Hydrophobicity Parameter—Capacity Factor Relationships of Iodoamino-Acids

The application of hydrophobicity parameters for the prediction of retention of a series of iodoamino acids and related compounds has been examined. On non-polar stationary phases with isocratic elution conditions these compounds exhibit a linear relationship between the logarithm of the octanol-water partition coefficient calculated from hydrophobic fragmental constants and the logarithm of the capacity factor. Using these relationships it is possible to predict the retention characteristics of a homologous compound from a minimum set of k′ measurements , e.g., k′ for diiodothyropropionic acid from diiodo to tetraiodo-thyroacetic acid k′ data. On a μBondapak-C18 column, the reverse iodothyronine isomers have a greater retention than the corresponding normal isomers with the same elution conditions. However, as a series the reverse isomers also follow a linear relationship which allows the influence of proximity effects and aromatic substitution orientation on partition coefficients to be determined.