adsorption of EV71 for Ni(2+)-chitosan beads at neutral or alkaline pH was favored. Under a competitive condition with albumin proteins, Ni(2+)-chitosan beads exhibited significant capacity of EV71 adsorption in culture media. The adsorption of EV71 on the Ni(2+)-chitosan beads was attributed to the strong binding between Ni(2+) ions chelated to the surface amino acid of EV71 capsids and Ni(2+) ions chelated on the chitosan materials. Moreover, the adsorbed EV71 retained its antigenicity and infectivity after desorption. The Ni(2+)-chitosan beads exhibit a promising application to EV71 adsorption and removal.     

Synthesis and property of chitosan graft copolymer by RAFT polymerization with tosylic acid-chitosan complex

pH- and thermo-sensitive (1→4)-2-amino-2-deoxy-β-d-glucan (i.e. chitosan) graft copolymer was prepared by reversible addition fragmentation chain transfer polymerizations of N-isopropylacrylamide with 4-methylbenzenesulfonic acid (i.e. tosylic acid)-chitosan complex. The polymerization was controlled well, and the amino group of chitosan could be deprotected easily and mildly with 15% Tris solution. The model aldehyde vanillin was conjugated with amino group of chitosan-g-PNIPAM via Schiff base bond (Loading efficiency, LE=77.6 mg/g), and the drug release could be controlled with temperature and pH. This property may promote the chitosan graft copolymer to be used in the field of "smart" drug delivery.     

In vitro antifungal activity of metal complexes of a quaternized chitosan derivative with copper ions

Antifungal activity of synthetic metal complexes of quaternized N-(propyl) chitosan derivatives with Сu(II) against yeastlike (Saccharomyces cereviseae, Rodothorula rubra, and Candida albicans) and mycelial fungi (Fusarium oxysporum, Alternaria alternata, Cladosporium herbarum) was studied. In vitro application (at 250?500 μg/mL) of the metal complex of quaternized N-(propyl) derivative of low-molecular chitosan with 53% substitution and 1.3% copper ions proved efficient against F. оxysporum, one of ten most common fungal plant pathogens. Water-soluble quaternized N-(propyl) chitosan derivatives with 40?58% degree of substitution were synthesized using glycidyltrimethylammonium chloride under optimally adjusted conditions. Metal complexes of the chitosan derivative with 53% degree of substitution with Сu(II) ions were obtained by dialysis. The quantity of copper ions in the metal complexes was determined by atomic emission spectrometry. The structure of chitosan derivatives was confirmed by spectral analysis (IR, ¹H NMR).     

Preparation and graft copolymerisation of thiolated β-chitin and chitosan derivatives

β-Chitin was extracted from squid pens and deacetylated to β-chitosan. Both polymers were treated with tosyl chloride, potassium thioacetate and sodium methoxide to form 6-mercaptochitin and 6-mercaptochitosan, respectively. The degrees of substitution were lower for the chitosan derivatives and both types of polymer were less substituted than related polymers prepared from α-chitin. The thiolated polymers were reacted with MMA to form grafted copolymers. The solvent had an influence on the success of the polymerisation with the chitosan polymers giving highly grafted materials in aqueous acetic acid solution.     

The contribution of acidulant to the antibacterial activity of acid soluble α- and β-chitosan solutions and their films

This study evaluated individual contributions of dissolving acids (acetic acid, lactic acid, and hydrochloric acid) or acid solubilized chitosan to the antibacterial activity against Listeria innocua and Escherichia coli as solutions and dried films. Solutions containing chitosan showed significantly (P?<?0.05) different inhibitory activity (measured as percentage of inhibition (PI), in percent) against L. innocua and E. coli, compared to equivalent acid solutions. This increase was calculated as additional inhibition (AI, in percent), which could be as high as 65 % in solutions containing 300–320 kDa chitosan depending on the acid type, bacterial species, and the chitosan form (α or β). Solutions containing 4–5 kDa chitosan had lower AI and showed much greater variability among the different chitosan forms, acid types, and bacterial species. Higher molecular weight (Mw) chitosan also showed significantly higher levels of adsorption to bacterial cells than that of lower Mw samples, suggesting that the observed increase in inhibition was the result of surface phenomena. The contribution of acids to the antibacterial activity of chitosan films was assessed by comparing non-rinsed and rinsed films (rinsed in the appropriate broth to remove residual acids and active fragments formed on the dried film). Rinsing β-chitosan films has reduced PI by as much as 28 % compared with non-rinsed films, indicating that part of the antibacterial activity of chitosan films is due to the presence of soluble acid compounds and/or other active fragments. Overall, both acidulant and chitosan were found to contribute to the antibacterial activity of acid solubilized α- and β-chitosan, with the exact antibacterial activity of chitosan varying based on the solution and film properties, suggesting a complex interaction.     

Synthesis of UV-curable chitosan derivatives and palladium (II) adsorption behavior on their UV-exposed films

Novel chitosan derivatives with UV-curable functional groups, such as 3-methoxy-4-(2-hydroxy-3-methacryloyloxypropoxy)benzyl, 3,4-bis(2-hydroxy-3-methacryloyloxypropoxy)benzyl, 3-methoxy-4-methacryloyloxybenzyl, and 3,5-dimethacryloyloxybenzyl groups, were prepared. Introduction of photosensitive functional groups to chitosan was accomplished by reductive N-alkylation via Schiff’s bases using corresponding photosensitive aldehydes. Compared to starting chitosan, UV-curable chitosan derivatives showed better solubility in several organic solvents, such as DMSO and 70% methacrylic acid. The solubility of these compounds increased with an increase in the degree of substitution of the N-alkyl side chains. After UV irradiation for 20 s under a high-pressure mercury lamp at a distance of 15 cm from the samples, acidic methanol solutions of these derivatives were transformed to gels in the presence of photo-initiator, and their dried films adsorbed palladium (II) at pH 1.1 and pH 5.3. The UV-curable chitosan derivatives were successfully used as coating materials for electroless plating on non-conductive substances.     

Incorporation of chemoselective functionalities into peptoids via solid-phase submonomer synthesis

A simple route to the introduction of a number of chemoselective functional groups into peptoids (oligo(N-substituted glycines)) by an extension of the standard solid-phase submonomer method is reported. The following groups were introduced: aminooxyacetamide, N-(carbamoylmethyl)acetohydrazide, mercaptoacetamide, 2-pyridinesulfenylmercaptoacetamide, and aldehyde-terminated peptoids. The method uses commercially available reagents, is fully compatible with standard peptoid submonomer synthesis conditions, is easily automated, and generates the desired functionalized peptoid in high yield and purity. Peptoids with suitable pairs of chemoselective ligation groups were joined in high yield.     

Immunomodulating activity of chitosan derivatives with salicylic acid and its fragments

A study of biological activity of the derivatives of the chitin-chitosan oligomer with salicylic acid and its fragments showed that chitosan salicylate actively protected potato tubers against Phytophthora infestans but sharply inhibited reparation of potato tissues. N-(2-hydroxybenzyl)chitosan exhibited good protective properties but did not influence wound reparation. N-(2-hydroxy-3-methoxybenzyl)-N-pyridoxchitosan, which contained the pyridoxal and 2-hydroxy-3-methoxy fragments, was the most efficient, stimulating both defense against late blight and wound reparation in potato tissues.     

Superoxide anion scavenging activity of graft chitosan derivatives

Two kinds of graft chitosan derivatives (CMCTS-g-MAS and HPCTS-g-MAS) were prepared by the graft copolymerization of maleic acid sodium onto etherified chitosans-carboxymethyl chitosan (CMCTS) and hydroxypropyl chitosan (HPCTS), respectively. Superoxide anion scavenging activity of the derivatives was evaluated in a luminal-enhanced autoxidaton of pyrogallol by chemiluminescence techniques. Compared with chitosan, the graft chitosan derivatives have much improved scavenging ability against superoxide anion. They have similar 50% inhibition concentrations (IC₅₀s) as ascorbic acid and superoxide dismutase (SOD). Graft chitosan derivatives with hydroxypropyl groups have relatively higher superoxide anion scavenging ability owing to the incorporation of hydroxyl groups. The graft chitosan derivatives (HPCTS-g-MAS 1, 2, and 3) with different grafting percentages exhibit IC₅₀s values ranging from 243 to 308 μg/mL, which could be related to the contents of active hydroxyl and amino groups in the polymer chains.     

Preparation, characterization and antifungal properties of 2-(α-arylamino phosphonate)-chitosan

In this paper, 20 kinds of different 2-(α-arylamino phosphonate)-chitosan (2-α-AAPCS) were prepared by different Schiff bases of chitosan (CS) reacted with di-alkyl phosphite in benzene solution. The structures of the derivatives (2-α-AAPCS) were characterized by FT-IR spectroscopy and elemental analysis. In addition, the antifungal activities of the derivatives against four kinds of fungi were evaluated in the experiment. The results indicated that all the prepared 2-α-AAPCS had a significant inhibiting effect on the investigated fungi when the derivatives concentration ranged from 50 to 500 μg mL⁻¹. Furthermore, the antifungal activities of the derivatives increased with increasing the molecular weight and concentration. And the antifungal activities of the derivatives were affected by their dimensional effect and charge density. Besides, the rule and mechanism of the antifungal activities of them were discussed in this paper.