Interaction of ferroceneboronic acid with diols at aqueous and non-aqueous conditions - signalling and binding abilities of an electrochemical probe for saccharides Karel Lacina a, *, Jan Novotný a, b , Zden  ek Moravec a, c , Petr Skládal a, d a CEITEC, Masaryk University, Kamenice 5, Brno 625 00, Czech Republic b NCBR, Masaryk University, Kamenice 5, Brno 625 00, Czech Republic c Department of Chemistry, Faculty of Science, Masaryk University, Kamenice 5, Brno 625 00, Czech Republic d Department of Biochemistry, Faculty of Science, Masaryk University, Kamenice 5, Brno 625 00, Czech Republic A R T I C L E I N F O Article history: Received 15 August 2014 Received in revised form 1 December 2014 Accepted 2 December 2014 Available online 4 December 2014 Keywords: Ferroceneboronic acid Lewis acid Non-aqueous environment Binding properties Detection of saccharides A B S T R A C T Ferroceneboronic acid (FcBA) was employed as a model compound for clarification of binding and signalling properties of molecular probe for saccharides. As the simplest electrochemically active boronic acid, its interactions with diverse diols were studied in homogeneous phase under aqueous and non- aqueous conditions. The FcBA-diol system was examined by cyclic voltammetry resulting in two redox pairs corresponding to free and bound forms of FcBA. Redox potential of the bound form of FcBA was shifted in the cathodic direction in aqueous conditions due to coordination of the hydroxyl group to the boron atom. Oppositely, the anodic shift of the redox potential was observed upon the interaction of FcBA with diols in non-aqueous solvents. The binding properties and signalling mechanism of electrochemi- cally active boronic acids were deduced and the assumptions resulting from the electrochemical behaviour were confirmed by 1 H and 11 B NMR spectroscopies. The binding constants of the tested diols in aqueous and non-aqueous media were determined and compared. ã 2014 Elsevier Ltd. All rights reserved. 1. Introduction Boronic acids (BAs) are nowadays widely studied for their ability to form reversible cyclic boronate esters with 1,2- and 1,3- diols even in such a competitive environment as water [1]. This ability is essential especially for the design of molecular probes for diverse diols with biological activity, for the design of therapeutic agents and following applications [2,3]. Moreover, the crucial synthetic reaction, the Suzuki-Miyaura cross-coupling utilises boronic acid derivatives as an initial reagent [4]. The need to develop a simple detection scheme for monitoring of the progress of this synthetic process working in both aqueous and non- aqueous solutions seems straightforward. The proper characteri- sation of the BA-diol interactions in both environments is thus of high importance. Since the pivotal systematic study by Lorand and Edwards [5], enormous work has been devoted to illumination of the mechanism of the interaction between boronic acid and polyols. Several publications have also been revealing the structure of the resulting boronate esters [1,6–12]. A majority of these studies considered foremost the complexes of boronates with glucose in aqueous solutions due to its key role in the human metabolism. Also the signalling mechanism of the binding event was not neglected and it was intensively studied especially for possible optical sensing [1,13–15]. Generally, the signalling abilities of boronic acids stem from the change of some physico-chemical property due to transformation of the trigonal planar sp 2 form of boron to the tetrahedral sp 3 form. Usually, this structural change is induced by the interaction with a suitable Lewis base including hydroxyl groups, fluoride and also nitrogen atoms from either secondary or tertiary amine groups. Although the BA-diol systems are being extensively explored for more than 20 years [1], even today some new and unexpected findings can be obtained [14], even in such a well known interaction of Alizarin Red S with phenylboronic acid. The previously anticipated fluorescence emission due to the presence of the tetrahedral form of boron was severely questioned and new and different mechanism of the interaction with diols and the following emission of fluorescence in the presence of trigonal boron was proposed [14]. In addition, the generally accepted scheme of the boronic acid creating 5- and 6- * Corresponding author. Tel.: +420 54949 7611. E-mail address: lacinak@chemi.muni.cz (K. Lacina). http://dx.doi.org/10.1016/j.electacta.2014.12.009 0013-4686/ ã 2014 Elsevier Ltd. All rights reserved. Electrochimica Acta 153 (2015) 280–286 Contents lists available at ScienceDirect Electrochimica Acta journal homepa ge: www.elsev ier.com/locate/electacta