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1.
A. Noda S. Nakamura Y. Iwashita S. Sakabe M. Hashida T. Shirai S. Shimizu H. Tongu H. Ito H. Souda A. Yamazaki M. Tanabe H. Daido M. Mori M. Kado A. Sagisaka K. Ogura M. Nishiuchi S. Orimo Y. Hayashi A. Yogo S. Bulanov T. Esirkepov A. Nagashima T. Kimura T. Tajima T. Takeuchi K. Matsukado A. Fukumi Z. Li 《Laser Physics》2006,16(4):647-653
In order to widely spread out particle beams utilized in cancer therapy, laser-produced ions are developed as the injection beam for an ion synchrotron dedicated for cancer therapy. Such a laser ion source is expected to contribute largely to the realization of compactness of the size and low cost of the cancer therapy accelerator. The energy spectrum of the laser-produced ions, however, has no peak, but their intensities decrease exponentially according to the increase of the energy. For the purpose of modifying such a situation, we have proposed a scheme to rotate the beam in the longitudinal phase space with the use of the RF electric field, which is phase-adjusted with the pulse laser. We aim for a reduction of the energy spread of ± 5% selected by an energy analyzer and slits to ±1% by such phase rotation. For this purpose, a quarter wavelength resonator with two gaps with the same resonant frequency as the source laser has already been fabricated, together with its RF power source. The above phase rotation system and its recent experimental realization are presented. 相似文献
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Protocatechuic acid esters (= 3,4‐dihydroxybenzoates) scavenge ca. 5 equiv. of radical in alcoholic solvents, whereas they consume only 2 equiv. of radical in nonalcoholic solvents. While the high radical‐scavenging activity of protocatechuic acid esters in alcoholic solvents as compared to that in nonalcoholic solvents is due to a nucleophilic addition of an alcohol molecule at C(2) of an intermediate o‐quinone structure, thus regenerating a catechol (= benzene‐1,2‐diol) structure, it is still unclear why protocatechuic acid esters scavenge more than 4 equiv. of radical (C(2) refers to the protocatechuic acid numbering). Therefore, to elucidate the oxidation mechanism beyond the formation of the C(2) alcohol adduct, 3,4‐dihydroxy‐2‐methoxybenzoic acid methyl ester ( 4 ), the C(2) MeOH adduct, which is an oxidation product of methyl protocatechuate ( 1 ) in MeOH, was oxidized by the DPPH radical (= 2,2‐diphenyl‐1‐picrylhydrazyl) or o‐chloranil (= 3,4,5,6‐tetrachlorocyclohexa‐3,5‐diene‐1,2‐dione) in CD3OD/(D6)acetone 3 : 1). The oxidation mixtures were directly analyzed by NMR. Oxidation with both the DPPH radical and o‐chloranil produced a C(2),C(6) bis‐methanol adduct ( 7 ), which could scavenge additional 2 equiv. of radical. Calculations of LUMO electron densities of o‐quinones corroborated the regioselective nucleophilic addition of alcohol molecules with o‐quinones. Our results strongly suggest that the regeneration of a catechol structure via a nucleophilic addition of an alcohol molecule with a o‐quinone is a key reaction for the high radical‐scavenging activity of protocatechuic acid esters in alcoholic solvents. 相似文献
4.
Miyoshi D Matsumura S Nakano S Sugimoto N 《Journal of the American Chemical Society》2004,126(1):165-169
Because of the importance of telomere DNAs, the structures of these DNAs in vivo are currently of great research interest in the medical, pharmaceutical, chemical, and industrial fields. To understand the structure of biomolecules in vivo, their properties studied in vitro are extrapolated to the in vivo condition, while the condition in a living cell is inherently molecularly crowded and a nonideal solution contains various biomolecules. We investigated the effect of molecular crowding, which is one of the most important cellular environmental conditions, on the structure and stability of the telomere and G-rich and C-rich DNAs using circular dichroism (CD) spectra, CD melting curves, and isothermal titration calorimetry (ITC). The CD spectra and CD melting curves of G-rich DNA, C-rich DNA, and the 1:1 mixture of G-rich and C-rich DNAs showed that each G-rich DNA, C-rich DNA, and the 1:1 mixture form the antiparallel G-quadruplex, I-motif, and duplex, respectively, in the noncrowding condition as previously considered. On the contrary, the G-rich and C-rich DNAs individually form the parallel G-quadruplex and I-motif, respectively, in the molecular crowding condition, and the 1:1 mixture folds into the parallel G-quadruplex and I-motif but does not form a duplex. The ITC measurements indicated that the thermodynamic stability (DeltaG degrees (20)) of the duplex formation between the G-rich and C-rich DNAs in the noncrowding condition was -10.2 kcal mol(-)(1), while only a small heat change was observed in the ITC measurements in the molecular crowding condition. These ITC results also demonstrated that the molecular crowding condition prevents any duplex formation between G-rich and C-rich DNAs. These results indicate that a structural polymorphism of the telomere DNAs is induced by molecular crowding in vivo. 相似文献
5.
Two 1-thiazolyl-2-thienylcyclopentene derivatives, 1a and 2a, and a 1-thiazolyl-2-vinylcyclopentene derivative 3a have been synthesized in an attempt to obtain photochromic compounds which change the color from colorless to yellow, and have low photocycloreversion quantum yields and high absorption coefficients of the colored isomers. All of these compounds underwent reversible photochromic reactions. Compounds 1a and 2a in toluene solutions changed the color upon 313 nm light irradiation from colorless to orange and pink, in which absorption maxima were observed at 494 nm (ε=10,000 M−1 cm−1) and 525 nm (ε=8500 M−1 cm−1), respectively. On the other hand, the colorless toluene solution of 3a turned yellow upon irradiation with 313 nm light, in which the absorption maximum was observed at 416 nm (ε=17,100 M−1 cm−1). The photocyclization/cycloreversion quantum yields of 3 were 0.19 and 0.0014, respectively. The conversion from the open- to the closed-ring isomer of 3 in the photostationary state under irradiation with 313 nm light was close to 100%. 相似文献
6.
Photochemical and photophysical processes of organosilicon compounds have been studied. Dual (local and CT) emission has been found in aromatic disilanes. The intramolecular CT fluorescence has a broad and structureless band with a large Stokes shift. The CT process in the excited state occurs very rapidly with a time constant less than 10 ps even in rigid glass at 77 K This finding shows that the CT mechanism is quite different from TICT (or OICT) which needs twisting or internal rotation during the lifetime in the excited state. The CT emission originates from the 1(2pσ,3dσ) state having an in-plane long-axis polarization, which is produced by the 2pσ* (aromatic ring) vacant 3dσ (Si-Si bond) intramolecular charge transfer. The CT state plays an important role in the photochemical and photophysical properties of phenyldisilanes. At room temperature a long-lived 425 nm transient (silene) is produced with a time constant of 30 ps from the CT state. The photolysis of cyclotetrasilanes is remarkably dependent on their molecular structures: two molecules of the corresponding disilene are produced from the S1 state of planar cyclotetrasilanes, while silylene is generated by ring contraction in the S1 state of bent cyclotetrasilanes. Remarkably large Stokes shifts are observed in these cyclotetrasilanes. Dimethylsilylene with a transient peak at 470 nm is observed by laser photolysis of cyclohexasilanes. The dynamic behaviours of the intermediates have been studied by nanosecond laser photolysis. The phenylsilyl radical is generated by photolysis of phenylsilanes in rigid glass at 77 K, which gives a structured emission similar to that of benzyl radical. 相似文献
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8.
In the last decade, there has been growing interests in studies aimed at delineating the strategies used by various nucleic acid enzymes to facilitate catalysis. Insights gained from such studies would enable the design of better DNA/RNA catalysts for various applications such as biosensing. DNA and RNA catalysts have been shown to be able to catalyze myriads of reactions, including peroxidation reactions, which are catalyzed by G-quadruplexes. In this report, we provide data that clarifies how G-quadruplex peroxidases achieve catalysis. Firstly, we show that by covalently linking a hemin cofactor to DNAzymes, anti-parallel G-quadruplexes, which have been previously shown to be catalytically inefficient, can be "resurrected" to become good peroxidation catalysts. We also reveal that the relative rates of peroxidation by DNAzyme peroxidases depend on the nature of the organic reductant, arguing for a special binding site in the peroxidase-mimicking DNAzymes for catalysis. 相似文献
9.
Nakayama S Kelsey I Wang J Roelofs K Stefane B Luo Y Lee VT Sintim HO 《Journal of the American Chemical Society》2011,133(13):4856-4864
Recently, there has been an explosion of research activities in the cyclic dinucleotides field. Cyclic dinucleotides, such as c-di-GMP and c-di-AMP, have been shown to regulate bacterial virulence and biofilm formation. c-di-GMP can exist in different aggregate forms, and it has been demonstrated that the polymorphism of c-di-GMP is influenced by the nature of cation that is present in solution. In previous work, polymorphism of c-di-GMP could only be demonstrated at hundreds of micromolar concentrations of the dinucleotide, and it has been a matter of debate if polymorphism of c-di-GMP exists under in vivo conditions. In this Article, we demonstrate that c-di-GMP can form G-quadruplexes at low micromolar concentrations when aromatic molecules such as thiazole orange template the quadruplex formation. We then use this property of aromatic molecule-induced G-quadruplex formation of c-di-GMP to design a thiazole orange-based fluorescent detection of this important signaling molecule. We determine, using this thiazole orange assay on a crude bacterial cell lysate, that WspR D70E (a constitutively activated diguanylate cyclase) is functional in vivo when overexpressed in E. Coli . The intracellular concentration of c-di-GMP in an E. Coli cell that is overexpressed with WspR D70E is very high and can reach 2.92 mM. 相似文献
10.
Hsieh S Thida T Nyamumbo MK Smith KA Naamad N Linck RG 《The journal of physical chemistry. A》2011,115(48):14040-14044
We present laser photoacoustic spectra of ethyl hydroperoxide (EHP) for 3-6 quanta of O-H stretch. Spectra are consistent with ab initio spectral simulations that take into account the influence of torsional motion about the O-O bond on O-H stretch overtone excitation. Experimental and simulated spectra share two trends. First, spectral features due to torsional excitation, including hot bands, become more prominent with increasing O-H stretch excitation, as has been shown previously for similar molecules such as methyl hydroperoxide. Second, contributions from the two different EHP conformers become clearly distinguishable at higher O-H stretch excitation, mainly due to the role of torsional motion. Results are consistent with a higher energy separation (330 cm(-1)) between the lower energy anti and the higher energy gauche conformers than predicted by electronic structure calculations (137 cm(-1)). Calculated absorption intensities are consistently higher than experimental values by ~30% but within the experimental uncertainty. With each additional O-H stretch overtone, the dropoff in calculated integrated absorption intensities at room temperature becomes less extreme, with a 14-fold dropoff from 3ν(OH) to 4ν(OH) and an 8-fold decrease from 5ν(OH) to 6ν(OH). 相似文献