posted on 2020-03-18, 17:03authored byAgata Królikowska, Janusz Cukras, Marcin Witkowski, Dagmara Tymecka, Agnieszka Hernik-Magoń, Aleksandra Misicka, Wojciech Dzwolak
Tiny
changes in the covalent structure of a noble-metal-anchored
peptide may affect its surface-enhanced Raman scattering (SERS) signature.
While SERS spectra of Cys-Trp peptides are dominated by the bands arising from the
aromatic Trp side chain, a thorough study of the impact of modifications
in SERS-silent regions concerning such dipeptides was yet to be performed.
Thus, here we conduct an extensive SERS study of a series of Cys-
and Trp-containing dipeptides, varying both the main-chain direction
(Cys-Trp/Trp-Cys) and the presence of typical covalent modifications
at N- and C-termini (acetylation/amidation). We use three different
SERS-active substrates: oxidation–reduction cycling-roughened
silver (Ag ORC), gold (Au ORC), and chemically synthesized colloidal
silver nanoparticles (Ag NPs). Interpretation of the experimental
data was aided with density functional theory (DFT) calculations.
Potential energy distribution (PED) analysis was used for the assignment
of dipeptide vibrational bands. IR and normal Raman spectra were also
examined to get a complete vibrational analysis. This work may be
considered the first report on the effect of terminal group modification
and reversing the peptide sequence on the adsorptive behavior of dipeptide
on silver and gold surface studied by SERS spectroscopy, supported
by full vibrational assignment by means of the DFT method.