# Induced Effect of Gold Nanoparticles (AuNPs) and Halide Ions on Pyridoxine Molecule Stability
## 1 Introduction  
Vitamin B\({}_{6}\) (other names: pyridoxine, pyridoxol, pyridoxine hydrochloride) belongs to the group of soluble B vitamins that are involved in metabolic processes and plays an important role in human health and especially in DNA repair, for which it is an essential cofactor [1]. It is involved in the pathways of methyl-group metabolism as a cofactor for different important enzymes, thus being a protective nutrient for pancreatic cancer by preventing the alteration of the DNA methylation mechanism [2]. Precisely because of its importance in the body, this vitamin has been introduced in food supplements to combat its deficiency as a food additive with an antioxidant role and even in drugs, alone or in various multivitamin complexes. B\({}_{6}\) vitamers with common 2-methyl-3-hydroxypyridine structures (pyridoxine--P, pyridoxal--PO, pyridoxamine--PN and the corresponding 5'-phosphorylated derivatives; pyridoxine 5'-phosphate--P5P, pyridoxal 5'-phosphate--PO5P and pyridoxamine 5'-phosphate--PN5P) are biologically active compounds, known since the early 1900s and comprising six interconvertible members under the action of specific enzymes [1]. Pyridoxal-5'-phosphate is the form of B\({}_{6}\) vitamin that is biologically active, being produced in human organisms from the vitamers. It is involved in the regulation mechanisms of the glucose, lipid and amino-acid metabolism as a co-enzyme for about 160 different enzymatic reactions. The survival rate of non-small cell lung cancer patients was correlated with high levels of pyridoxal kinase, while the vitamin B\({}_{6}\) intake was inverse associated with colorectal cancer risk [3]. The antagonistic properties of B\({}_{6}\) vitamers have been discovered over time, so they are powerful antioxidants (inactivatereactive oxygen species) but can also act as endogenous photosensizers that lead to the formation of reactive oxygen species [1]. Along with vitamin B1 and B12, pyridoxine is involved in peripheral nerve repair processes through mechanisms that are yet to be fully understood. The evidence for this role was provided by numerous animal studies over time, and now these elements are referred to as \"neurotropic\" vitamins. Pyridoxine plays a very important role in the synthesis of neurotransmitters and in inhibition of neurotoxic glutamate [4]. Vitamin B6 is obtained industrially through fermentation processes, so it was necessary to develop more and more efficient methods to ensure maximum production efficiency and, on the other hand, a simple and accurate method of determining the concentration of this vitamin. Application of the liquid chromatography (LC) method using different detection techniques for determination of vitamin B6 in pharmaceutical formulations, plant foods, human plasma and serum demonstrated a high degree of sensitivity, precision and linearity [5; 6; 7; 8; 9; 10]. Determination of vitamin B6 in tablets by LC with electrochemical detection using a carbon fiber electrode showed a detection limit of 2.5 ng for P and 1.0 ng for PO and PN [5]. LC coupled to mass spectrometry (MS) provided a good linearity between 5.0 and 400.0 ng \(\times\) mL\({}^{-1}\)[6]. High-performance LC (HPLC) with coulometric electrochemical and ultraviolet detection using C18 column type indicated detection limits of 2.7 [7] and 0.18 ng \(\times\) mL\({}^{-1}\)[8]. Simultaneous determination of vitamin B6 in the presence of co-administered compounds such as other vitamins or antiepiletips showed a good predictability with reversed-phase HPLC (RP-HPLC) [9; 10]. Limits of quantification of 0.39 ug \(\times\) mL\({}^{-1}\) and 0.11 ng \(\times\) mL\({}^{-1}\) were obtained in the presence of levetiracetam and B1/B12, respectively. Experimental determination of vitamin B6 can involve some analytical impediments due to its complex structure that can lead to the appearance of intermolecular interferences.