QSTR mathematical models for the toxicity of aliphatic carboxylic acids on tetrahymena pyriformis

The present work represents an attempt to improve QSTR models for aquatic toxicity of 3838 aliphatic carboxylic acids tested in the Tetrahymena pyriformis population growth assay, using the topological index ZEP and the following nine main electrotopological and molecular descriptors: acidic dissociation constant, 1-octanol/water partition coefficient, the energy of the lowest unoccupied molecular orbital, acidic dissociation constant, molar refractivity, refraction index, surface tension, polarizability and, electrotopological states. Several different relations between toxicity [loglog(IGC50-1)] and the molecular and topological properties were examined, and a group of multiple linear regression models with high fitness scores were generated.

Influence of certain urinary solutes on acidic dissociation constant of ammonium at 37°C

The acidic dissociation constant (pKa ' ) of ammonium was studied at 37 °C over a physiologic range of ionic strength. It was demonstrated that certain ions commonly found in high concentration in urine had no discernible effect on the pka' other than that resulting from their contribution to ionic strength. Urea in a concentration of 0.5 moles/l. had no significant effect on pka '. The data are taken to indicate that in urines of usual composition, ammonium pka ' should closely follow the predictions of Debye-Hückel theory. Submitted on June 19, 1959