A water-soluble, chiral calix[4]arene has been found to form hydrogels when triggered by the presence of specific anions, with efficacy linked to the Hofmeister series; the gel properties are modified by the associated cations, and gelation can be reversibly switched off by increasing pH.

Herein we demonstrate that ionic liquids can form long-lived double layers, generating electric fields detectable by straightforward open circuit potential (OCP) measurements. In imidazolium-based ionic liquids an external negative voltage pulse leads to an exceedingly stable near-surface dipolar layer, whose field manifests as long-lived (∼1–100 h) discrete plateaus in OCP versus time traces. These plateaus occur within an ionic liquid-specific and sharp potential window, defining a simple experimental method to probe the onset of interfacial ordering phenomena, such as overscreening and crowding. Molecular dynamics modeling reveals that the OCP arises from the alignment of the individual ion dipoles to the external electric field pulse, with the magnitude of the resulting OCP correlating with the product of the projected dipole moment of the cation and the ratio between the cation diffusion coefficient and its volume. Our findings also reveal that a stable overscreened structure is more likely to form if the interface is first forced through crowding, possibly accounting for the scattered literature data on relaxation kinetics of near-surface structures in ionic liquids.

Solution-phase and solid-state structural studies indicate that the remarkable hydrogelation properties of a proline-functionalised calix[4]arene emerge as a result of extended helical structures formed via inclusion of a proline moiety in a neighbouring calixarene cavity.

The thermal annealing behaviour of an electrolyte-triggered calixarene hydrogelator is found to depend strongly on the specific metal chloride used. While the lithium chloride gel showed typical gel-sol transitions as a function of temperature, the magnesium chloride gel was found to repeatedly strengthen with heat-cool cycles. Structural investigations using small-angle neutron scattering, and scanning probe microscopy, suggest that the annealing behaviour is associated with a change in morphology of the fibrous structures supporting the gel. On prolonged standing at room temperature, the magnesium chloride gel underwent a gel-crystal transition, with the collapsing gel accompanied by the deposition of crystals of a magnesium complex of the proline-functionalised calix[4]arene gelator.

The identification and quantification of illicit substances in the field is often desirable. Fourier transform infrared spectroscopy (FT-IR) has both qualitative and quantitative capabilities and field portable instruments are commercially available. Transmission infrared spectra of mixtures containing ephedrine hydrochloride, glucose, and caffeine and attenuated total reflection (ATR) infrared spectra of mixtures composed of methylamphetamine hydrochloride, glucose, and caffeine were used to develop principal component regression (PCR) calibration models. The root mean sum of errors of predictions (RMSEP) of all individual components in a mixture from a single measurement was <6% w/w, which reduced to approximately 3% w/w when triplicates were averaged. Sample mixing and grinding are essential to minimize the effect of heterogeneity, as deviations of up to 20% w/w were observed for single measurements of unground samples. Poor predictions of the components in a mixture occurred when samples were "contaminated" with substances not present in the calibration set, as would be expected. When only a single analyte (drug) was targeted, using a calibration set that contained both contaminated and uncontaminated samples, an RMSEP of approximately 4% w/w was achieved. The results demonstrate that ATR-FT-IR has the potential to quantify methylamphetamine samples, and possibly other licit or illicit substances, in at-seizure and on-site scenarios.