Charge Transfer Surface-Enhanced Raman and Absorption Spectra of the Zwitterionic Form of Cysteine Adsorbed on M@Au 12 (M = Au, Ag, Pt, and Pd) Nanoclusters.

The effect of the core atom type of the M@Au 12 nanocluster (M = Au, Ag, Pt, and Pd) on the normal (NR) and charge-transfer surface-enhanced Raman spectroscopy (CT-SERS) of the zwitterion form of l-cysteine (ZWCYS) adsorbed on two different sites (D1 and D2) of the nanocluster is investigated separately in the gas phase and water. Because SERS requires the calculation of the absorption spectrum, the effect of the core atom type on the absorption spectrum of M@Au 12 and its complex with the ZWCYS has also been investigated. The vibrational bands that show the intensity enhancement in the CT-SERS of the ZWCYS interacting with the D1 site of M@Au 12 nanocluster in water are O─C═O asymmetric stretching (M = Au and Ag), NH 2 bending (M = Ag), S-H stretching (M = Ag, Pt, and Pd), CH 2 bending (M = Pt), and CH 2 symmetric stretching (M = Pt and Pd). The ZWCYS at the D 2 site of the M@Au 12 nanocluster in water exhibits intensity enhancement for O─C═O asymmetric stretching (M = Pt), NH 3 wagging (M = Au), and S-H stretching (M = Pd). The intensity of the vibrational bands of ZWCYS does not increase for M = Ag but decreases for O─C═O asymmetric stretching, S-H stretching, CH 2 symmetric stretching, CH 2 asymmetric stretching, and especially NH 2 symmetric stretching.