Vibrational Assignments of Two Polymorphic Forms of Metaxolone by Using DFT Calculations and the SQM Methodology
Human Journals Research Article January
A theoretical study has been performed on the muscle relaxant 5-[(3, 5-dimethylphenoxy)methyl]-1,3-oxazolidin-2-one, of generic name metaxolone (MTX), by using the hybrid B3LYP/6-31G calculations in the gas phase and the experimental available infrared and Raman spectra in the solid phase. Three C1, C2 and C3 isomers were found in the potential energy surface (PES) but only two of them, C1 and C2 correspond to those experimentally reported polymorphic forms A and B, respectively. The absence of
... C3 isomer could be easily explained by the quite high values in the dihedral C5-C7-O2-C9 and O1-C5-C7-O2 angles different from those experimental structures reported for the two polymorphic forms A and B of MTX. On the other hand, the higher bond orders values together with the high topological properties observed for the oxazolidinone ring of C1 could possibly support their existence despite this isomer has highest energy than C2 and C3. The natural bond orbital (NBO) analyses reveal the high stabilities of C1 and C2 while the atoms in molecules(AIM) study suggests that the ring dimethylphenoxy-methyl practically do not have influence on the properties of MTX. The frontier orbitals show that the isomers of MTX have reactivities and electrophilicity indexes similar to antiviral thymidine while their nucleophilicity indexes present values closer to antimicrobial thione. In addition, the complete vibrational assignments of those two stable isomers were performed by using the experimental available FT-IR and FT-Raman spectra, their normal internal coordinates,the scaled quantum mechanical force field (SQMFF) methodology and the Molvib program.The harmonic force fields for the two isomers and their corresponding force constants were also reported. The force constants values are in agreement with values reported in the literature for species with similar groups.