Sodium cationization can disrupt the intramolecular hydrogen bond that mediates the sunscreen activity of oxybenzone

A key decay pathway by which organic sunscreen molecules dissipate harmful UV energy involves excited-state hydrogen atom transfer between proximal enol and keto functional groups. Structural modifications of this molecular architecture have the potential to block ultrafast decay processes, and hence promote direct excited-state molecular dissociation, profoundly affecting the efficiency of an organic sunscreen. Herein, we investigate the binding of alkali metal cations to a prototype organic sunscreen molecule, oxybenzone, using IR characterization. Mass-selective IR action spectroscopy was conducted at the free electron laser for infrared experiments, FELIX (600-1800 cm-1), on complexes of Na+, K+ and Rb+ bound to oxybenzone. The IR spectra reveal that K+ and Rb+ adopt binding positions away from the key OH intermolecular hydrogen bond, while the smaller Na+ cation binds directly between the keto and enol oxygens, thus breaking the intramolecular hydrogen bond. UV laser photodissociation spectroscopy was also performed on the series of complexes, with the Na+ complex displaying a distinctive electronic spectrum compared to those of K+ and Rb+, in line with the IR spectroscopy results. TD-DFT calculations reveal that the origin of the changes in the electronic spectra can be linked to rupture of the intramolecular bond in the sodium cationized complex. The implications of our results for the performance of sunscreens in mixtures and environments with high concentrations of metal cations are discussed

Facile synthesis of hierarchical Cu2O nanocubes as visible light photocatalysts

Hierarchically structured Cu2O nanocubes have been synthesized by a facile and cost-effective one-pot, solution phase process. Self-assembly of 5 nm Cu2O nanocrystallites induced through reduction by glucose affords a mesoporous 375 nm cubic architecture with superior visible light photocatalytic performance in both methylene blue dye degradation and hydrogen production from water than conventional non-porous analogues. Hierarchical nanocubes offer improved accessible surface active sites and optical/electronic properties, which act in concert to confer 200–300% rate-enhancements for the photocatalytic decomposition of organic pollutants and solar fuels

Using hyperpolarised NMR and DFT to rationalise the unexpected hydrogenation of quinazoline to 3,4-dihydroquinazoline

PHIP and SABRE hyperpolarized NMR methods are used to follow the unexpected metal-catalysed hydrogenation of quinazoline (Qu) to 3,4-dihydroquinazoline as the sole product. A solution of [IrCl(IMes)(COD)] in dichloromethane reacts with H2 and Qu to form [IrCl(H)2(IMes)(Qu)2] (2). The addition of methanol then results in its conversion to [Ir(H)2(IMes)(Qu)3]Cl (3) which catalyses the hydrogenation reaction. Density functional theory calculations are used to rationalise a proposed outer sphere mechanism in which (3) converts to [IrCl(H)2(H2)(IMes)(Qu)2]Cl (4) and neutral [Ir(H)3(IMes)(Qu)2] (6), both of which are involved in the formation of 3,4-dihydroquinazoline via the stepwise transfer of H+ and H−, with H2 identified as the reductant. Successive ligand exchange in 3 results in the production of thermodynamically stable [Ir(H)2(IMes)(3,4-dihydroquinazoline)3]Cl (5)

P25@CoAl layered double hydroxide heterojunction nanocomposites for CO2 photocatalytic reduction

Artificial photosynthesis driven by inorganic photocatalysts offers a promising route to renewable solar fuels, however efficient CO2 photoreduction remains a challenge. A family of hierarchical nanocomposites, comprising P25 nanoparticles encapsulated within microporous CoAl-layered double hydroxides (CoAl-LDHs) were prepared via a one-pot hydrothermal synthesis. Heterojunction formation between the visible light absorbing CoAl-LDH and UV light absorbing P25 semiconductors extends utilisation of the solar spectrum, while the solid basicity of the CoAl-LDH increases CO2 availability at photocatalytic surfaces. Matching of the semiconductor band structures and strong donor–acceptor coupling improves photoinduced charge carrier separation and transfer via the heterojunction. Hierarchical P25@CoAl-LDH nanocomposites exhibit good activity and selectivity (>90%) for aqueous CO2 photoreduction to CO, without a sacrificial hole acceptor. This represents a facile and cost-effective strategy for the design and development of LDH-based nanomaterials for efficient photocatalysis for renewable solar fuel production from particularly CO2 and aqueous water

The influence of an alkenyl terminal group on the mesomorphic behaviour and electro-optic properties of fluorinated terphenyl liquid crystals

Novel liquid crystal terphenyls with two, three and four lateral fluoro substituents and an alkene unit at the end of a terminal chain are presented in terms of synthesis, mesomorphic behaviour and electro-optic properties. The difluoro analogues were found to exhibit the smectic C phase over a wide temperature range, with short temperature ranges of the smectic A and the nematic phase above. Very low melting points were recorded for the trifluoro analogues, and the shorter chain homologues of these materials exhibit the nematic phase over a wide temperatures with a monotropic smectic C phase and the higher homologues exhibit the smectic C phase over a wide temperature range with the nematic phase above. The tetrafluoroterphenyls exhibit the nematic phase over a wide temperature range with the complete absence of smectic phases. As appropriate, the materials were evaluated for dielectric anisotropy and threshold voltage in nematic phase, and mixed with a chiral dopant to evaluate the spontaneous polarisation, tilt angle and switching times in the chiral smectic C phase. The results show that these compounds are strong potential candidates for application in both vertically aligned nematic (VAN) and ferroelectric liquid crystal (FLC) devices

Contrasting Photochemical and Thermal Catalysis by Ruthenium Arsine Complexes Revealed by Parahydrogen Enhanced NMR Spectroscopy

The thermal and photochemical reactivity of Ru(CO)3(dpae) (1) and Ru(CO)2(dpae)(PPh3) (2) towards H2 and diphenylacetylene is described. These reactions are monitored by NMR spectroscopy in conjunction with the parahydrogen induced polarisation (PHIP) effect, spatially resolved chemical shift imaging and the Only Parahydrogen Spectroscopy (OPSY) signal filtering method. The results are supported by DFT. The thermal and photochemical reactions of 1 with H2 proceed by CO loss and form Ru(H)2(CO)2(dpae) (3). 1 catalyses the formation of 1,2 diphenylethane, cis- and trans-stilbene, and 1,2,3,4 tetraphenylbutadiene under 325 nm irradiation at 295 K in a reaction where Ru(CO)2(dpae)(η2-CHPh=CPhCPh=CHPh) forms. When the same reaction is monitored under thermal conditions at 333 K the η2-diene complex is no longer detected but hydride containing Ru(CHPhCH2Ph)(H)(CO)2(dpae) and Ru(CO)2(dpae)(trans-stilbene) are seen. For 1, the photochemical promotion of hydrogenation through 325 nm irradiation results in an approximate 5.5-fold increase in turnover at 333 K when compared to no irradiation. In contrast, 2 reacts thermally with H2 at 295 K through PPh3 and CO loss with both Ru(H)2(CO)(dpae)(solvent) and 3 being detected. Under irradiation, CO loss dominates and two isomers of Ru(H)2(CO)(dpae)(PPh3) form. While 2 forms the same 4 organic products at 295 K and a second isomer of Ru(CHPhCH2Ph)(H)(CO)2(dpae) alongside the diene complex no photochemical promotion of hydrogenation is observed