Comparative Studies on IR, Raman, and Surface Enhanced Raman Scattering Spectroscopy of Dipeptides Containing ΔAla and ΔPhe

Abstract

Three dipeptides containing dehydroresidues (ΔAla, Δ((Z))Phe, and Δ((E))Phe) were examined by IR, Raman, and surface-enhanced Raman techniques for the first time. The effect of the size and isomer type of the β-substituent in the dehydroresidue on the conformational structure of the peptide was evaluated by using the analysis of IR and Raman bands. Additionally, SERS spectroscopy provided insight into the adsorption mechanism of these species on the metal surface. SERS spectra were recorded at alkaline pH on the silver sol using visible light excitation. The dehydroresidues studied here strongly influenced the SERS profile of the peptides. The most pronounced SERS signal for all dipeptides was assigned to the symmetric stretching vibration of the carboxylate ions. This indicates that the dehydropeptides studied here primarily adsorb via the deprotonated carboxylic group. Additionally, the enhanced SERS bands in the range 1550-1650 cm(-1) show differences in contribution of the dehydroresidue to the adsorption mechanism of the studied peptides.

Surface enhanced Raman scattering and quantum‐mechanical calculations on self‐assembling oligopeptides

“…ν CC [7,8,25,26] 889 w 882 sh 882 sh --τ HCCN [8] ν CC [26,29] 817 w 816 vw 822 vw 815 w τ HCCO [31] Amide V [26] 760 w 758 vw 756 br 770 w τ HCCC [29] Amide IV [7] 640 vw 655 br 658 br 654 vw 657 w δ COO - [29,31,32] ω COO - [8,25,26,30,37] 600 vw 603 vw 613 vw…”

“…Amide VI [27,33] 555 vw 563 br 561 br ---562 br ω COO - [7,30] Note. These assignments were confirmed by those reported in literature.…”

“…However, a different orientation of the "scrambled" peptide with respect to the Ag surface can be deduced by the disappearance of the lower wavenumber bands due to δ COO − (about 650 cm −1 ) and ω COO − (560 cm −1 ), visible in the SERS spectra of pept1 and pept2. [7] ν CC [40] ν CC [29] 1,058 w 1,043 w τCH 2 [29] ν 18a [34] 1,020 m ν CC [25] 938 vw 937 w ν C-COO - [6,8,30,37] Fermi resonance [8,25,31,34,37] 856 s; 829 s 854 s; 832 m Amide V [26] 773 w Amide IV [7] 668 vw ν 6b [7,8,25,34] 644 s 645 m ω COO - [8,25,26,30,37] 600 w 613 m Amide VI [7,8,26] ρ C¼O [33] 555 vw 564 vw ρ C¼O [27] 540 vw ω COO - [7,30] τ NH 3 + [32] 480 w Note. SERS = surface-enhanced Raman scattering.…”

Handedness preference and switching of peptide helices. Part II: Helices based on noncodedα‐amino acids

“…Spectroscopic measurements were extensively employed for the assessment of the local (NMR) and overall (IR absorption) conformational properties of ΔPhe‐rich peptides in solution; although with these compounds, CD spectroscopy (refer to later in the text) proved by far to be the technique of choice. In particular, IR absorption studies were not only conducted in solvents of low polarity but also extended to the solid state (KBr film, ZnSe crystal surface, Ag nanocolloids, and electrodes) as well, where related spectroscopies (Raman, surface‐enhanced Raman scattering, and vibrational CD) were also utilized . These analyses were expanded to N α ‐methylated ΔPhe residues where the cis tertiary amide conformation was shown to prevail.…”

Imaging of macrophages by Surface Enhanced Raman Spectroscopy (SERS)

“…Surface enhanced Raman spectroscopy has been explored as a sensitive method in bioanalysis [3] as well as in the determination of adsorbate-metal interactions [9]. SERS technique also provides a valuable tool for the ultrasensitive detection of biologically relevant molecules present in the cellular environment.…”