Charge Transfer Surface-Enhanced Raman and Absorption Spectra of the Zwitterionic Form of Cysteine Adsorbed on M@Au₁₂...

The effect of the core atom type of the M@Au₁₂ 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@Au₁₂ 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@Au₁₂ nanocluster in water are O─C═O asymmetric stretching (M = Au and Ag), NH₂ bending (M = Ag), S-H stretching (M = Ag, Pt, and Pd), CH₂ bending (M = Pt), and CH₂ symmetric stretching (M = Pt and Pd). The ZWCYS at the D₂ site of the M@Au₁₂ nanocluster in water exhibits intensity enhancement for O─C═O asymmetric stretching (M = Pt), NH₃ 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, CH₂ symmetric stretching, CH₂ asymmetric stretching, and especially NH₂ symmetric stretching.