Guar Gum as an Eco-Friendly Corrosion Inhibitor for N80 Carbon Steel under Sweet Environment in Saline Solution: Electrochemical, Surface, and Spectroscopic Studies.

In this study, the corrosion inhibition performance of the natural polysaccharide guar gum (GG) for N80 carbon steel in CO2-saturated saline solution at different temperatures and immersion times was investigated by weight loss and electrochemical measurements. The results have revealed that GG showed good inhibition performance at lower and higher temperatures. The inhibition efficiency observed via weight loss measurements reached 76.16 and 63.19% with 0.4 g L-1 of GG, at 25 and 50 °C, respectively. The inhibition efficiency of GG increased as the inhibitor concentration and immersion time increased but decreased with increasing temperature. EIS measurements have shown that, even after prolonged exposure, GG was still able to protect the metal surface. Potentiodynamic measurements showed the mixed-type nature of GG inhibitive action. The Temkin and Dubinin-Radushkevich adsorption isotherm models give accurate fitting of the estimated data, and the calculated parameters indicated that the adsorption of GG occurred mainly via an electrostatic or physical adsorption process. The associated activation energy (Ea) and the heat of adsorption (Qa) supported the physical adsorption nature of GG. FTIR analysis was used to explain the adsorption interaction between the inhibitor and the N80 carbon steel surface. SEM-EDS and AFM confirmed the adsorption of GG and the formation of an adsorptive layer of GG on the metal surface.

Micro- and Nanoscale Spectroscopic Investigations of Threonine Influence on the Corrosion Process of the Modified Fe Surface by Cu Nanoparticles.

The work presents a comprehensive vibrational analysis of the process of adsorption of threonine (Thr) onto an Fe surface with deposited Cu nanoparticles (NPs) (of about 4-5 nm in size) in a corrosive environment. The application of surface-enhanced Raman spectroscopy (SERS) and surface-enhanced infrared absorption spectroscopy (SEIRA) provides the opportunity for detailed description of adsorption geometry of amino acid onto a metal surface. The combination of conventional infrared spectroscopy (IR) with atomic force microscopy (AFM) resulted in a nano-SEIRA technique which made it possible to provide a precise description of adsorbate binding to the metal surface. The studies presented confirmed that there is a very good correlation between the spectra recorded by the SERS, SEIRA, and nano-SEIRA techniques. Threonine significantly influenced the process of corrosion of the investigated surface due to the existing strong interaction between the protonated amine and carboxylate groups and the CuNPs deposited onto the Fe surface. In addition, the application of two polarization modulations (s and p) in nano-SEIRA allows subtle changes to be observed in the molecule geometry upon adsorption, with the carboxylate group of Thr being almost horizontally oriented onto the metal surface; whereas the amine group that contains nitrogen is oriented perpendicular to this surface.

SERS characterization of neuropeptide Y and its C-terminal fragments deposited onto colloidal gold nanoparticle surface.

It has been suggested that the family of neuropeptide Y (NPY) peptides is a promising target for the neuroprotective therapy; therefore, knowledge of the structure of these biologically active compounds and their behavior at solid/liquid interface is important in order to design new analogues. Because there is still a lack of detailed information on the behavior of NPY and its mutated analogues at the solid/liquid interfaces, in this work surface-enhanced Raman spectroscopy (SERS) analysis was used to investigate NPY and its native NPY3-36, NPY13-36, and NPY22-36 and mutated acetyl-(Leu28,31)-NPY24-36C-terminal fragments, acting on Y2 receptors (Y2R), in order to determine their possible metal surface/molecule interactions. In these studies, colloidal gold nanoparticle surface served as a solid surface, whereas an aqueous solution was used as a liquid medium. The observed differences in the band intensities, wavenumbers, and widths allowed us to draw conclusions on an adsorption mode of NPY and on changes in this mode upon the shortening of the peptide chain and increase in solution pH (from pH 3 to pH 11). Briefly, three different species of Tyr were identified onto the colloidal gold surface depending upon the length of the peptide chain and solution pH. Tyrosine (TyrOH) is present in a basic medium. Tyrosinate (TyrO-) is present in an acidic solution, whereas phenoxyl radical (Tyr*) appears at neutral pH for peptides having relatively short peptide chain (acetyl-(Leu28,31)-NPY24-36). The elongation of the peptide chain partially (NPY13-36 and NPY22-36) or completely (NPY3-36 and NPY) protects the Tyr residue against conversion to the radical form.

Neuropeptide Y and its C-terminal fragments acting on Y2 receptor: Raman and SERS spectroscopy studies.

In this paper, we present spectroscopic studies of neuropeptide Y (NPY) and its native NPY(3-36), NPY(13-36), and NPY(22-36) and mutated acetyl-(Leu(28,31))-NPY(24-36)C-terminal fragments acting on Y2 receptor. Since there is some evidence for the correlation between the SERS patterns and the receptor binding ability, we performed a detailed analysis for these compounds at the metal/water interface using Raman spectroscopy (RS) and surface-enhanced Raman spectroscopy (SERS) methods. Many studies have suggested that interactions of this kind are crucial for a variety of biomedical and biochemical phenomena. The identification of amino acids in these peptide sequences by SERS allowed us to determine which molecular fragments were responsible for the interaction with the silver nanoparticle surface. Our findings demonstrated that in all of the investigated compounds, the NPY(32-36)C-terminal fragment (Thr(32)-Arg(33)-Gln(34)-Arg(35)-Tyr(36)NH2) was involved in the adsorption process onto metal substrate. The results of the present study suggest that the same molecular fragment interacts with the Y2 receptor, what proved the usefulness of the SERS method in the study of these biologically active compounds. The search for analogs acting on Y2 receptor may be important from the viewpoint of possible future clinical applications.