Borate Diester Research Articles

Studies on borate esters. Part 5. The system glucarate–borate–calcium(II) as studied by1H,11B, and13C nuclear magnetic resonance spectroscopy

A combination of 1H, 11B, and 13C n.m.r. spectroscopy is used to determine the identity, structure, and stability of compounds present in the aqueous glucarate–borate–calcium(II) system. Borate ester formation was found to occur preferbly at the threo-3,4-position of glucarate. Two diastereoisomeric borate diesters of glucarate are the major calcium(II) co-ordinating species. Each borate diester contains two calcium(II) co-ordinating sites consisting of two carboxylate groups, two borate ester ring oxygens, and, depending on the α-CHOH configurations, up to two α-hydroxy groups. The overall calcium(II) co-ordinating strength of both borate diester diastereoisomers of glucarate is about equal, whereas this is not the case for the arabinonate diastereoisomers.

Studies on borate, esters. Part 8. Interactions of cations with oxyacid anion-bridged esters of D-glucarate in alkaline media

Cation co-ordination has been studied in aqueous cation–borate–D-glucarate systems using 11B n.m.r. spectroscopy. The univalent cations KI, NaI, and AgI do not show preferential co-ordination by the borate esters of D-glucarate. The divalent cations MgII, CaII, CoII, NiII, SrII, CdII, and BaII are co-ordinated by the borate diesters. The cations that ionize the α-hydroxyl functions of D-glucarate, CuII, ZnII PrIII and PbII and/or compete with borate for the diol functions, AlIII and FeIII, are more strongly co-ordinated by free D-glucarate than by its borate diester. The different behaviour of the cations is discussed in terms of differences in charge/radius density and polarizing ability. In the CaII–oxyacid anion–D-glucarate system, CaII ion-selective electrode measurements and CaII sequestering capacity determinations have been performed. Apart from borate, synergic CaII co-ordination is observed at high pH for the oxyacid anion esters of D-glucarate of antimonite, stannate, aluminate, and germanate.

Studies on Borate Esters, Part VII Borate esters of some 1,3‐diones

AbstractAn NMR study of 1,3‐dione‐boric acid systems in DMSO is presented. Formation of borate diesters is preferred over that of borate monoesters. The 1,3‐dione moiety of the borate diester closely resembles that of the free enol tautomer. Addition of proton acids favours borate ester formation.

Studies on borate esters IV. Structural analysis of borate esters of polyhydroxycarboxylates in water using 13C and 1H NMR spectroscopys

AbstractA combined 13C and 1H NMR study on borate esters of a series of polyhydroxycarboxylates is presented. 13C substituent effects upon borate ester formation, as obtained from a set of model compounds, established that borate esters of the threo‐3,4‐diol functions of gluconate, glucarate, idarate and probably also of gulonate are preferred. The conformations of the free polyhydroxycarboxylates and the corresponding borate esters were determined using vicinal proton coupling constants. Both in 1H and 13C NMR spectra, peak doubling, due to diastereomerism in borate diesters, is observed.

Borate Exchanges of Lemna minor L. as Studied with the Help of the Enriched Stable Isotopes and of a (n,α) Nuclear Reaction

Despite the lack of a convenient radioisotope of boron, it is possible to measure unidirectional fluxes of borate between cellular systems and their external medium. It was accomplished by using the two purified stable isotopes ((10)B and (11)B), with (10)B specifically detected by a (n,alpha) nuclear reaction. The method was applied to compartmental analysis of borate with intact plants of Lemna minor L. Four compartments were suggested. Three of them apparently correspond to the three classical ones: free space (including easily dissociable borate monoesters), cytoplasm, and vacuole. The fourth one was interpreted as corresponding to very stable borate diesters in the cell walls. The method allows the determination of the borate capacities of the various compartments and of the borate unidirectional fluxes between the different compartments, at borate flux equilibrium. Other physicochemical data (mono and diester mass action constants, turn over numbers) were evaluated. The results are consistent with what is known of pure substances.