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 determin ed values to give a set of 76 values. Excluding one value for benzamide, th e log P-eh values are correlated through our general solvation equation, lo g P-eh = 0.336 - 0.075R(2) - 1.201 pi(2)(H) - 3.786 Sigma alpha(2)(H) - 2.2 01 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 d ipolarity/polarizability, Sigma alpha(2)(H) and Sigma beta(2)(H) are the ov erall hydrogen bond acidity and basicity, and V-x is the McGowan volume. Th e log P-eh equation has then been used to obtain descriptors for eleven pep tides, all of which are end-protected. It is shown that for these end-prote cted peptides, hydrogen bond basicity makes a greater contribution to log P -eh than does hydrogen bond acidity.