title: UV/vis, 1H, and 13C NMR spectroscopic studies to determine mangiferin pKa values.
abstract: The acid constants of mangiferin (a natural xanthonoid) in aqueous solution were determined through an UV/vis spectroscopic study employing the SQUAD program as a computational tool. A NMR study complements the pK(a) values assignment and evidences a H-bridge presence on 1-C. The chemical model used was consistent with the experimental data obtained. The pK(a) values determined with this procedure were as follows: H(4)(MGF)=H(3)(MGF)(-)+H(+), pKa1 (6-H)=6.52+/-0.06; H(3)(MGF)(-)=H(2)(MGF)(2-)+H(+), pKa2 (3-H)=7.97+/-0.06; H(2)(MGF)(2-)=H(MGF)(3-)+H(+), pKa3 (7-H)=9.44+/-0.04; H(MGF)(3-)=(MGF)(4-)+H(+), pKa4 (1-H)=12.10+/-0.01; where it has been considered mangiferin C(19)H(18)O(11) as H(4)(MGF). Mangiferin UV/vis spectral behavior, stability study in aqueous solution as well as NMR spectroscopy studies: one-dimensional (1)H,(13)C, 2D correlated (1)H/(13)C performed by (g)-HSQC and (g)-HMBC methods; are also presented. pK(a) values determination of H(4)(MGF) in aqueous solution is a necessary contribution to subsequent pharmacokinetic study, and a step towards the understanding of its biological effects.
authors.affiliation: Universidad Autónoma Metropolitana-Iztapalapa, Depto. Química, Area de Química Analítica, Apdo. Postal 55-534, 09340 México DF, México.
authors.forename: Berenice
authors.initials: B
authors.lastname: Gómez-Zaleta
authors.forename: María Teresa
authors.initials: MT
authors.lastname: Ramírez-Silva
authors.forename: Atilano
authors.initials: A
authors.lastname: Gutiérrez
authors.forename: Enrique
authors.initials: E
authors.lastname: González-Vergara
authors.forename: Marisol
authors.initials: M
authors.lastname: Güizado-Rodríguez
authors.forename: Alberto
authors.initials: A
authors.lastname: Rojas-Hernández
mesh_terms: D002247:Carbon Isotopes / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D008279:Magnetic Resonance Imaging / Q000379:methods; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D011522:Protons; D012972:Sodium Hydroxide / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet / Q000379:methods*; D014466:Ultraviolet Rays; D044004:Xanthones / Q000737:chemistry
chemical_list: D002247:Carbon Isotopes; D011522:Protons; D044004:Xanthones; C013592:mangiferin; D012972:Sodium Hydroxide