D－葡萄糖、D－果糖与Ca^（2＋）、Mg^（2＋）、Cu^（2＋）、Zn^（2＋）、Cd^（2＋）反应的热力学函数

Determination of the Thermodynamic Functions of the Reactions of D-Glucose and D-Fructose with Ca￣(2+),Mg￣(2+),Cu￣(2+),Zn￣(2+)and Cd￣(2+)

Ｄ－葡萄糖、Ｄ－果糖与Ｃａ^（２＋）、Ｍｇ^（２＋）、Ｃｕ^（２＋）、Ｚｎ^（２＋）、Ｃｄ^（２＋）反应的热力学函数张保林（南京大学配位化学研究所，配位化学国家重点实验室，南京，２１０００８）王文清，陶祖贻（北京大学技术物理系，北京）（兰州大学现代物理系?..

The thermodynamic functions of the reactions of D-glucose and D-fructose with Ca2+,Mg2+,Cu2+,Zn2+,and Cd2+ were determined by titration calorimetry combined with computer fit program,respectively.The results show the following :(1) The stable constants of the metallic-fructose complexes are greater than those of corresponding glucose complexes.(2) The entropy of the system decreases during the formation of the complexes except for Ca2+.(3) Enthalpy and entropy changes for fructose or glucose-Ca2+complexes formation are considerably different from the corresponding hexose-Mg2+. The results are explained on the basis of the hexose structure and the metal ion radii. Because in aqueous solutions fructose exists mainly in the much more flexible acyclic form,and in this there are three pairs of hydroxyl groups favorably oriented for metal ion complexes formation with the lactol form without bond strain or steric hindrance,than with glucose. As a result, the fructose complexes are generally stable than the glucose complexes. The formation of the complexes results in the loss of rotational freedom for the -CH2OH group, and is reflected in the negative entropy changes. The positive entropy changes for the formation of Ca2+ complexes may results from its larger radius by the facile mutual loss of the water molecules. It is interesting to note that there is considerable difference in thermodynamic behavior between Ca2+ and Mg2+.