Spotlights Cite This: J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
pubs.acs.org/JACS
Spotlights on Recent JACS Publications
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PRECISE MAPPING OF A MAMMALIAN mRNA MODIFICATION
BUILDING A NANOBALL WITH TEMPLATE-DIRECTED SYNTHESIS Ever since the discovery in the 1980s of the geodesic domeshaped buckminsterfullerenes, known as buckyballs, chemists have focused on developing rational strategies for synthesizing other π-conjugated molecular cages. Although metal coordination or boronic ester condensation reactions can reliably produce cages or capsules, these methods do not lead to πconjugated connections. Other approaches, such as imine formation, alkene metathesis, and alkyne metathesis, do produce π-conjugated connections, but the resulting molecules lack long-range conjugation. Harry L. Anderson and co-workers have found a solution to this dilemma via simple molecular templates (DOI: 10.1021/ jacs.8b02552). Using phenylene-pyridine molecules as templates, the researchers join two perpendicular intersecting conjugation pathways, one containing six alkyne-linked porphyrin units and the other containing 10 porphyrin units, to create a 14-porphyrin prolate-ellipsoidal cagea nanoball. Competing ligands can displace the template molecules from this cage. Tests show that when all 14 porphyrin units are bound to the templates, electronic excitation delocalizes over the entire three-dimensional system in 0.3 ps, indicating longrange conjugation. However, when the templates are absent, the delocalization time increases to about 2 ps, denoting diminished conjugation. This synthetic approach to produce πconjugated geodesic cages could find use in both basic and practical applications, the authors suggest. Christen Brownlee
Xiang Zhou, Xiaocheng Weng, and co-workers report a deoxythymidine analogue that can be used to distinguish unmodified adenosine from m6A, an N-6 methylated adenosine base, and map the location of the latter within an RNA strand (DOI: 10.1021/jacs.7b13633). The modified nucleotide m6A plays an important regulatory role in mammalian gene expression and other biological processes. Existing methods for mapping m6A have shortcomings that limit their utility. The researchers substitute sulfur and then selenium for oxygen at the 4-position in deoxythymidine triphosphate (dTTP) and find that the selenium analogue effectively base pairs with adenosine itself but not with m6A. When an mRNA strand containing m6A is reverse transcribed into complementary DNA, the result is a truncated product that can be sequenced to determine the location of m6A. Because m6A is the most prevalent mRNA modification, precisely locating it in the mammalian transcriptome could help to advance understanding of its role in genetic regulation. Sonja Krane, Ph.D.
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MIMICKING METALLOENZYMES WITH CATALYTIC SINGLE-CHAIN NANOPARTICLES
When it comes to creating catalysts that provide improved product selectivity, researchers sometimes turn to mimicking nature’s biological catalysts: enzymes. In a JACS Perspective, Peter W. Roesky, Christopher Barner-Kowollik, and co-workers discuss the state of the art of developing catalytic single-chain nanoparticles as tailor-made constructs inspired by metalloenzymes (DOI: 10.1021/jacs.8b02135). The authors explain the challenges in synthesizing these catalysts, which consist of a metal-containing polymeric chain that folds to create “nanoreactors” that mimic the folded structure and active sites of metalloenzymes. An important hurdle to overcome, they write, is creating a structure that allows the diffusion of both starting materials and products freely in and out of the nanoreactors, while selectively shielding the catalytic center to make it accessible only for target substrates. Once accomplished, these structures often provide advantages over molecular metal catalysts, for example by preventing reduction or loss of catalytic activity due to aggregation, inhibition by the solvent, lability of metal−ligand bonds, or undesired oxidation. Another advantage is the ability of the polymer chains to be further tailored to account for different reaction conditions or for substrates with different functional groups. The authors suggest that these synthetic metalloenzyme mimics could represent the next generation of catalytic materials. Christen Brownlee © XXXX American Chemical Society
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REAL-TIME TRACKING OF CAPSID ASSEMBLY Viruses perform amazing feats of natural engineering by spontaneously self-assembling identical components to create protective protein shells called capsids. Understanding capsid construction is important to aid in antiviral drug development, but the process is largely a mystery. Martin F. Jarrold, Adam Zlotnick, and co-workers have uncovered new details by using charge detection mass spectrometry to observe hepatitis B virus (HBV) capsid assembly in real time (DOI: 10.1021/jacs.8b01804). From truncated Cp149 proteins, HBV assembles 120 dimers to form an icosahedral T = 4 capsid. The researchers obtain interesting results when they vary salt concentration. At low concentration, initial capsid assembly rate is slow with a limited amount of intermediate formation, indicative of downhill energy pathways. At higher concentration, the initial assembly rate increases. However, only about half of the assembly products contain the 120 dimers of the T = 4 capsid; the other half are 90-dimer intermediates, indicating a pathway divergence. Eventually, the smaller intermediates overcome an activation energy and shift to the full mass of the capsid.
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DOI: 10.1021/jacs.8b04465 J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
Journal of the American Chemical Society
Spotlights
Because high ionic strength increases dimer−dimer interactions, the authors hypothesize that the delay stems from either a defect in the growing capsid or a hole closure prior to full assembly. They favor the latter explanation and conclude this model likely fits capsid assembly in general. Kristy G. Lahoda, Ph.D.
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NANOPARTICLE STRUCTURE SPEEDS UP OPTICALLY INDUCED SPIN TRANSITION Solids that exhibit electronic spin transitions commonly change volumesometimes by 10% or moreafter changing from one spin state to the other. This thermally or optically induced volume change could be harnessed to make precise microactuators. To better control the mechanical movement of these devices, researchers want to understand how the interface between materials influences a spin transition. Daniel R. Talham, Mark W. Meisel, Kamel Boukheddaden, and their colleagues report that a thin shell surrounding an optically switchable material can speed a spin transition from minutes to seconds (DOI: 10.1021/jacs.8b02148). The team has prepared nanoparticles using two isostructural Prussian blue analogues. In these particles, a thin shell of KjNik[Cr(CN)6]l· nH2O surrounds a core of light-switchable RbaCob[Fe(CN)6]c· mH2O. The researchers measure the spin transition of the core using temperature-dependent powder X-ray diffraction, SQUID magnetometry, and computer modeling. They find that the particle’s outer shell limits the core’s constriction when it cools from a high spin to a low spin state. This confinement makes the core less rigid in its low-spin state and better able to expand into its high-spin state, thus speeding the rate of light triggered switching. Melissae Fellet, Ph.D.
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ONE IS NOT THE LONELIEST NUMBER: BREAKING C−H BONDS WITH TIN The number of chemical bonds to a metalits coordination numbercritically controls the chemistry it can perform. By accessing metal complexes that exhibit new or rare coordination numbers, chemists can uncover new reactivity patterns. For example, the activation of unreactive C−H bonds using earthabundant metal complexes, as alternatives to rare or costly transition-metal complexes, remains a key challenge. The need for new approaches to C−H bond activation has become a critical opportunity in the fuels and chemicals industry, as hydraulic fracturing technologies has rapidly increased the supply of methane. In a new example, Philip P. Power and colleagues have prepared a one-coordinate tin radical from a diarylstannylene that has a bulky organic ligand designed for homolytic cleavage from the tin metal center (DOI: 10.1021/jacs.8b01878). The researchers find that this tin(I) complex is especially reactive under mild conditions, allowing for radical-induced activation of previously inaccessible C−H bonds of arenes such as toluene, m-xylene, and mesitylene. The activation of such strong bonds under mild conditions is especially notable for a main-group element, for which there is little precedent. This new class of low-coordinate tin radical may facilitate further exploration into practical applications of C−H activation by earth-abundant-metal catalysts. Matthew P. McLaughlin, Ph.D.
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DOI: 10.1021/jacs.8b04465 J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
