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This paper reports the synthesis of the Ni +2 , Cu +2 and Zn +2 complexes of L-3,4-dihydroxyphenylalanine ( l -dopa) using a solvent-free solid-state grinding procedure. The synthesized complexes are characterized by elemental, molar conductance, EDAX-SEM, TG/DTA, infrared, electronic absorption, fluorescence and XRD analyses; confirming a 1:2 metal-ligand stoichiometry of the complexes and involvement of the carboxyl and amino groups in complex formation. Phase-diagram and the kinetic parameters of the interactions between l -dopa and the metal ions are also explored. Molecular structures of the metal complexes are modeled within the framework of density functional theory in a vacuum and implicit aqueous environment using the most stable l -dopa conformers determined at the MP2/6–311++G(d,p) level. The gas and aqueous phase metal-binding affinities; theoretical IR and UV–vis spectral aspects; partial atomic charges; Wiberg bond indices; HOMO-LUMO energy gaps and dipole moments of the l -dopa conformers as well as their complexes are calculated and analyzed at B3LYP/6–311++G(d,p) level. The singlet state of the Ni( l -dopa) 2 complex is found to be more favorable from thermodynamic perspectives as compared to the triplet state. Use of BHandHLYP and dispersion-corrected B3LYP (at DFT-D2 level) methods in conjugation with the 6–311++G(d,p) basis set affords us to accurately predict the binding affinity order of the three Lewis acids investigated, assess the influence of metal-aromatic π interactions on the thermodynamic stability of metalated l -dopa, and explore the effectiveness of the aforesaid methodologies in predicting a certain set of spectral and electronic properties of bioactive molecules. UV–vis titration and docking studies reveal that the metal complexes of l -dopa are able to bind to the surface of DNA. |
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