Ab initio- and density-functional studies of conformational behaviour of N-formylmethionine in gaseous phase

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AbstractThe current work is a study of the conformational space of the non-ionic N-formylmethionine molecule around its seven structurally significant internal backbone torsional angles at B3LYP/6-31++G(d,p) levels of theory in the gaseous phase. The potential energy surface exploration reveals that a total of 432 different conformers would result if all the possible combinations of the internal rotations were to be considered. A set of twelve conformers of the N-formylmethionine molecule are then further analysed in terms of their relative stabilities, theoretically predicted harmonic vibrational frequencies, HOMO-LUMO energy gaps, ESP charges, rotational constants and dipole moments calculated using MP2/6-31++G(d,p) and B3LYP/6-311++G(d,p) levels. The calculated relative energy-range of the conformers at the MP2 level is 11.08 kcal mol−1 (1 kcal = 4.1868 kJ), whereas the same obtained at the B3LYP level is 10.02 kcal mol−1. The results of this study provide a good account of the role of four types of intramolecular H-bonds, namely O…H—O, O…H—N, O…H—C and N…H—C, in influencing the energies of the conformers as well as their conformational and vibrational spectroscopic aspects. The relative stability order of the conformers appears to depend on the level of theory used while the vibrational frequencies calculated at the B3LYP level are in better agreement with the experimental values.