Structure, Stability, and Spectroscopic Properties of H‑Bonded Complexes of HOSO and CH₃SO with H₂O

Quantum chemical calculations have been carried out to investigate the structure and stability of 1:1 and 1:2 HOSO–water and CH₃SO–water complexes. All of the geometries have been optimized at the DFT and at the CCSD levels of theory using 6-311++G­(2df,2pd) and aug-cc-pVDZ basis sets, respectively. The energetics of the hydrogen-bonded complexes are reported at G4 and CBS-QB3 levels of theory. A general characteristic future of the minimum-energy structure complexes is cyclic double H bonding for 1:1 complexes and cyclic triple H bonding for 1:2 complexes. Calculations predict relative large binding energies of 8.2 and 16.8 kcal mol^–1 for 1:1 and 1:2 HOSO–water complexes, respectively, at the CBS-QB3 level of theory. CH₃SO–water complexes have somewhat lower stability; the binding energy of 3.8 kcal mol^–1 for the 1:1 CH₃SO–water complex increases to 9.5 kcal mol^–1 for the 1:2 complex. The calculated shifts in vibrational frequencies due to complex formation show that the frequencies and intensities of H-bonded OH stretching regions are most affected by complex formation. The large frequency shift is mainly oriented to these OH bonds involved in H-bonding interactions. Vertical electronic excitation energies and the corresponding oscillator strengths have been calculated for the representative radical–water complexes using the TDDFT method and aug-cc-pVTZ basis set. No significant excitation energy difference was observed between the low-lying electronic states of either HOSO within the HOSO–water complexes or CH₃SO within the CH₃SO–water 1:1 complexes

Amino acids as corrosion inhibitors for copper in acidic medium: Experimental and theoretical study

Experimental electrochemical methods combined with quantum chemical calculations and molecular dynamics simulations were used to investigate the possibility of use various amino acids as “green” corrosion inhibitors for copper in 0.5 M HCl solution. Among eleven amino acids studied, cysteine achieved the highest inhibitor effectiveness reaching 52% at 10 mM concentration. Other amino acids reached achieved effectiveness less than 25%, some of them even acted as corrosion accelerators. Based on the experimental results, theoretical calculations and simulations were focused on cysteine and alanine. The electronic and reactivity parameters of their protonated forms in electrical double layer were evaluated by density functional calculations. In addition, molecular dynamic simulations were introduced to follow the adsorption behaviour of these two amino acids at the Cu(111) surface in the electrolyte solution. The results indicate that the orientation of both molecules is nearly parallel to the surface except of ammonium group which is directed away from the surface. Therefore, as the orientation of the cysteine and alanine molecules at the surface is similar, thiol functional group is responsible for superior inhibition efficiency of cysteine