title: The effect of electron correlation on the conformational space of melatonin.
abstract: The pineal gland hormone melatonin regulates several physiological processes including circadian rhythm and also alleviates oxidative stress-induced degenerative diseases. In spite of its important biological roles, no high level ab initio conformational study has been conducted to reveal its structural features. In this work, the conformational flexibility of melatonin was investigated using correlated ab initio calculations. Conformers, obtained previously at the Hartree-Fock level (HF/6-31G*), were fully optimized using second order Møller-Plesset perturbation theory applying the frozen core approximation (MP2(FC)/6-31G*). Furthermore, single-point MP4(SDQ,FC)/6-31G*//MP2(FC)/6-31G* computations were performed to investigate the effect of higher order perturbation terms. The HF and MP2 conformational spaces are considerably different: the initial 128 structures converged into 102 different local minima as confirmed by frequency calculations; 28 new minima appeared and 26 previous HF local minima disappeared; no "all-trans" C3 side chain conformations are seen at the MP2(FC) level. The MP2 global minimum conformation is stabilized by an aromatic-side chain interaction.
authors.affiliation: Department of Biomedical Sciences, Creighton University Medical Center, 2500 California Plaza, Omaha, Nebraska 68178, USA.
authors.forename: József
authors.initials: J
authors.lastname: Csontos
authors.forename: Péter
authors.initials: P
authors.lastname: Kálmán
authors.forename: Gyula
authors.initials: G
authors.lastname: Tasi
authors.forename: Miklós
authors.initials: M
authors.lastname: Kálmán
authors.forename: Richard F
authors.initials: RF
authors.lastname: Murphy
authors.forename: Sándor
authors.initials: S
authors.lastname: Lovas
mesh_terms: D003198:Computer Simulation; D004583:Electrons; D008550:Melatonin / Q000737:chemistry*; D008954:Models, Biological; D008968:Molecular Conformation; D011789:Quantum Theory
chemical_list: D008550:Melatonin