POLAR INTERMOLECULAR INTERACTIONS ENCODED IN PARTITION-COEFFICIENTS - AN INDIRECT ESTIMATION OF HYDROGEN-BOND PARAMETERS OF POLYFUNCTIONAL SOLUTES

Lipophilicity (expressed as log P, the logarithm of partition coefficients) is known to be decomposable into a cavity/volume term V expressing mainly hydrophobic and dispersive solute-solvent interactions, and polar terms reflecting electrostatic solute-solvent interactions, e.g. log P = aV + b-pi* + c-alpha + d-beta, where pi*, alpha, and beta are solvatochromic parameters, i.e., the dipolarity/polarizability, H-bond donor acidity, and H-bond acceptor basicity, respectively. Here, we define a parameter LAMBDA such that LAMBDA = b-pi* + c-alpha + d-beta and show that LAMBDA(oct) (i.e., LAMBDA calculated from 1-octanol/water log P values) is correlated mainly with beta (r2 = 0.867; n = 168), while LAMBDA(alk) (i.e., LAMBDA-calculated from alkane/water log P values) is correlated mainly with alpha and beta (r2 = 0.897; n = 104). Thus, and within the explored range of values, a fair estimate of the H-bond donor acidity and acceptor basicity of solutes can be obtained from their log P(oct) and log P(alk) values and calculated molecular volumes.