The boric acid-eatechol system in aqueous solutions has been studied by means of "B, 'H and '"C NMR over wide ranges of concentration and pH. "B spectra show a striking difference between the complexation possibilities of dilute and more concentrated solutions of boric acid. Both the 1 : 1 and 1 : 2 complexes can be simultaneously observed by '"C NMR.The interaction of boric acid and borate ions with hydroxy compounds has been used for analytical purposes' and structural studies of polyols,2 carbohydrates3 and nucleo~ides.~ Potentiometric methods have also been developed, mainly to identify the corresponding equilibrium systems in aqueous solution^.^ Spectroscopic methods, such as W6 and Raman: have not been so widely utilized. Surprisingly, extensive NMR studies have only been recently conducted in this area, although the "B, I3C and 'H nuclei are appropriate probes. Some early work was carried out on the "B NMR spectra of diol-monoborate equilibrium systems at a fixed pH value of 12;8 direct evidence for the existence of two types of anionic complexes was provided and different chemical shifts for the 1 : 1 and 1 : 2 complexes demonstrated.More recently, Pizer and Babcock have reported kinetic and mechanistic studies of the reaction of both boric B(OH), and phenylboric PhB(OH), acids with catechols.' Their titration results consistently showed that only 1 : 1 complexes were formed in the boric acid-catechol solutions, although a similar previous study indicated the formation of two complexes."Pizer's data has been interpreted in terms of the following overall reaction, in contrast to the interac-tion of the borate ion with diols which can be represented by the equilibria below:8These equilibria are rapidly established in aqueous solution, but the reaction rates proved to be sufficiently low for separate resonances to be observed.8 In * Author to whom correspondence should be addressed. contrast, this must be compared with the boric acidborate anion system which exhibits one single "B signal, broadened and p H dependent owing to the rapid interconversion of various short-lived species. The appearance of a recent "BNMR study of the complex formation of borate with catechol and Ldopa" prompts the publication of our results.In the present work, the boric acid-catechol system was studied by "B, I3C and 'HNMR spectroscopy over wide ranges of concentration and pH. "B NMR SPECTROSCOPIC EXAMINATIONTwo molar ratios of catechol to boric acid were used, i.e. 4: 1 and 1:1. Furthermore, in each case, two concentration ranges were investigated: the initial boric acid concentration, CHB, was either 0.05 M or 0.5 M; the formation of polyborates could be neglected at the 0.05 M concentration.8For both 4 : 1 molar ratio solutions (C,, = 0.2 M and 2 M, respectively) two peaks were observed, at 8.9 and 14.3ppm, in the 7-11pD range. The width at half height of each line was 26 Hz. These were assigned to the 1 : 1 (BD-) and 1 : 2 (BDJ complexes. At approximately pD 11 a third signal was observed at 2.8 ppm and assigned to the monomer...

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Phosphorus-31 NMR has been applied to the characterization of terminal phosphates on fragments of calf thymus DNA induced by three different nuclease systems: DNase I, DNase II and the artificial nuclease 'Mn-TMPyP/KHSO5'. In this last case, the oxidative damage to deoxyribose leads to two monophosphates esters (at the 3' and 5' ends) on both sides of the cleavage site. This method constitutes a promising approach to visualise the phosphate termini generated in DNA or RNA cleavage by cytotoxic drugs or chemical nucleases and provides a novel insight into the molecular aspects of their mechanism of action.