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

Abstract

Cation co-ordination has been studied in aqueous cation-borate-D-glucarate systems using "B n.m.r. spectroscopy. The univalent cations K1, Nal, and Agl do not show preferential co-ordination by the borate esters of D-glucarate. The divalent cations Mg", Call, Coil, Nil1, Sr", C d Y and Ball are co-ordinated by the borate diesters. The cations that ionize the a-hydroxyl functions of Dglucarate, Cull, Zn", Prlll, and Pb", and/or compete with borate for the diol functions, and Fell1, are more strongly co-ordinated by free o-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 CaI I-oxyacid anion-o-glucarate system, Call ion-selective electrode measurements and CaI I sequestering capacity determinations have been performed. Apart from borate, synergic Call co-ordination is observed at high p H for the oxyacid anion esters of D-glucarate of antimonite, stannate, aluminate, and germanate.Aqueous alkaline solutions of borate and polyhydroxycarboxylates possess good cation sequestering abilities and are applied in the galvanic, glass, and cement industries, and in pharmaceutical^.^ In addition, these systems have potential as triphosphate substitutes in detergent^.^,^ We have determined the stability and structure of borate mono-and di-esters of a series of polyhydroxycarboxylates (Figure 1) using multinuclear n.m.r. ~p e c t r o s c o p y . ~* ~The synergic Ca" co-ordination in these systems finds its origin in the high Ca" co-ordinating strength of the borate diesters of the polyhydroxycarboxylates.2-8 This effect is most pronounced for D-glucarate (Figure 2) as the polyhydroxy~arboxylate.~~~~~ Formation of the threo-3,4borate diesters of D-glucarate results in the creation of new multidentate Ca" co-ordinating sites.' Each of these sites is composed of two carboxylate oxygens, two borate ester ring oxygens, and, depending on the configuration, up to two hydroxyl oxygens (Figure 3).2*8 Borate (B"') is not unique in forming oxyacid anion esters (or complexes) with diol functions. Other oxyacid anions (X -) such as aluminate (Al"'), silicate (Si"), germanate (Gel'), arsenite (As"'), selenite (SeIV), stannate (Sn"), antimonate (Sb'), tellurate (Te"), and periodiate (Iv") are also capable of doing

Crosslinking Mechanism of Boric Acid with Diols Revisited

“…Effects of deprotonation of the polymer chain could be anticipated at the highest pH value tested, 12.8, but because of the amount of scatter, it is difficult to state that the experimental curve drops below the theoretical curve. Experiments by van Duin et al [23] do show that at deprotonation conditions, 0.5 m NaOH, the complex formation constant K 2 drops to zero and estimates that effects of pH are noticeable at a pH Ͼ 13.…”

“…[17,23] The reason that has been forwarded at high pH values, Ͼ 13, is charge repulsion because of deprotonation of the diol group. [13,23] Although we propose compounds containing trivalent boron, B and X 1 B, as the reactant species, B and X 1 B are still in rapid equilibrium with B -and X 1 B -respectively. As a consequence, the boron nucleus will be negatively charged on average and therefore subject to charge repulsion.…”

Anionic Saccharides Activate Liposomes Containing Phospholipids Bearing a Boronic Acid for Ca2+-Dependent Fusion

“…Although vesicles containing certain N-acylated phosphatidylethanolamines are known to become fusogenic in the presence of Ca 2+ , we expected that this tendency would be attenuated if the DOPEBA was mixed at a 1:1 ratio with the lamellar-favoring POPC. 6a, Boronic acids are known to spontaneously form reversible chelated complexes with saccharide vicinal-diol groups . Of particular relevance here is the knowledge that borate complexes of polyhydroxycarboxylates are able to sequester Ca 2+ ions . We hypothesized that monoanionic DOPEBA would combine with anionic saccharides to form multianionic head groups that would associate more strongly with Ca 2+ ions and increase the propensity for vesicle aggregation and subsequent fusion.…”