Nanocomposites consisting of liquid crystals and nanoparticles have been studied for their applications in devices, such as photovoltaics and to model biological devices. Understanding the structure the liquid crystal assumes in the vicinity of the nanoparticles, and how it compares to the bulk structure of the liquid crystals gives us an idea of how light, and electrons are transmitted from the liquid crystal to the nanoparticle and how sharp is this transmission. The structure depends on the functionalization (or lack of it) that the nanoparticle has and seems to reflect the faceting or the arrangement of the nanoparticle. 相似文献
Stabilized short helical heptapeptides containing a combination of an α-aminoisobutyric acid as a helical promoter and l/d-serine derivatives to produce cross-linked units were synthesized. The cyclic peptide R3,7R-2, which had d-serine derivatives at its 3rd and 7th positions, formed a stable right-handed (P) α-helix in solution and the crystalline state. Furthermore, its N-terminal free helical peptide catalyzed the enantioselective epoxidation of (E)-chalcone to afford the epoxide in a high yield and moderate enantioselectivity. 相似文献
Stapled helical l-leucine-based heptapeptides were synthesized and used as catalysts for the enantioselective epoxidation of α,β-unsaturated ketones. All N-terminal free stapled peptides were successfully used as chiral catalysts. Among them, the use of H-hS3,7hS-10 gave epoxide products with high enantioselectivities of up to 99% ee. Furthermore, the dominant conformations of the N-terminal protected stapled peptides R3,7R-10 and hS3,7hS-10 were investigated by 1H NMR, IR, CD spectra, and X-ray crystallographic analysis. The peptide R3,7R-10 formed a right-handed (P) α-helix in solution and in the crystalline state, while hS3,7hS-10 formed a right-handed (P) 310-helix in solution. 相似文献
Three-dimensional head models with the structures constructed from the MR head images of 40 volunteers were constructed to analyze light propagation in the subject-specific head models. The mean optical path length in the head and the partial optical path length in the brain at 13 fiducial points for each volunteer were estimated to evaluate the intersubject and spatial variability in the optical path lengths. Although the intersubject variability in the optical path lengths is very high, the spatial variability in the average of the mean optical path length and partial optical path length is similar to the previously reported data. The mean optical path length in the head increases, whereas the partial optical path length in the brain decreases with an increase in the depth of the brain surface. The partial optical path length is highly correlated with the depth of the brain surface in comparison to the mean optical path length in the head. 相似文献
The reaction of UO2(ClO4)·nH2O with 15-crown-5 and 18-crown-6 in acetonitrile yielded the title complexes. [UO2(OH2)5] [ClO4]2·3(15-crown-5)·CH3CN crystallizes in the triclinic space groupPT with (at–150°C)a=8.288(6),b=12.874(7),c=24.678(7) Å, =82.62(4), =76.06(5), =81.06(5)°, andDcalc=1.67 g cm–3 forZ=2 formula units. Least-squares refinement using 6248 independent observed reflections [Fo5(Fo)] led toR=0.111. [UO2(OH2)5] [ClO4]2·2(18-crown-6)·2CH3CN·H2O is orthorhombicP212121 with (at–150 °C)a=12.280(2),b=17.311(7),c=22.056(3) Å,Dcalc=1.68 g cm–3,Z=4, andR=0.032 (3777 observed reflections). In each complex the crown ether molecules are hydrogen bonded to the water molecules of the pentagonal bipyramidal [UO2(OH2)5]2+ ions, each crown ether having exclusive use of two hydrogen atoms from one water molecule and one hydrogen from another water molecule. In the 15-crown-5 complex the remaining hydrogen bonding interaction is between one of the water molecules and one of the perchlorate anions. The solvent molecule has a close contact between the methyl group and a perchlorate anion suggesting a weak interaction. There are a total of three U-OH...OClO3 hydrogen bonds to the two perchlorate anions in [UO2(OH2)5] [ClO4]2·(18-crown-6)·2CH3CN ·H2O. The remaining coordinated water hydrogen bond is to the uncoordinated 2H2O molecule, which in turn is hydrogen bonded to a perchlorate oxygen atom and an acetonitrile nitrogen atom. One solvent methyl group interacts with an anion, the other with one of the 18-crown-6 molecules. Unlike the 15-crown-5 structure, the hydrogen bonding in this complex results in a polymeric network with formula units joined by hydrogen bonds from one of the solvent molecules and the uncoordinated water molecule.
Supplementary data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82051 (37 pages).For Part 10, see reference [1]. 相似文献
On the move : Irradiation of azobenzene‐doped liquid crystalline films with UV/Vis light results in the photocontrolled translational motion of microscale solid object on the surface, which occurs through cis–trans isomerization of the azobenzene unit. Irradiation with an Ar+ laser (488 nm) resulted in precise control of the translational motion so that the particle always moved away from the irradiation position (see picture).
The protonation states of buried histidine residues in human deoxyhemoglobin were unambiguously identified by using a neutron crystallographic technique. Unexpectedly, the neutron structure reveals that both the alpha- and beta-distal histidines (Hisalpha58 and Hisbeta63) adopt a positively charged, fully (doubly) protonated form, suggesting their contribution to the Bohr effect. In addition, the neutron data provide an accurate picture of the alpha1beta1 hydrogen-bonding network and allow us to observe unambiguously the nature of the intradimeric interactions at an atomic level. 相似文献
A catalytic flow-injection (FI) method was developed for the determination of 10−9 mol l−1 levels of vanadium(IV, V). The method is based on the catalytic effect of vanadium(V) on oxidation of N-(3-sulfopropyl)-3,3′,5,5′-tetramethylbenzidine (TMBZ·PS) using bromate as oxidant to form a yellow dye (λmax=460 nm). The use of 5-sulfosalicylic acid (SSA) as an activator enhanced the sensitivity of the method. The calibration graphs with a working range 0.05–8.0 ng ml−1 were obtained for vanadium(V). Vanadium(IV) was also determined, being oxidized by bromate. The detection limit (signal/noise, S/N=3) was 0.01 ng ml−1 (ca. 2×10−10 mol l−1) vanadium. The relative standard deviations (R.S.D.) for 15 determinations of 0.5 ng ml−1 vanadium, and for ten determinations of 0.1 and 1.0 ng ml−1 vanadium were 0.41, 2.6 and 0.25%, respectively, with a sampling rate of 15 samples h−1. The proposed method was successfully applied to the determination of vanadium in natural waters. 相似文献