In situ surface-enhanced Raman scattering and X-ray photoelectron spectroscopic investigation of coenzyme Q₁₀ on silver electrode

In this study, coenzyme Q₁₀ (CoQ₁₀) has been investigated by in situ near-infrared Fourier transform surface-enhanced Raman scattering (NIR-FT-SERS) spectroelectrochemistry and angle-resolved X-ray photoelectron spectroscopy (AR-XPS) on silver surface. The surface adsorption behavior of the coenzyme Q₁₀ radical intermediate could be monitored by potential-dependent SERS technique. At the applied potential lower than -0.30 V vs. SCE, the radical intermediate CoQ₁₀H stands perpendicularly on the silver surface with both oxygen atoms of the aromatic ring and isoprenoid side chains. When the applied potential is more positive than -0.30 V vs. SCE or at open circuit potential, the quinone ring (benzene ring) of reduced form of coenzyme Q₁₀ (CoQ₁₀H₂) adopts a face-on surface configuration on the surface. The responsible mechanism for the potential-dependent SERS spectra is presented. Moreover, the adsorption conformation of CoQ₁₀ has been further confirmed by AR-XPS at the silver surface.