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61.
The linear sandwich tripalladium complexes [Pd3{Ar(CH=CH)4Ar}2[BArf]2 (Ar = Ph, p-t-Bu-C6H4, p-styryl-C6H4) undergo photoinduced isomerization involving face-inversion of the tetraene ligands. Irradiation of these complexes with visible light (>510 nm) resulted in rac (staggered sandwich) to meso (eclipsed sandwich) isomerization. The structures of rac and meso isomers are determined by X-ray crystallographic analyses.  相似文献   
62.
6-(ω-Alkenyl)-2-pyrones 3a-c and 8a, b were prepared and the photochemical reactions were investigated. Photosensitized reactions of 3b, c gave intramolecular [2+2]-cycloadducts 11b, c as tricyclic lactones, site-and regio-specifically. They are not frontier-orbital-controlled adducts. On the other hand, 3a, 8a, b afforded cyclobutenecarboxylic acids, 10a, 14a, b , respectively. The end-ester group at the side-chain is thought not to be effective for the intramolecular phptoaddition.  相似文献   
63.
MnO(2) nanoparticle-loaded TiO(2) prepared by a green process capable of removing harmful MnO(4)(-) ions from water exhibits catalytic activity for a test reaction, H(2)O(2) decomposition, in the dark with its activity enhanced by UV light irradiation.  相似文献   
64.
Copper(II) complexes 1a and 1b, supported by tridentate ligand bpa [bis(2-pyridylmethyl)amine] and tetradentate ligand tpa [tris(2-pyridylmethyl)amine], respectively, react with cumene hydroperoxide (CmOOH) in the presence of triethylamine in CH(3)CN to provide the corresponding copper(II) cumylperoxo complexes 2a and 2b, the formation of which has been confirmed by resonance Raman and ESI-MS analyses using (18)O-labeled CmOOH. UV-vis and ESR spectra as well as DFT calculations indicate that 2a has a 5-coordinate square-pyramidal structure involving CmOO(-) at an equatorial position and one solvent molecule at an axial position at low temperature (-90 °C), whereas a 4-coordinate square-planar structure that has lost the axial solvent ligand is predominant at higher temperatures (above 0 °C). Complex 2b, on the other hand, has a typical trigonal bipyramidal structure with the tripodal tetradentate tpa ligand, where the cumylperoxo ligand occupies an axial position. Both cumylperoxo copper(II) complexes 2a and 2b are fairly stable at ambient temperature, but decompose at a higher temperature (60 °C) in CH(3)CN. Detailed product analyses and DFT studies indicate that the self-decomposition involves O-O bond homolytic cleavage of the peroxo moiety; concomitant hydrogen-atom abstraction from the solvent is partially involved. In the presence of 1,4-cyclohexadiene (CHD), the cumylperoxo complexes react smoothly at 30 °C to give benzene as one product. Detailed product analyses and DFT studies indicate that reaction with CHD involves concerted O-O bond homolytic cleavage and hydrogen-atom abstraction from the substrate, with the oxygen atom directly bonded to the copper(II) ion (proximal oxygen) involved in the C-H bond activation step.  相似文献   
65.
A novel technique called the "lipid-coated ice droplet hydration method" is presented for the preparation of giant vesicles with a controlled size between 4 and 20 microm and entrapment yields for water-soluble molecules of up to about 30%. The method consists of three main steps. In the first step, a monodisperse water-in-oil emulsion with a predetermined average droplet diameter between 4 and 20 microm is prepared by microchannel emulsification, using sorbitan monooleate (Span 80) and stearylamine as emulsifiers and hexane as oil. In the second step, the water droplets of the emulsion are frozen and separated from the supernatant hexane solution by precipitation, followed by a removal of the supernatant and followed by the replacement of Span 80 by using a hexane solution containing egg yolk phosphatidylcholine, cholesterol, and stearylamine (5:5:1, molar ratio). This procedure is performed at -10 degrees C to keep the water droplets of the emulsion in a frozen state and thereby to avoid extensive water droplet coalescence. In the third step, hexane is evaporated at -4 to -7 degrees C and an external water phase is added to the remaining mixture of lipids and water droplets to form giant vesicles that have an average size in the range of that of the initial emulsion droplets (4-20 microm). The entrapment yield and the lamellarity of the vesicles obtained depend on the lipid/water droplet ratio and on the composition of the external water phase. At high lipid/water droplet ratio, the giant vesicles have a thicker membrane (indicating multilamellarity) and a higher entrapment yield than in the case of a low lipid/water droplet ratio. The highest entrapment yield ( approximately 35%) is obtained if the added external water phase contains preformed unilamellar egg phosphatidylcholine vesicles with an average diameter of 50 nm. The addition of these small vesicles minimizes the water droplet coalescence during the third step of the vesicle preparation, thereby decreasing the extent of release of water-soluble molecules originally present in the water droplets. The GVs prepared can be extruded through polycarbonate membranes to yield large unilamellar vesicles with about 100 nm diameter. This size reduction, however, leads to a decrease in the entrapment yield to about 12% due to solute leakage from the vesicles during the extrusion process.  相似文献   
66.
In contrast to B-DNA that has a right-handed double helical structure with Watson-Crick base pairing under the ordinary physiological conditions, repetitive DNA sequences under certain conditions have the potential to fold into non-B DNA structures such as hairpin, triplex, cruciform, left-handed Z-form, tetraplex, A-motif, etc. Since the non-B DNA-forming sequences induce the genetic instability and consequently can cause human diseases, the molecular mechanism for their genetic instability has been extensively investigated. On the contrary, non-B DNA can be widely used for application in biotechnology because many DNA breakage hotspots are mapped in or near the sequences that have the potential to adopt non-B DNA structures. In addition, they are regarded as a fascinating material for the nanotechnology using non-B DNAs because they do not produce any toxic byproducts and are robust enough for the repetitive working cycle. This being the case, an understanding on the mechanism and dynamics of their structural changes is important. In this critical review, we describe the latest studies on the conformational dynamics of non-B DNAs, with a focus on G-quadruplex, i-motif, Z-DNA, A-motif, hairpin and triplex (189 references).  相似文献   
67.
Biological self-assembly is a natural process that involves various biomolecules, and finding the missing partner in these interactions is crucial for a specific biological function. Previously, we showed that evanescent-field-coupled waveguide-mode sensor in conjunction with a SiO2 waveguide, the surfaces which contain cylindrical nanometric holes produced by atomic bombardment, allowed us to detect efficiently the biomolecular interactions. In the present studies, we showed that the assembly of biomolecules can be monitored using the evanescent-field-coupled waveguide-mode biosensor and thus provide a methodology in monitoring assembly process in macromolecular machines while they are assembling. Evanescent-field-coupled waveguide-mode sensor Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   
68.
The photocatalytic degradation processes of ethylene glycol (EG) during the UV or visible light irradiation of pure anatase and nitrogen (N)-doped TiO2 powders (TiO(2-x)N(x), x = 0, 0.002, 0.003, and 0.007) were investigated using time-resolved diffuse reflectance (TDR) and solid-state NMR spectroscopies. The TDR spectra and time traces observed for the charge carriers indicated that the scavenging of photogenerated holes (h+) by EG occurred during the 355-nm laser photolysis of the N-doped TiO2 powders, while no direct oxidation reaction of EG by h+ occurred during the 460-nm laser photolysis, although the charge carriers were sufficiently generated upon excitation. The solid-state magic-angle spinning (MAS) NMR measurements revealed that EG is preferentially chemisorbed on the surface of the N-doped TiO2 powders, in contrast to the pure TiO2, and degrades under visible light irradiation.  相似文献   
69.
Photoinduced electron transfer (PET) processes of 1,8-naphthalimide-linker-phenothiazine (NI-L-PTZ) dyads have been investigated using the nanosecond- and picosecond-transient absorption measurements. Two kinds of linker were introduced, i.e., polymethylene-linked dyad (NI-C8-PTZ and NI-C11-PTZ) and a poly(ethyl ether)-linked one (NI-O-PTZ). The 355 nm pulsed laser excitation of NI-C8-PTZ, NI-C11-PTZ, and NI-O-PTZ in acetonitrile produced NI radical anion (NI*-) and PTZ radical cation (PTZ*+) with the absorption bands around 420 and 520 nm, respectively, through charge transfer from PTZ to NI in the singlet excited state (NI(S1)) as well as in the triplet excited states (NI(T1)) in acetonitrile. On the other hand, the charge transfer process occurred only from NI(S1) in nonpolar solvents. The rates of charge transfer and charge recombination processes largely depended on the solvent polarity and they are affected by the length of linkers and electronic coupling through polyether linker. The PET mechanism is discussed in terms of the free energy change for the charge transfer.  相似文献   
70.
Emission from several 1-(arylethynyl)pyrenes with a substituent on the aryl group (REPy, R = phenyl (PEPy), 4-dimethylaminophenyl (NPEPy), 4-isopropoxyphenyl (OPEPy), 2-quinonyl (QEPy), and 9-(10-cyanoanthracenyl) (AEPy)) was studied with time-resolved fluorescence measurements during pulse radiolysis in benzene. NPEPy and AEPy showed only monomer emission, while PEPy, OPEPy, and QEPy showed both monomer and excimer emissions during pulse radiolysis. In addition, REPy's also showed long-lived emissions with very weak intensities in the absence of oxygen, which were assigned to the "P-type" delayed fluorescence derived from the triplet-triplet annihilation. The formation of REPy's in the singlet excited state (1REPy*) can be interpreted as the charge recombination between the REPy radical cation and anion (REPy*+ and REPy*-, respectively), which are initially generated from the radiolytic reaction in benzene. Both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of PEPy are localized on the 1-pyrenyl (Py) moiety, while the HOMO of REPy's with an electron donating or withdrawing substituent on the benzene ring (R(D)EPy such as NPEPy and OPEPy or R(A)EPy such as QEPy and AEPy) is mainly localized on the donor moieties (R(D) or Py) and the LUMO on the acceptor ones (Py or R(A), respectively). Therefore, it is suggested that the one-electron oxidation and reduction of REPy's can occur from the donor and acceptor moieties, respectively. This scheme reasonably explains the relationship between the annihilation enthalpy changes (-Delta H' degrees) for the charge recombination of REPy*+ and REPy*- and the singlet excitation energies (E'(S1) of the REPy's. The results are compared with those in electrogenerated chemiluminescence.  相似文献   
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