RAMAN, SERS AND UV - CIRCULAR DICHROISM SPECTROSCOPIC STUDY OF N-ACETYL-L-CYSTEINE IN AQUEOUS SOLUTIONS

A. R. COBOS PICOT; M. PUIATTI; A. BEN ALTABEF; R. J. G. RUBIRA; S. SANCHEZ CORTES; S. B. DIAZ; M. E. TUTTOLOMONDO

NEW JOURNAL OF CHEMISTRY

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2019

1144-0546

The aim of this work is to evaluate the vibrational and structural properties of N-acetyl-Lcysteine(NAC), its molecular structure and electronic properties in relation to the action ofthiol and amine groups at different pH. Raman and Surface Enhanced Raman Spectroscopy(SERS) spectra were measured in aqueous solution. The influence of an aqueousenvironment on the NAC spectra was simulated by means of implicit (polarizablecontinuum model) method. SERS spectra indicate that the S atom is interacting with thesurface through the sulfur atom. One of the consequences of the interaction with the surfaceis the deprotonation of the SH group, as revealed by the disappearance of the ν(S−H) band.The calculations made for the Ag ? NAC complex confirm the experimental data obtainedby SERS, where the S - Ag interaction is the most important. These results are veryinteresting when one can formulate a drug feasibility of NAC using silver nanoparticles as acarrier. Raman spectra were registered to compare the behavior of different functionalgroups in the molecule, both in solid phase and in aqueous solution at different pH.Apparent ionization constants (pK? values) for the S-H group at high ionic strengths werecalculated from the intensity of the 2580 cm-l frequency as a function of pH. The UV andcircular dichroism spectra were also measured in aqueous solution at different pH. Finally,the study was completed with natural bond orbital (NBO) analysis to determine thepresence of hyper-conjugative interactions. It is important to observe the behavior of theC2-N bond with the delocalization effect, as the pH increases the hyperconjugativeinteraction on this bond decreases in the same way as in the case of the ν CN. The way bywhich the LP π O1→ σ*C2-N interaction and the ν CN decreases is an inverse reflection ofthe fractional ionization SH.