Use of voltammetry for in vitro equilibrium and transport studies of ionisable drugs

In this review, we will briefly outline the voltammetric investigations of the transfer of ionisable drugs at the interface between two immiscible electrolyte solutions. The voltammetric techniques enable the determination of some key in vitro properties of ionisable drugs, including partition coefficient, diffusion coefficient and membrane permeability. Some successful applications will be highlighted, together with the background methodologies

Functionalization of graphene at the organic/water interface

A simple method for the deposition of noble metal (Pd, Au) nanoparticles on a free-standing chemical vapour deposited graphene (CVD GR) monolayer is reported. The method consists of assembling the high purity CVD GR, by transfer from poly (methyl methacrylate) (PMMA), at the organic/water interface. Metal deposition can then proceed using either spontaneous or electrochemically-controlled processes. The resultant graphene-based metal nanoclusters are characterized using atomic force and electron microscopy techniques, and the location of the nanostructures underneath the graphene layer is determined from the position and the intensity changes of the Raman bands (D, G, 2D). This novel process for decoration of a single-layer graphene sheet with metal nanoparticles using liquid/liquid interfaces opens an alternative and useful way to prepare low dimensional carbon-based nanocomposites and electrode materials

Electrowetting on conductors: Anatomy of the phenomenon

We have recently reported that reversible electrowetting can be observed on the basal plane of graphite, without the presence of a dielectric layer, in both liquid/air and liquid/liquid configurations. The influence of carbon structure on the wetting phenomenon is investigated in more detail here. Specifically, it is shown that the adsorption of adventitious impurities on the graphite surface markedly suppresses the electrowetting response. Similarly, the use of pyrolysed carbon films, although exhibiting a roughness below the threshold previously identified as the barrier to wetting on basal plane graphite, does not give a noticeable electrowetting response, which leads us to conclude that specific interactions at the water–graphite interface as well as graphite crystallinity are responsible for the reversible response seen in the latter case. Preliminary experiments on mechanically exfoliated and chemical vapour deposition grown graphene are also reported.</p

Exfoliation of natural van der Waals heterostructures to a single unit cell thickness

Weak interlayer interactions in van der Waals crystals facilitate their mechanical exfoliation to monolayer and few-layer two-dimensional materials, which often exhibit striking physical phenomena absent in their bulk form. Here we utilize mechanical exfoliation to produce a two-dimensional form of a mineral franckeite and show that the phase segregation of chemical species into discrete layers at the sub-nanometre scale facilitates franckeite's layered structure and basal cleavage down to a single unit cell thickness. This behaviour is likely to be common in a wider family of complex minerals and could be exploited for a single-step synthesis of van der Waals heterostructures, as an alternative to artificial stacking of individual two-dimensional crystals. We demonstrate p-type electrical conductivity and remarkable electrochemical properties of the exfoliated crystals, showing promise for a range of applications, and use the density functional theory calculations of franckeite's electronic band structure to rationalize the experimental results

Mechanism of Ion Transfer in Supported Liquid Membrane Systems: Electrochemical Control over Membrane Distribution

[Image: see text] A polarization study carried out on a thin supported liquid membrane separating two aqueous compartments is presented. Transfer of both the ionized and uncharged form of an organic tracer dye, rhodamine B ([9-(2-carboxyphenyl)-6-diethylamino-3-xanthenylidene]-diethylammonium chloride), across supported liquid membranes composed of one of 1-octanol (octan-1-ol), 1,9-decadiene (deca-1,9-diene), 1,2-dichlorobenzene, or nitrophenyl octyl ether (1-(2-nitrophenoxy)octane) was studied using cyclic voltammetry and UV–vis absorption spectrophotometry. Concentration analysis indicates that the high membrane concentration of rhodamine B determines the ionic transfer observed via voltammetry, which is consistent with the low aqueous ionic concentration and large membrane/aqueous distribution of the molecule. The observed double-transfer voltammogram, although it has been largely neglected in previous literature, is a logical consequence of the presence of two liquid–liquid interfaces and is rationalized in terms of ion transfer across the two interfaces on either side of the membrane and supported by voltammograms obtained for a series of ions of varied lipophilicity. The bipolar nature of the voltammetric response offers an effective way of mass transport control via changing polarity of the applied voltage and finds immediate use in extraction, purification, and separation applications