Conformational analysis medium effects

The analysis of the parameters representing the effect of the medium in terms of extrathermodynamical relations has shown (see above, section A.2) that the hydrophobic substituent constant it depends on the molecules from which it is derived. For example, hydrophobic constants derived from the octanol/water partition coefficients of aromatic molecules differ from those obtained from aliphatic molecules (112). Collander s equation (111) provides the empirical basis for the evaluation of logP values for the same molecule in different solvents. However, solvents with markedly different solvation properties (e.g., hydrogen bonding ability) do not conform to Collander s equation (see below, section C.3). 

In structural work, the exact conformation may be affected by a combination of intra- and inter-complex interactions such as counterion, medium of recrystallization, hydrogen bonding and steric effects of the particular substituted nucleobase studied [4, 5]. These effects have to be somewhat separated from inherent effects such as the dihedral angles discussed above, although the interplay is complicated. The various parameters have been summarized for bis(purine), bis(pyrimidine) and mixed purine and pyrimidine complexes and for hydrogen bonding patterns. The reader is referred to the references [69—71] for detailed analysis of these points. 

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