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The ability of some crystalline porous coordination polymers (PCP) to undergo guest-induced reversible structural changes is of great interest for practical applications such as guest separation and storage. Now, using liquid-phase atomic force microscopy, a team led by Nobuhiko Hosono and Susumu Kitagawa has imaged structural transformations occurring at the crystal–solvent interface of a PCP. The surface (illustrated on the cover) was shown to be more flexible than anticipated. It undergoes a sharp, reversible transition between tetragonal and rhombic lattices in the absence and presence of biphenyl guest molecules — even at guest concentrations that are too low to trigger structural transformations of the bulk crystal.
The elements of the periodic table are more integral to our daily lives now than they have ever been before. Bruce C. Gibb takes a look at the factors used to decide just how critical the supply of any given mineral is.
Intersystem crossing plays a role in the mechanism of many reactive collisions between atomic species and organic molecules, and has been generally observed when the reactants are still approaching one another. Now, intersystem crossing has been observed to also occur after their initial interaction.
Strained boronate complexes have now been shown to enable an unprecedented cross-coupling reaction across a C–C σ-bond. Using this approach, highly functionalized cyclobutanes can be prepared with excellent stereocontrol from readily available reagents.
Most compounds form crystals so small that scientists cannot experimentally determine their atomic structures using X-ray crystallography. Microcrystal electron diffraction now provides a unique solution for this challenge.
Some porous coordination polymers (PCPs) are known to be flexible and guest-responsive. Now, the guest-induced sharp, reversible structural transformation of the surface of a single-crystalline PCP has been visualized by in situ liquid-phase atomic force microscopy. This local response occurred at a guest concentration that was too low to trigger changes to the bulk crystal.
Widely used palladium-mediated cross-couplings typically operate via a handful of fundamental reaction steps. Now, the reactivity between palladium and C–C σ-bonds has been described. This carbopalladation enables the coupling of organoboronic esters and aryl triflates across a C–C σ-bond of a bicyclo[1.1.0]butane to form disastereomerically pure trisubstituted cyclobutanes.
Intersystem crossing (ISC) is a radiationless process that is important in many photophysical systems. It has now been observed to take place in the exit channel for the reaction of ground-state atomic oxygen with alkylamines.
The SN2 reaction, a fundamental process associated with ionic chemistry, can be incorporated into a photochemical approach to creating radicals from alkyl electrophiles. This method occurs readily under visible-light irradiation, exhibits broad functional-group tolerance, and enables the formation of open-shell intermediates from substrates that are incompatible with traditional radical-generating strategies.
The creation of a viable technology that enables precise control over the monomer sequence in synthetic polymers remains a significant challenge. High-purity sequence-defined polyethers with readily tailored side-chain functionalities have now been made through liquid-phase iterative synthesis combined with size-exclusion molecular sieving and real-time monitoring.
In native photosystem II (PSII), multi-chromophore antennas surround the reaction centre, capturing light and triggering the quantized (four-flashes) photo-oxidation of water to oxygen. The PSII ‘quantasome’ is the most efficient photo-electrolyser built so far. An artificial quantasome has now been developed; it is specifically designed for oxygen evolution by self-assembling light-harvesting-perylene bisimides with a ruthenium polyoxometalate water-oxidation catalyst.
Nitrogen fixation—the direct conversion of dinitrogen into ammonia or other nitrogen-containing products—is notoriously difficult to promote under mild conditions. Now, the reactivity of a multimetallic diuranium(iii) complex recently found capable of reducing and functionalizing N2 has been explored, replacing its nitride bridge with an oxo bridge, which resulted in a markedly different reactivity.
Preparation of well-defined N-glycans is very demanding, which hampers progress in glycoscience. Now, a biomimetic synthetic approach has been developed in which a readily available bi-antennary glycan can be converted in ten or fewer steps into multi-antennary N-glycans. This approach enables each arm to be uniquely extended by glycosyltransferases to give complex branched N-glycans.
Solid acid heterogeneous catalysts are widely used in industrial chemical processes, but understanding the exact molecular structures responsible for catalytic activity has proved difficult. Now, the structure of the strong Brønsted acid site for a sulfated zirconium-based metal–organic framework has been shown to consist of a specific arrangement of adsorbed water and sulfate moieties on the zirconium clusters.
Typical methods for the enantioselective α-functionalizations of ketones join ketone enolate nucleophiles with carbon or heteroatom electrophiles. We report an umpolung strategy to achieve this transformation with masked ketone electrophiles and a wide range of conventional heteroatom and carbon nucleophiles catalysed by a metallacyclic iridium catalyst in high yield and enantioselectivity.
Lanthanum is the first lanthanide — or the last. Or it’s not a lanthanide at all. In any case, Brett Thornton and Shawn Burdette are sure that it’s an element that might or might not be in group three of the periodic table.