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Structure and Reactivity of Folic Acid

Folic acid (FA, also known vitamin B9) (Fig. 1) is water-soluble essential vitamin that is yellow orange in color and is known to aid in the metabolism of amino acids and is necessary for the biosynthesis of DNA and RNA [1-2]. FA is responsible for many bodily functions, especially in creating new cells and maintaining them. This vitamin plays an important role in human health and disease processes [3]. The deficiency in FA has been ascribed to various disease processes including cancer, neurological dysfunction, and heart disease [4-5]. The optimization structure of FA (Fig. 1) was carried out, in gas phase, by using B3LYP method in combination with 6-1+G(d, p) basis set. Obtained structural parameters were compared with the X-Ray crystallographic data. The bond lengths between the crystallographic data of FA and its calculated geometrical parameters has percentage errors amount 2.2 %. It should be noted that the some bond has higher percentage errors. This discrepancy can be ascribed to the packing in the crystal. Obtained results show that B3LYP good reproduce the bond lengths of molecule FA by mean the correlation coefficient is 0.98 and absolute errors for bond length amount 0.03Å. The antioxidant activities of FA are related to their ability to transfer their phenolic H-atom to a free radical. The reactive radical species (R•) in the radical scavenging mechanisms are inactivated by accepting a hydrogen atom from a NH of the FA. It has been recognized that this reaction proceeds via at least three different mechanisms: hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET) [6, 7]. Reaction enthalpies related to these mechanisms are calculated by applying B3LYP/6-31+G(d, p) model. The species necessary to perform these calculations were generated from the most stable conformation of FA (Fig.1). Calculations were performed in the gaseous phase. Which of the mechanisms is preferred can be estimated from the lowest value of BDE, IP, and PA. The calculated thermodinamical parameters are presented in Table 1. The preferred mechanism of antioxidant action of FA is HAT (Table 1), because the BDE values of NH groups of FA are significantly lower than the corresponding IP and PA values. On the basis of obtained values for BDE, it is clear that N10-H group should be more reactive NH group of FA, indicating this position as the first site that can donate its H-atom, followed by N3-H and N8`-H. As can be seen from Table 1, it is clear that the PA and IP values are much higher than the corresponding BDE values, implicating that SET-PT and SPLET are not operative mechanisms.

Folic acid ; X-Ray ; DFT ; HAT

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