RESUMO
It is shown that when two different volumes of the second phase are employed in a single dual-phase potentiometric titration, the partition coefficients of the most highly ionized species can be readily calculated by refinement of the parameters for the dual-purpose titration equations. Graphical comparison of the calculated titration curve with that obtained experimentally is helpful in making initial estimates of the parameters.
Assuntos
Ácidos/química , Preparações Farmacêuticas/química , Piridinas/química , Matemática , TitulometriaRESUMO
The potentiometric determination of the partition and distribution coefficients of two dianionic hexapeptide derivatives is described. For each of these compounds, the partition coefficient of the dianion makes the largest contribution to the distribution coefficient at pH 7.4.
Assuntos
Antagonistas dos Receptores de Endotelina , Endotelinas/antagonistas & inibidores , Oligopeptídeos/química , Sequência de Aminoácidos , Concentração de Íons de Hidrogênio , Dados de Sequência Molecular , Octanóis , Potenciometria , SolubilidadeRESUMO
A convenient procedure has been developed for the determination of partition and distribution coefficients. The method involves the potentiometric titration of the compound, first in water and then in a rapidly stirred mixture of water and octanol. An automatic titrator is used, and the data is collected and analyzed by curve fitting on a microcomputer with 64 K of memory. The method is rapid and accurate for compounds with pKa values between 4 and 10. Partition coefficients can be measured for monoprotic and diprotic acids and bases. The partition coefficients of the neutral compound and its ion(s) can be determined by varying the ratio of octanol to water. Distribution coefficients calculated over a wide range of pH values are presented graphically as "distribution profiles". It is shown that subtraction of the titration curve of solvent alone from that of the compound in the solvent offers advantages for pKa determination by curve fitting for compounds of low aqueous solubility.
