Spotlights pubs.acs.org/JACS
Spotlights on Recent JACS Publications
■
■
WATER-SOLUBLE FOLDAMER CAPSULES WELCOME GUESTS
CATALYSTS AND SUBSTRATES WORK HAND IN HAND Achieving complete control over the stereochemistry, or handedness, of a compound remains a longstanding challenge in organic synthesis. While many methods are effective in generating a single stereocenter, accessing all possible stereoisomers of a compound typically requires redesign of the catalyst, substrates, and reaction conditions. In a new Perspective, Simon Krautwald and Erick Carreira describe a solution to this challenge based on the cooperativity of two distinct catalysts in a single reaction (DOI: 10.1021/ jacs.6b13340). This concept of stereodivergent dual catalysis suggests that with the suitable catalyst combination, any stereoisomer can be accessed in a given system. The authors highlight the power and efficiency of this approach in the development of stereodivergent carbonyl allylation reactions. Application of this strategy in target-oriented synthesis provides convenient access to the full complement of stereoisomers of a targeted natural product through the same synthetic sequence. Future opportunities in stereodivergent asymmetric catalysis include identifying methods that achieve complete control over distal stereocenters and extending this strategy to new transformations. In particular, stereodivergent aldol reactions would enable rapid access to a variety of synthetic building blocks and streamline the synthesis of natural products and drug candidates. Nicole Camasso, Ph.D.
Drawing on inspiration from naturally occurring biopolymers, scientists have aimed to create artificial synthetic molecules that are able to adopt well-defined, stable secondary structures with functional capabilities. Such oligomeric molecules, known as foldamers, have enormous potential for applications ranging from biomaterials to biosensing and therapeutics. To date, foldamersin particular foldamer capsuleshave been largely limited to use in organic solvents, a characteristic that would limit their use in biological applications. Researchers led by Gilles Guichard present the first report of a water-soluble foldamer assembly capable of recognizing and encapsulating simple molecules in aqueous solution (DOI: 10.1021/jacs.7b00181). The team designs a foldamer helix bundle, and in a series of studies, they demonstrate its ability to encapsulate primary alcohols within its internal cavity. The researchers report seven high-resolution aqueous crystal structures along with molecular dynamics and high-field NMR studies, highlighting both the robustness and the structural flexibility of the bundle capsule. The new study demonstrates the potential for future development of foldamers that are able to carry out their function in an aqueous environment, an important step toward applications in biosensing or drug delivery. Christine Herman, Ph.D.
■
■
DIAGNOSING THE ROLE OF ISOPRENE IN THE ATMOSPHERE
EFFECTS OF FLEXIBLE LIGANDS ON PHASE-CHANGING MOFS Traditionally, metal−organic frameworks (MOFs) for selective gas absorption have been constructed from metal ions and coordinating organic ligands that yield rigid, porous materials with a wide range of topologies. More recently, the field has seen a shift toward soft porous materials that distort and/or change phase upon gas uptake. The potential advantages of shapechanging materials include increased uptake capacity and selectivity for gases that induce the structural change. Now, researchers led by Catharine Esterhuysen and Leonard Barbour report two MOFs that undergo solvent- and pressure-induced phase changes, with both experimental and theoretical data showing the effects of flexible ligand orientation on pore size and gas absorption behavior (DOI: 10.1021/jacs.7b01764). The team shows that the phase changes result in the formation of new narrow-channel forms of the materials with a greatly reduced solvent-accessible volume. Complementary molecular modeling simulations shed light on the mechanism underlying the phase change, including the energetic changes involved. This seminal study in the field of coordination polymers may help lay the foundation for the design of new materials of this type. Christine Herman, Ph.D.
Although air pollution is typically associated with anthropogenic emissions resulting in aerosol and tropospheric (lower atmosphere) ozone formation, biogenic sources can be an important factor as well. Paul Wennberg and co-workers provide new insights into the mechanism of the oxidation of isoprene, a natural plant product emitted mainly from deciduous trees (DOI: 10.1021/jacs.6b12838). Isoprene plays a well-known but poorly understood role in the complicated atmospheric chemistry controlling air quality. Upon emission into the atmosphere, OH radicals oxidize isoprene, thereby initiating a complex dynamical system involving peroxy radicals that can react with a variety of molecules such as NO or HO2 to further impact the atmosphere. With a novel experimental approach to measure isomer-specific yields, the authors elucidate the first few steps of isoprene oxidation. They measure radical kinetics in an environmental chamber with full temperature and pressure control, monitoring the evolution of isomer-specific reaction products as a function of the peroxy radical lifetime. Understanding the impact of isoprene emission and its subsequent oxidation on our atmosphere is critical to formulating an effective strategy to combat air pollution. Dalia Yablon, Ph.D. © 2017 American Chemical Society
Published: May 3, 2017 6017
DOI: 10.1021/jacs.7b03876 J. Am. Chem. Soc. 2017, 139, 6017−6017
