Borate binding

Abstract: Recently, much scientific effort has been centered on the control of the ionic transport properties of solid state nanochannels and the rational design and integration of chemical systems to induce changes in the ionic transport by means of interactions with selected target molecules. Here, we report the fabrication of a novel nanofluidic device based on solid-state nanochannels, which combines silane chemistry with both track-etched and atomic layer deposition (ALD) technologies. Nanodevice construction involves the coating of bullet-shaped single-pore nanochannels with silica (SiO2) by ALD and subsequent surface modification by reaction between silanol groups exposed on pore walls and N-(3-triethoxysilylpropyl)-gluconamide, in order to create a gluconamide-decorated nanochannel surface. The formation of a boroester derivative resulting from the selective reaction of borate with the appended saccharides leads to important changes in the surface charge density and, concomitantly, in the iontronic properties of the nanochannel. Furthermore, we propose a binding model to rationalize the specific interaction saccharide–borate in the surface. Besides, this unique nanodevice exhibits a highly selective and reversible response towards borate/fructose exposure. On the basis of the surface charge variation resulting from borate binding, the nanochannel can reversibly switch between “ON” and “OFF” states in the presence of borate and fructose, respectively. In addition, this work describes the first report of the functionalization of PET/SiO2 nanochannels by the ALD technique. We believe that this work provides a promising framework for the development of new nanochannel-based platforms suitable for multiple applications, such as water quality monitoring or directed molecular transport and separation.

Abstract: A fluorescein boronic acid conjugate has been used as a pH-sensitive dye in the root apoplast and because of its likely links to boric acid-binding sites. The marker (Glusenkamp et al.; German Patent Application) is non-toxic to cell growth up to concentrations of 100 μM and stains almost exclusively the apoplastic space of sunflower and maize roots. The meristematic zone behind the calyptra is hardly stained, which is in line with the assumption of a lack of demand for boron (B) during cell divison. By contrast, the expansion zone shows a more intense staining in a part of the longitudinal walls which is indicative of an intensive secretion of B-binding cell wall material into this part. A ‘banding’ of the stain in sunflower roots hints to a pulsating extension growth or at least intermittent secretion of B binding moieties. Root hairs seem to be more intensively stained than other cells of this region, especially at their tips. Experiments are under way to further characterize the bonds and to apply other boronic acid-coupled dyes for the histological identification of boric acid-binding ligands.