Theoretical Study of Structure and Acidity of Uric Acid and its Metal Complexes: M(UA)+n (M= Li+, Be++, Na+, Mg++, K+, Ca++) and M(UA)2+n (M= Zn+2, Cd+2, Cu+, Ag+)

Uric acid (UA) is a biological molecule which is susceptible to be investigated theoretically. A theoretical investigation is carried out in the gas phase and by water effect at the ground state by using density functional theory method (DFT) at the B3LYP/6-31(d) and B3LYP/ LANL2DZ levels on the structure of different chemical forms of Uric Acid (UA) and its metal complexes. Solvent effect (water) is included using the polarizable continuum model (PCM). Neutral structures (ketonic, enolic, dimeric, monohydrate) and anionic structures has been fully optimized. Furthermore, and in order to estimate the Brönsted acidity of (UA), the interaction of both enolic and ketonic forms with alkali meta cations (Li+, Na+, K+, Be++, Mg++, Ca++) was calculated in M(UA)+n complex structures. Proton acidity of (UA) and its complexes was estimated by calculating deprotonation energy (DE) and δ (ppm)11H NMR chemical shift using GIAO method. Metal cations effects on distinct N-H and O-H stretching vibrational modes of studied structures have also been examined. Further, we explored the geometry, and acidity of several uric acid transition metal complexes M(UA)2+n (M= Zn+2, Cd+2, Ag+, Cu+) in water. The complex was calculated using mixed basis set 6-31G(d) and LANL2DZ (on the transition metal).