Spotlights Cite This: J. Am. Chem. Soc. 2017, 139, 14815-14816
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Spotlights on Recent JACS Publications
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FLUORESCENT SENSOR DETECTS OPIOIDS IN URINE Misuse of opioid drugs is becoming a public health epidemic around the world, leading to increased addiction and deaths from overdoses. Clinical, forensic, and occupational toxicologists have analytical tests to detect opioids such as heroin, morphine, and oxycodone. But these tests often require expensive equipment and specialized training. Pavel Anzenbacher and his colleagues simplify opioid testing, particularly in complex body fluids such as urine (DOI: 10.1021/jacs.7b06371). They synthesize three different acyclic cucurbiturils, each ending with a different arrangement of naphthalene rings, as sensors. Opiates or their metabolites binding in a sensor’s open cavity activate the fluorescence of its naphthalene walls. The intensity of the fluorescent signal is unique for each opioid, allowing the researchers to use one sensor to quantify molecules in a mixture. After calibrating one sensor to detect morphine and two of its metabolites in urine, the researchers are able to quantify the molecules in an unknown sample. The sensor also works in a high-throughput assay, potentially making it useful for highthroughput clinical settings. Melissae Fellet, Ph.D.
WHAT SUPRAMOLECULAR CHEMISTRY CAN DO FOR PROTEIN BIOLOGY Protein interactions are central to nearly all biological processes inside the cell, which makes them obvious drug targets. For example, extensive research has focused on the use of small molecules to target enzymes and interfere with binding to native ligands. But an even greater challenge lies in modulating protein−protein interactions (PPIs), which can be difficult to achieve with small molecules since they involve larger protein elements or multiple “hot spots” on the protein’s surface. To this end, researchers have looked to synthetic supramolecular assemblies. In a Perspective, Luc Brunsveld and colleagues present a comprehensive overview of the use of synthetic supramolecular systems for the recognition of amino acids, peptides, and whole proteins (DOI: 10.1021/jacs.7b01979). The authors focus on structural insights acquired from X-ray crystallography and NMR spectroscopy and emphasize the challenges of developing supramolecular host−guest systems that function in water, where hydrophobic and electrostatic interactions dominate. The researchers highlight how future success in the field will rely on structure-guided design of synthetic hosts that can serve as PPI modulators and shed light on protein assembly processes. Such work could ultimately lead to new therapeutic approaches and advances in sensor technology, protein immobilization techniques, and protein-based materials. Christine Herman, Ph.D.
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EXPLORING ANION−π CATALYSIS ON FULLERENES Until a few years ago, the only non-covalent interactions known to occur between ions and aromatic surfaces were cation−π interactions, which take place when electron-rich aromatic systems are drawn to electron-deficient cations. In 2013, the first reported evidence of anion−π interactions involved in chemical transformation emerged when researchers led by Stefan Matile found that electron-deficient, or π-acidic, aromatic surfaces can stabilize anionic transition states. Following those initial studies came others probing applications of this rare phenomenon. In a new report, Antonio Frontera, Stefan Matile, and coworkers describe the first anion−π catalysis involving fullerenesmolecules of carbon in the form of a hollow sphere (DOI: 10.1021/jacs.7b08113). The fullerene serves as a suitable catalyst for a Diels−Alder cycloaddition reaction thanks to the unique properties, including high-polarizability localized π holes on their surface. To make these fullerenes even more capable of anion stabilization, the researchers add tertiary amines to the surface, fine-tuning the positioning of the electron-withdrawing groups to accelerate otherwise disfavored enolate addition and exo Diels−Alder reactions. The selectivities are found to be consistent with computational simulations. The findings add to our understanding of anion−π interactions in general and may lead to the exploration of additional carbon allotropes, such as carbon nanotubes and graphene, in catalysis. Christine Herman, Ph.D. © 2017 American Chemical Society
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SMALL HELIUM HAS BIG EFFECT IN PEROVSKITE CHEMISTRY Perovskite materials, ABX3, are of great interest for applications due, in large part, to their compositional versatility. For example, substitution of small organic cations at the A site has led to halide-based perovskites that are attractive for use in photovoltaics. The introduction of small neutral molecules on this site may lead to other properties. Previously only dinitrogen has been thus incorporated, but in an adventitious fashion. The controlled introduction of other gases allows for the creation of new functional materials. Making strides in this direction, Angus Wilkinson and colleagues report A-site insertion of helium into the negative thermal expansion (NTE) material CaZrF6 at 300 K and high pressures (DOI: 10.1021/jacs.7b07860). The helium becomes trapped in the structure below 150 K, resulting in defect perovskites that persist at ambient pressure and low temperature. At room temperature, conversion between the defect and pristine material is reversible. The inserted helium affords enhanced structural stability and weakens the NTE. This work greatly expands perovskite chemistry by demonstrating controlled, site-specific introduction of a small neutral species. As the authors note, incorporation of other gases, such as Published: October 25, 2017 14815
DOI: 10.1021/jacs.7b11051 J. Am. Chem. Soc. 2017, 139, 14815−14816
Journal of the American Chemical Society
Spotlights
hydrogen, may be possible by modification of composition and experimental conditions, potentially leading to interesting gas storage materials. Katie Meihaus, Ph.D.
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A NEW, PROMISING, SOLID ELECTROLYTE INCREASES SAFETY FOR LITHIUM BATTERIES A continuing safety issue with current lithium batteries is that their liquid electrolytes expose them to leakage, flammability, and poor chemical stability. One solution to this problem is the use of solid electrolytes. They are less prone to chemical alterations during charge−discharge cycling, do not leak, and pose less of a fire threat. In addition, solid electrolytes, especially in the form of flexible films, facilitate the manufacture of lithium batteries. An obvious drawback of solid electrolytes is their lower ionic mobility. Poor mechanical properties are also a problem. CeWen Nan, Yang Shen, and co-workers report a promising solution (DOI: 10.1021/jacs.7b06364). They combine flexible polymers PVDF, a poly(vinylidene fluoride) polymer matrix, with LLZO, a ceramic filler, to form composite polymer electrolytes (CPEs). Their studies show that the PVDF matrix works with LLZO filler in synergy, resulting in an electrolyte with excellent ionic conductivity as well as better mechanical properties than current solid electrolytes. Testing the garnet membrane in a prototype lithium cell reports good rate capability and cycling stability at room temperature. The study indicates that CPEs are promising for applications in all-solidstate lithium batteries. Alexander Hellemans
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ISOTOPE EXCHANGE EXPLAINS MISSING HYDROGEN MYSTERY Without the cofactor NADPH, photosynthesis would come to a halt. It is also important in many other critical biochemical reactions, including the synthesis of amino acids, DNA subunits, and fatty acids. To understand how much of the cofactor is produced via various pathways, researchers have labeled substrates with deuterium and traced its incorporation into NADPH. These methods have led to a mystery, howeverin some cases, researchers can account, via known pathways, for only part of the NADPH produced. Though some have proposed that there must be another, yet unidentified NADPH production pathway, Joshua Rabinowitz and colleagues now show that a different phenomenon is at playthe exchange of hydrogen and deuterium between water and NADPH (DOI: 10.1021/jacs.7b08012). Usually the bonds between carbon and hydrogen in a molecule like NADPH do not exchange isotopes with hydrogen atoms in water. However, Rabinowitz and co-workers show that flavin enzymes can catalyze such an isotopic switch, and that it happens inside cells. By figuring out the magnitude of this exchange, the authors can reconstruct how much NADPH is actually biologically produced through specific pathways. The work enables accurate interpretation of deuterium tracing studies of redox cofactor and fatty acid metabolism. Deirdre Lockwood, Ph.D.
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DOI: 10.1021/jacs.7b11051 J. Am. Chem. Soc. 2017, 139, 14815−14816
