Interaction of potassium ¯uoride with a-D-glucose Regino Gonza Âlez a,b,* , Pedro Ortiz a,b , Edilso Reguera a,c , Jose  F. Bertra Ân a,d a Centro de Investigacio Ân en Ciencia Aplica y Tecnologõ Âa Avanzada del Instituto, Polite Âcnico Nacional CICATA-IPN), Calzada Legaria, No. 694, Colonia Irrigacio Ân, Delegacio Ân Miguel Hidalgo, Mexico D.F., C.P. 11500, Mexico b Facultad de Quõ Âmica-IMRE, Universidad de la Habana, Habana 10400, Cuba c IMRE, Universidad de La Habana, Habana 10400, Cuba d Centro de Quõ Âmica Farmaceu Âtica, Habana, Cuba Received 25 September 2000; accepted 23 January 2001 Abstract Addition of KF to solutions of a-D-glucose aDG) in DMSO-d 6 and D 2 O alters the 1 H NMR spectra, which is attributed to an interaction of the hydrogen atoms of the ±OH groups with the basic F  anions of the salt. It is shown that K  cations do not interact with the oxygen atoms of the ±OH groups of the aDG. Mutarotation rates of aDGinD 2 O in the presence of potassium halides and alkaline chlorides were measured from the integrated 13 C NMR signal of the anomeric protons. The mutarotation rates were higher with KF than other potassium halides. In order to shed light on the interactions of KF with the aDG, the mutarotation of aDG in the presence of KF and KOH were also studied using polarimetric measurements. At similar pH values, the effect of KF on the mutarotation rate is about ®ve times that observed for KOH, indicating a major af®nity for the F  anion by the anomeric proton as compared with OH  . The acceleration of the mutarotation process of aDG is evidence for KF±aDG interactions, since NMR spectra of b conformer are also altered by the presence of KF. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Potassium ¯uoride KF); a-D-Glucose; Proton NMR; Mutarotation 1. Introduction Theinteractionofmetalliccationswithcarbohydratesisa subject of growing interest in recent years due to the importanceofthecomplexesinchemistry[1±3]andbiology [4±8]. Most of the work has been carried out in aqueous solutions.Themodelsusedfortheanalysisoftheinteraction are based in the structure of the sugars and the properties of the cations charge, size, polarizability) with practically no reference to the role of the anions [9]. Recently, it has been reported on the interaction in the solid state of alkali ¯uorides with acidic substances where thestabilityoftheacid¯uorideanion,HF 2  ,determinesthe course of the mechanochemical reactions [10]. A strong interaction is also observed between KF and D-xylose, both in solid state and from methanolic solutions, with formation of a KF±xylose complex [11]. According to IR and NMR spectra, the driving force of the complex formation is the interaction of F  with the ±OH protons. Mutarotationofallreducingsugarsarecatalyzedbyacids and bases [12], with a same value of the mutarotation constant for a- and b-D-glucose over a wide temperature range, from 0 to 408C [13]. Also, the reaction constant is independentoftheconcentrationofsugaroverawiderange. Later work revealed that catalysis of mutarotation is not an exclusive property of hydrogen and hydroxyl ions [13]. It hasbeenreported[14]thatthedeterminationofthecatalytic activity of anions of weak acids requires adjustment of the pH of the solution in order to keep the concentration of hydroxyl ion low, because the catalytic activity of the hydroxyl ions resulting from hydrolysis of the salt is so great that it masks the smaller catalytic effect of the anion. Evaluation of the catalytic activity of the hydroxyl ion is dif®cult, because the mutarotation becomes too rapid to allow an accurate measurement. Small variations in the hydroxyl ion concentration cause large differences in the reaction rates. It has been reported that the mutarotation process of aDG follows kinetics of pseudo-®rst-order [13]. Theaimofthepresentpaperistoshedlightonthenatureof aDG±KF interactions using NMR spectroscopy and polari- metric measurements. According to the obtained evidence, themainroleisplayedbytheF  ionandnotbytheK  ion.In ordertodiscardtheeffectofthesalthydrolysisintheobserved interactions, parallel polarimetric experiments were carried out adding KOH to the aDG aqueous solution instead of KF. Journal of Fluorine Chemistry 110 2001) 5±10 * Corresponding author. E-mail address: reginog@yahoo.es R. Gonza Âlez). 0022-1139/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0022-113901)00359-1