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901.
Robert D. Richardson Matthias G. J. Baud Claire E. Weston Henry S. Rzepa Marina K. Kuimova Matthew J. Fuchter 《Chemical science》2015,6(7):3853-3862
Asymmetric photochemical synthesis using circularly polarized (CP) light is theoretically attractive as a means of absolute asymmetric synthesis and postulated as an explanation for homochirality on Earth. Using an asymmetric photochemical synthesis of a dihydrohelicene as an example, we demonstrate the principle that two wavelengths of CP light can be used to control separate reactions. In doing so, a photostationary state (PSS) is set up in such a way that the enantiomeric induction intrinsic to each step can combine additively, significantly increasing the asymmetric induction possible in these reactions. Moreover, we show that the effects of this dual wavelength approach can be accurately determined by kinetic modelling of the PSS. Finally, by coupling a PSS to a thermal reaction to trap the photoproduct, we demonstrate that higher enantioselectivity can be achieved than that obtainable with single wavelength irradiation, without compromising the yield of the final product. 相似文献
902.
The closed-form shifting (CFS) algorithm is a simple mathematical methodology which determines the unique solution in the process of constructing master curves at selected reference temperature and pressure conditions. In a previous paper, the CFS algorithm has been fully described for monotonically increasing or monotonically decreasing functions only. This paper presents detailed steps of the generalized CFS methodology for non-monotonic functions, like the loss tangent. Performing shifting on the loss tangent, which does not require vertical shifting, is particularly important for materials which require vertical adjustment of dynamic viscoelastic functions, i.e., loss and storage moduli. Thus, based on horizontal shifting of the loss tangent, the CFS-based procedure of consecutive horizontal-vertical superposition for the storage modulus is proposed and analyzed. The analysis is done on the example of two synthetically generated non-monotonic tan delta segments and corresponding storage modulus segments in respect to different experimental parameters. It has been shown that the error brought by the shifting method into non-monotonic loss tangent and storage modulus master curves is twice smaller than the corresponding experimental noise level. 相似文献
903.
Oleg V. Mikhailov Marina A. Kazymova Tatyana A. Shumilova Svetlana S. Solovieva 《Transition Metal Chemistry》2004,29(7):732-736
Novel complexing processes in the CuII-thiocarbohydrazide-diacetyl triple system proceeding to a copper(II)hexacyanoferrate gelatin-immobilized matrix system in contact with aqueous-alkaline (pH 12) solutions containing thiocarbohydrazide and diacetyl, have been studied. It has been shown that mild template synthesis of copper(II) coordination compounds with (N,S,N,S)- and (N,N,N,N)- tetradentate ligands - 4,5-dimethyl-2,3,6,7-tetraazaoctadien-3,5-dithiohydrazide-1,8 and 3,10-dithio--6,7,13,14-tetramethyl-1,2,4,5,8,9,11,12-octaazacyclotetradecatetraene-1,5,7,12 take place, respectively. At the same time, the complexing process in the system under examination, when it occurs in aqueous-ethanol solution between CuCl2 and the organic compounds indicated, leads to copper(II) coordination compounds with another (N,S,N,S)-tetradentate ligand - 3,9,10,16-tetramethyl-6,13--dimercapto-2,17-dioxo-4,5,7,8,11,12,14,15-tetraazaoctadecahexaene - 3,6,8,10,12,15. In both cases, thiocarbohydrazide and diacetyl are ligand synthons in these complexing processes. 相似文献
904.
905.
Pere Castell Angels Serra Marina Gali Marta Giamberini Cossimo Carfagna 《Journal of polymer science. Part A, Polymer chemistry》2003,41(1):1-12
Novel epoxy‐terminated monomers based on imine groups were synthesized and their mesogenic properties studied. Aliphatic spacers of different lengths were introduced between the rigid unit and the glycidylic group, and their liquid‐crystalline behavior was examined. They were reacted with primary aromatic diamines inside a magnetic field so that the formation of anisotropic networks could be investigated. The influence of curing conditions and the structure of monomers and amines on the formation of liquid‐crystal thermosets were investigated. Thermosets with locked nematic textures were obtained in all cases. The influence of a 7.1 T magnetic field on the macroscopic orientation of these materials was studied, and mechanical properties of the resulting networks were evaluated by dynamic mechanical analysis. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1–12, 2003 相似文献
906.
907.
The use of the acetone monoadduct, [Rh2(O2CCF3)4·(OCMe2)], instead of unligated dirhodium(II) tetrakis(trifluoroacetate) in sublimation-deposition reactions allowed us to study coordination of thermally sensitive 1,4-diiodo-1,3-butadiyne. A new mixed-ligand organometallic compound, [Rh2(O2CCF3)4·(OCMe2)]2·(C4I2), has been isolated in crystalline form and shown by X-ray diffraction study to have an η2(1,2):η2(3,4)-bridging mode of diyne. This has demonstrated the donor ability of the diiodobutadiyne that was previously known to act as a π-acceptor through the Lewis acidic iodine atoms. This work has expanded the temperature limits of the solvent-free synthesis strategy for potential study of thermally unstable species. 相似文献
908.
909.
The choice of appropriate density functional for the calculation of static first hyperpolarizability of azochromophores and stacking dimers 下载免费PDF全文
Olga D. Fominykh Anastasiya V. Sharipova Marina Yu. Balakina 《International journal of quantum chemistry》2016,116(2):103-112
The effect of the stacked azo‐chromophore dimer formation on the values of static first hyperpolarizability is studied in the framework of the DFT‐based approach; calculations were also performed at the MP2 level. A number of dispersion‐corrected density functionals—В97D, ωВ97X‐D, and M06‐2X—is tested to calculate the structure of the dimer, the value of binding energy, and molecular nonlinear optical characteristics. According to the QTAIM analysis, the presence of bond critical points is revealed in the intermolecular region, the signs and values of topological characteristics giving evidence for the noncovalent van der Waals interaction between the chromophores. The formation of stacks results in moderate increase of dimer static first hyperpolarizability as compared to that of a single chromophore, the effect depending on the relative shift of the chromophores in dimer. In a special case of greatly shifted chromophores, this enhancement of the first hyperpolarizability becomes appreciable and achieves 72%. © 2015 Wiley Periodicals, Inc. 相似文献
910.
Marina V. Bukhtiyarova Aleksandra S. Ivanova Lyudmila M. Plyasova Galina S. Litvak Anna A. Budneva Evgenii A. Paukshtis 《Reaction Kinetics and Catalysis Letters》2008,93(2):375-387
Hexaaluminates SrAl12O19, BaAl12O19 and LaAl11O18 were prepared by co-precipitation of soluble nitrates of Sr, Ba, or La and Al using NH4HCO3 as a precipitating agent with subsequent calcination at 700–1400°C. The samples were characterized by adsorption methods,
thermal analysis (TA and DTG), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy of adsorbed probe
molecules (CO and CDCl3). It was shown that calcination at 1200°C resulted in the formation of single-phase hexaaluminates in all the samples except
for LaAl11O18, where an additional phase was found. The specific surface area of the samples was obtained in the range 16–22 m2/g. After the treatment at comparable conditions, the total concentrations of both surface Lewis acid sites and basic sites
were found to increase in the series: BaAl12O19 < SrAl12O19 < LaAl11O18. However, the strongest basic sites were detected on the surface of BaAl12O19. 相似文献