Ogawa Etsuyo, Takahashi Rheo, Yajima Hirofumi, Nishinari Katsuyoshi
Showagakuin Junior College, Higashisugano, Ichikawa, Chiba 272-0823, Japan.
Biopolymers. 2005 Nov;79(4):207-17. doi: 10.1002/bip.20349.
Using 5 samples of well-purified Na-gellans (Na-gellans G1-G5, weight-average molar mass M(w) = 120 x 10(3)-32 x 10(3) at 40 degrees C), the effects of molar mass on the coil-to-double-helix transition in aqueous solutions with 25 mM NaCl were studied by light scattering and circular dichroism (CD) measurements, viscometry, and differential scanning calorimetry (DSC). From the temperature dependence of M(w), molar ellipticity at 201 nm [theta]201, intrinsic viscosity [eta], and DSC exothermic curves, it was found that the coil-to-double-helix transitions for G1-G5 samples took place at almost the same temperature. The [eta] and M(w) obtained in the temperature range from 40 to 25 degrees C can be explained by a simple coil/double-helix equilibrium model using the double-helix contents determined from CD data. The van't Hoff's transition enthalpy deltaH(vH) of Na-gellans depended on M(w). It is concluded that the coil-to-double-helix transitions of Na-gellans are all-or-none type transitions, and are accelerated with increasing M(w).
使用5个纯化良好的钠型结冷胶样品（钠型结冷胶G1 - G5，40℃下重均摩尔质量M(w) = 120×10(3) - 32×10(3)），通过光散射、圆二色性（CD）测量、粘度测定和差示扫描量热法（DSC）研究了摩尔质量对含25 mM NaCl水溶液中从单链螺旋到双链螺旋转变的影响。从M(w)、201 nm处的摩尔椭圆率[θ]201、特性粘度[η]以及DSC放热曲线的温度依赖性发现，G1 - G5样品从单链螺旋到双链螺旋的转变几乎在相同温度下发生。在40至25℃温度范围内获得的[η]和M(w)可以通过一个简单的单链螺旋/双链螺旋平衡模型来解释，该模型使用从CD数据确定的双链螺旋含量。钠型结冷胶的范特霍夫转变焓ΔH(vH)取决于M(w)。得出结论，钠型结冷胶从单链螺旋到双链螺旋的转变是全或无型转变，并且随着M(w)的增加而加速。
