Influence of aliphatic spacer group on adsorption mechanisms of phosphonate derivatives of l-phenylalanine: Surface-enhanced Raman, Raman, and infrared studies

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• 作者：E. Podstawka ; A. Kudelski ; P. Kafarski ; L.M. Proniewicz
• 关键词：Surface enhanced Raman scattering ; SERS ; Fourier-transform Raman scattering ; FT-RS ; Fourier-transform infrared spectroscopy ; FT-IR ; Silver colloid ; Electrochemically roughened silver substrate ; l-Phenylalanine phosphonate deriv
• 刊名：Surface Science
• 出版年：2007
• 期刊代码：104_00396028
• 类别：ch
• 出版时间：1 October 2007
• 卷：601
• 期：19
• 页码：4586-4597
• 文件大小：538 K

摘要

The nature of phosphonopeptides containing N-terminal l-phenylalanine (l-Phe), namely l-Phe-dl-NH–CH(CH(CH₃)₂)–PO₃H₂ (A), l-Phe-l-NH–CH(CH₃)–PO₃H₂ (B), and l-Phe-dl-NH–CH(CH₂CH₂COOH)–PO₃H₂ (C) (Fig. 1 presents molecular structure of these molecules), adsorbed on electrochemically roughened and colloidal silver surfaces has been explored by surface-enhanced Raman spectroscopy (SERS). To reveal adsorption mechanism of these species on the basis of their SERS spectra at first Fourier-transform Raman (FT-RS) and absorption infrared (FT-IR) spectra of non-adsorbed molecules were measured. Examination of enhancement, frequency shifts, and changes in relative intensities of SERS bands due to adsorption and surface roughens variation reveals that the tilted compounds adsorb on the electrochemically roughened silver substrate in similar way, while they behave differently on the colloidal silver surface. A stronger enhancement of in-plane ring vibrations of the l-Phe ring, i.e., ν₃ and ν_18b (B₂), over these of the A₂ symmetry in all SERS spectra on the electrochemically roughened silver substrate suggests that the ring interacts with this surface adopting slightly deflect orientation from the perpendicular one. Also, enhancement of PO and –CH₂–/–CH₃ fragments vibrations points out that they are involved in adsorption process on this substrate. This conclusion was drawn on the basis of the enhancement of 1274–1279 and 1138–1152 (ν(PO)), 1393–1400 (δ(CH) + ρ_b(CNH₂) + ν(C–C_O) + δ(CH₃)), 1455 (δ(CCH₃/CCH₂) + ρ_b(CH₃/CH₂), and 1505–1512 cm⁻¹ (δ(CH₂) + Phe(ν_19a)) bands. Although a relative intensity ratio of these bands in the presented SERS spectra is different. On the other hand, on the colloidal silver nanoparticles, the aromatic ring of all molecules is lying flat or takes almost parallel orientation to this surface. Besides, A interacts also via P-terminal group (568, 765, 827, 1040, and 1150 cm⁻¹), whereas B mainly through NH₂–C–(CO)–CNH–(712 and 1255 cm⁻¹). In the case of C, it adsorbs on the silver colloidal surface mainly through the aromatic ring of l-Phe, while other fragments of the molecule are in close proximity to this surface as comes off the weak enhancement of bands due to the aliphatic vibrations.