Influence of Pyramidal M20 (M = Cu, Ag and Au) Clusters on SERS and Noncovalent Interactions toward Tuberculosis Drug Pretomanid (PTD): DFT Study

The study of interaction and adsorption of drug molecules on the active surface of noble metal nanocluster is of particular interest due to effective change in the properties of the drug molecules. Surface-enhanced Raman scattering (SERS) theoretical calculations were performed to investigate the adsorption properties of pretomanid (PTD) on pyramidal Ag-20/Au-20/Cu-20 metal clusters. The charge transfer process from the M-20 pyramids is revealed by MEP and electronic analysis. The frequencies of PTD are enhanced in the PTD-metal complexes due to the noticeable SERS effect, and the binding energies were calculated to be -36.2 kcal/mol, -46.3 kcal/mol and -43.6 kcal/mol with Ag, Au and Cu structures, respectively. For the PTD-metal clusters, there is an entire potential rearrangement due to adsorption process which is due to charge transfer and adsorptions as chemisorption. The polarizability variations are predicted in the order PTD-Au > PTD-Cu > PTD-Ag which contribute the SERS enhancement due to adsorption. Changes in thermodynamic parameters reveal that adsorption is exothermic and at the same time spontaneous with ordered interactions due to the negative values. There is a redshift for the ultraviolet-visible (UV-vis) absorption of PTD-metal complexes with a lowering intensity in comparison with that of PTD, more likely indicating a chemisorption process. SERS enhancement factors are remarkable due to adsorption of conformationally flexible PTD on metal clusters. The noncovalent interactions between PTD and the metal pyramids were also determined. The study provided key information on designing a molecular structure with a good pharmacological profile by calculating bioactivity and drug similarity parameters for bioactive drug molecules.