Abstract
The distribution behavior of the tetracyclines in the presence of haloacetic acids at acidic conditions has been markedly influenced by the addition of alcohols in organic phase through the solvation of ion pair. The influences of variables, such as pH, anions, temperature on the distribution of tetracyclines into n-hexane containing various alcohols were studied. Stability constants, Kc, for solvated ion pairs and number of alcohol molecules associated with each ion pair, n, were determined. Kc values were highly dependent on the change in substituents of tetracyclines and on the nature of the pairing anions. A linear relationship with unit slope was found between log Kc and that of apparent distribution coefficient of intact tetracyclines. Thermodynamic parameters for ion paired chlortetracycline indicated that alcohol solvation facilitates the distribution processes of ion pair. Both values of Kc and n were influenced by the structural factors of solvating alcohols such as chain length, branching located near the OH group, and cyclic alkyl group. The solvation of alcohol with ion pair was discussed in terms of hydrophobic and hydrogen bonding.
