THE EFFECT OF TEMPERATURE AND SOLVENT ENVIRONMENT ON THE CONFORMATIONAL STABILITY OF 11-CIS RETINAL
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Date
1975
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Publisher
Ohio State University
Abstract
The effect of temperature and solvent environment on the relative stability of the distorted 12-s-cis and distorted 12-s-trans conformers of 11-cis retinal is analysed using an approximate solvent effect theory. The formalism includes the partitioning of the salvation energy into van der Waals’, electrostatic and cavity formation terms and the use of multiple linear regression techniques to obtain information about the molecular characteristics of the solute conformers. The 12-s-trans con-former is observed to have a cavity radius 0.02 {\AA} larger, and a dipole moment at least 0.2 D larger, than those of the 12-s-cis conformer. The free apace energies of the two conformers differ by only 0.6 Kcal/mole with the 12-S-cis the more stable. In hydrocarbon solvent at room temperature, the ratio of 12-s-cis to 12-s-trans conformer is roughly two to one, hut increasing solvent polarity or decreasing solution temperature will increase the population of 12-a-trans conformer by increasing the importance of the electrostatic term at the expense of the cavity formation term. The former term favors population of the conformer with the Larger dipole moment (12-s-trans) whereas the latter term favors population of the conformer with the smaller cavity size (12-s-cis). The van der Waals’ term is relatively insensitive to solute conformational changes and is of negligible importance in determining solute conformational stability.
Description
Author Institution: Department of Chemistry, Harvard University