Effect of potential on temperature-dependent SERS spectra of neuromedin B on Cu electrode

SERS Investigation on Oligopeptides Used as Biomimetic Coatings for Medical Devices

The surface-enhanced Raman scattering (SERS) spectra of three amphiphilic oligopeptides derived from EAK16 (AEAEAKAK)₂ were examined to study systematic amino acid substitution effects on the corresponding interaction with Ag colloidal nanoparticles. Such self-assembling molecular systems, known as “molecular Lego”, are of particular interest for their uses in tissue engineering and as biomimetic coatings for medical devices because they can form insoluble macroscopic membranes under physiological conditions. Spectra were collected for both native and gamma-irradiated samples. Quantum mechanical data on two of the examined oligopeptides were also obtained to clarify the assignment of the prominent significative bands observed in the spectra. In general, the peptide–nanoparticles interaction occurs through the COO⁻ groups, with the amide bond and the aliphatic chain close to the colloid surface. After gamma irradiation, mimicking a free oxidative radical attack, the SERS spectra of the biomaterials show that COO⁻ groups still provide the main peptide–nanoparticle interactions. However, the spatial arrangement of the peptides is different, exhibiting a systematic decrease in the distance between aliphatic chains and colloid nanoparticles.

Application of Alanine Scanning to Determination of Amino Acids Essential for Peptide Adsorption at the Solid/Solution Interface and Binding to the Receptor: Surface-Enhanced Raman/Infrared Spectroscopy versus Bioactivity Assays

The article describes the application of the alanine-scanning technique used in combination with Raman, surface-enhanced Raman, attenuated total reflection Fourier transform infrared, and surface-enhanced infrared absorption (SEIRA) spectroscopies, which allowed defining the role of individual amino acid residues in the C-terminal 6-14 fragment of the bombesin chain (BN6-14) on the path of its adsorption on the surface of Ag (AgNPs) and Au nanoparticles (AuNPs). A reliable analysis of the SEIRA spectra of these peptides was possible, thanks to a curve fitting of these spectra. By combining alanine-scanning with biological activity studies using cell lines overexpressing bombesin receptors and the intracellular inositol monophosphate assay, it was possible to determine which peptide side chains play a significant role in binding a peptide to membrane-bound G protein-coupled receptors (GPCRs). Based on the analysis of spectral profiles and bioactivity results, conclusions for the specific peptide-metal and peptide-GPCR interactions were drawn and compared.

Reflection Absorption Infrared Spectroscopy Characterization of SAM Formation from 8-Mercapto-N-(phenethyl)octanamide Thiols with Phe Ring and Amide Groups

Multifunctional amide-containing self-assembled monolayers (SAMs) provide prospects for the construction of interfaces with required physicochemical properties and distinctive stability. In this study, we report the synthesis of amide-containing thiols with terminal phenylalanine (Phe) ring functionality (HS(CH₂)₇CONH(CH₂)₂C₆H₅) and the characterization of the formation of SAMs from these thiols on gold by reflection absorption infrared spectroscopy (RAIRS). For reliable assignments of vibrational bands, ring deuterated analogs were synthesized and studied as well. Adsorption time induced changes in Amide-II band frequency and relative intensity of Amide-II/Amide-I bands revealed two-state sigmoidal form dependence with a transition inflection points at 2.2 ± 0.5 and 4.7 ± 0.5 min, respectively. The transition from initial (disordered) to final (hydrogen-bonded, ordered) structure resulted in increased Amide-II frequency from 1548 to 1557 cm^-1, which is diagnostic for a strongly hydrogen-bonded amide network in trans conformation. However, the lateral interactions between the alkyl chains were found to be somewhat reduced when compared with well-ordered alkane thiol monolayers.

Far-Off Resonance: Multiwavelength Raman Spectroscopy Probing Amide Bands of Amyloid-β-(37-42) Peptide

Several neurodegenerative diseases, like Alzheimer's and Parkinson's are linked with protein aggregation into amyloid fibrils. Conformational changes of native protein into the β-sheet structure are associated with a significant change in the vibrational spectrum. This is especially true for amide bands which are inherently sensitive to the secondary structure of a protein. Raman amide bands are greatly intensified under resonance conditions, in the UV spectral range, allowing for the selective probing of the peptide backbone. In this work, we examine parallel β-sheet forming GGVVIA, the C-terminus segment of amyloid-β peptide, using UV-Vis, FTIR, and multiwavelength Raman spectroscopy. We find that amide bands are enhanced far from the expected UV range, i.e., at 442 nm. A reasonable two-fold relative intensity increase is observed for amide II mode (normalized according to the δCH2/δCH3 vibration) while comparing 442 and 633 nm excitations; an increase in relative intensity of other amide bands was also visible. The observed relative intensification of amide II, amide S, and amide III modes in the Raman spectrum recorded at 442 nm comparing with longer wavelength (633/785/830 nm) excited spectra allows unambiguous identification of amide bands in the complex Raman spectra of peptides and proteins containing the β-sheet structure.

Encapsulation of Aspartic Protease in Nonlamellar Lipid Liquid Crystalline Phases

Encapsulation of proteins within lipid inverse bicontinuous cubic phases (Q₂) has been widely studied for many applications, such as protein crystallization or drug delivery of proteins for food and pharmaceutical purposes. However, the use of the lipid sponge (L₃) phase for encapsulation of proteins has not yet been well explored. Here, we have employed a lipid system that forms highly swollen sponge phases to entrap aspartic protease (34 kDa), an enzyme used for food processing, e.g., to control the cheese-ripening process. Small-angle x-ray scattering showed that although the L₃ phase was maintained at low enzyme concentrations (≤15 mg/mL), higher concentration induces a transition to more curved structures, i.e., transition from L₃ to inverse bicontinuous cubic (Q₂) phase. The Raman spectroscopy data showed minor conformational changes assigned to the lipid molecules that confirm the lipid-protein interactions. However, the peaks assigned to the protein showed that the structure was not significantly affected. This was consistent with the higher activity presented by the encapsulated aspartic protease compared to the free enzyme stored at the same temperature. Finally, the encapsulation efficiency of aspartic protease in lipid sponge-like nanoparticles was 81% as examined by size-exclusion chromatography. Based on these results, we discuss the large potential of lipid sponge phases as carriers for proteins.

Interaction of 4-imidazolemethanol with a copper electrode revealed by isotope-edited SERS and theoretical modeling

Adsorption of 4-imidazolemethanol (ImMeOH) on a copper electrode has been investigated by in situ isotope-edited (H/D and (63)Cu/(65)Cu) surface enhanced Raman spectroscopy (SERS) in aqueous solutions at physiological pH (7.0) in a potential window from -0.500 to -1.100 V. Theoretical modeling by DFT calculations at the B3LYP/6-311++G(d,p) level for light atoms and LANL2DZ with ECP for copper atoms have been employed for the interpretation of experimental data. The copper surface was modeled by a cluster of 6 atoms. It was found that the imidazole ring adopts Tautomer-I form in the adsorbed state and coordinates with the Cu surface through the N3 atom. Linear potential-dependence of ν(C4=C5) mode with the slope of (15 ± 1) cm(-1) V(-1) was experimentally observed. The imidazole ring mode near 1492 cm(-1) primarily due to ν(C2-N3) + β(C2H) vibration has also showed a considerable decrease in frequency at more negative electrode potentials with the slope of (9 ± 2) cm(-1) V(-1). Both modes can be used as sensitive probes for analysis of interaction of the imidazole ring with the metal surface. In agreement with experimental data theoretical modeling has predicted higher stability of surface bound Tautomer-I compared with Tautomer-II. The formation of a covalent bond between the metal and adsorbate was experimentally evidenced by metal isotopic ((63)Cu/(65)Cu) frequency shift of ν(Cu-N) mode at 222 cm(-1), combined with theoretical modeling of the surface complex.