SERS spectroscopy of kaempferol and galangin under the interaction of human serum albumin with adsorbed silver nanoparticles

Raman and surface-enhanced Raman scattering (SERS) spectroscopy were employed to probe the interaction of the flavonol drugs, kaempferol and galangin, with human serum albumin (HSA). SERS spectra of both flavonol derivatives were obtained from a colloidal silver surface in physiological condition, based on the high performance of the enhanced substrate, the most enhanced modes of kaempferol and galangin were those with certain motions perpendicular to the metal surface. The SERS spectra were allowed to predict similar orientation geometry for both of the drugs on the colloidal surface with minor difference. In addition, both flavonols–HSA complexes were prepared in different concentration ratios and the orientated differences between kaempferol and galangin were investigated by SERS.

Graphical abstractAlthough the pharmaceutical molecules share the common mother nucleus structure and consequently the similar orientation when adsorbed on Ag colloid particles, for galangin (d), the coplanarity of ring A, B and C is damaged, while the plane of kaempferol (b) is unchanged.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Kaempferol and galangin have the same binding site to HSA in their dissociated states in subdomain IIA. ► When adsorbed on Ag particles, the plane of galangin is damaged while the plane of kaempferol is unchanged. ► When interacting with HSA in high concentration, binding behaviors of kaempferol and galangin exhibit similar transformation.