Spectrophotometric Determination and Thermodynamic Parameters of Charge Transfer Complexation Between Stavudine and Chloranilic Acid

Wo Obonga,Eo Omeje,Pf Uzor,Mo Ugwu

doi:10.4314/tjpr.v10i6.16

Abstract

Purpose: The official assay methods for most antiretroviral drugs are limited by cost and unavailability of good test equipment in several developing countries. Therefore, this study investigates the use of charge transfer complexation in the spectrophotometric assay of stavudine as an alternative method to conventional methods. Methods: Charge transfer complex formation between stavudine (n-donor) and chloranilic acid (Π-acceptor) in 1,4-dioxan using a spectrophotometer was employed. Thermodynamic parameters of the complex formed were determined. The proposed method was employed in the analysis of commercially available stavudine dosage form. Results: The wavelength of maximum absorption (λmax) of the complex was at 526 nm compared to 457 nm for p-acceptor alone. Beer’s law was obeyed in the range of 5 - 40 mg % while the stoichiometry of the complex was found to be 2:1. The complex formed was still stable 24 h later. Its formation was spontaneous with a ΔHo of -3.78×103 J/mol. The standard entropy change was from 12.18 ± 0.78 to 11.08 ± 1.23 cal/deg/mol over the temperature range of 30 - 60 o C while molar absorptivity decreased from 2.45×105 to 1.2×105 over the same temperature range. The assay result of the standard stavudine solution was of high accuracy with a recovery value of 99.85 ± 1.95 %. Conclusion: The proposed method is reliable and reproducible and should be suitable for the quality control of stavudine in bulk and dosage forms. Keywords: Assay, Charge transfer, Stavudine, Spectrophotometric analysis, Chloranilic acid, Thermodynamic.

Highlights

Molecular interactions between electron donors and electron acceptors are generally associated with the formation of intensely colored charge-transfer complexes, which absorb radiation in the visible region [1]
Charge transfer complexes are formed between electron donors having sufficiently low ionization potential, and electron acceptors having sufficiently high electron affinity
Instantaneous purple color was obtained on reaction of the yellow chloranilic acid solution with the solution of the stavudine in methanol

Summary

Introduction

Molecular interactions between electron donors and electron acceptors are generally associated with the formation of intensely colored charge-transfer complexes, which absorb radiation in the visible region [1]. Chloranilic acid and a variety of other electron-accepting compounds have been reported to yield charge-transfer complexes leading to their utility in the development of simple and convenient spectrophotometric methods for the analysis of many drugs [3,4,5,6,7,8]. Such a complexation reaction is usually simple, fast, reproducible and reliable.

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Conclusion