Regression equations steric effects

To verify such a steric effect a quantitative structure-property relationship study (QSPR) on a series of distinct solute-selector pairs, namely various DNB-amino acid/quinine carbamate CSPpairs with different carbamate residues (Rso) and distinct amino acid residues (Rsa), has been set up [59], To provide a quantitative measure of the effect of the steric bulkiness on the separation factors within this solute-selector series, a-values were correlated by multiple linear and nonlinear regression analysis with the Taft s steric parameter Es that represents a quantitative estimation of the steric bulkiness of a substituent (Note s,sa indicates the independent variable describing the bulkiness of the amino acid residue and i s.so that of the carbamate residue). For example, the steric bulkiness increases in the order methyl < ethyl < n-propyl < n-butyl < i-propyl < cyclohexyl < -butyl < iec.-butyl < t-butyl < 1-adamantyl < phenyl < trityl and simultaneously, the s drops from -1.24 to -6.03. In other words, the smaller the Es, the more bulky is the substituent. The obtained QSPR equation reads as follows ... 

Our objective in this work is to present surveys of the methods now available for the quantitative treatment of steric effects in the design of bioactive molecules. Commonly, this consists in the modification of a lead compound by structural changes which result in a set of bioactive substances. The bioactivity is determined and then related to structure. This is generally carried out by means of multiple linear regression analysis using a correlation equation of the type... 

This strongly supports the assumption of pore diffusion being a limiting factor for sulfonamides with a MW of > 300. The activity, on the other hand, depends only on the steric influence of the o-substituents of the 5-sulfanilamido-l-phenylpyrazoles. The regression coefficient with MR0 in the two derived equations is constant in both systems and accounts for the negative steric effect of the o-substituents for the interaction with the active site at the synthase. 

X, and the molecule, R, (e.g., polar and steric effects). The validity of equation 19 in empirically correlating the observed rate constants with the polar and steric parameters is determined by the independence of the parameters. It can be shown that o does not correlate with Eg to any significant degree. Regression of a on Eg (10) gives the following equation... 

Quantitative structure-activity relationships QSAR. The QSAR approach pioneered by Hansch and co-workers relates biological data of congeneric structures to physical properties such as hydrophobicity, electronic, and steric effects using linear regression techniques to estimate the relative importance of each of those effects contributing to the biological effect. The molecular descriptors used can be 1-D or 3-D (3D-QSAR). A statistically sound QSAR regression equation can be used for lead optimization. 

Pyridines substituted at the ortho position by bulky substituents fall below the regression line. These deviations A AG have been attributed mainly to steric effects. Indeed, they are well correlated by the steric upsilon (u) parameter of the substituent (Equation 4.34) ... 

The analysis, in composite over the four classes of L-aspartyl dipeptides suggests that the electron-withdrawing effect of substituents directed to the peptide bond, and the steric dimensions of the molecules, are important in eliciting the sweet taste. The values of the regression coefficients of the a term in the QSAR equations for L-aspartic acid amides, L-aspartylaminoethylesters, and L-aspartylaminopropionates all... 

If electronics effects do not fully predict the activity of the compounds in Table 12.5, then perhaps sterics will. Performing a regression on 7 -values affords Equation 12.21. 

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