11B NMR Investigations of Borate Esters in Aqueous Solutions and Wine

The element boron plays a role in medical and biological fluids [1] which is not yet well investigat­ ed. Further it is questionable if boron is needed as a trace element in the hum an food. But due to its toxicity, boron containing drugs are largely for­ bidden in this country [2], With the daily food, boron is incorporated in amounts which are esti­ mated to 1 through 40 mg per day [3], where the consumption of wine plays an important role, since wine contains boron in amounts of some mg/liter [4], This results from the fact that the vine involves boron in its metabolic processes [4]. Boron has two isotopes, "B and 10B, which are accessible to nuclear magnetic resonance (NM R) in­ vestigations, and UB N M R studies in aqueous solu­ tions with millimolal concentrations are possible due to the favourable N M R properties o f this isotope as has been shown recently in a detailed in­ vestigation of aqueous solutions of borates and boric acid [5]. The "B N M R signals of red wine [6] (see also Fig. 3), confirmed the cited content of boron but also indicated the existence of at least two boron con­ taining complex species as is not unlikely, since wine is a complex fluid with many ingredients [7], for instance different carboxylic acids. Many n B NM R investigations on organic com ­ pounds have been published as can be verified from some recent reviews [8 11] but rather few data are available for aqueous solutions (see [5] and refer­ ences therein).