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

Abstract

Twelve measured ethylene glycol-heptane partition coefficients, Peh, 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 Peh values are correlated through our general solvation equation, log Peh = 0.336 - 0.075R2 - 1. 201pi2H - 3.786 Sigmaalpha2H - 2.201 Sigmabeta2H + 2.085Vx with r2 = 0.966, sd = 0.28, and F = 386. The solute descriptor R2 is the excess molar refraction, pi2H is the dipolarity/polarizability, Sigmaalpha2H and Sigmabeta2H are the overall hydrogen bond acidity and basicity, and Vx is the McGowan volume. The log Peh 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 Peh than does hydrogen bond acidity.

Models for Liquid–Liquid Partition in the System Ethylene Glycol–Organic Solvent and Their Use for Estimating Descriptors for Organic Compounds

“…There is good qualitative agreement with the model proposed by Abraham [20] for the n-heptane-ethylene glycol biphasic system as can be seen by comparing Eqs. (1) and (4).…”

“…Plot of partition coefficients taken from[20] against those measured in this work showing a high level of correlation (see text for statistical details)…”

“…(2) having a value of 0 for the data in Table 2 and a value of 1 for the data taken from [20] for which optimized descriptor values were available. This provided the model, .…”

“…The partition coefficients were used to build a correlation model for the permeability coefficient across cell membranes. The above partition coefficients together with some further experimental and estimated values were used by Abraham et al [20] to assign system constants (solvation parameter model) for partitioning in the n-heptane-ethylene glycol system. The model obtained for the partition coefficients, log K p , is: logK p ¼ 0:343ðAE0:066Þ À 1:247ðAE0:112ÞS À 3:807ðAE0:172ÞA À 2:194ðAE0:162ÞB þ 2:065ðAE0:089ÞV ð1Þ…”

The correlation and prediction of the solubility of compounds in water using an amended solvation energy relationship

“…The coefficients in eq 6 are found by multiple linear regression analysis, using a set of solutes for which the descriptors are known. There are numerous applications of eq 6 to physicochemical properties, both by ourselves [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] and by other workers, [48][49][50][51][52][53][54][55][56][57][58][59] so that eq 6 can be regarded as a well-established general equation. Tables 2 and 3 in ref 7.…”