Adsorption of dipeptide L-alanyl-L-tryptophan on gold colloidal nanoparticles studied by surface-enhanced Raman spectroscopy

  • Spectrochim Acta A Mol Biomol Spectrosc. 2021 Feb 15:247:119064. doi: 10.1016/j.saa.2020.119064.
Daedu Lee  1 ,  Shafqat Hussain  2 ,  Juhyun Yeo  1 ,  Yoonsoo Pang  3
Affiliations
  • 1. Department of Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Republic of Korea.
  • 2. Department of Physics and Photon Science, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Republic of Korea.
  • 3. Department of Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Republic of Korea. Electronic address: [email protected].
PMID: 33091739 DOI: 10.1016/j.saa.2020.119064
Abstract

Surface adsorption of a dipeptide L-alanyl-L-tryptophan (Ala-Trp) on gold nanoparticles reduced by citrate (CT) and borohydride (BH) ions was investigated by a surface-enhanced Raman scattering (SERS) technique. Two distinct SERS spectra of Ala-Trp depending on the types of gold nanoparticles were observed, and the vibrational assignments were based on the density functional theory simulations and the previous SERS results of Trp. Ala-Trp mainly adsorbs through the amine group on CT gold nanoparticles with a perpendicular orientation of the indole ring to the surface. In contrast, the adsorption occurs via the π electrons of the indole ring on the BH gold surfaces while maintaining a flat geometry of the indole ring to the surface. The amide I band of Ala-Trp was observed only with the CT gold colloids in acidic and neutral conditions where partial surface adsorption via the amide group is expected.

Keywords
Amide I band; Citrate and borohydride-reduced; Gold colloidal nanoparticles; L-alanyl-L-tryptophan; Surface-enhanced Raman scattering.
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