THERMODYNAMIC STUDIES ON THE CHARGE-TRANSFER COMPLEX BETWEEN AMITRIPTYLINE AND CHLORANILIC ACID

Abstract

Spectrophotometric technique was employed to investigate thermodynamic parameters associated with the interaction between amitriptyline and chloranilic acid in non-aqueous medium. The molecular complex produced a purple colour with absorption maximum at 520 nm and was stable over 9 h. The equilibrium constant, K_e^AD, at 298^oK and 333^oK were generally low, i.e. 0.2304 and 0.3896 respectively; there was slight increases as the temperature was elevated. The enthalpy change (ΔH) and entropy change (ΔS) of interaction were respectively –1.21 ± RSD 0.96% KJ mol^-1 and –0.029 ± RSD 0.026% KJ mol^-1. The apparent free energy change (ΔG) was similarly low, i.e. –3.6378 KJ mol^-1 at 298^oK and –2.6102 KJ mol^-1 at 333^oK. A gradual decrease in ΔG was similarly observed as the temperature was increased suggesting that the complexation was exothermic. Comparison of the K_e^AD values with literature data indicate that these values are lower by a factor of 10³ while ΔG decreased by a factor of between 5 and 6. These values clearly indicate the influence of stereochemistry of amitriptyline on the complexation reaction. The molar absorbtivity and Sandell's sensitivity for the complex were 4666 l mol^-1 cm^-1 and 18 ng/ml respectively.


KEY WORDS: Amitriptyline , chloranilic acid, thermodynamic parameters


Global Jnl Pure & Applied Sciences Vol.10(1) 2004: 147-153