Rong Huei Chen

EFFECT OF TEMPERATURE ON THE INTRINSIC VISCOSITY AND CONFORMATION OF CHITOSANS IN DILUTE HCL SOLUTION

The effects of temperature on the intrinsic viscosity and on the conformation of chitosans in dilute HCI solution were studied. Ten chitosans with the same degree of deacetylation but different molecular weights were produced by alkali deacetylation of chitin which was prepared from red shrimp wastes. The degree of deacetylation at 83% and weight average molecular weight of the chitosans ranging 78-914 kDa were determined by infrared spectroscopy and static light scattering, respectively. The intrinsic viscosities ([eta]) of these 10 chitosans in 0.01 M hydrochloric acid were measured at 10, 20, 30, 40, and 50 degrees C. Then, d ln [eta]/d(l/T) and the Mark-Houwink exponents were calculated as the indices for chain flexibility and molecule conformation, respectively. These results showed: the intrinsic viscosities decreased linearly with increasing temperature, therefore, a temperature-induced conformational transition did not occur for all 10 different molecular weight chitosans in the temperature range studied. Values of d In [eta]/d(l/T) were between 633 and 1334 and increased with decreasing molecular weight, indicating that higher molecular weight chitosans are more flexible. Between 10 degrees and 50 degrees C, the Mark-Houwink exponents ranged 0.64-0.76 and increased with increasing temperature, indicating that the conformation of these chitosans were all in random coil, and a temperature-induced conformational transition did not occur. The a* and a** Mark-Houwink exponents represent those chitosans whose molecular weights are larger and smaller than 223 kDa, respectively, and were obtained by using 223 kDa as the break point in the double logarithmic plots of the intrinsic viscosities and weight average molecular weight. Values of a** were between 0.41 and 0.54, while the a* values were from 0.96 to 1.07. These values for a** and a* indicate that larger and smaller molecular weight chitosans were in random coil and rod shape, respectively.

Relationships between the chain flexibilities of chitosan molecules and the physical properties of their casted films

Abstract Relationships between the chain flexibilities of chitosan molecules in solutions and the physical properties (gel swelling index, maximum melting temperature, and tensile strength) of their casted films were studied in order to manipulate the conditions to tailor the physical properties of the films made. The chain flexibilities of chitosan molecules in solutions were manipulated by using chitosans with different degrees of deacetylation (DD), pH and ionic strength of the media, and solvent systems. The results show the gel swelling index was independent of the media pH, and decreased with increasing DD of chitosans used, whereas maximum melting temperature and tensile strength increased with the increase of DD of the chitosan molecules. The differences were attributed to different crystalline regions in the films.

In vitro antioxidant activities of low-molecular-weight polysaccharides with various functional groups.

The objectives of this study were to evaluate the effect of different functional groups of sulfate, amine, and hydroxyl and/or their ionized groups on in vitro antioxidant capacities of low-molecular-weight polysaccharides (LMPS) prepared from agar (LMAG), chitosan (LMCH), and starch (LMST), respectively, and to elucidate their structure-activity relationship. Ascorbic acid and ethylenediaminetetraacetic acid (EDTA) were used as positive controls. The in vitro antioxidant capacities of LMAG and LMCH were higher than that of LMST in the DPPH radical, superoxide radical, hydrogen peroxide, and nitric oxide radical scavenging and ferrous metal-chelating capacities. The different scavenging capacities may be due to the combined effects of the different sizes of the electron-cloud density and the different accessibility between free radical and LMPS, which, in turn, depends upon the different hydrophobicities of the constituent sugars.

Effects of chain flexibility of chitosan molecules on the preparation, physical, and release characteristics of the prepared capsule

Abstract The effects of chain flexibility of chitosan molecules on the preparation, physical, and release characteristics of the prepared capsule were studied. The chain flexibility of chitosan molecules in solution was manipulated by using chitosans with different degrees of deacetylation (DD) (67.9%, 81.3%, 90.5%, 92.2%), different pHs (2.0, 3.0, 4.0), and NaCl concentrations (0, 0.3%). The solutions were then used to encapsulate hemoglobin or dextran by the orifice method to make the capsules. Axial ratios and break strengths were used to characterize the appearance and mechanical properties of the prepared capsules. D. S. C. was employed to measure enthalpies and maximum melting temperatures to be used as a quantitative index of hydrogen bond formation in the walls of the capsules. Release rate was used as a pore size indicator. The results show axial ratios of the capsules increased with a decrease in molecular weight and also with an increase in DD of chitosan used. Axial ratios also increased when 0.3% NaCl was added to the solutions used. The effects of solution pH show that capsules prepared from pH 3.0 solutions were smaller than those from pH 2.0 and/or pH 4.0 solutions. Capsules of lower break strengths had higher axial ratios. The enthalpies of the chitosan capsules increased with increasing DD of chitosans used, and also with increasing NaCl concentration in the solutions used. However the maximum melting temperatures showed no linear relationship with the DDs of chitosan used. Maximum melting point temperatures of capsules also increased with an increase in NaCl concentrations in solutions used. The hemoglobin and dextran release percentages from the capsule at 25 °C for 24 h increased with an increase of DD of chitosan used. The release rate also increased with the addition of NaCl in the chitosan solution used. The release percentages of capsules prepared from pH 4.0 solutions were higher than those from pH 2.0 and/or pH 3.0 solutions. Release percentages of dextran of different molecular weights from capsules of 81.3% DD chitosan and pH 3 solutions were 52.7% for 19600 Da dextran, 26.3% for 87000 Da dextran and 12.4% for 162000 Da dextran.

Effects of ionic strength and pH on the diffusion coefficients and conformation of chitosans molecule in solution

The effects of ionic strength and pH on the diffusion coefficients and gross conformation of chitosan molecules in solution were studied. Chitosan with 83% degree of deacetylation (DD) was prepared from red shrimp (Solemocera prominenitis) processing waste. Ten different molecular weight chitosans were prepared by ultrasonic degradation, and their molecular weights were determined by static light scattering. The weight-average molecular weight (Mw) were between 78 to 914 kilo dalton (KDa). Solution of different ionic strengths (I = 0.01, 0.10, and 0.20) but the same pH (2.18) and different pHs (2.37, 3.10, and 4.14) but the same ionic strength (I = 0.05) were prepared to measure their mutual diffusion coefficient (Dm). The diffusion coefficients for standard condition (D20,w) were derived from Dm. Intrinsic viscosities ([η]) were determined by a capillary viscometer in different pH solutions. The Mark–Houwink exponents a and e were obtained from plots of Log [η] and Log D20,w versus Log Mw, respectively. The results show that diffusion coefficients increased with increasing ionic strength or with increasing pH or with decreasing Mw. Value of e and a were between 0.503 to 0.571 and ranged from 0.543 to 0.632, respectively. The results indicates that chitosans conformation were in random coil in solutions in the ranges of ionic strength and pH studied. The values of a*, e* and a**, e**, Mark–Houwink exponents of smaller and higher than 223 KDa chitosans, respectively, were between 0.752 to 0.988 and 0.585 to 0.777 for smaller Mw chitosans and 0.406 to 0.428 and 0.430 to 0.518 for larger Mw chitosans, respectively. Molecular-weight-induced conformational transition occurred because smaller Mw chitosans was more extended than higher Mw chitosans.

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.

Effect of preparation method and characteristics of chitosan on the mechanical and release properties of the prepared capsule

The objective of this study is to elucidate the effect of preparation method and the characteristics of chitosan used on the mechanical and release properties of the prepared capsule. The characteristics of the chitosan explored include molecular weight (1.8, 5.6, 20.2, and 31.8 × 105 Dalton) and chain flexibility parameter (B), which was manipulated by a varying degree of deacetylation (DD, 67.9, 81.3, 90.5, and 92.2%), and sodium chloride concentration (0 or 0.3%). The orifice method was used to encapsulate hemoglobin, whereas complex coacervation was used to encapsulate the bovine serum albumin (BSA). The axial ratio was measured to characterize the appearance of the capsule. Break strength was used as an index of mechanical strength. Release percent of protein was used as a pore size indicator. The results show axial ratio and hemoglobin release percent of the capsule prepared by the orifice method increased with the increase of the chain flexibility parameter (B), but decreased with the increase of the chitosan molecular weight. However, break force behaved just opposite from that of the axial ratio and release percent of hemoglobin. The capsule cannot be prepared from 92.2% DD chitosan. Break strength and BSA release percent of the capsule prepared by complex coacervation did not vary with different DD, molecular weight of chitosan, and sodium chloride concentration.

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.

Urea‐induced conformational changes of chitosan molecules and the shift of break point of Mark–Houwink equation by increasing urea concentration

Chitosan solutions of the same 83% degree of deacetylation (DD) but different weight average molecular weights (Mws) (78–914 kDa) in 0.01M HCl containing different concentrations of urea (0–6M) were prepared. Intrinsic viscosity ([η]) and weight average molecular weight (Mw) of chitosan were measured with a capillary viscometer and light scattering, respectively. Mark–Houwink exponent a was used as the parameter of conformational index. The Mark–Houwink exponent a increased with increasing concentrations of urea. When solutions contained 0, 2, 3, 4, and 6M urea, the value of a increased from 0.715 to 0.839, 0.894, 1.000, and 1.060, respectively. This indicates the occurrence of urea-induced conformational transitions of chitosans. The break point shifted from 223 kDa in solutions containing no urea to 280 kDa in 2M urea solutions, to 362 kDa in 4M urea solutions and further to 481 kDa in 6M urea solutions.

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.