Hydrogen bonding. 47. Characterization of the ethylene glycol-heptane partition system: Hydrogen bond acidity and basicity of peptides

Twelve measured ethylene glycol-heptane partition coefficients, P(eh), have been combined with 20 measured literature values and 44 indirectly determined values to give a set of 76 values. Excluding one value for benzamide, the log P(eh) values are correlated through our general solvation equation, log P(eh) = 0.336 - 0.075R(2) - 1.201 pi(2)(H) - 3.786 Sigma alpha(2)(H) - 2.201 Sigma beta(2)(H) + 2.085 V(x) with r(2) = 0.966, sd = 0.28, and F = 386. The solute descriptor R(2) is the excess molar refraction, pi(2)(H) is the dipolarity/polarizability, Sigma alpha(2)(H) and Sigma beta(2)(H) are the overall hydrogen bond acidity and basicity, and V(x) is the McGowan volume. The log P(eh) equation has then been used to obtain descriptors for eleven peptides, all of which are end-protected. It is shown that for these end-protected peptides, hydrogen bond basicity makes a greater contribution to log P(eh) than does hydrogen bond acidity.