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

Spectroscopic studies under properties of chlorpromazine conjugated to gold nanoparticles

Scientific studies have demonstrated that conjugates of anticancer drugs with metal nanoparticles (MeNPs) lead to a more effective deactivation of tumor cells compared to free drugs. Similarly, it has been established that conjugates of antibiotics with MeNPs exhibit higher biocidal activity against bacteria than their unbound counterparts. However, limited information is available regarding conjugates formed from drugs other than anticancer and antibiotics. Therefore, our research aims to develop synthesis methods for conjugates of chlorpromazine (CPZ), a neuroleptic, with gold nanoparticles (AuNPs). CPZ-AuNP conjugates were prepared through a ligand exchange reaction conducted on the surface of quasi-spherical, negatively charged citrate-stabilized TC-AuNPs with an average size of 55 ± 5 nm. UV-vis spectroscopy was employed to determine the stability range of the conjugates under controlled conditions of pH and ionic strength. Based on electrokinetic measurements, it was observed that the zeta potential of CPZ-AuNP conjugates strongly depends on the amount of CPZ adsorbed on the TC-AuNP surface. Additionally, the conjugates exhibited an isoelectric point at pH 8.8. Surface-enhanced Raman spectroscopy (SERS) and surface-enhanced infrared absorption spectroscopy (SEIRA) were employed to elucidate the adsorption structure of CPZ on TC-AuNPs. The interpretation of the spectra was conducted based on the Raman and FTIR spectra of CPZ, along with calculations performed using Density Functional Theory (DFT). The results indicated that CPZ primarily interacts with the TC-AuNP surface through the angularly oriented phenothiazine ring and the propylene bridge. Furthermore, it was demonstrated that the C-N-C fragment is perpendicular to the surface of the TC-AuNP with which it interacts. The findings from this analysis suggest the potential for further research on the use of these conjugates in biomedical applications.

In Situ and Ex Situ Raman Studies of Cysteine’s Behavior on a Titanium Surface in Buffer Solution

In this paper, surface-enhanced Raman spectroscopy (SERS) was used to investigate the adsorption process of cysteine (Cys). Studies were carried out in the presence of phosphate-buffered saline solution (PBS), at pH 7.4, and acidified to pH 5, 3, and 1, on the surface of Ti for implant application. In situ SERS spectra obtained for the Cys/Ti solution system, after 24 h of immersion time, indicated that the buffer solution strongly influences the adsorption behavior of Cys on the Ti surface. This results in a decrease in Cys adsorption on the Ti surface, in the range of pH 7.4 to 3. The strong interaction between a sulfur atom of Cys and a Ti surface was observed only at pH = 1, under strongly acidic conditions. In contrast, ex situ SERS spectra recorded for the same samples but in a dried Cys/Ti system show a completely different behavior of Cys on the Ti surface. Formation of a disulfide (S-S) bond has occurred as a result of the dimerization or aggregation of Cys molecules on the Ti surface. Detailed analysis of the adsorption behavior of Cys on the Ti surface can be very important in the preparation of bioactive materials (i.e., coated by organic layers).

Spectroscopic Investigations of 316L Stainless Steel under Simulated Inflammatory Conditions for Implant Applications: The Effect of Tryptophan as Corrosion Inhibitor/Hydrophobicity Marker

In this paper, the conformational changes of tryptophan (Trp) on the corroded 316 L stainless steel (SS) surface obtained under controlled simulated inflammatory conditions have been studied by Raman (RS) and Fourier-transform infrared (FT-IR) spectroscopy methods. The corrosion behavior and protective efficiency of the investigated samples were performed using the potentiodynamic polarization (PDP) technique in phosphate-buffered saline (PBS) solution acidified to pH 3.0 at 37 °C in the presence and absence of 10−2 M Trp, with different immersion times (2 h and 24 h). The amino acid is adsorbed onto the corroded SS surface mainly through the lone electron pair of the nitrogen atom of the indole ring, which adopts a more/less tilted orientation, and the protonated amine group. The visible differences in the intensity of the Fermi doublet upon adsorption of Trp onto the corroded SS surface, which is a sensitive marker of the local environment, suggested that a stronger hydrophobic environment is observed. This may result in an improvement of the corrosion resistance, after 2 h than 24 h of exposure time. The electrochemical results confirm this statement—the inhibition efficiency of Trp, acting as a mixed-type inhibitor, is made drastically higher after a short period of immersion.