Atomic hydrophobicity constants

A convenient way of estimating the lipophilicity of a ligand consists in using the lipophilicity increments n determined by Hansch for various structural fragments and groups of atoms (39—41). The hydrophobic constant nx for a substituent X is given by the following relation ... 

The software program SMILOGP for the calculation of logP is based on the Broto-Moreau-Vandycke hydrophobic constants and the SMILES notation for the recognition of molecule atom-centred fragments [Convard etal, 1994]. 

A set of 120 atom types was proposed. The corresponding hydrophobic constants were evaluated by multivariate regression analysis using a training set of 893 compounds, = 0.856 and s = 0.496. This approach is actually called the ALOGP method [Viswanadhan et al, 1993], and a similar approach was also proposed for - molar refractivity. As in the Broto-Moreau-Vandycke approach, correction factors are avoided, while hydrogen atoms are considered instead. 

A set of 130 atom/fragment hydrophobic constants was evaluated, together with 235 correction factors. 

Thus, in the series of Ti measurements of 2-octanol (42, Fig. 2.27) for the methyl group at the hydrophobic end of the molecule, the signal intensity passes through zero at Tq = 3.8 s. From this, using equation 10, a spin-lattice relaxation time of Ti = 5.5 s can be calculated. A complete relaxation of this methyl C atom requires about five times longer (more than 30 s) than is shown in the last experiment of the series (Fig. 2.27) Tj itself is the time constant for an exponential increase, in other words, after T/ the difference between the observed signal intensity and its final value is still 1/e of the final amplitude. 

FIG. 1 Critical micelle concentration as a function of the number of carbon atoms in the hydrophobic rest of sodium a-sulfo fatty acid methyl esters. Methods O, surface tension +, conductivity A, solubilization of a dye x, solubility (all without electrolyte) , surface tension with a constant electrolyte concentration of 5 x 10"2 mol/L. (From Ref. 57.)... 

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