Extensive quantum chemical calculations have been carried out to investigate the thermochemical properties as well as IR vibrational frequencies of different 1,4-benzodiapazine derivatives, namely, lorazepam, temazepam and oxazepam. Indeed, the obtained theoretical results clarified the interpretation of biological stabilities of these compounds. In order to evaluate and suggest the optimum method and basis set, all considered calculations have been carried out at three different levels of RHF, B3LYP and SVWN theories using 3-21G, 6-311G and 6-311++G** basis sets . In each case, we were focused on finding the optimal quantum chemical model through either fitting these theoretical data with experimental measurements or comparing amongst theoretical data. For IR frequency calculations, the absence of imaginary frequencies indicated the stationary points correspond to minima on the potential energy surfaces. In addition, the thermochemical parameters including thermal energy, entropy, Gibbs free energy and entropy of compounds have been computed and based on these obtained data the structural stabilities of these drugs have been discussed. However, in a series of drugs presented here the natural bond orbital (NBO) analysis has been performed which seemed quite informative to show some important atomic and structural features. This article is expected to be used for general bioinformatics researchers interested in drug design and will also provide update information to those who have been actively pursuing this field of research.
Key words: 1, 4-Benzodiapazine, IR frequency, thermochemical parameters, natural bond orbital (NBO), ab initio.
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