Fletcher–Powell minimization of analytical potentiometric data by microcomputer: application to the Cu(II) complexes of biological polyamines

Abstract

The Fletcher–Powell minimization algorithm has been successfully implemented for the extraction of metal complex stability constants from analytical potentiometric data. The procedure has been adapted to run on a microcomputer with acceptable execution times, and several strategies are employed to speed convergence and avoid false minima. This allows economical minimization for a large number of models of speciation, and improves the reliability of the proposed best fit by encouraging the checking of more models than previously possible. The Ni(II)–glycine system has been analyzed and excellent agreement with the stability constants of an earlier multi-laboratory study has been attained. The system proves useful in the evaluation of both analytical and computational methods. The procedure has also been used for speciation analysis of the Cu(II) complexes of the growth regulating polyamines, spermine, and spermidine. Both systems form fully deprotonated complexes at physiological pH, which are relevant to their biological activity.