Chen R H, Tsaih M L
Department of Marine Food Science, National Taiwan Ocean University, Keelung.
Int J Biol Macromol. 1998 Aug;23(2):135-41. doi: 10.1016/s0141-8130(98)00036-1.
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.
研究了温度对稀盐酸溶液中壳聚糖特性粘度和构象的影响。通过对由红虾废弃物制备的甲壳素进行碱脱乙酰化反应，制备了10种脱乙酰度相同但分子量不同的壳聚糖。分别采用红外光谱法和静态光散射法测定了壳聚糖的脱乙酰度（83%）和重均分子量（78 - 914 kDa）。在10、20、30、40和50℃下，测定了这10种壳聚糖在0.01 M盐酸中的特性粘度([η])。然后，分别计算d ln [η]/d(1/T)和Mark-Houwink指数，作为链柔性和分子构象的指标。结果表明：特性粘度随温度升高呈线性下降，因此，在所研究的温度范围内，10种不同分子量的壳聚糖均未发生温度诱导的构象转变。d In [η]/d(1/T)的值在633至1334之间，且随分子量降低而增大，表明较高分子量的壳聚糖更具柔性。在10℃至50℃之间，Mark-Houwink指数范围为0.64 - 0.76，且随温度升高而增大，表明这些壳聚糖的构象均为无规线团，未发生温度诱导的构象转变。a和a* Mark-Houwink指数分别代表分子量大于和小于223 kDa的壳聚糖，通过在特性粘度和重均分子量的双对数图中以223 kDa为断点获得。a的值在0.41至0.54之间，而a*值在0.96至1.07之间。这些a和a*值表明，分子量较大和较小的壳聚糖分别为无规线团和棒状构象。
