Paradossi G, Cavalieri F, Crescenzi V
Dipartimento di Scienze e Tecnologie Chimiche, Universitá di Roma Tor Vergata, Italy.
Carbohydr Res. 1997 May 9;300(1):77-84. doi: 10.1016/s0008-6215(97)00023-2.
The results of measurements of longitudinal and transverse proton relaxation times for a chemical network obtained by reacting chitosan with oxidized beta-cyclodextrin (beta-cyclodextrin polyaldehyde) are presented. The network was characterized by a 'two-component' transverse relaxation mechanism relative to structurally different environments experienced by water molecules. Different environments were also indicated by the temperature of the spin-spin relaxation times (T2) studied in the range 4-50 degrees C. Between 4 and 18 degrees C, proton exchange between the matrix and water prevails on the inter- and intra-molecular dipolar interactions of the water confined in the meshes of the network, resulting in a marked change in the slope of T2 with temperature. Stiffness of the matrix and reduced mobility of water in the gel meshes are prerequisites for observing such relaxation phenomena. Possible mechanisms contributing to the activation energy in the case of chitosan-cyclodextrin networks are discussed. The behaviour of the chitosan-cyclodextrin hydrogel is compared with that of a gellan gel.
本文给出了壳聚糖与氧化β-环糊精（β-环糊精聚醛）反应得到的化学网络中质子纵向和横向弛豫时间的测量结果。该网络具有“双组分”横向弛豫机制，这与水分子所经历的结构不同的环境有关。自旋-自旋弛豫时间（T2）在4-50℃范围内研究时，不同的环境也通过温度体现出来。在4至18℃之间，基质与水之间的质子交换比网络网格中受限水的分子间和分子内偶极相互作用更为显著，导致T2随温度的斜率发生明显变化。基质的刚性和凝胶网格中水流动性的降低是观察到这种弛豫现象的先决条件。文中讨论了壳聚糖-环糊精网络中可能对活化能有贡献的机制。将壳聚糖-环糊精水凝胶的行为与结冷胶水凝胶的行为进行了比较。
