The effect of reaction time and temperature during heterogenous alkali deacetylation on degree of deacetylation and molecular weight of resulting chitosan

The objective of the study is to elucidate the effect of reaction time and temperature during heterogenous alkali reaction on degree of deacetylation (DD) and molecular weight (MW) of the resulting chitosans, and to establish the reaction conditions to obtain desired DD and MW chitosan products. Chitin was extracted from red shrimp process waste. DDs and MWs were determined by infrared spectroscopy (IR) and static light scattering, respectively. The results are as follow: The DD and MW of chitin obtained were 31.9% and 5637 kDa, respectively. The DD of the resulting chitosan increased along with reaction time and/or reaction temperature. The DDs of the resulting chitosan that were obtained from 140°C were higher than those reacted at 99°C. The highest DD of the resulting chitosans after alkali deacetylation at 99 and 140°C were 92.2 and 95.1%, respectively. The DDs of chitosans increased fast at the beginning of reaction process then slowed over time. The reaction rate and rate constant of the deacetylation reaction decreased with increasing DD of the reactant. The MWs of chitosans decreased along with the deacetylation time. MW of those chitosans reacted at 140°C are smaller than those at 99°C. The rate of chitosan degradation was above 43.6%/h in the initial stage, then decreased to about 20%/h. The degradation rate constants raised substantially in the late stage. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2917–2923, 2003     

Effect of N-acetylation on the acidic solution stability and thermal and mechanical properties of membranes prepared from different chain flexibility chitosans

A series of chitosan membranes and their N-acetylated counterparts were prepared and their differences in acidic solution stability and thermal and mechanical properties were studied. The differences were attributed to differences in crystallinity of the membrane as the result of preparation conditions and N-acetylation. The results show that after N-acetylation, the acidic solution stability of N-acetylated membranes increased and the tensile strengths and the enthalpies of those membranes prepared from lower DD chitosans became higher and those from higher DD ones became lower. However, the swelling index of those modified membranes prepared from lower DD chitosans decreased and that from higher DD chitosans increased. Original membranes were prepared by using chitosans with different degrees of deacetylation (DD) and solution pHs to manipulate different chain flexibilities. © 1996 John Wiley & Sons, Inc.     

Effect of the Characters of Chitosans Used and Regeneration Conditions on the Yield and Physicochemical Characteristics of Regenerated Products

The objective of this study was to explore the effect of the character of chitosans used, and the regeneration conditions employed on, the yield and physicochemical characteristics of regenerated products. Different concentrations of acetic acid were used to dissolve chitosans of 61.7% and 94.9% degree of deacetylation (DD), and weight-average molecular weight (Mw) of 176 and 97 kDa, respectively; they were then precipitated with an 8 N NaOH solution, followed by washing and neutral and freeze drying to get the regenerated products. Yields of regenerated products and their physicochemical properties, such as ash content, bulk density, Mw, polydispersity index (PDI), DD, and crystallinity were measured. A higher concentration of acetic acid used resulted in a higher yield. The purity of the regenerated product increased significantly, whereas the bulk density and crystallinity decreased significantly after regeneration. The regeneration process showed its merits of narrowing down the PDI of regenerated products. The DD and structure of chitosan was changed insignificantly after the regeneration process.     

Moisture retention and antibacterial activity of modified chitosan by hydrogen peroxide

A series of chitosans with various molecular weights from 1.2 × 10³ to 30.0 × 10⁴ were prepared by oxidative degradation with H₂O₂ and characterized by IR, ¹³C‐NMR, and gel permeation chromatography. Their carboxylic contents increased with a decrease in molecular weight (M_w). The moisture‐absorption and moisture‐retention capacities of resulting chitosans were dependent on both the molecular weight and the degree of deacetylation (DD). Microcalorimetry was first used to study the kinetics of action of the chitosans on a strain of Staphylococcus aureus at pH 7. The antibacterial activity of the water‐soluble chitosan against S. aureus, Escherichia coli, and Salmonella typhi was evaluated by the conventional agar plate method at pH 7. The water‐soluble product with M_w of 0.45 × 10⁴ from initial chitosan of DD of 90% showed high moisture‐absorption and moisture‐retention capacities, and <2% concentration can completely inhibit the growth of these bacteria. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1724–1730, 2002     

Molecular weight determination of 83% degree of decetylation chitosan with non‐Gaussian and wide range distribution by high‐performance size exclusion chromatography and capillary viscometry

Molecular weight determination of 83% degree of deacetylation (DD) chitosan with non‐Gaussian and broad molecular weight distribution by high‐performance size exclusion chromatography (HPSEC) and by capillary viscometry were proposed. The relationships between weight average retention volumes (RVw) of HPSEC and intrinsic viscosities ([η]) measured by capillary viscometer and the weight average molecular weight (Mw) measured by static light scattering were established for routine molecular weight determination of chitosans either by HPSEC or by the capillary viscometry method, respectively. These results showed: relationships of RVw and Mw for different Mw of 83.0% DD chitosans can be expressed by the equation Log Mw = −0.433 RVw + 11.66. The RVw of other DD chitosans do not correlate well with this equation. It indicated that DD of chitosan affected the relationship of RVw and Mw of chitosans studied. The Mark–Houwink constant a decreased from 0.715 to 0.521, as the solution ionic strength increased from 0.01M to 0.30M, whereas constant k increased from 5.48 × 10⁻⁴ to 2.04 × 10⁻³ over the same range of ionic strength solutions. The established RVw and Mw equation and [η] and Mw equation (Mark–Houwink equation) can be routinely used to determine the molecular weight from RVw or [η] of chitosan by HPSEC or by capillary viscometer, respectively, without the need of expensive instrumentation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1905–1913, 1999     

Aggregation of hydrophobically modified chitosan in solution and at the air–water interface

Oleoyl‐chitosans (O‐chitosans), with three degrees of substitution (DS), were synthesized by reacting chitosan with oleoyl chloride. The chemical structures of these polymers were characterized by ¹H NMR and FTIR. The results suggested the formation of an amide linkage between amino groups of chitosan and carboxyl groups of oleic acid. These O‐chitosans exhibited poor solubility in aqueous acidic solution. The solubility of O‐chitosans decreased as the DS values increased. The transmittance of O‐chitosans (2 g/L) with DS 5%, 11%, 27% in 1% (v/v) HCl solution were 69.5%, 62.7%, 48.6%, respectively. These O‐chitosans were not soluble at neutral or alkali pH. Formation of self‐aggregation was observed using pyrene as a fluorescent probe in the O‐chitosans aqueous solution. The increase of DS of O‐chitosans resulted in significant decrease of critical aggregation concentration (CAC). The CAC of the O‐chitosans with DS 5%, 11%, 27% were 79.43, 31.6, 10 mg/L, respectively. The surface tension of solution could be reduced slightly by all of the O‐chitosans. The surface tension of O‐chitosans solution decreased with the increase of DS values. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1968–1973, 2006     

Effect of degree of deacetylation of chitosan on the kinetics of ultrasonic degradation of chitosan

The objective of the study was to explore the effect of the degree of deacetylation (DD) of the chitosan used on the degradation rate and rate constant during ultrasonic degradation. Chitin was extracted from red shrimp process waste. Four different DD chitosans were prepared from chitin by alkali deacetylation. Those chitosans were degraded by ultrasonic radiation to different molecular weights. Changes of the molecular weight were determined by light scattering, and data of molecular weight changes were used to calculate the degradation rate and rate constant. The results were as follows: The molecular weight of chitosans decreased with an increasing ultrasonication time. The curves of the molecular weight versus the ultrasonication time were broken at 1‐h treatment. The degradation rate and rate constant of sonolysis decreased with an increasing ultrasonication time. This may be because the chances of being attacked by the cavitation energy increased with an increasing molecular weight species and may be because smaller molecular weight species have shorter relaxation times and, thus, can alleviate the sonication stress easier. However, the degradation rate and rate constant of sonolysis increased with an increasing DD of the chitosan used. This may be because the flexibilitier molecules of higher DD chitosans are more susceptible to the shear force of elongation flow generated by the cavitation field or due to the bond energy difference of acetamido and β‐1,4‐glucoside linkage or hydrogen bonds. Breakage of the β‐1,4‐glucoside linkage will result in lower molecular weight and an increasing reaction rate and rate constant. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3526–3531, 2003     

Relationship between molecular structure and moisture‐retention ability of carboxymethyl chitin and chitosan

Carboxymethyl chitins and chitosans (CM‐chitins, CM‐chitosans) of different substitution sites were prepared under different reaction conditions, and partially depolymerized carboxymethyl chitins of various molecular weights from 24.8 × 10⁴ to 0.26 × 10⁴ were obtained by degrading with chemical reagents. Degree of substitution (DS) was estimated by potentiometric titration. Substitution site was confirmed by infrared and ¹³C‐NMR spectra. Molecular weights were determined with gel permeation chromatography and gel permeation chromatography combined with laser light scattering (GPC‐LLS). Moisture‐absorption and retention abilities of these compounds were tested in comparison with those of hyaluronic acid (HA). The results reveal that 6‐carboxymethyl group in the molecular structure of chitin and chitosan is a main active site responsible for moisture retention. Although carboxymethylation at OH‐3 and N position is not essential, they contribute to the ability. Moisture‐retention ability is also related to molecular weight; that is, higher molecular weight helps to improve moisture‐retention ability. 6‐O‐CM‐chitin (chitosan) with a DS above 0.8 and molecular weight higher than 24.8 × 10⁴ has the potential to substitute for HA for use in cosmetics and clinical medicine. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1233–1241, 2002     

Self-aggregation and antibacterial activity of N-acylated chitosan

Chitosan was selectively N-acylated with acetic, propionic and hexanoic anhydrides under homogeneous condition to prepare N-acetyl chitosan (NACS), N-propionyl chitosan (NPCS) and N-hexanoyl chitosan (NHCS), respectively. NACSs with different N-acetylation degrees were obtained by controlling the degree of N-acetylation. The chemical structures of N-acylated chitosans including degree of deacetylation (DD), weight-average molecular weight (M_w), radius of gyration (〈S₂〉_Z^1/2) and crystal structure were studied by FTIR, GPC-LLS and X-ray diffraction techniques. Aggregation behavior of N-acylated chitosan was investigated by rheometer. Intramolecular aggregation of NPCS and NACS was stronger with NPCS stronger than NACS. The effect of concentration of polymer, concentration of salt and temperature on self-aggregation of NACS and NPCS was investigated. Hydrophobic interaction of N-acylated chitosan substituted with longer acyl chains was stronger. With moderate DD, intramolecular aggregation occurs predominantly. In vitro antibacterial activity test of N-acylated chitosans was evaluated against two Gram-positive bacteria and two Gram-negative bacteria. Relative inhibition time (RIT) of NHCS with concentration of 1 mg/ml against Escherichia coli and Pseudomonas aeruginosa was more than 2-6 times longer than that of NACS and NPCS. N-acylated chitosan with lower DD had inhibitory effect on the growth of bacteria than that with moderate DD. The results showed that intermolecular aggregation characteristic of N-acetylated chitosans with low DD may help in forming bridge to interact with bacterial cell.     

Influence of degree of deacetylation on critical concentration of chitosan/dichloroacetic acid liquid‐crystalline solution

We prepared chitosans with various degrees of deacetylation (DDAs) by mixing completely deacetylated chitosan and acetic anhydride at room temperature without serious degradation and O‐substitution. We obtained a standard curve to measure DDA by plotting the IR absorbance ratio of A₁₅₆₀/A₂₈₈₀ against the known DDAs (from 1–100%) of 10 specimens. The effect of DDA on the critical concentration (C*) of chitosan/dichloroacetic acid solutions required to form mesophase was investigated by optical methods. A maximum C* value of 23 wt % appeared at a relative medium DDA (～20%). The effect was explained by the disordering of chains with medium composition ratios of the copolymer of glucosamine and N‐acetyl glucosamine. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1204–1208, 2002     

Preparation and properties of chemical cellulose from ascidian tunic and their regenerated cellulose fibers

Chemical cellulose (dissolving pulp) was prepared from ascidian tunic by modified paper‐pulp process (prehydrolysis with acidic aqueous solution of H₂SO₄, digestion with alkali aqueous solution of NaOH/Na₂S, bleaching with aqueous NaOCl solution, and washing with acetone/water). The α‐ cellulose content and the degree of polymerization (DPw) of the chemical cellulose was about 98 wt % and 918, respectively. The Japanese Industrial Standard (JIS) whiteness of the chemical cellulose was about 98%. From the X‐ray diffraction patterns and ¹³C‐NMR spectrum, it was found that the chemical cellulose obtained here has cellulose Iβ crystal structure. A new regenerated cellulose fiber was prepared from the chemical cellulose by dry–wet spinning using N‐methylmorpholine‐ N‐oxide (NMMO)/water (87/13 wt %) as solvent. The new regenerated cellulose fiber prepared in this study has a higher ratio of wet‐to‐dry strength (<0.97) than commercially regenerated cellulose fibers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1634–1643, 2002.     

Molecular weight effect on antimicrobial activity of chitosan treated cotton fabrics

The effect of the molecular weight of chitosan on antimicrobial activity was investigated using three chitosans of different molecular weights [1800 (water soluble), 100,000, and 210,000] and similar degrees of deacetylation (86–89%). Cotton fabrics were treated with chitosan by the pad–dry–cure method. The molecular weight dependence of the antimicrobial activity of chitosan was more pronounced at a low treatment concentration. Chitosans with molecular weight of 100,000 and 210,000 effectively inhibited Staphylococcus aureus at a 0.5% treatment concentration. Chitosan with a molecular weight of 1800 was effective against S. aureus at a 1.0% treatment concentration. Escherichia coli was effectively inhibited by chitosan with a molecular weight of 210,000 at a 0.3% treatment concentration and by chitosans with a molecular weight of 1800 and 100,000 at a 1.0% treatment concentration. Proteus vulgaris was effectively inhibited by chitosans with molecular weight of 100,000 and 210,000 at a 0.3% treatment concentration and by chitosan with a molecular weight of 1800 at a 0.5% treatment concentration. None of the chitosans significantly inhibited Klebsiella pneumoniae and Pseudomonas aeruginosa below a 1.0% treatment concentration. Chitosans with high molecular weights were more effective in inhibiting bacterial growth than chitosans with low molecular weights. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2495–2501, 2001     

Optimization of the production of chitosan from beet molasses by response surface methodology

Chitosan was produced by Rhizopus oryzae 00.4367 in shake flask culture and a stirred tank fermenter. Synthetic medium, treated and untreated beet molasses were used as cultivation media in shake flask cultures. In the stirred tank fermenter, the cultivation media were synthetic medium and untreated beet molasses. Shake flask culture containing untreated molasses with a sugar concentration of 40 g dm^?3 produced the maximum chitosan yield (961 mg dm^?3). Chitosan concentration reached its maximum value at the late exponential growth phase of R oryzae. In all experiments almost 8–10% of biomass and 32–38% of alkali‐insoluble material was extracted as chitosan. A central composite design was employed to determine the optimum values of process variables (aeration rate, agitation speed and initial sugar concentration) leading to maximum chitosan concentration in the stirred tank fermenter. In all cases, the fit of the model was found to be good. Aeration rate, agitation speed and initial sugar concentration had a strong linear effect on chitosan concentration. Moreover, the concentration of chitosan was significantly influenced by the negative quadratic effects of the given variables and by their positive or negative interactions. A maximum chitosan concentration of 1109.32 mg dm^?3 was obtained in untreated molasses medium containing an initial sugar concentration of 45.37 g dm^?3 with an aeration rate and agitation speed of 2.10 vvm and 338.93 rpm, respectively. Copyright © 2004 Society of Chemical Industry     

Synthesis and rheological behavior of a novel N‐sulfonate ampholyte chitosan

Modified chitosan derivatives with different degrees of substitution varying from 0.17 to 0.96 were synthesized by the heterogeneous reaction of chitosan with 3‐chloro‐2‐hydroxy propanesulfate in a neutral aqueous solution. The modified chitosans with a degree of substitution higher than 0.36 were soluble in water, whatsoever the pH. The structures of the polymers were characterized by Fourier transform infrared and ¹H‐nuclear magnetic resonance spectroscopies. The potentiometric titration revealed that the modified chitosan had an isoelectric point at around pH = 5.7, and its rheological behaviors in aqueous solution were studied under different conditions. The results showed that the modified chitosan had typical polyampholyte characteristics, which exhibited polyelectrolyte effect at pH = 1.7 or 13 and antipolyelectrolyte effect at pH = 8. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Cationic polyelectrolytes from natural building blocks of chitosan and inulin

Novel chitosan-N-inulin graft copolymers with different degree of substitution (DS) of chitosan were synthesized via water-soluble 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide mediated reaction. Chemical structure and composition of the chitosan derivatives was confirmed by chemical analysis, FT-IR, XPS, ¹H and ¹³C NMR spectroscopy, and potentiometry. Chitosan–inulin copolymers were high-molecular-weight hydrophilic products soluble in water in a wide pH range forming extraordinary viscous solutions. Intrinsic viscosity of N-modified chitosans was sharply suppressed by added electrolyte and had tendency to decrease at higher DS of chitosan. pK_α values of the chitosan–inulin copolymers determined from potentiometric titration data using Henderson–Hasselbalch equation were in the range 6–7 slightly increasing at higher DS. Novel water-soluble chitosan copolymers retained cationic properties of chitosan and could be used as surface conditioners.     

低分子量壳聚糖的制备

利用H2O2的强氧化性制备低分子量分布的壳聚糖是将虾皮用HC l浸泡去除碳酸钙盐;再用稀碱除去蛋白质得甲壳素;然后浓碱在50℃与其反应,并控制反应时间,分别制备出脱乙酰度为85%,93%,99%的壳聚糖,最后用H2O2氧化不同脱乙酰化壳聚糖,得到不同低分子量的壳聚糖。其中,脱乙酰度为85%壳聚糖用不同浓度的H2O2降解,得到了4.7×105,3.5×105,2.5×105,1.2×105,8×105等5个不同分子量段的壳聚糖产品。H2O2浓度越大,降解所得壳聚糖的分子量就越小。     

Effects of chitosan characteristics on the physicochemical properties,antibacterial activity,and cytotoxicity of chitosan/2‐glycerophosphate/nanosilver hydrogels

The effects of molecular weight (MW) and the degree of deacetylation (DD) of chitosan (CS) on the physicochemical properties, antibacterial activity, and cytotoxicity of CS/2‐glycerophosphate (GP)/nanosilver hydrogel in the development of a thermosensitive in situ formed wound dressing are examined herein. The gelation temperatures for the hydrogels were measured in the range of 32–37°C by manipulating the MW and DD of CS and the GP concentration. The structure of 88% DD CS hydrogel was more porous, uniform, and connective than that of the 80% DD CS hydrogel. The superior water vapor transmission rates of hydrogels with 80% and 88% DD CS were 7150 ± 52 and 9044 ± 221 gm^?2 d^?1, respectively. The skin permeations of nanosilver by the 80% and 88% DD CS hydrogels were 3.82 and 4.99 μg cm^?2, respectively, in 24 h tests. Both the hydrogels with 6 and 12 ppm nanosilver showed cytotoxicity for HS68 cells. The diameters of the hydrogel's inhibition zones for Pseudomonas aeruginosa and Staphylococcus aureus increased when the concentration of nanosilver increased and the MW of the CS decreased. Therefore, the hydrogel could be prepared with lower MW CS and lower concentration of nanosilver in order to reduce the cytotoxicity of nanosilver, while maintaining similar antibacterial activity for a hydrogel prepared with higher concentration nanosilver and higher MW CS. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Acid hydrolysis of commercial chitosans

Commercial chitosans were subjected to controlled acid hydrolysis and their degrees of deacetylation (DD), molecular size and rheological flow profiles determined (pre‐ and post‐hydrolysis) by ¹H‐NMR spectroscopy, high‐performance size‐exclusion chromatography and rheometry, respectively. Hydrolysis resulted in DD increases between 4 and 11%. Unhydrolysed chitosans had M_w and M_n values in the ranges 700–1200 and 130–210 kDa, respectively. Chitosan with the smallest initial molecular size averages had the smallest averages after hydrolysis; however, a chitosan with an intermediate initial molecular size proved to be most resistant to hydrolysis. Molecular size trends were paralleled by zero shear viscosity (η₀) measurements determined by application of the Williamson model to rheological flow profile data. Viscosity is obviously related to molecular size, but does not necessarily reflect relative ease of hydrolysis, since specific hydrolysis conditions affect structurally similar polysaccharides in different ways (in terms of rate of depolymerisation and de‐N‐acetylation, etc), which are not simply due to differences in molecular size profiles pre‐hydrolysis. Copyright © 2005 Society of Chemical Industry     

Effects of molecular structural parameters of carboxymethyl chitosan on the growth of fibroblasts in vitro

A series of carboxymethyl chitosan samples (CMCHs) with different molecular structural parameters were synthesized to estimate their different influences on the growth of fibroblasts. All the CMCHs stimulated the fibroblasts proliferation and CMCHs with different molecular weight (MW) had the similar effect on fibroblasts proliferation. The least concentration for CMCHs (the degree of deacetylation, DD 70.3–79.9%, the degree of substitution, DS 1.12–1.26) exhibiting acceleratory effect on fibroblasts proliferation was 50 μg mL^?1. As the DD increased from 70.3 to 93.6%, CMCH's ability of stimulating fibroblasts proliferation increased significantly. CMCH possessed much higher proliferation rate with the DS increasing to 2.39. CM40 with 92.4% DD and 2.39 DS had the strongest acceleratory fibroblasts proliferation at the range tested. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

A new approach for the preparation of chitosan from γ‐irradiation of prawn shell: effects of radiation on the characteristics of chitosan

Chitosan is a biodegradable polymer composed of randomly distributed β‐(1,4)‐linked D ‐glucosamine (deacetylated unit) and N‐acetyl‐D ‐glucosamine (acetylated unit). It is produced commercially by deacetylation of chitin, which is the structural element in the exoskeleton of crustaceans (such as crabs and shrimps) and the cell walls of fungi. In the work reported, we developed a facile technique for the preparation of chitosan by irradiating prawn shell at various intensities from 2 to 50 kGy. It was observed that γ‐irradiation of prawn shell increased the degree of deacetylation (DD) of chitin at a relatively low alkali concentration during the deacetylation process. Among the various irradiation doses applied to prawn shell, a dose of 50 kGy and 4 h heating in 50% NaOH solution yielded 84.56% DD while the chitosan obtained from non‐irradiated prawn shell with the same reaction conditions had only 74.70% DD. In order to evaluate the effect of γ‐irradiation on the various physicochemical, thermomechanical and morphological properties, the chitosan samples were again irradiated (2–100 kGy) with γ‐radiation. Molecular weight, DD, thermal properties with differential scanning calorimetry and thermogravimetric analysis, particle morphology by scanning electron microscopy, water binding capacity (WBC), fat binding capacity (FBC) and antimicrobial activity were determined and the effects of various γ‐radiation doses were assessed. The DD, WBC, FBC and antimicrobial activity of the chitosan were found to improve on irradiation. It was obvious that irradiation caused a decrease of molecular weight from 187 128 to 64 972 g mol^?1 after applying a radiation dose of 100 kGy which occurred due to the chain scission of chitosan molecules at glycosidic linkages. The decrease of molecular weight increased the water solubility of the chitosan, the extent of which was explored for biomedical applications. Copyright © 2012 Society of Chemical Industry