Transport of Glycosides through Liquid Organic Membranes Mediated by Reversible Boronate Formation is a Diffusion-Controlled Process

Abstract

The ability of phenylboronic acid, [3-( 1-adamantylcarboxamido)phenyl]boronic acid, and diphenylborinic acid to extract and transport p-nitrophenyl /?-D-glucopyranoside (glucoside), p-nitrophenyl 6-D-galactopyranoside (galactoside), and p-nitrophenyl 8-D-mannopyranoside (mannoside) through a liquid organic membrane, in the presence of trioctylmethylammonium or tetrabutylammonium chloride, was determined. Under the conditions examined, glycoside transport was facilitated by the reversible formation of covalent tetrahedral, anionic glycoside-boronate complexes, which partitioned into the organic membrane as lipophilic ion pairs. The results of various experiments indicated the rate-limiting step in the transport process was diffusion of the solutes through the narrow unstirred boundary layers adjacent the organic/aqueous interfaces. A plot of glycoside transport rate versus glycoside extraction constant, K,,, formed an approximate bell-shaped relationship. Maximal transport occurred when the carrier admixture had an extraction constant of log Kc,(,,,) -2.2. Under low extraction conditions (Kcx < Kcx(max))r movement of the glycoside from the receiving phase into the organic membrane was the rate-determining step, and under high extraction conditions (Kcx > Kcx(max)), exit from the membrane into the receiving phase was rate-determining. Because transport was dependent on K,,, an analysis of the structural and environmental factors that controlled transport could be reduced to an analysis of the factors that changed K,, relative to Kex(max). The factors examined included the following; pH, boron acid acidity, diol structure, polarity of the organic layer, boron acid lipophilicity, glycoside lipophilicity, quaternary ammonium lipophilicity, and the presence of competing lipophilic anions. The importance of Kcx(mx) as the parameter determining transport stereoselectivity is discussed.

A supported liquid membrane (SLM) with resorcinarene for facilitated transport of methyl glycopyranosides: Parameters and mechanism relating to the transport

“…According to the results of Table 3, we find that the values of apparent diffusion coefficients obtained (about 10 −4 cm 2 s −1 ) for each studied methyl aldopyranoside are higher compared to literature values (about 10 −6 cm 2 s −1 ) [15,19,[35][36][37][38]. The same remark was made for alditols and sugars [12,23,39,40].…”

“…To explain this phenomenon, we suggested in the transport of alditols [23], that the diffusion process is perhaps accompanied by a convection movement, which would be responsible for accelerating the diffusion of complexes in the membrane. While the hypothesis of "fixed-site jumping" proposed by Smith et al in the transport of sugar through a plasticized membrane of triacetate cellulose [18][19][20][21][35][36][37][38][41][42][43] is another suggestion, more likely to clarify this point. This theory assumes that the substrate moves by jumping from site to site, inside the membrane.…”

Identification of enantioselective extractants for chiral separation of amines and aminoalcohols

“…The operational enantioselectivity is defined as the relative transport rates of the two enantiomers. The transport rate is determined by the ratio K R /K S in solution as well as by the transport rate through the liquid membrane, 32 the decomplexation rate, and so forth. The selectivity therefore originates from the ratio K R /K S , but there may be a kinetic contri-bution.…”

Sugar Separation Using Liquid Membranes and Boronic Acid Carriers

“…The transport mechanism invoked to explain these observations is described in Figure 1. Subsequent studies by Czarnik (14,15) and our group (16)(17)(18)(19)(20) showed that other hydrophilic diol-containing compounds, namely nucleosides and aryl glycosides, could be transported by this ionpair process. Under low extraction conditions the order of transport enhancements reflected the known order of boronic acid affinities for cyclic diols which is cis-α,β-diol > cis-a,y-diol > trans-a,y-diol » trans-a,P-diol.…”