Partitioning of tryptophan side-chain analogs between water and cyclohexane.
Partitioning of tryptophan side-chain analogs between water and cyclohexane.
复制标题
色氨酸侧链类似物在水和环己烷之间的分配。
DOI：
10.1021/bi00166a015
复制
发表时间：
1992
期刊：
影响因子：
2.9
通讯作者：
White,SH
中科院分区：
文献类型：
--
作者：
Wimley,WC;White,SH
Revised Manuscript Received October 13, 1992 abstract: We have measured the partitioning of the tryptophan side-chain analogs 3-methylindole and JV-methylindole between water and cyclohexane over the temperature range 8-55 C to investigatethe relative contribution of the imine-NH-to the free energy of transfer. We take advantage of the fact that the indole imine nitrogen is blockedby a methyl group in JV-methylindole. Unlike previousstudies, we take into accountthe water present in the cyclohexane phase. Free energies of partitioning were calculated using mole-fraction, volume-fraction, and Flory-Huggins-corrected volume-fraction partition coefficients [De Young, L. R., & Dill, K. A.(1990) J. Phys. Chem. 94, 801-809; Sharp, KA, Nicholls, A., Friedman, R., & Honig, B.(1991) Biochemistry 30, 9686-9697], These approaches account for configurational entropy changes in different ways and thus lead to different values for the calculated free energies of transfer. There is a 2-3-fold difference in the freeenergies calculated from our measurements, using the different units. Independent of units, the partitioning of both compounds involves identical entropy changes. However, 3-methylindole has an additional unfavorable enthalpic contribution to partitioning into cyclohexane of+ 1.6 kcal/mol (independent of units) which is presumably the cost of removing the indole-NH-group from water and transferring it to cyclohexane. In cyclohexane, 3-methylindole forms hydrogen bonds with water that cause water to copartition into cyclohexane with the solute. A method is described which allows the partitioning process to be examined independent of subsequent interactions with water in the solvent.
