Spotlights on Recent JACS Publications

1 Spotlights on RecentJACSP ublications METAL ORGANIC CAGES CAPTURE AND RELEASEMOLECULAR PRISONERST here is a new tool in the chemist s toolbox for the creation ofmultifunctional materials that allow molecules to be captured andreleased in response to stimuli or over time. Researchers led byJonathan Nitschke describe a new method for the creation ofpolymeric hydrogels that employ metal organic cages to captureand release guest molecules in response to stimuli ( ).The team creates a polymeric hydrogel capable of capturingmolecules in two distinct ways: by binding them between cross-linked polymer threads or byfirmly locking them away in thecavities of metal organic cages that form cross-links between thethreads.

2 The researchers use droplet-based microfluidics tofabricate the hydrogels into microparticles and demonstrate theirresponsiveness to multiple stimuli for the triggered release of themolecular , the release profiles for the two modes of capture aredistinct, as the loosely bound molecules can readily leach out ofthe gel matrix, while those held inside the molecular cages, whichare formed via the metal-templated condensation of amine andaldehyde subcomponents, require a specific chemical stimulus toeffect their release. Metal organic cage-cross-linked polymerstherefore represent a platform for the development of newmultifunctional materials, the authors Herman, ORDER FROM CHAOS WITH BLUEPRINT FORDNA-ASSISTED CRYSTALLIZATIONR ecently, Marcus Weck, David Pine, and colleagues reportedsuccess in coaxing micrometer-sized spheres into uniform,crystalline arrangements with the help of selectively stickyDNA ( ).

3 The key wascreating DNA-coated particles that could rearrange themselvesand anneal like atoms in traditional, well-studied crystals. Suchcolloidal crystallization has been achieved before with nano-particles, but larger spheres had proved much more the researchers present a detailed blueprint for how tomake these micrometer-sized DNA-coated particles ( ). The particles chemical compositioncan vary polymers, inorganic materials, and hybrids all work but the sphere surface must be smooth and the DNA linkers mustbe dense. Colloids can be the same material or different, ofsimilar size or not, and crystallization patterns can beprogrammed by using complementary DNA ability to mix and crystallize micrometer-sized particles ofdifferent materials is ideal for the fabrication of photonic crystals,which require ordered arrangements of high and low refractiveindex materials.

4 Detailed studies of plasmonic and magneticphenomena also require precisely engineered arrangements. Theauthors careful and thoughtful explanations of experimentalprocedures make this paper a useful resource for those who seekto explore DNA-directed assembly, and the uniform arrange-ments of particles in the micro Morber, READY OR KNOT, HERE COME SYNTHETICANION-BINDING MOLECULESN aturally occurring molecular knots, with mechanically inter-locked architectures, have been found in both DNA and chemists have successfully created artificial molecularknots, previous reports have not shown any interesting orunusual chemical properties.

5 In a new report, researchers led byDavid Leigh describe molecular knots and links that selectivelybind anions with surprisingly strong affinities ( ).The team has synthesized three molecules a molecularpentafoil knot, and doubly and triply entwined [2]catenanemolecules which are all based on circular Fe(II) doublehelicate scaffolds. Using X-ray crystallography, the researchersfind that the molecules salts contain well-ordered anionsassociated with their central cavities. Solid-state and NMRanalyses show the binding is facilitated by both hydrogen-bonding and long-range electrostatic interactions.

6 One moleculeexhibits an affinity of ( ) 1010M 1in acetonitrilesolvent, and this unique property places it among the strongestsynthetic noncovalent binders of halide anions found to Herman, PROPER SUBSTITUENTS KEY TO CREATINGALTERNATING SEQUENCE POLYMERSS ynthetic polymers with controlled monomer sequences andmicrostructures are highly desirable for their ability to createhigh-order structures that mimic biological macromoleculespossessing unique functions and properties. Established methodsfor synthesizing lengthy, well-defined polymers typically involvethe use of solid supports and laborious protection deprotectionsteps.

7 Now, Benjamin Elling and Yan Xia report a new methodfor the creation of polymers with precisely alternating sequenceand high microstructure regularity without these time-intensivesteps ( ).Using a technique known as living alternating ring-openingmetathesis polymerization (AROMP), the researchers cancombine two monomers together with a metal catalyst to createpolymers with well-defined molecular weights and end groupsand narrow molecular weight distribution. The polymers alsohave precisely alternating sequences, made possible by the use ofmonomer substituents that prevent homoaddition.

8 In otherwords, the monomers do not react with themselves but insteadtake turns adding one at a time in an alternating fashion. Thesubstituents in the judiciously designed monomers also helpprevent undesirable side reactions known as secondarymetatheses, which include both intermolecular chain transferand intramolecular backbiting . This chemistry advances ourability to control polymer sequences and microstructures inhomogeneous polymerizations. Well-defined polymers such asthese products could provide useful properties for a broad rangeof engineering Herman, :August 12, 2015 American Chemical Society9759 DOI: , 137, 9759 9759