# Induced Effect of Gold Nanoparticles (AuNPs) and Halide Ions on Pyridoxine Molecule Stability
## 3 Results and Discussion
### The Influence of Bromide Ions on Electrochemical Behavior of Pyridoxine  
Electrode processes are influenced by the nature and composition of the electrolyte solution. At high values of anodic overvoltage, the working electrode is active; thus, the composition and structure of the surface layer differ with the nature of the counterion. Figure 8 shows the cyclic voltammograms of the gold electrode in the absence and presence of pyridoxine and gold nanoparticles in the supporting electrolyte represented by 0.1 mol \(\times\) L\({}^{-1}\) NaBr. A comparison of typical cyclic voltammograms, in the absence and presence of pyridoxine and AuNPs, for the gold electrode in aqueous NaBr solution is presented. For all the considered electrolyte systems, the observed voltammetric response was in accordance with previous findings in the literature [58; 59; 60]. The systems are characterized by an anodic peak in the forward step and the absence of any peak on the reverse scan, indicating that the reaction is irreversible in all cases. As can be seen, pyridoxine provides smaller peaks at the same potential values relative to the Au electrode. However, the decrease is not very significant, from 21 to 16 mA \(\times\) cm\({}^{-2}\). This is due to the very good electrocatalytic properties of gold and implicitly to the phenomena of chemisorption of pyridoxine molecules on the surface of the gold electrode. The nature of the ion present in the working solution also has a major influence on the electrochemical mechanism. It can be seen that the bromide ion shifts the onset potential of pyridoxine oxidation to lower values compared to other anions, without being able to make a clear separation between the electrogeneration processes of oxybrominated species and the electrooxidation/electrotransformation processes of pyridoxine. A peculiarity of the cyclic voltammograms recorded in the presence of bromide is the absence of the cathodic peak attributed to the reduction of oxygen species (gold oxides/hydroxides) on the metal surface. To investigate the effect of bromide and AuNPs on the electrochemical stability of pyridoxine, a series of spectrophotometric experiments was performed in the corresponding binary and ternary electrolyte solutions (Figure 9). Figure 8: Cyclic voltammetry responses of gold electrode in 0.1 mol \(\times\) L\({}^{-1}\) NaBr support electrolyte in the absence and in the presence of 75 mg \(\times\) L\({}^{-1}\) gold nanoparticles (AuNPs) and 2.9 \(\times\) 10\({}^{-4}\) mol \(\times\) L\({}^{-1}\) pyridoxine (vitamin B\({}_{6}\)). The UV-Vis spectrum of the supporting electrolyte solution, obtained after (NaBr\(-\)a) recording the cyclic voltammogram, shows a slightly contoured peak at a wavelength of 331 nm, attributed to the brominated electrogenerated species [51]. The presence of electrogenerated brominated species leads to the degradation of pyridoxine molecules both by direct mechanisms and by indirect and electromediated mechanisms. The spectra shown in Figure 9 demonstrate this, so that the spectrum recorded after performing the cyclic voltammetry shows a significant change in absorbance. The characteristic peak of AuNPs, at a wavelength of 570 nm, disappears in both cases, both in the absence and in the presence of pyridoxine molecules. To investigate the influence of AuNPs and halogen ions on the electrochemical behavior of pyridoxine, the spectrophotometric response of solutions subjected to electrolysis at constant current density was studied in the mixed electrolyte systems mentioned above (Figure 10). Figure 10: UV–Vis absorption spectra of sample as the electrochemical processes progress over time in NaBr/B\({}_{6}\)/AuNP systems (i = 50 mA \(\times\) cm\({}^{-2}\)). Figure 9: UV–Vis absorption spectra of electrolyte solution containing NaBr/B\({}_{6}\)/AuNP systems; b—before and a—after performing cyclic voltammetry.