THERMODYNAMIC STUDIES ON THE CHARGE-TRANSFER COMPLEX BETWEEN AMITRIPTYLINE AND CHLORANILIC ACID
AbstractSpectrophotometric 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, KeAD, at 298oK and 333oK 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 298oK and –2.6102 KJ mol-1 at 333oK. A gradual decrease in ΔG was similarly observed as the temperature was increased suggesting that the complexation was exothermic. Comparison of the KeAD 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