Deducing the molecular properties of zwitterionic, protonated, deprotonated, and double-deprotonated forms of L-cysteine from vibrational spectroscopy (IR, Raman, VCD) and quantum chemical calculations.

摘要: The behavior of L-cysteine (C3H7NO2S, (2R)-2-amino-3-sulfanylpropanoic acid) in water at different pH values was analyzed both experimentally and theoretically. studied 5.21 (at this pH, is a zwitterionic species), 1.00 (protonated 8.84 (monodeprotonated 13.00 (dideprotonated species). We carried out vibrational study using nonchiroptical (IR–Raman) chiroptical (VCD) techniques complemented by quantum chemical calculations. adopted dual strategy, as follows. (i) hybrid density functionals B3LYP M062X the ab initio MP2 method were employed, with same 6-311++G (d,p) basis set, order to characterize relative energies structures an extensive set conformers L-cysteine. presence included utilizing IEF-PCM implicit solvation model. (ii) analysis made chirality-sensitive technique chirality-insensitive (IR, including MIR FIR, Raman), especially aqueous solution. results obtained theoretically compared deduce most stable each pH. Moreover, for first time, monodeprotonated anion detected solution means IR, Raman circular dichroism (VCD). Finally, low-frequency region IR shown be very important way understanding conformational preference species.