Two-step adsorption on jungle-gym-type porous coordination polymers: dependence on hydrogen-bonding capability of adsorbates, ligand-substituent effect, and temperature

A preliminary study of isopropanol (IPA) adsorption/desorption isotherms on a jungle-gym-type porous coordination polymer, [Zn(2)(bdc)(2)(dabco)](n) (1, H(2)bdc = 1,4-benzenedicarboxylic acid, dabco =1,4-diazabicyclo[2.2.2]octane), showed unambiguous two-step profiles via a highly shrunk intermediate framework. The results of adsorption measurements on 1, using probing gas molecules of alcohol (MeOH and EtOH) for the size effect and Me(2)CO for the influence of hydrogen bonding, show that alcohol adsorption isotherms are gradual two-step profiles, whereas the Me(2)CO isotherm is a typical type-I isotherm, indicating that a two-step adsorption/desorption is involved with hydrogen bonds. To further clarify these characteristic adsorption/desorption behaviors, selecting nitroterephthalate (bdc-NO(2)), bromoterephthalate (bdc-Br), and 2,5-dichloroterephthalate (bdc-Cl(2)) as substituted dicarboxylate ligands, isomorphous jungle-gym-type porous coordination polymers, {[Zn(2)(bdc-NO(2))(2)(dabco)]·solvents}(n) (2 ? solvents), {[Zn(2)(bdc-Br)(2)(dabco)]·solvents}(n) (3 ? solvents), and {[Zn(2)(bdc-Cl(2))(2)(dabco)]·solvents}(n) (4 ? solvents), were synthesized and characterized by single-crystal X-ray analyses. Thermal gravimetry, X-ray powder diffraction, and N(2) adsorption at 77 K measurements reveal that [Zn(2)(bdc-NO(2))(2)(dabco)](n) (2), [Zn(2)(bdc-Br)(2)(dabco)](n) (3), and [Zn(2)(bdc-Cl(2))(2)(dabco)](n) (4) maintain their frameworks without guest molecules with Brunauer-Emmett-Teller (BET) surface areas of 1568 (2), 1292 (3), and 1216 (4) m(2) g(-1). As found in results of MeOH, EtOH, IPA, and Me(2)CO adsorption/desorption on 2-4, only MeOH adsorption on 2 shows an obvious two-step profile. Considering the substituent effects and adsorbate sizes, the hydrogen bonds, which are triggers for two-step adsorption, are formed between adsorbates and carboxylate groups at the corners in the pores, inducing wide pores to become narrow pores. Interestingly, such a two-step MeOH adsorption on 2 depends on the temperature, attributed to the small free-energy difference (ΔF(host)) between the two guest-free forms, wide and narrow pores.     

Photocatalytic oxidation of propylene with molecular oxygen over highly dispersed titanium, vanadium, and chromium oxides on silica

Photocatalytic oxidation of propylene with molecular oxygen at room temperature was investigated over various silica-supported metal oxides with low loading. The photocatalytic active site is assumed to be the isolated tetrahedrally coordinated metal oxides in the ligand-to-metal charge-transferred state, such as (Mdelta- -OLdelta+). Photocatalytic epoxidation of propylene into propylene oxide was promoted over silica-supported V and Ti oxides at steady state. Over silica-supported Cr oxide, the propylene oxide formation rate was remarkably decreased with the time course in the reaction. The oxidation state and the coordination environment of the supported Ti, V, and Cr oxide species were determined by diffuse reflectance UV-vis spectroscopy (DRS) and electron spin resonance (ESR). During the photocatalytic oxidation, the oxidation state of the Ti4+ species was not varied. On the other hand, the V5+ species was partially reduced to V4+ and the Cr6+ species was successively reduced to Cr5+ and Cr3+. An isotopic tracer study of the C3H6-18O2 reaction suggests the difference of the active oxygen species between TiO2/SiO2 and V2O5/SiO2. The active oxygen species on TiO2/SiO2 is derived from molecular oxygen. On the other hand, the photogenerated products on V2O5/SiO2 incorporate the lattice oxygen of the surface metal oxide species. It is suggested that the kinds of terminal ligand (hydroxyl or oxo) of the tetrahedrally coordinated metal oxides on silica decide the active oxygen species in the photocatalytic oxidation. A photoinduced hole center on the monohydroxyl (SiO)3Ti-OH species activates molecular oxygen that reacts with propylene. In the case of the monooxo (SiO)3V=O and dioxo (SiO)2Cr=O2 species, the photoactivated lattice oxygen (OL-) directly reacts with propylene.     

Novel UV devices on high-quality AlGaN using grooved underlying layer

A grooved Al_0.25Ga_0.75N underlying layer on an AlN-coated sapphire substrate was used to grow crack free and low dislocation density Al_0.25Ga_0.75N to successfully realize high-performance UV A light emitters. A light-emitting diode grown on a grooved AlGaN underlying layer exhibited an output power of 12 mW at a DC current of 50 mA for a peak emission wavelength of 345 nm with an external quantum efficiency of 6.7%, which is the highest to date in this wavelength region. We also fabricated UV A laser diodes with an emission wavelength of 356 nm at a pulsed injection current of 414 mA.     

Highly efficient broadband near-infrared luminescence in Ni-doped glass ceramics films containing cordierite nanocrystals

We report on highly efficient broadband near-infrared photoluminescence (PL) in Ni²⁺-doped glass ceramics (GCs) films fabricated by annealing Si/Ni²⁺-doped glass superlattices (SNGS). Over two orders of magnitude enhancement of PL can be achieved in comparison with that from the annealed glass film. The PL lifetime of the annealed SNGS is several milliseconds, which is much longer than those of bulk GCs. The strong PL enhancement results from the formation of high-quality cordierite nanocrystals because the Si layers act as Si source for the crystal growth. This technique can be extended to fabricate other types of high-quality GCs films.     

Exciton migration in a fluctuating medium I

A statistical mechanical theory of exciton migration in a fluctuating environment is developed with the use of the time-convolutionless equation formalism. This gives a satisfactory result when the stochastic perturbations acting on excitons are assumed to be Gaussian.Our theory is valid for any timescale and is applicable to the case of off-diagonal randomness as well as the diagonal randomness. For the Gaussian-Markoffian process, a basic equation can be solved analytically to give optical absorption spectra and the density of states. These quantities show systematic variations when certain characteristic parameters are changed.     

Rigorous solution to a microscopic laser model - formation of phase coherence

An extended version of a quantum statistical mechanical laser model is solved rigorously. With the use of coherent states and orthogonal polynomials, the original equation is solved to give a continued fraction. The average of the induced atomic dipole moment is evaluated to give the cooperative rotational motion.     

High‐performance affinity chromatography method for identification of L‐arginine interacting factors using magnetic nanobeads

L‐Arginine exhibits a wide range of biological activities through a complex and highly regulated set of pathways that remain incompletely understood at both the whole‐body and the cellular levels. The aim of this study is to develop and validate effective purification system for L‐arginine interacting factors (AIFs). We have recently developed novel magnetic nanobeads (FG beads) composed of magnetite particles/glycidyl methacrylate (GMA)–styrene copolymer/covered GMA. These nanobeads have shown higher performance compared with commercially available magnetic beads in terms of purification efficiency. In this study, we have newly developed L‐arginine methyl ester (L‐AME)‐immobilized beads by conjugating L‐AME to the surface of these nanobeads. Firstly, we showed that inducible nitric oxide synthase, which binds and uses L‐arginine as a substrate, specifically bound to L‐AME‐immobilized beads. Secondly, we newly identified phosphofructokinase, RuvB‐like 1 and RuvB‐like 2 as AIFs from crude extracts of HeLa cells using this affinity chromatographic system. The data presented here demonstrate that L‐AME‐immobilized beads are effective tool for purification of AIFs directly from crude cell extracts. We expect that the present method can be used to purify AIFs from various types of cells. Copyright © 2009 John Wiley & Sons, Ltd.     

A generalized stochastic liouville equation. Non-Markovian versus memoryless master equations

The interrelation between the well-known non-Markovian master equation and the new memoryless one used in the previous paper is clarified on the basis of damping theory. The latter equation is generalized to include cases in which the Hamiltonian or the Liouvillian is a random function of time, and is written in a form feasible for perturbational analysis. Thus, the existing stochastic theory in which those cases mentioned above are discussed is equipped with a more tractable basic equation. Two problems discussed in the previous paper, i.e., the random frequency modulation of a quantal oscillator and the Brownian motion of a spin, are treated from the viewpoint of the stochastic theory without such explicit consideration of external reservoirs as was taken in the previous paper.     

N-fused pentaphyrins and their rhodium complexes: oxidation-induced rhodium rearrangement

meso-Aryl-substituted pentaphyrins were isolated in the modified Rothemund-Lindsey porphyrin synthesis as a 22-pi-electron N-fused pentaphyrin ([22]NFP5) and a 24-pi-electron N-fused pentaphyrin ([24]NFP5), which were reversibly interconvertible by means of two-electron reduction with NaBH4 or two-electron oxidation with dichlorodicyanobenzoquinone (DDQ). Judging from 1H NMR data, [22]NFP5 is aromatic and possesses a diatropic ring current, while [24]NFP5 exhibits partial anti-aromatic character. Metalation of [22]NFP5 1 with a rhodium(I) salt led to isolation of rhodium complexes 9 and 10, whose structures were unambiguously characterized by X-ray diffraction analyses and were assigned as conjugated 24-pi and 22-pi electronic systems, respectively. In the rhodium(I) metalation of 1, the complex 9 was a major product at 20 degrees C, but the complex 10 became preferential at 55 degrees C. Upon treatment with DDQ, compound 9 was converted to 10 with an unprecedented rearrangement of the rhodium atom.     

Rhodium-catalyzed cyclopropanation using ene-yne-imino ether compounds as precursors of (2-pyrrolyl)carbenoids

[reaction: see text] The reaction of alkenes with conjugated ene-yne-imino ether or ene-yne-aldimine in the presence of a catalytic amount of [Rh(OAc)(2)](2) gives (2-pyrrolyl)cyclopropanes in good yields. The key intermediate of this cyclopropanation is a (2-pyrrolyl)carbenoid generated by the nucleophilic attack of imine nitrogen atom at an internal alkyne carbon activated by rhodium complex. The intramolecular reaction also proceeds to afford a polycyclic pyrrole.