Semi-analytic method for slow light photonic crystal waveguide design

We present a semi-analytic method to calculate the dispersion curves and the group velocity of photonic crystal waveguide modes in two-dimensional geometries. We model the waveguide as a homogenous strip, surrounded by photonic crystal acting as diffracting mirrors. Following conventional guided-wave optics, the properties of the photonic crystal waveguide may be calculated from the phase upon propagation over the strip and the phase upon reflection. The cases of interest require a theory including the specular order and one other diffracted reflected order. The computational advantages let us scan a large parameter space, allowing us to find novel types of solutions.     

Preparation of Hybrid Thiol‐Acrylate Emulsion‐Templated Porous Polymers by Interfacial Copolymerization of High Internal Phase Emulsions

Emulsion‐templated highly porous polymers (polyHIPEs), containing distinct regions differing in composition, morphology, and/or properties, are prepared by the simultaneous polymerization of two high internal phase emulsions (HIPEs) contained within the same mould. The HIPEs are placed together in the mould and subjected to thiol‐acrylate photopolymerization. The resulting polyHIPE material is found to contain two distinct semicircular regions, reflecting the composition of each HIPE. The original interface between the two emulsions becomes a copolymerized band between 100 and 300 μm wide, which is found to be mechanically robust. The separate polyHIPE layers are distinguished from one another by their differing average void diameter, chemical composition, and extent of contraction upon drying.

     

A Visible‐Light‐Promoted O‐Glycosylation with a Thioglycoside Donor

Visible‐light irradiation of 4‐p‐methoxyphenyl‐3‐butenylthioglucoside donors in the presence of Umemoto's reagent and alcohol acceptors serves as a mild approach to O‐glycosylation. Visible‐light photocatalysts are not required for activation, and alkyl‐ and arylthioglycosides not bearing the p‐methoxystyrene are inert to these conditions. Experimental and computational evidence for an intervening electron donor–acceptor complex, which is necessary for reactivity, is provided. Yields with primary, secondary, and tertiary alcohol acceptors range from moderate to high. Complete β‐selectivity can be attained through neighboring‐group participation.     

Generation and reactions of Pentacyclo[4.3.0.0(2,4).0(3,8).0(5,7)]non-4-ene

The highly pyramidalized alkene, pentacyclo[4.3.0.0(2,4).0(3,8).0(5,7)]non-4-ene (9), has been generated via treatment of 4,5-diiodopentacyclo[4.3.0.0(2,4).0(3,8).0(5,7)]nonane (12) with n-butyllithium and tert-butyllithium. The title alkene has also been trapped as its Diels-Alder adduct with 1,3-diphenylisobenzofuran, 2,5-dimethylfuran, and spiro[2.4]hepta-4,6-diene. Products resulting from alkyllithium addition to the pyramidalized double bond of 9 have been isolated and fully characterized spectroscopically. The geometry, olefin strain energy, heat of hydrogenation, and relative HOMO/LUMO energies of 9 have been obtained by ab initio calculations at the MP2 and B3LYP levels using the 6-31G* basis set.     

Organic solar cells processed from green solvents

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In vitro characterization of an electroactive carbon-nanotube-based nanofiber scaffold for tissue engineering

In an effort to reduce organ replacement and enhance tissue repair, there has been a tremendous effort to create biomechanically optimized scaffolds for tissue engineering applications. In contrast, the development and characterization of electroactive scaffolds has attracted little attention. Consequently, the creation and characterization of a carbon nanotube based poly(lactic acid) nanofiber scaffold is described herein. After 28 d in physiological solution at 37 °C, a change in the mass, chemical properties and polymer morphology is seen, while the mechanical properties and physical integrity are unaltered. No adverse cytotoxic affects are seen when mesenchymal stem cells are cultured in the presence of the scaffold. Taken together, these data auger well for electroactive tissue engineering.

     

Topological variations of the PDP ligand and its prospects in molybdenum(0) dearomatization agents

The compounds fac-(κ(3)-PDP)Mo(CO)(3) {1; PDP = 2-[[2-(1-(pyridin-2-ylmethyl)pyrrolidin-2-yl)pyrrolidin-1-yl]methyl]pyridine}, [(cis-β-PDP)Mo(NO)(CO)]PF(6) ([cis-β-3]PF(6)), [(cis-α-PDP)Mo(NO)(CO)]PF(6) ([cis-α-3]PF(6)), [(cis-α-PDP)Mo(NO)Br]PF(6) ([4]PF(6)), [(trans-PDP)Cu](BF(4))(2)·CH(3)CN ([5](BF(4))(2)·CH(3)CN), and [(trans-PDP)Cu](OSO(2)CF(3))(2) ([5](OSO(2)CF(3))(2)) have been synthesized and structurally characterized by single-crystal X-ray diffraction. These are the first reported complexes of PDP on metal centers other than iron(II). The observed configurations indicate a broader range of accessible PDP topologies than has been reported. The {(cis-α-PDP)Mo(NO)}(+) fragment is found to be less π-basic than the dearomatizing {Tp(MeIm)Mo(NO)} fragment [Tp = hydridotris(1-pyrazolyl)borato; MeIm = 1-methylimidazole].     

Raising the Speed Limit for β-Hairpin Formation

Understanding the folding of the β-hairpin is a crucial step in studying how β-rich proteins fold. We have studied CLN025, an optimized ten residue synthetic peptide, which adopts a compact, well-structured β-hairpin conformation. Formation of the component β-sheet and β-turn structures of CLN025 was probed independently using a combination of equilibrium Fourier transform infrared spectroscopy and laser-induced temperature jump coupled with time-resolved infrared and fluorescence spectroscopies. We find that CLN025 is an ultrafast folder due to its small free energy barrier to folding and that it exceeds the predicted speed limit for β-hairpin formation by an order of magnitude. We also find that the folding mechanism cannot be described by a simple two-state model, but rather is a heterogeneous process involving two independent parallel processes. Formation of stabilizing cross-strand hydrophobic interactions and turn alignment occur competitively, with relaxation lifetimes of 82 ± 10 and 124 ± 10 ns, respectively, at the highest probed temperature. The ultrafast and heterogeneous folding kinetics observed for CLN025 provide evidence for folding on a nearly barrierless free energy landscape, and recalibrate the speed limit for the formation of a β-hairpin.