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71.
Om V SinghHyunsoo Han 《Tetrahedron letters》2003,44(11):2387-2391
A general methodology for the stereoselective synthesis of 1-deoxymannojirimycin and its three other stereoisomers is described. The achiral olefin 6 was converted through the common olefin intermediate 12 to the target compounds in a highly stereocontrolled manner. The regioselective asymmetric aminohydroxylation (AA) and diastereoselective dihydroxylation reactions were used for the introduction of all four stereocenters in the targets, and the ring-closing metathesis (RCM) reaction was utilized for the construction of the required six-membered ring. 相似文献
72.
Several newSchiff base derivatives of antimony(III) have been synthesized by the reaction of antimony(III) isopropoxide with theSchiff bases having the donor system, O–N–O. The reactions in 1:1 and 2:3 molar ratios [Sb(O-i-C3H7)3: :Schiff base] have yielded Sb(O-i-C3H7) (SB) and Sb2 (SB)3 type of derivatives (whereSB represents the anion of theSchiff base andSBH2=o-hydroxyacetophenone-2-hydroxy-1-propylimine, o-hydroxycetophenone-3-hydroxy-1-propylimine, salicylidene-2-hydroxyethylamine, salicylidene-2-hydroxy-1-propylamine and 2-hydroxy-1-naphthylidene-2-hydroxyethylamine) resp. In the resultingSchiff base derivatives, the central antimony atom appears to be tetracoordinated as indicated by their monomeric state determined ebullioscopically. The infrared spectra of the resulting complexes have been recorded and tentative structures indicated. The thermogravimetric analysis of antimony-monoisopropoxysalicylidene-2-hydroxy-1-propylamine has also been carried out.With 1 Figure 相似文献
73.
An amperometric titration of cobalt(II) with hexacyanoferrate(III) in aqueous ammonium citrate or aqueous glycine solution at pH 9.8 or pH 8.0 respectively, is reported. Cobalt concentrations of 2-30 mg/l were successfully determined. In citrate solutions cerium(III) and iron(III) interfered, and in glycine solutions, copper(II) and vanadium(V). 相似文献
74.
75.
Linnea Lindh Olga Gordivska Samuel Persson Hannes Michaels Hao Fan Pavel Chbera Nils W. Rosemann Arvind Kumar Gupta Iacopo Benesperi Jens Uhlig Om Prakash Esmaeil Sheibani Kasper S. Kjaer Gerrit Boschloo Arkady Yartsev Marina Freitag Reiner Lomoth Petter Persson Kenneth Wrnmark 《Chemical science》2021,12(48):16035
A new generation of octahedral iron(ii)–N-heterocyclic carbene (NHC) complexes, employing different tridentate C^N^C ligands, has been designed and synthesized as earth-abundant photosensitizers for dye sensitized solar cells (DSSCs) and related solar energy conversion applications. This work introduces a linearly aligned push–pull design principle that reaches from the ligand having nitrogen-based electron donors, over the Fe(ii) centre, to the ligand having an electron withdrawing carboxylic acid anchor group. A combination of spectroscopy, electrochemistry, and quantum chemical calculations demonstrate the improved molecular excited state properties in terms of a broader absorption spectrum compared to the reference complex, as well as directional charge-transfer displacement of the lowest excited state towards the semiconductor substrate in accordance with the push–pull design. Prototype DSSCs based on one of the new Fe NHC photosensitizers demonstrate a power conversion efficiency exceeding 1% already for a basic DSSC set-up using only the I−/I3− redox mediator and standard operating conditions, outcompeting the corresponding DSSC based on the homoleptic reference complex. Transient photovoltage measurements confirmed that adding the co-sensitizer chenodeoxycholic acid helped in improving the efficiency by increasing the electron lifetime in TiO2. Time-resolved spectroscopy revealed spectral signatures for successful ultrafast (<100 fs) interfacial electron injection from the heteroleptic dyes to TiO2. However, an ultrafast recombination process results in undesirable fast charge recombination from TiO2 back to the oxidized dye, leaving only 5–10% of the initially excited dyes available to contribute to a current in the DSSC. On slower timescales, time-resolved spectroscopy also found that the recombination dynamics (longer than 40 μs) were significantly slower than the regeneration of the oxidized dye by the redox mediator (6–8 μs). Therefore it is the ultrafast recombination down to fs-timescales, between the oxidized dye and the injected electron, that remains as one of the main bottlenecks to be targeted for achieving further improved solar energy conversion efficiencies in future work.Iron-based photosensitizers for dye-sensitized solar cells with a rod-like push–pull design. Solar cell performance was limited by ultrafast (sub-ps) recombination, but yielded better performance than the homoleptic parent photosensitizer. 相似文献
76.
Om P. Agrawal 《Journal of Mathematical Analysis and Applications》2008,337(1):1-12
This paper presents a general finite element formulation for a class of Fractional Variational Problems (FVPs). The fractional derivative is defined in the Riemann-Liouville sense. For FVPs the Euler-Lagrange and the transversality conditions are developed. In the Fractional Finite Element Formulation (FFEF) presented here, the domain of the equations is divided into several elements, and the functional is approximated in terms of nodal variables. Minimization of this functional leads to a set of algebraic equations which are solved using a numerical scheme. Three examples are considered to show the performance of the algorithm. Results show that as the number of discretization is increased, the numerical solutions approach the analytical solutions, and as the order of the derivative approaches an integer value, the solution for the integer order system is recovered. For unspecified boundary conditions, the numerical solutions satisfy the transversality conditions. This indicates that for the class of problems considered, the numerical solutions can be obtained directly from the functional, and there is no need to solve the fractional Euler-Lagrange equations. Thus, the formulation extends the traditional finite element approach to FVPs. 相似文献
77.
Om P. Khatri 《Applied Surface Science》2009,255(24):9817-9821
Vacuum ultraviolet (VUV, λ = 172 nm) patterning of alkyl monolayer on silicon surface has been demonstrated with emphasis on the diffusion of VUV induced oxygen-derived active species, which are accountable for the pattern broadening. The VUV photons photo-dissociates the atmospheric oxygen and water molecules into the oxygen-derived active species (oxidants). These oxidants photo-oxidize the hexadecyl (HD) monolayer in VUV irradiated regions (Khatri et al., Langmuir. 24 (2008) 12077), as well as the little concentration of oxidants diffuses towards the masked areas. In this study, we performed VUV patterning at a vacuum pressure of 10 Pa to track the diffusion pathways for the oxidants with help of gold nanoparticles (AuNPs; ? = 10 nm) immobilization. At VUV irradiated sites AuNPs are found as uniformly distributed, but adjacent to the pattern boundary we observed quasi-linear arrays of AuNPs, which are determined by diffusion pathways of the oxidants. The diffusion of oxidants plays vital role in pattern broadening. The site selective anchoring of AuNPs demonstrates the utility of VUV photons for the construction of functional materials with microstructural architecture. 相似文献
78.
ZnO nanoparticles, of average size of 10–15 nm, homogeneously dispersed in a silica matrix were prepared by a two stage citric
acid/sol–gel process and thermal treatments up to 700 °C. The precursors formed at the early stages of the synthesis and their
thermal evolution were investigated by FTIR, 29Si NMR MAS and CPMAS, 13C CPMAS and T1ρ(1H). A unidentate complex was revealed in the gel, together with other complexes in which citrate carboxylate groups are bound
to one Zn2+ ion or act as a bridge between two Zn2+ ions. A comparison of the results from nanocomposite and silica samples prepared by the same method showed that chemical
interactions between amorphous silica and zinc ions are not present either in the precursors or in the final materials. As
a consequence, ZnO particles do not react with silica matrix when they are heated up to 700 °C. This result is ascribed to
a nanophase segregation of zinc citrate complexes from the host matrix. 相似文献
79.
This paper is a first comprehensive study on the correlated ion transport mechanisms contributing to the overall conductivity behavior in a new class of poly(ethylene oxide)-polyurethane/polyacrylonitrile (PEO-PU/PAN) semi-interpenetrating polymer networks (semi-IPNs)-salt complex polymer electrolytes. A simultaneous investigation of the electrical response on PEO-PU/PAN/LiClO(4) and PEO-PU/PAN/LiCF(3)SO(3) semi-IPNs with varying EO/Li mole ratios (100, 60, 30, 20, 15, 10) has been carried out by impedance spectroscopy. Analysis of the complex plane and spectroscopic plots indicated the presence of two microscopic phases corresponding to the PEO-PU and PAN domains, which leads to space charge polarization in these systems. A suitably modified approach based on the universal power law (UPL) considering the independent contribution from the individual microphases of semi-IPNs facilitates a complete interpretation of the spectroscopic profiles for the real component of conductivity (sigma'(omega)). The sigma'(omega) spectroscopic profiles were fitted with two power law equations, where the frequency region up to approximately 300 kHz is the conductivity profile associated with the PAN phase and beyond this is the superimposed contribution of the PEO-PU phase. Simulated fits using the UPL equation revealed two relaxation times (tau(PEO)(-)(PU), tau(PAN)) related to ionic hopping in the PEO-PU and PAN phases in addition to the conductivity relaxation time (tau(peak)) determined from the Debye peaks. The respective power law exponents (n(PEO)(-)(PU) approximately 0.5-0.8, n(PAN) approximately 1.0-1.6) indicate that though cationic hopping in the softer PEO-PU phase is favored, anionic hopping in the PAN phase contributes significantly to the charge transport processes in these semi-IPNs. Correlation of the experimental results with the simulated fits enable us to distinguish the effects of semi-IPN composition, temperature, morphology, ion-ion, and ion-polymer interactions, which influence the microscopic molecular events, involved in the charge transport in these complex semi-IPN polymer electrolytes. 相似文献
80.
Summary Several new dioxouranium(VI) complexes with the tridentate dibasic Schiff bases derived from salicylaldehyde, 5-chloro-, 5-bromo-, 5-nitro-, 3,5-dichloro-, 4-methoxy-, 5-methoxy- and 3-ethoxysalicylaldehyde and 2-hydroxy-1-naphthaldehyde ando-aminobenzyl alcohol, have been synthesized from uranyl acetate dihydrate and the Schiff base in methanol. The complexes are of the type UO2(AAA). MeOH (where AAAH2 = a tridentate dibasic Schiff base). The complexes have been characterized by elemental analyses, i.r. and electronic spectra, conductance, magnetic susceptibility and molecular weight measurements. Thev (U=O) stretching frequency of the complexes occurs atca. 900 cm–1 and the U-O distance is 1.74Å. The complexes are monomers, diamagnetic and octahedral. 相似文献