Boronic acid-facilitated α-hydroxy-carboxylate anion transfer at liquid/liquid electrode systems: the EICrev mechanism
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The transfer of the α-hydroxy-carboxylates of glycolic, lactic, mandelic and gluconic acid from the aqueous electrolyte phase into an organic 4-(3-phenylpropyl)-pyridine (PPP) phase is studied at a triple-phase boundary electrode system. The tetraphenylporphyrinato complex MnTPP dissolved in PPP is employed to drive the anion transfer reaction and naphthalene-2-boronic acid (NBA) is employed as a facilitator. In the absence of a facilitator, the ability of α-hydroxy-carboxylates to transfer into the organic phase improves, consistent with hydrophobicity considerations giving relative transfer potentials (for aqueous 0.1 M solution) of gluconate>glycolate>lactate>mandelate. In the presence of NBA, a shift of the reversible transfer potential to more negative values is indicating fast reversible binding (the mechanism for the electrode process is EICrev) and the binding constants are determined as K glycolate = 2 M−1, K mandelate = 60 M−1, K lactate = 130 M−1 and K gluconate = 2,000 M−1. The surprisingly strong interaction for gluconate is rationalised based on secondary interactions between the gluconate anion and NBA.
KeywordsBoronic acid Carbohydrate α-Hydroxy carboxylic acid Voltammetry Liquid/liquid interface Electrocatalysis Sensors
NK thanks the RSC and EPSRC for the award of an Analytical Studentship. JSF thanks the Leverhulme Trust (F/00/351/P) and the Royal Society Research Grants Scheme (2007/R2). Financial support for AMK from the Leverhulme Trust (F/00351/R) is gratefully acknowledged.
- 1.Bard AJ, Faulkner LR (2001) Electrochemical methods, 2nd edn. Wiley, New York, p 471Google Scholar
- 3.Liu B, Mirkin MV (2000) Electroanalysis 12:1433 doi: 10.1002/1521-4109(200012)12:18<1433::AID-ELAN1433>3.0.CO;2-2 CrossRefGoogle Scholar
- 4.Reymond F, Girault HH (2000) Electrochemistry at liquid–liquid interfaces. In: Meyers RA (ed) Encyclopedia of analytical chemistry. Wiley, New YorkGoogle Scholar
- 6.Scholz F, Schröder U, Gulaboski R (2005) Electrochemistry of immobilized particles and droplets. Springer, BerlinGoogle Scholar
- 9.Guo SX, Unwin PR, Whitworth AL, Zhang J (2004) Prog React Kinet Mech 29:43Google Scholar
- 15.James TD, Phillips MD, Shinkai S (2006) Boronic acids in saccharide recognition. The Royal Society of Chemistry, CambridgeGoogle Scholar
- 28.Scholz F, Schröder U, Gulaboski R (2005) Electrochemistry of immobilized particles and droplets. Springer, Berlin, p 214Google Scholar
- 30.Lide DR (ed) (1962) CRC handbook of chemistry and physics. CRC, FloridaGoogle Scholar
- 32.Zhao JZ, James TD (2005) Chem Commun (Camb) 1889–1891Google Scholar