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.     

Preparation of polymeric micelles based on chitosan bearing a small amount of highly hydrophobic groups

A method has been developed to obtain micelles based on amphiphilic chitosan derivatives which were synthesized by grafting hydrophobic stearoyl, palmitoyl and octanoyl aliphatic chains onto molecules of chitosan with degrees of substitution from 0.9% to 29.6%. The N-fatty acylations were carried out by reacting carboxylic anhydride with chitosan in dimethyl sulfoxide. The chitosan derivative-based micelles were spherical as observed by transmission electron microscope (TEM). Their sizes were in the range of 140–278 nm as measured by dynamic light scattering (DLS). The micellar critical aggregation concentration (CAC) can reach 1.99 × 10⁻³ mg/mL, indicating that they are more stable upon dilution than micelles based on other chitosan derivatives such as deoxycholic acid-modified chitosan reported previously.     

Synthesis of methylated chitosan containing aromatic moieties: Chemoselectivity and effect on molecular weight

N-Arylated chitosans were synthesized via Schiff bases formed by the reaction between the primary amino group of chitosan with aromatic aldehydes followed by reduction of the Schiff base intermediates with sodium cyanoborohydride. Treatment of chitosan containing N,N-dimethylaminobenzyl and N-pyridylmethyl substituents with iodomethane under basic conditions led to quaternized N-(4-N,N-dimethylaminobenzyl) chitosan and quaternized N-(4-pyridylmethyl) chitosan. Methylation occurred at either N,N-dimethylaminobenzyl and N-pyridylmethyl groups before the residual primary amino groups of chitosan GlcN units were substituted. The total degree of quaternization of each chitosan varied depending on the extent of N-substitution (ES) and the sodium hydroxide concentration used in methylation. Increasing ES increased the total degree of quaternization but reduced attack at the GlcN units. N,N-dimethylation and N-methylation at the primary amino group of chitosan decreased at higher ES’s. Higher total degrees of quaternization and degrees of O-methylation resulted when higher concentrations of sodium hydroxide were used. The molecular weight of chitosan before and after methylation was determined by gel permeation chromatography under mild acidic condition. The methylation of the N,N-dimethylaminobenzyl derivative with iodomethane was accompanied by numerous backbone cleavages and a concomitant reduction in the molecular weight of the methylated product was observed. The antibacterial activity of water-soluble methylated chitosan derivatives was determined using Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria; minimum inhibitory concentrations (MIC) of these derivatives ranged from 32 to 128 μg/mL. The presence of the N,N-dimethylaminobenzyl and N-pyridylmethyl substituents on chitosan backbone after methylation did not enhance the antibacterial activity against S. aureus. However, N-(4-N,N-dimethylaminobenzyl) chitosan with degree of quaternization at the aromatic substituent and the primary amino group of chitosan of 17% and 16–30%, respectively, exhibited a slightly increased antibacterial activity against E. coli.     

A series of novel chitosan derivatives: Synthesis, characterization and micellar solubilization of paclitaxel

A series of novel chitosan derivatives with octyl, sulfate and polyethylene glycol monomethyl ether (mPEG) groups as hydrophobic and hydrophilic moieties, respectively, were synthesized. These PEGylated amphiphilic chitosan derivatives were characterized with ¹H NMR, ¹³C NMR, FTIR and elemental analysis. And their physical properties were measured by wide angle X-ray diffraction (WAXD) and thermogravimetric analysis (TG). The critical micelle concentrations (CMCs) of the modified chitosans determined by using pyrene as a hydrophobic probe in fluorescence spectroscopy were found to be 0.011–0.079 mg/ml, and the log CMC was linearly relative to four structure parameters, that is the degree of substitution (DS) of chitosan unit, sulfate group, PEG unit and octyl group by mole per kilogram. Paclitaxel, a water-insoluble anticancer drug, was solubilized into the polymeric micelles formed by these derivatives utilizing physical entrapment method, with micellar particle size around 100–130 nm, and the highest paclitaxel concentration of 3.94 mg/ml was found in N-mPEG-N-octyl-O-sulfate chitosan (mPEGOSC) micellar solution, which was much higher than that in water (less than 0.001 mg/ml). Therefore, N-mPEG-N-octyl-O-sulfate chitosan micelles may be useful as a prospective carrier for paclitaxel.     

Prolyl endopeptidase inhibitory activity of chitosan sulfates with different degree of deacetylation

Three kinds of partially deacetylated chitosan, 90% deacetylated chitosan, 75% deacetylated chitosan and 50% deacetylated chitosan, were prepared from crab chitin by N-deacetylation with 40% (w/w) sodium hydroxide solution for different durations. In order to improve biological activity and solubility, their sulfated derivatives were prepared, and prolyl endopeptidase (PEP) inhibitory activities were investigated. Fifty percent-deacetylated chitosan sulfate (50-CS) exhibited the highest inhibitory activity, and inhibition rate was a dose-dependant. In addition, Dixon plots suggested that 50-CS was act as competitive inhibitor, and the inhibition constant (K_i) was 2.6 mg/ml.     

Thermal depolymerization of alginate in the solid state

A new method of introduction carboxyl groups to chitosan sulfate by the acylation reaction between hydroxyethyl chitosan sulfates and butane dioic anhydride in homogeneous solution was used to obtain carboxybutyrylated hydroxyethyl chitosan sulfates. The structures of the derivatives were characterized by element analysis, FT-IR, ¹³C-NMR, and gel permeation chromatography. The content and position of the carboxyl groups could be controlled favorably. Their anticoagulant activity was determined for human plasma with respect to activated partial thromboplastin time (APTT), thrombin time (TT), and prothombin time (PT). The introducing of carboxyl groups to amino groups greatly prolonged the APTT and TT. The best result occurred when the degree of substitution of the carboxyl groups was about 0.4/unit that prolonged APTT and TT with about 5 and 1.5 times compared to that of the uncarboxylated hydroxyethyl chitosan sulfates; another conclusion is that introducing of carboxyl groups into N,O-position gave better results than that just into N-positions. Low S% chitosan sulfate and 6-O-desulfated chitosan sulfate showed little anticoagulant activity but their N,O-carboxybutyrylated derivatives (0.6/unit ds) showed increased APTT or TT, while their N-carboxybutyrylated derivatives (0.6/unit ds) gave no improvement. Generally, the introducing of carboxyl groups could not increase PT in spite of the position introduced.     

Quaternization of N-aryl chitosan derivatives: synthesis, characterization, and antibacterial activity

Chemical modification of chitosan by introducing quaternary ammonium moieties into the polymer backbone renders excellent antimicrobial activity to the adducts. In the present study, we have synthesized 17 derivatives of chitosan consisting of a variety of N-aryl substituents bearing either electron-donating or electron-withdrawing groups. Selective N-arylation of chitosan was performed via Schiff bases formed by the reaction between the 2-amino groups of the glucosamine residue of chitosan with aromatic aldehydes under acidic conditions, followed by reduction of the Schiff base intermediates with sodium cyanoborohydride. Each of the derivatives was further quaternized using N-(3-chloro-2-hydroxypropyl)trimethylammonium chloride (Quat-188) as the quaternizing agent that reacted with either the primary amino or hydroxyl groups of the glucosamine residue of chitosan. The resulting quaternized materials were water soluble at neutral pH. Minimum inhibitory concentration (MIC) antimicrobial studies of these materials were carried out on Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria in order to explore the impact of the extent of N-substitution (ES) on their biological activities. At ES less than 10%, the presence of the hydrophobic substituent, such as benzyl and thiophenylmethyl, yielded derivatives with lower MIC values than chitosan Quat-188. Derivatives with higher ES exhibited reduced antibacterial activity due to low quaternary ammonium moiety content. At the same degree of quaternization, all quaternized N-aryl chitosan derivatives bearing either electron-donating or electron-withdrawing substituents did not contribute antibacterial activity relative to chitosan Quat-188. Neither the functional group nor its orientation impacted the MIC values significantly.     

Effect of transglutaminase and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide on the solubility of fish gelatin–chitosan films

The possibility of decreasing the water solubility of the films made from fish gelatin and chitosan by modification with TGase was investigated. The effectiveness of enzymatic treatment was also compared with chemical crosslinking using EDC. The treatment of the components with TGase in concentration of 0.2 mg/ml of the film-forming solution limited the solubility of the films at 25 °C from 65% to 28% at pH 6 and from 96% to 37% at pH 3. After 15 min of heating at 100 °C, the modified films were soluble in 23% at pH 6 and in 41% at pH 3. Further decrease of the solubility of the fish gelatin–chitosan films was achieved when enzymatic modification was conducted in the presence of 5–10 mM DTT; the solubility was about twice lower than that without DTT at both studied temperatures and pH values. Generally, the composite films modified with EDC in concentration of 30 mM were distinctly less soluble than films made from the components modified with TGase in the presence of DTT.     

Chitosan staple fibers and their chemical modification with some aldehydes

Nine wet-spinning conditions were examined for the preparation of chitosan staple fibers, and novel five N-alkylidene and N-arylidene-chitosan staple fibers were obtained by the post-treatment of the chitosan fibers with aldehydes including vanillin. The tenacity and elongation values of the chitosan filaments were almost unchanged by their post-treatment with monoaldehydes except that with formaldehyde and glyoxal. However, these values decreased significantly in the partially N-modified filaments, which were obtained by the pre-treatment with vanillin. The chitosan filaments (31–79 μm in diameter) had a scaly structure on the filament surface as examined by SEM observation.     

TEMPO-mediated oxidation of chitin, regenerated chitin and N-acetylated chitosan

A commercial chitin, regenerated chitin prepared from chitin solutions in 6.8% NaOH and N-acetylated chitosans with degrees of N-acetylation (DNAc) of 77–93% were subjected to oxidization in water with NaClO and catalytic amounts of 2,2,6,6-tetramethylpiperidinyloxy radical (TEMPO) and NaBr. When regenerated chitin with DNAc of 87% and N-acetylated chitosan with DNAc of 93% were used as starting materials, water-soluble β-1,4-linked poly-N-acetylglucosaminuronic acid (chitouronic acid) Na salts with degrees of polymerization of ca. 300 were obtained quantitatively within 70 min. On the other hand, the original chitin and N-acetylated chitosan with DNAc of 77% did not give water-soluble products, owing to incomplete oxidation. The high crystallinity of the original chitin brought about low reactivity, and the high C2-amino group content of the N-acetylated chitosan with DNAc of 77% led to degradations rather than the selective oxidation at the C6 hydroxyls. The obtained chitouronic acid had low viscosities in water, and clear biodegradability by soil microorganisms.     

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.     

Novel super pH-sensitive nanoparticles responsive to tumor extracellular pH

The objective of this study was to evaluate Camptothecin (CAMP)-loaded poly(N-isopropylacrylamide) (NIPAAm)/chitosan nanoparticles as a pH-sensitive carrier for specifically targeting tumors. The synthesis and properties of the system was studied by adjusting the mass ratio of NIPAAm and chitosan. The drug release characteristics of nanoparticles in vitro were investigated. The results showed that when the charge ratio between NIPAAm and chitosan of 4:1 (w/w) was achieved, the drug-loaded nanoparticles were most sensitive to tumor pH. Encapsulation efficiencies and loading were 73.7% and 8.4%, respectively. The cumulative release rate of CAMP was optimal at pH 6.8 and decreased rapidly either below pH 6.5 or above pH 6.9 in 37 °C. Based on MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium) test and fluorescence microscopy results, CAMP-loaded nanoparticles showed cytotoxicity at pH 6.8 but minimal cytotoxicity at pH 7.4. The pH-sensitive poly NIPAAm/chitosan nanoparticles provided some distinct advantages in delivering anti-cancer drugs to targeted tissues.     

Preparation and important functional properties of water-soluble chitosan produced through Maillard reaction

The objective of this research was to improve the solubility of chitosan at neutral or basic pH using the Maillard-type reaction method. To prepare the water-soluble chitosans, various chitosans and saccharides were used under various operating conditions. Biological and physicochemical properties of the chitosan-saccharide derivatives were investigated as well. Results indicated that the solubility of modified chitosan is significantly greater than that of native chitosan, and the chitosan-maltose derivative remained soluble when the pH approached 10. Among chitosan-saccharide derivatives, the solubility of chitosan-fructose derivative was highest at 17.1 g/l. Considering yield, solubility and pH stability, the chitosan-glucosamine derivative was deemed the optimal water-soluble derivative. Compared with the acid-soluble chitosan, the chitosan-glucosamine derivative exhibited high chelating capacity for Zn(2+), Fe(2+) and Cu(2+) ions. Relatively high antibacterial activity against Escherichia coli and Staphylococcus aureus was noted for the chitosan-glucosamine derivative as compared with native chitosan. Results suggest that the water-soluble chitosan produced using the Maillard reaction may be a promising commercial substitute for acid-soluble chitosan.     

Phenylethanolamine N-methyltransferase has beta-carboline 2N-methyltransferase activity: hypothetical relevance to Parkinson's disease

Mammalian brain has a β-carboline 2N-methyltransferase activity that converts β-carbolines, such as norharman and harman, into 2N-methylated β-carbolinium cations, which are structural and functional analogs of the Parkinsonian-inducing toxin 1-methyl-4-phenylpyridinium cation (MPP⁺). The identity and physiological function of this β-carboline 2N-methylation activity was previously unknown. We report pharmacological and biochemical evidence that phenylethanolamine N-methyltransferase (EC 2.1.1.28) has β-carboline 2N-methyltransferase activity. Specifically, purified phenylethanolamine N-methyltransferase (PNMT) catalyzes the 2N-methylation (21.1 pmol/h per unit PNMT) of 9-methylnorharman, but not the 9N-methylation of 2-methylnorharmanium cation. LY134046, a selective inhibitor of phenylethanolamine N-methyltransferase, inhibits (IC₅₀ 1.9 μM) the 2N-methylation of 9-methylnorharman, a substrate for β-carboline 2N-methyltransferase. Substrates of phenylethanolamine N-methyltransferase also inhibit β-carboline 2N-methyltransferase activity in a concentration-dependent manner. β-Carboline 2N-methyltransferase activity (43.7 pmol/h/mg protein) is present in human adrenal medulla, a tissue with high phenylethanolamine N-methyltransferase activity.

We are investigating the potential role of N-methylated β-carbolinium cations in the pathogenesis of idiopathic Parkinson’s disease. Presuming that phenylethanolamine N-methyltransferase activity forms toxic 2N-methylated β-carbolinium cations, we propose a novel hypothesis regarding Parkinson’s disease—a hypothesis that includes a role for phenylethanolamine N-methyltransferase-catalyzed formation of MPP⁺-like 2N-methylated β-carbolinium cations.     

The swelling behavior and network parameters of guar gum/poly(acrylic acid) semi-interpenetrating polymer network hydrogels

Guar gum/poly(acrylic acid) semi-interpenetrating polymer network (IPN) hydrogels have been prepared via free radical polymerization in the presence of a crosslinker of N,N′-methylene bisacrylamide (MBA). The kinetics of swelling and the water transport mechanism were studied as a function of the composition of the hydrogels and the pH of the swelling medium. Hydrogels showed enormous swelling in aqueous medium and displayed swelling characteristics, which were highly dependent on the chemical composition of the hydrogels and pH of the medium in which hydrogels were immersed (ionic strength I = 0.15 mol/L). The semi-INP hydrogels were characterized by evaluating various network parameters such as average molecular weight between crosslinks (M_c) crosslink density (ρ) and mesh size ξ.     

Modified chitosans carrying sulfonic acid groups

The sulfonic acid function was introduced into chitosan by reacting it with 5-formyl-2-furansulfonic acid, sodium salt, under the mild conditions of the Schiff reaction, thus avoiding polymer degradation and O-substitution. The reaction of chitosan (degree of deacetylation 0·58) with 5-formyl-2-furansulfonic acid, sodium salt produced a viscous solution that, upon hydrogenation, yielded N-sulfofurfuryl chitosan sodium salt. Infrared spectrometry, alkalimetry and elemental analysis provided evidence that the degree of substitution was 0·26. Circular dichroism measurements on solutions showed multiple Cotton bands in the pH interval 7·1–8·3, while at lower and higher pH values just one negative band was observed, thus providing indication of the polyampholyte nature of N-sulfofurfuryl chitosan. The ¹³C-NMR and FTIR spectra showed typical signals of furane carbons. Metal ion solutions at concentrations in the range 0·1–5·0 m , pH 6, promoted precipitation of metal ion complexes of N-sulfofurfuryl chitosan, with most effective removal from the solutions for Cu(II), Pb(II) and Ni(II). Sulfoethyl N-carboxymethyl chitosan was also synthesized from 2-chloroethanesulfonic acid in organic media: the sulfur content was similar (3·7%) in both polymers.     

Synthesis and characterization of sugar-bearing chitosan derivatives: aqueous solubility and biodegradability

The extended use of chitosan in biomedical fields has been limited by its insoluble nature in a biological solution. To endow the water solubility in a broad range of pH, chitosan derivatives were prepared by the covalent attachment of a hydrophilic sugar moiety, gluconic acid, through the formation of an amide bond. These sugar-bearing chitosans (SBCs) were further modified by the N-acetylation in an alcoholic aqueous solution. Thereafter, the effect of the gluconyl group and the degree of N-acetylation (DA) on the water solubility at different pHs and on the biodegradability of chitosan were investigated. The SBCs showed the water solubility in a broader range of pH than chitosan, whereas they were still insoluble at neutral and alkali pH. The N-acetylation of SBCs significantly affected the water solubility, for example, the SBCs with the DA, ranging from 29% to 63%, were soluble in the whole range of pH. This might result from the improved hydrophilicity by the gluconyl group, accompanied by the role of the N-acetyl group that disturbed the hydrogen bonding between amino groups of chitosan. From the biodegradation tests, determined by the decrease in the viscosity of a polymer solution exposed to lysozyme, it was evident that the gluconyl group attached to chitosan improved the biodegradability. Thus, it was possible to control the biodegradability of chitosan by adjusting the amounts of gluconyl and N-acetyl groups in the chitosan backbone. The N-acetylated SBCs, soluble in the broad range of pH, might be useful for various biomedical applications.     

Degradation of fully water-soluble, partially N-acetylated chitosans with lysozyme

Chitosans, prepared by homogeneous N-deacetylation of chitin, with degrees of N-acetylation ranging from 4 to 60% (F_A = 0·04 to 0·60) exhibiting full water solubility and known random distribution of acetyl groups, were degraded with lysozyme. Initial degradation rates (r) were determined from plots of the viscosity decrease (Δ1/[η]) against time of degradation. The time course of degradation of chitosans with lysozyme were non-linear, while the time course of degradation of chitosans with an oxidative-reductive depolymerization reaction (using H₂O₂) showed the expected linear relationship for a first-order, random depolymerization reaction, independent of the chemical composition of the chitosan.

The effect of lysozyme concentration and substrate concentration on the initial degradation rates were determined, showing that this lysozyme-chitosan system obeys Michaelis-Menten kinetics.

The initial degradation rates of chitosan with lysozyme increased strongly with increasing fraction of acetylated units (F_A). From a Michaelis-Menten analysis of the degradation data that assumes different catalytic activities of lysozyme for the different hexameric substrates in the polysaccharide chain, it is concluded that the hexameric substrates that contain three-four or more acetylated units contribute mostly to the initial degradation rate when lysozyme degrades partially N-acetylated chitosans.

A chitosan with a very low fraction of acetylated units (F_A = 0·010) was studied as an enzyme inhibitor. Initial degradation rates of chitosan (with different F_A values) decreased as the inhibitor concentration increased, while the relative rates stayed constant, indicating that the ratio between initial reaction rates for productive sites (hexamers containing three-four or more N-acetylated units) are unaffected by non-productive sites, as deduced from the theory of competing substrates.     

Esters and amides of 2,3-dimethoxy-8,9-methylenedioxy-benzo[i]phenanthridine-12-carboxylic acid: potent cytotoxic and topoisomerase I-targeting agents

The exceptional topoisomerase I-targeting activity and antitumor activity of 5-(2-N,N-dimethylamino)ethyl-8,9-dimethoxy-2,3-methylenedioxy-5H-dibenzo[c,h][1,6]naphthyridin-6-one (ARC-111, topovale) prompted studies on similarly substituted benzo[i]phenanthridine-12-carboxylic ester and amide derivatives. Among the benzo[i]phenanthridine-12-carboxylic esters evaluated, the 2-(N,N-dimethylamino)ethyl, 2-(N,N-dimethylamino)-1-methylethyl, and 2-(N,N-dimethylamino)-1,1-dimethylethyl esters possessed similar cytotoxicity, ranging from 30 to 55 nM in RPMI8402 and KB3-1 cells. Several of the carboxamide derivatives possess potent topoisomerase I-targeting activity and cytotoxicity. The 2-(N,N-dimethylamino)ethyl, 2-(N,N-diethylamino)ethyl, and 2-(pyrrolidin-1-yl)ethyl amides were among the more cytotoxic benzo[i]phenanthridine-12-carboxylic derivatives, with IC₅₀ values ranging from 0.4 to 5.0 nM in RPMI8402 and KB3-1 cells.     

Kinetics of tributyrin hydrolysis by lipase

The kinetics for the tributyrin hydrolysis using lipase (Pseudomonas fluorscenes CCRC-17015) were investigated in the liquid–liquid and liquid–solid–liquid reaction systems in a batch reactor. The lipase was covalently immobilized onto the surface of porous polymethylacrylamide (PMAA) crosslinking with N,N-methylene biacrylamide with a spacer of ethylenediamine actived by glutaraldehyde. The conditions such as tributyrin concentration, temperature, agitation, and pH value, were evaluated to achieve the optimum reaction conditions for both free lipase and immobilized lipase. The kinetic parameters in the reaction system were also obtained for two reaction systems. The turnover numbers calculated for free lipase and immobilized lipase were 29 and 5.7 s⁻¹, respectively. The parameters of k and k_m obtained using Lineweaver-Burk plot method were 26.2 mol/(mg min) and 1.35 mol/dm³ for free lipase, 5.2 mol/(mg min) and 0.2 mol/dm³ for immobilized lipase, respectively. The experimental results revealed good thermal stability, with greater stability at higher pH value for immobilized lipase in the liquid–solid–liquid reaction.