Thermal Stability and Decomposition Kinetic Studies of Acyclovir and Zidovudine Drug Compounds

Abstract

Investigations on thermal behavior of drug samples such as acyclovir and zidovudine are interesting not only for obtaining stability information for their processing in pharmaceutical industry but also for predicting their shelf lives and suitable storage conditions. The present work describes thermal behaviors and decomposition kinetics of acyclovir and zidovudine in solid state, studied by some thermal analysis techniques including differential scanning calorimetry (DSC) and simultaneous thermogravimetry-differential thermal analysis (TG/DTA). TG analysis revealed that thermal degradation of the acyclovir and zidovudine is started at the temperatures of 400°C and 190°C, respectively. Meanwhile, TG-DTA analysis of acyclovir indicated that this drug melts at about 256°C. However, melting of zidovudine occurred at 142°C, which is 100°C before starting its decomposition (242°C). Different heating rates were applied to study the DSC behavior of drug samples in order to compute their thermokinetic and thermodynamic parameters by non-isothermal kinetic methods. Thermokinetic data showed that both drugs at the room temperature have slow degradation reaction rates and long shelf lives. However, acyclovir is considerably more thermally stable than zidovudine.

Thermal Stability and Kinetic of Decomposition of Mono- and Dicationic Imidazolium-Based Ionic Liquids

“…The entropy (∆S ‡ ), enthalpy (∆H ‡ ) and Gibbs free energy (∆G ‡ ) of activation were calculated using the following equations. 28 (4) (5) (6) In equations 4, 5 and 6, υ = k B T/h (where k B is Boltzmann constant and h is Plank constant), T is the temperature in K, and R is the gas constant in kJ mol -1 . The kinetics and activation data of monocationic and dicationic ILs were obtained in 10 and 50% of activity loss and are presented in Table 2.…”

Role of Metal Oxide Nanomaterials on Thermal Stability of 1,3,6‐Trinitrocarbazole

“…Ta ble 2p ermits comparisono ft he thermodynamic parameters and reveals thatt he value of DS # for the TENT-Al 2 O 3 is higher than pure TENT and TENT-TiO 2 nanocomposite. In otherw ord, the activated complex for the TENT-Al 2 O 3 decomposition reactionh as al ower degree of arrangement than its initial state;w hile TENT-TiO 2 has ar everse trend.T he theory of activated complex or transition theory [32] extrapolated this lower value of DS # for thermal decomposition of TENT-Al 2 O 3 as as low reaction, while the TENT-TiO 2 is ar elative fast reaction. However,t he values of DG # for the decompositions of pure TENT and both energeticn anocomposites arec omparable.M eantime, the valueo fa ctivation enthalpies (DH # )f or the decompositions of pure TENT is considerably lower than TENT-Al 2 O 3 but higher than TENT-TiO 2 .T he calculatedv alues of DG # and DH # for pure TENTand both energeticn anocomposites are positive, which reveal that their decompositionr eactions are dependent to the heat introduced and can be considered as non-spontaneous reactions.…”

“…Reaction rate constants for the decompositiono fp ure TENT and nanocomposites were determined using Equation (1), where the mechanisms of the reactions were assumed to be first-o rder [32]:…”

“…Critical ignition temperature (T b )i sd efined as the lowest temperature for as pecific compound that might be heated without undertaking thermal runaway.D etermination of this parameter is vitalf or the safe handling and storageo f energetic compounds [28,32].T his temperature is predictable based on combustiont heory using the thermokinetic data of the compound, i.e.,activation energy and pre-exponentialfactor obtained by kineticm ethods.…”

Effect of Nanomaterials onThermal Stability of 1,3,6,8-Tetranitro Carbazole

“…This means that the corresponding activated complex for TNC-CNT decomposition has a lower degree of arrangement (higher entropy) than its initial state, while the TNC-Al 2 O 3 material follows an opposite trend. This trend means (according to the theory of activated complex or transition theory [38,39]) that the thermal decomposition of TNC-CNT can be interpreted as a slow reaction, while that for TNC-Al 2 O 3 has a fast reaction rate. On the other hand, the value of ΔG # for the decomposition of pure TNC and its energetic nanocomposites are comparable.…”