Study Title:

The Science of Calcium Fuctoborate

Study Abstract

Calcium fructoborate samples of composition Ca(C6H10O6BO)2 x 3 x 5H2O were characterized by chemical analysis, infrared and Raman spectroscopy, and thermoanalytical (thermogravimetric and differential thermal analysis) data. Theoretical studies, using density functional theory, were made for seven different structural models of the fructoborate moiety, and the most stable structure could be derived from these calculations. The results of the theoretical study also allow improving the assignment of the vibrational spectra of the compound.

Introduction

Boron has been recognized as an essential trace element for higher plants since the 1920s [1–4], but only recently, evidence has been accumulated indicating that it may be an essential nutrient for humans and animals. It apparently has an essential function that
somehow regulates parathyroid hormone action and, therefore, indirectly influences metabolism of calcium, magnesium, phosphorus, and cholecalciferol (vitamin D3) [5–7].

Foods of plant origin, especially fruits, leafy vegetables, nut, and legumes, are rich sources of boron. Wine, cider, and beer are also high in boron [3, 6]. An analysis of both human and animal data suggests that an acceptable safe range of mean intake of boron for
adults could well be 1–13 mg/day [3, 7]. Notwithstanding, recent findings indicate that a significant number of people do not consistently consume more than 1 mg/day, suggesting that boron could be a practical nutritional or clinical concern [7]. Besides, the requirement
for boron seems especially crucial in the case of metabolic stress situations [5–7].

Traditionally, boric acid and some of the most common inorganic borates have been used for boron supplementation [3]. Recently, some other boron compounds have been introduced by the pharmaceutical industry in the market for this same purpose. One of them
is calcium fructoborate, marketed by FutureCeutical Corporation as Fruitex-B®, and protected by a U.S. patent [8]. This commercial product presents different beneficial biological and wound healing effects, and it has recently shown to also posses an interesting
antioxidant and antiinflammatory activity [9, 10]. Notwithstanding, the compound has so far not been very well characterized from the physicochemical point of view.

To advance into a better characterization of this interesting boron compound, we have investigated its thermal and spectroscopic behavior and performed some theoretical quantum-chemical calculations, using the density functional approach, to attain an insight
into its molecular conformation. It is well known that boron, in the form of boric acid, can form complexes with different organic compounds having pairs of adjacent OH groups in the cis position. Sugar, sugar alcohols, and other polyhydroxylated molecules are typical examples of species able to generate this type of boric acid esters, containing –R–C–O–B linkages [11]. D-fructose (C6H12O6) interacts with boric acid generating two linkages of this type and leaving one unbound B–OH group of the acid, i.e., C6H10O6BOH. After deprotonation, two of this moieties become stabilized by Ca(II), generating the investigated fructoborate of composition Ca(C6H10O6BO)2·nH2O=Ca(fruBor)2·nH2O.

Conclusions

A known preparative method for the synthesis of calcium fructoborate was used. Results of the chemical analysis combined with thermogravimetric data show that, under the employed experimental conditions, a compound of Ca(C6H10O6BO)2·3.5H2O stoichiometry
is obtained. The hydration water is given off up to about 130°C, and the total degradation of the compound occurs in three successive thermogravimetric steps up to 600°C with the generation of CaB2O4 as the final thermolysis residue. An approximate assignment of
the most characteristic IR and Raman spectra could be performed, partially supported by the results of theoretical DFT calculations. The stability of seven different complexes formed between fructose and the borate anion were investigated theoretically. The most stable complex is about 6 Kcal mol−1 below the second more stable structure and this relatively large amount of energy suggests that only the most stable complex makes relevant contributions at room temperature conditions. The fact that the harmonic vibrational frequencies of the most stable structure compare very well with the experimental vibrational spectroscopic data supports this finding. All these facts point to relatively small lattice effects when the ionic solid is formed, as the geometry of a complex obtained in vacuum adequately describes some experimental properties of the compound.

Study Information

Wagner CC, Ferraresi Curotto V, Pis Diez R, Baran EJ.
Experimental and theoretical studies of calcium fructoborate.
Biol Trace Elem Res
2008 April
Departamento de Ingeniería Química, Facultad de Ingeniería, Universidad Nacional del Centro de la Provincia de Buenos Aires, 7400, Olavarría, Argentina.

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