Characterization of adsorption mode of new B₂ bradykinin receptor antagonists onto colloidal Ag substrate

Abstract

In this paper, the surface‐enhanced Raman scattering (SERS) spectra of the potent B2 bradykinin receptor antagonists, [D‐Arg0,Hyp3,Thi5,8,L‐Pip7]BK, Aaa[D‐Arg0,Hyp3,Thi5,8,L‐Pip7]BK, [D‐Arg0,Hyp3,Thi5,D‐Phe7,L‐Pip8]BK, and Aaa[D‐Arg0,Hyp3,Thi5,D‐Phe7,L‐Pip8]BK, were measured when immobilized onto a colloidal assembly of apparently randomly adhering Ag spheres with diameters of approximately 20 – 25 nm. The observed SERS bands corresponding to different vibrational modes of the molecule, attached to or near Ag, and the variations in these bands resulting from competitive interactions of the functional groups of the peptides with the SERS‐active Ag surfaces were analyzed in this study. Briefly, it was shown that Pip, in generally in vertical orientation, and Thi, in the edge‐on position, relative to the colloidal Ag surface interacted with this surface through their lone electron pairs on the nitrogen and sulfur atoms, respectively. The imide bond of the X‐Pro peptide linkage and the guanidine group of Arg were involved in the adsorption process. In addition, it was demonstrated that the specific differences in the amino acid sequences slightly influenced the mode of adsorption. For example, Aaa in Aaa[D‐Arg0,Hyp3,Thi5,8,L‐Pip7]BK and Aaa[D‐Arg0,Hyp3,Thi5,D‐Phe7,L‐Pip8]BK and D‐Phe (vertical with respect to the colloidal Ag surface) in [D‐Arg0,Hyp3,Thi5,D‐Phe7,L‐Pip8]BK, and Aaa[D‐Arg0,Hyp3,Thi5,D‐Phe7,L‐Pip8]BK assisted in the adsorption of these peptides onto the colloidal Ag particles. To discuss these spectral alterations due to the different surface adsorption mechanisms of these peptides, the spectral changes were analyzed according to the adsorption process and Fourier‐transform‐Raman spectra. Copyright © 2013 John Wiley & Sons, Ltd.

Role of Phe‐D5 isotopically labeled analogues of bradykinin on elucidation of its adsorption mode on Ag, Au, and Cu electrodes. Surface‐enhanced Raman spectroscopy studies

“…The wavenumbers of the observed bands in these spectra are listed in Table along with the appropriate vibrational assignment. This assignment was based on the previous studies on BK 32 and its specifically modified analogues, vibrational studies of D 5 ‐isotopically labeled toluene and other mono‐substituted benzenes, and infrared investigation of the matrix‐isolated phenyl‐D 5 radicals . As expected, the Raman spectra of [(Phe‐D 5 ) 5 ]BK and [(Phe‐D 5 ) 8 ]BK are identical and dominated by bands, which are mainly due to the vibrations of the Phe‐H 5 (native Phe) and Phe‐D 5 (deuterated Phe ring) residues.…”

“…Therefore, analyzing the surface‐enhanced Raman scattering (SERS) signal from the adsorbed species onto a given metal surface (enhancement, broadening, and shift in wavenumber relative to the Raman spectra) information on the possible ways in which a peptide interacts with the surrounding medium could be obtained . Therefore, previously we have applied the SERS spectroscopy for the determination of adsorbed molecular structures and changes in these structures as a result of substitution of the natural amino acids with synthetic ones of BK and its four antagonists ([D‐Arg 0 ,Hyp 3 ,Thi 5,8 ,L‐Pip 7 ]BK, Aaa[D‐Arg 0 ,Hyp 3 ,Thi 5,8 ,L‐Pip 7 ]BK, [D‐Arg 0 ,Hyp 3 ,Thi 5 ,D‐Phe 7 ,L‐Pip 8 ]BK, and Aaa[D‐Arg 0 ,Hyp 3 ,Thi 5 ,D‐Phe 7 ,L‐Pip 8 ]BK) deposited onto Ag colloidal and electrode surfaces . Very recently, we have also provided SERS characterization of the potential‐dependent changes in the adsorption mode of BK immobilized onto Ag, Au, and Cu electrodes .…”

Influence of applied potential on bradykinin adsorption onto Ag, Au, and Cu electrodes

“…Figures compare the SERS spectra of BK adsorbed onto the Ag, Au, and Cu electrode surfaces, respectively, at different applied electrode potentials (−1.000 V to 0.200 V, selected according to the standard oxidation/reduction potential of the metal at 25 °C: Au – +1.50 V, Ag – +0.80 V, and Cu – +0.34 V; the higher the reduction potential, the more easily molecule is reduced – the grater oxidizing power) excited at 785 nm. The position of the enhanced bands in these spectra, given in wavenumbers, is summarized in Table along with the appropriate vibrational assignment; these assignments were based on the previous studies of specifically modified BK analogues, small l ‐phenylalanine‐ (Phe) and l ‐proline‐containing (Pro) peptides, and l ‐arginine (Arg) in silver sol and on silver nanostructures . The wavenumbers of the corresponding bands in the Raman spectrum of BK in aqueous solution (Fig.…”

“…Despite numerous biological investigations, the literature still lacks detailed information about the structure/bioactivity relationship of BK. This paucity of information is one reason why we decided to undertake studies on BK and its specifically mutated analogues . Knowledge of the structure of native BK and its behavior at the solid/liquid interface (adsorption onto the solid surface formed in an aqueous solution) may be key to the design of new analogs with agonistic or antagonistic properties toward the B 2 receptor.…”

Identification of erlotinib adsorption pattern onto silver nanoparticles: SERS studies

“…Conventional Raman spectroscopy method (RS) provides information about vibrational structure and composition of the investigated compound, whereas the surface‐enhanced technique (SERS) allows for understanding how the molecule interacts with the potential metal nanocarriers . Due to the fact that the spectra recorded by means of SERS technique often differ from those collected using conventional Raman scattering, the molecule–metal substrate interaction can be characterized . This phenomenon is related to the surface phenomenon and surface selection rules that govern the observed SERS spectral intensities.…”