Estudo teórico das propriedades termodinâmicas e espectroscópicas do L-DOPA: um precursor da dopamina

Abstract

A comprehensive computational investigation of the structural, conformational, and electronic properties of L-DOPA was conducted within the framework of Density Functional Theory (DFT). Geometry optimizations, frequency calculations, systematic conformational searches, and Gibbs free energy evaluations identified the conformer geom09 as the global minimum, exhibiting the greatest thermodynamic stability when compared to the ten additional local minima identified in this study. These results were obtained employing the B3LYP and ωB97X-D functionals in conjunction with the 6-311++G(2d,2p) basis set. The inclusion of explicit dispersion corrections in ωB97X-D afforded an enhanced representation of intramolecular noncovalent interactions, such as hydrogen bonding and hyperconjugative effects, which exert a significant influence on the frontier molecular orbitals (HOMO and LUMO). The conformational analysis revealed that the stability of geom09 is predominantly governed by intramolecular hydrogen bonds, underscoring the necessity of accounting for dispersion and hyperconjugation effects when modeling complex biomolecular systems. Moreover, the infrared band associated with N–H bending, observed in both dopamine and L-DOPA, exhibited a markedly increased intensity in geom09 relative to dopamine. This enhancement indicates the formation of a hydrogen bond –N O–H. Such a spectral feature may be regarded as a fingerprint, pending experimental verification, of the more stable geometry of L-DOPA.