Spectrophotometric study of the charge transfer complexation of some amino acid derivative drugs as electron donors with 7,7,8,8-tetracyanoquinodimethane

Abstract

Charge transfer (CT) complexes of some drugs of amino acid derivatives, such as carbocysteine, aminobutyric acid, and levodopa, as electron donors with 7,7,8,8-tetracyanoquinodimethane (TCNQ) as electron acceptor have been studied. The spectra obtained for carbocysteine/TCNQ, aminobutyric acid/TCNQ, and levodopa/TCNQ systems show the maximum absorption bands at wavelengths of 422, 415, and 417 nm, respectively. The formation of such complexes was also confirmed by infrared measurements. The stoichiometry of the complexes was found to be 1:1 between the donor and the acceptor. The possible reaction mechanisms were explored. The thermodynamic standard reaction quantities of the complexes between donors and acceptor were estimated. Different variables affecting the reaction were carefully studied and optimized. At the optimum reaction conditions, Beer’s law was obeyed in a concentration limit of 1–30, 1–10, and 2–50 µg mL^-1 for carbocysteine, aminobutyric acid, and levodopa, respectively. The limits of detection ranged from 0.3 to 0.8 µg mL^-1. The developed methods could be applied successfully for the determination of the studied compounds in their pharmaceutical dosage forms with a good precision and accuracy compared to official and reported methods as revealed by t- and F-tests.

KEY WORDS: Amino acid derivative, Drug, 7,7,8,8-Tetracyanoquinodimethane (TCNQ), Charge transfer complex, Spectrophotometry

Bull. Chem. Soc. Ethiop. 2010, 24(1), 21-30.