Luminescent core-shell photonic crystals from poly(phenylene ethynylene) coated silica spheres

We describe the preparation and characterization of a photonic crystal filled with a luminescent conjugated polyelectrolyte, sulfonated poly(phenylene ethynylene). The conjugated polymer was coated onto the nanospheres by the layer-by-layer method and assembled directly into a fluorescent opal structure avoiding the defects associated with post-filling schemes. These structures exhibit strong angle-dependent luminescent properties. By using multiple layers, we further demonstrate control over the emissive bands of the opal.     

Suicide inactivation of dioldehydratase by glycolaldehyde and chloroacetaldehyde: an examination of the reaction mechanism

High-level ab initio calculations have been used to study the mechanism for the inactivation of diol dehydratase (DDH) by glycolaldehyde or 2-chloroacetaldehyde. As in the case of the catalytic substrates of DDH, e.g., ethane-1,2-diol, the 5'-deoxyadenosyl radical (Ado*) is able to abstract a hydrogen atom from both substrate analogues in the initial step on the reaction pathway, as evidenced by comparable energy barriers. However, in subsequent step(s), each substrate analogue produces the highly stable glycolaldehyde radical. The barrier for hydrogen atom reabstraction by the glycolaldehyde radical is calculated to be too high ( approximately 110 kJ mol-1) to allow Ado* to be regenerated and recombine with the cob(II)alamin radical, the latter therefore remaining tightly bound to DDH. As a consequence, the catalytic pathway is disrupted, and DDH becomes an impotent enzyme. Interconversion of equivalent structures of the glycolaldehyde radical via the symmetrical cis-ethanesemidione radical is calculated to require 38 kJ mol-1. EPR indications of a symmetrical cis-ethanesemidione structure are likely to be the result of formation of an equilibrium mixture of glycolaldehyde radical structures, this equilibration being facilitated by partial deprotonation of the glycolaldehyde radical by the carboxylate of an amino acid residue within the active site of DDH.     

Synthesis and catalytic properties of soluble platinum nanoparticles protected by a thiol monolayer

Several new platinum monolayer protected clusters (MPCs) have been synthesized and characterized. Two methods of platinum reduction were used depending on the solubility of the thiol: sodium borohydride for the water-soluble thiols and lithium triethylborohydride for the organic soluble thiols. In general, reactant solutions containing a 1:1 thiol/Pt ratio yielded the best particles in a single-phase reaction. Higher thiol/Pt ratios produced lower yields of MPCs, while much lower ratios produced gray-black precipitates. The Pt MPCs were used as catalysts to hydrogenate allyl alcohol to propanol by reducing the carbon-carbon double bond. The Pt-mercaptoammonium MPCs were also used as catalysts in the hydrogenation of maleic acid to succinic acid. Differences in the catalytic hydrogenation rates among the various monolayer coatings for MPCs are attributed to the variations in ligand chain length, branching, charged functional groups, packing density, and core size.     

Direct observation of the protonation state of an imino sugar glycosidase inhibitor upon binding

Glycosidases are some of the most ubiquitous enzyme in nature. Their biological significance, coupled to their enormous catalytic prowess derived from tight binding of the transition state, is reflected in their importance as therapeutic targets. Many glycosidase inhibitors are known. Imino sugars are often potent inhibitors, yet many facets of their mode of action, such as their degree, if any, of transition-state "mimicry" and their protonation state when bound to the target glycosidase remain unclear. Atomic resolution analysis of the endoglucanase, Cel5A, in complex with a cellobio-derived isofagomine in conjunction with the pH dependence of Ki and kcat/KM reveals that this compound binds as a protonated sugar. Surprisingly, both the enzymatic nucleophile and the acid/base are unprotonated in the complex.     

The Elusive beta-unsubstituted calix[5]pyrrole finally captured

[reaction: see text] The meso-decamethyl-calix[5]pyrrole 2b was synthesized from the furan-based analogue 1b via the homologation of the furan rings to pyrrole, and its solid-state structure was determined by X-ray crystallography: surprisingly, the binding constant of 2b toward chloride is found to be lower than that of the tetrameric analogue 2a.     

The absorption spectra of the phenoxyl radical in solid argon

Vacuum ultraviolet photolysis of phenol, phenol-d₆ and anisole during condensation with excess argon at 20 K has produced and trapped the phenoxyl radical as evidenced by structured absorptions at 397.2 and 628.1 nm. A broad photosensitive 416 ± 2 nm band is tentatively assigned to the phenol cation.     

Arylthallium trifluoroacetates carbon-13 and fluorine-19 nuclear magnetic resonance: The substituent effect of the bis(trifluoroacetato)- thallium(III) group

¹³C NMR data for a series of arylthallium trifluoroacetates (ArTlX₂, X = OCOCF₃) are reported and assigned. The range of carbon—thallium couplings to be expected, the dependence on the disposition of coupled nuclei, and chemical shift effects are discussed. The Tl(OCOCF₃)₂ group is shown to be a powerful electron withdrawing group, from both the ¹³C data and ¹⁹F substituent chemical shifts of the p-fluorophenyl derivative.     

The crystal and molecular structure of oxo-bis[tribenzylgermanium(IV)]

Crystals of oxo-bis[tribenzylgermanium(IV)], O[(PhCH₂)₃Ge]₂, are rhombohedral, space group R$\text{3}$, having a = 9.621(2) Å, α = 85.48(3)°. The structure was solved by Patterson methods using diffractometer data and refined by full-matrix least squares to R = 0.0876. The structure consists of molecules lying along the 3-fold axis of the unit cell, in which the GeOGe fragments are strictly linear and centrosymmetric. The GeO distance is 1.730(1) Å and the GeC distance is 1.980(5) Å.     

Synthesis,Characterization and Catalysis of Ce‐MCM‐41

The cerium‐containing MCM‐41 (Ce‐MCM‐41) has been synthesized by direct hydrothermal method. The low‐angle XRD patterns revealed the typical five major peaks of MCM‐41 type hexagonal structures. The interplanar spacing d₁₀₀ = 38.4 Å was obtained that can be indexed on a hexagonal unit cell parameter with a_o = 44.3 Å which was larger than that of pure siliceous MCM‐41 (Si‐MCM‐41). Transmission electron micrograph shows the regular hexagonal array of uniform channel characteristics of MCM‐41. The BET surface area of Ce‐MCM‐41 was 840 m²/g, which is much reduced as compared to that of Si‐MCM‐41, with the pore size of 26.9 Å and mesopore volume of 0.78 cm³/g were measured by nitrogen adsorption‐desorption isotherm at 77 K. Along with the results, the synthesized Ce‐MCM‐41 exhibited a well‐ordered MCM‐41‐type mesoporous structure with the incorporation of cerium. Using Ce‐MCM‐41 as a support, the Rh (0.5 wt%) catalyst exhibited very high activity for the NO/CO reactions.