Partition Coefficient Estimation

Minimization calculations can also be used to obtain estimates of the partition coefficients of a set of solutes between two solvents. After you have set up other parameters for a multiple minimization, including a primary solvent, select LogP estimation in the Comparison tab and choose the secondary solvent from the Secondary solvent menu.

Each molecule in the input file is minimized twice, once in each solvent. The results of each minimization are used to evaluate the free energy difference for the two solvents. Hence the logarithm of the partition coefficient, log P_solv1,solv2 is defined by the relationship

where P_solv1,solv2 = [Solute]_solv1 / [Solute]_solv2, ΔG_solvN is the free energy of solvation of the molecule in solvent N, R is the gas constant, and T is the temperature in kelvin. The results are collected in a table at the end of the log file and are added as properties to the output structure file.

The solvation models are parametrized for ambient conditions. If the temperature deviates significantly from these conditions the solvation energy estimates and hence the calculated log P_solv1,solv2 become less reliable.