Observation of a reentrant twist grain boundary phase

We report the occurrence of a reentrant twist grain boundary phase, which we designate as Re- TGB(A). Microscopic observations on a nonsymmetric dimer showed the phase sequence Iso- N*- TGB(A)-Sm- A-Re- TGB(A)- TGB(C*). Here N* and Sm- A stand for the chiral nematic and smectic- A phases, TGB(A) is the twist grain boundary phase with smectic- A blocks, and TGB(C*) that with smectic- C* blocks and exhibiting features of both the smectic- C* and TGB phases. The reentrance of the TGB(A) phase is unambiguously demonstrated using x-ray diffraction, selective reflection, and optical rotation data.     

Mononuclear iron(III) complexes of 3N ligands in organized assemblies: spectral and redox properties and attainment of regioselective extradiol dioxygenase activity

Four octahedral iron(III) complexes of the type [Fe(L)Cl(3)], where L is a tridentate 3N ligand like N,N-bis(pyrid-2-ylmethyl)amine (bpa, L1), N,N-bis(benzimidazol-2-ylmethyl)amine (bba, L2), 1,4,7-triazacyclononane (tacn, L3) and 2,2';6',2'-terpyridine (terpy, L4), have been isolated and their catechol dioxygenase activity investigated in dichloromethane, water and different aqueous micellar media. The positions of both the catecholato-to-iron(III) LMCT bands observed for the DBC(2-) (H(2)DBC = 3,5-di-tert-butylcatechol) adducts reveal that the adducts are present as cationic [Fe(L)(DBC)(H(2)O)](+) species, which interact strongly with anionic SDS micelles and dock themselves on the anionic micellar surface, and that they exist in the aqueous phase in CTAB and TX 100 micelles. The Fe(III)/Fe(II) redox potentials of the complexes throw light on the Lewis acidity of the iron(III) center as modified by the ligand donor atoms and hence the interaction of the complexes with different micelles. The DBSQ/DBC(2-) redox potentials in SDS micellar media are more positive than those in aqueous solution confirming the presence of the aqua species [Fe(L)(DBC)(H(2)O)](+). The DBC(2-) adducts of the iron(III) complexes of bpa, bba and tacn ligands, all with facial coordination, elicit extradiol (E) cleavage to different extents while the adduct of the terpy complex with meridional coordination of the ligand shows always intradiol (I) cleavage. It is remarkable that the bpa complex shows the highest yield of extradiol product and high product selectivity in aqueous SDS solution (E, 84.0%; E/I, 61.0?:?1) and in SDS?:?n-hexane reverse micellar medium (E, 93.7%) illustrating that a vacant or solvent coordinated site is essential for observing extradiol cleavage. Interestingly, the rates of dioxygenase reactions in aqueous and aqueous micellar solutions are significantly higher than those in non-aqueous solvents. Also, they diminish in the order, SDS > TX-100 > CTAB, illustrating the facile substitution of coordinated water molecule by molecular oxygen in [Fe(L)(DBC)(H(2)O)](+) bound to anionic SDS micelles.     

Photocatalytic reduction of CO2 over Cu-TiO2 /molecular sieve 5A composite

TiO(2) and different Cu wt% loaded TiO(2) (TC(0.5-5.0)), 10 wt% TC(2.0) supported on molecular sieve 5A (10 wt% TC(2.0)/MS) were prepared by impregnation and solid-state dispersion methods. The photocatalysts prepared were characterized using XRD, SEM, and UV-Vis DRS, TEM, XPS spectroscopy techniques. Photocatalytic reduction of CO(2) in water and alkaline solution are investigated in a batch reactor. The yield of oxalic acid increased notably when TC was supported on molecular sieve. The Cu-TiO(2) supported on molecular sieve catalyst promotes the charge separation that leads to an increase in the selective formation of oxalic acid in addition to methanol, acetic acid and traces of methane. The product formation is due to the high adsorption of CO(2), water and product shape selectivity of the composite photocatalyst. The maximum yield of oxalic acid was found to be 65.6 μg h(-1) g(-1) per cat using 0.2 N NaOH containing solution over 10 wt% TC(2.0)/MS photocatalyst. The difference in the photocatalytic activity is related to its physicochemical properties.     

Analytical expression of non-steady-state concentrations and current pertaining to compounds present in the enzyme membrane of biosensor

A mathematical model of trienzyme biosensor at an internal diffusion limitation for a non-steady-state condition has been developed. The model is based on diffusion equations containing a linear term related to Michaelis-Menten kinetics of the enzymatic reaction. Analytical expressions of concentrations and current of compounds in trienzyme membrane are derived. An excellent agreement with simulation data is noted. When time tends to infinity, the analytical expression of non-steady-state concentration and current approaches the steady-state value, thereby confirming the validity of the mathematical analysis. Furthermore, in this work we employ the complex inversion formula to solve the boundary value problem.     

一类紧致Khler流形上的Harnack估计

给出了一些紧致Khler流形上具有和时间相关的位势热方程的正解的Hanack估计.作为应用,得到了两个Khler-Ricci流下具有非负双截面曲率的单调熵.     

Salicylaldimine-based symmetric dimers: synthesis and thermal behaviour

Several symmetrical dimers comprised of salicylaldimine-moieties connected through ester linkages to the termini of odd-parity alkanediols have been synthesized and investigated for their thermal behaviour. In order to understand the structure-property relations, the lengths of the central alkylene spacers (C₃ and C₅) as well as those of the terminal alkoxy chains (C₆ to C₂₂) have been varied. The dimers with a C₃-alkylene spacer are non-liquid crystalline, while some of the compounds having a C₅-alkylene spacer exhibit liquid crystalline properties. The dimer, with a C₅-alkylene spacer and C₆-alkoxy tails, shows an intercalated smectic C (SmC_c) phase, whereas the C₈, C₁₀, C₁₁, and C₁₂ homologues are non-mesomorphic. The higher homologues of this series with C₁₆, C₁₈, C₂₀ and C₂₂ alkoxy tails show a mesophase that has the signatures of a two-dimensional banana (B₁) phase. This mesophase is enantiotropic in the C₁₆ and C₁₈ homologues while it is monotropic in the other homologues. In these dimers, the spacer length has a remarkable influence on the thermal behaviour.     

Achiral banana-shaped mesogenic bidentate ligands and their Cu(II) and Pd(II) complexes

The first achiral bent-core banana-shaped bidentate ligands and their Cu(II) and Pd(II) metal complexes have been synthesized and investigated for mesomorphic behaviour. The bidentate ligands exhibit only one enantiotropic mesophase. The ligand having C6 -alkoxy chains shows a mesophase that has been assigned as a two-dimensional B1 phase while the C8 and C10 homologues stabilize the fluid B2 mesophase showing antiferroelectric switching characteristics. In constrast, their corresponding Cu(II) and Pd(II) metal complexes are non-mesomorphic.     

Highly enantioselective carbon-carbon bond formation by Cu-catalyzed asymmetric [2,3]-sigmatropic rearrangement: application to the syntheses of seven-membered oxacycles and six-membered carbocycles

A concise route for the syntheses of enantioenriched functionalized scaffolds of medium-sized oxacycles and carbocycles employing the chiral auxiliary-mediated Cu-catalyzed ylide formation/[2,3]-sigmatropic rearrangement as a key step was developed.     

Quantitative generation of cation radicals and dications using aromatic oxidants: effect of added electrolyte on the redox potentials of aromatic electron donors

Redox titrations using robust aromatic oxidants allow for a quantitative analysis of redox and optical properties of organic electron donors in their oxidized states. Unlike spectroelectrochemistry, redox titrations can be performed without added electrolyte in relatively nonpolar solvents, affording quick access to the redox and optical properties of a given electron donor without the need of a complex electrochemical setup. However, the redox potentials obtained by the two methods are not the same. To establish the direction and magnitude of this discrepancy, we have performed a systematic case study using a set of tetraarylethylene donors and a tetrasubstituted hydroquinone ether cation radical (^THEO^+?) as a stable aromatic oxidant. We show that redox potentials (especially second and higher oxidation potentials) measured by electrochemical methods are systematically lower compared with the redox potentials obtained by redox titrations in the absence of electrolyte, because of the enhanced stabilization of dications and polycations by electrolyte. We have also uncovered that the smaller cation radicals (e.g., a para‐hydroquinone or ortho‐hydroquinone ether cation radicals) are much more effectively stabilized when compared with the cation radicals in which charge is delocalized over larger area (e.g., tetraarylethylene cation radicals) in the presence of electrolyte because of increased ionic strength of the solution. Copyright © 2015 John Wiley & Sons, Ltd.