Triphasic nature of polymers of intrinsic microporosity (PIM-1 and PIM-PY) induces storage and catalysis effects in hydrogen and oxygen reactivity at electrode surfaces

Hydrogen oxidation and oxygen reduction are two crucial energy conversion reactions, which are shown to be both strongly affected by the presence of intrinsically microporous polymer coatings on electrodes. Polymers of intrinsic microporosity (PIMs) are known to possess extremely high internal surface area and ability to bind gases under dry conditions. It is shown here that both, hydrogen‐ and oxygen gas binding into PIMs, also occurs under wet or “triphasic” conditions in aqueous electrolyte environments (when immersed in 0.01 M phosphate buffer at pH 7). For two known PIM materials (PIM‐1 and PIM‐PY), nanoparticles are formed by an anti‐solvent precipitation protocol and then cast as a film onto platinum or glassy carbon electrodes. Voltammetry experiments reveal evidence for hydrogen and oxygen binding. Both, PIM‐1 and PIM‐PY, locally store hydrogen or oxygen gas at the electrode surface and thereby significantly affect electrocatalytic reactivity. The onset of oxygen reduction on glassy carbon is shifted by 0.15 V in the positive direction

Quantitative chemical exchange saturation transfer imaging of nuclear overhauser effects in acute ischemic stroke

Purpose In chemical exchange saturation transfer imaging, saturation effects between − 2 to − 5 ppm (nuclear Overhauser effects, NOEs) have been shown to exhibit contrast in preclinical stroke models. Our previous work on NOEs in human stroke used an analysis model that combined NOEs and semisolid MT; however their combination might feasibly have reduced sensitivity to changes in NOEs. The aim of this study was to explore the information a 4-pool Bloch–McConnell model provides about the NOE contribution in ischemic stroke, contrasting that with an intentionally approximate 3-pool model. Methods MRI data from 12 patients presenting with ischemic stroke were retrospectively analyzed, as well as from six animals induced with an ischemic lesion. Two Bloch–McConnell models (4 pools, and a 3-pool approximation) were compared for their ability to distinguish pathological tissue in acute stroke. The association of NOEs with pH was also explored, using pH phantoms that mimic the intracellular environment of naïve mouse brain. Results The 4-pool measure of NOEs exhibited a different association with tissue outcome compared to 3-pool approximation in the ischemic core and in tissue that underwent delayed infarction. In the ischemic core, the 4-pool measure was elevated in patient white matter ( 1.20±0.20 ) and in animals ( 1.27±0.20 ). In the naïve brain pH phantoms, significant positive correlation between the NOE and pH was observed. Conclusion Associations of NOEs with tissue pathology were found using the 4-pool metric that were not observed using the 3-pool approximation. The 4-pool model more adequately captured in vivo changes in NOEs and revealed trends depending on tissue pathology in stroke

High-capacity methane storage in flexible alkane-linked porous aromatic network polymers

Adsorbed natural gas (ANG) technology is a viable alternative to conventional liquefied or compressed natural-gas storage. Many different porous materials have been considered for adsorptive, reversible methane storage, but fall short of the US Department of Energy targets (0.5 g(-1), 26311(-1)). Here, we prepare a flexible porous polymer, made from benzene and 1,2-dichloroethane in kilogram batches, that has a high methane working capacity of 0.625 g g(-1) and 29411(-1) when cycled between 5 and 100 bar pressure. We suggest that the flexibility provides rapid desorption and thermal management, while the hydrophobicity and the nature of the covalently bonded framework allow the material to tolerate harsh conditions. The polymer also shows an adsorbate memory effect, where a less adsorptive gas (N-2) follows the isotherm profile of a high-capacity adsorbate (CO2), which is attributed to the thermal expansion caused by the adsorption enthalpy. The high methane capacity and memory effect make flexible porous polymers promising candidates for ANG technology

Porous organic molecular solids by dynamic covalent scrambling

The main strategy for constructing porous solids from discrete organic molecules is crystal engineering, which involves forming regular crystalline arrays. Here, we present a chemical approach for desymmetrizing organic cages by dynamic covalent scrambling reactions. This leads to molecules with a distribution of shapes which cannot pack effectively and, hence, do not crystallize, creating porosity in the amorphous solid. The porous properties can be fine tuned by varying the ratio of reagents in the scrambling reaction, and this allows the preparation of materials with high gas selectivities. The molecular engineering of porous amorphous solids complements crystal engineering strategies and may have advantages in some applications, for example, in the compatibilization of functionalities that do not readily cocrystallize