The early events in the triplet 4-carboxybenzophenone (CB)-induced oxidation of N-acetyl-methionine methyl ester (N-Ac-Met-OCH3) are investigated in aqueous solution. Upon electron transfer from the methionine residue of N-Ac-Met-OCH3 to 3CB*, the resulting sulfur radical cation undergoes further reactions: (1) back electron transfer, (2) escape of the radical
ions from the solvent cage, or (3) proton transfer and escape of the radicals. The yields and paths of these reactions are
shown to depend strongly on the pH of the solution, and, similar to the previously reported results for dipeptides (Met-Gly
and Gly-Met), on the structural nature of the methionine substituents. In the experiments performed in this work, low quencher
concentrations were used to avoid formation of intermolecular transients (e.g., dimeric sulfur-centered radical cation (S∴S)+). Under these experimental conditions, the one-electron oxidized sulfur does not seem to become stabilized in an (S∴N)+ three-electron bonded intramolecular complex. The proposed mechanism is further supported by the stable products analysis.
A detailed mechanism involving characterization of the transients is discussed and compared to that of methionine and methionine-containing
dipeptides (Met-Gly and Gly-Met). Moreover, a newly installed transient absorption laser system is described in details. 相似文献
Powders and thin films of nanocrystalline yttrium disilicate (Y2Si2O7) doped with Ce3+ have been prepared by a sol–gel method. Structure and morphology of the synthesised samples have been determined and spectroscopic
properties compared. The triclinic α-Y2Si2O7 form (space group P 1-) for the powders annealed between 1000°C and 1200°C has been found. A total conversion into a thortveitite-type
monoclinic β-Y2Si2O7 polymorph after annealing of powder samples at 1400°C (space group C2/m) has been observed. In the case of films even at
1300°C the basically pure triclinic α-Y2Si2O7 phase was observed with luminescent spectroscopy. The influence of grain size, controlled by thermal treatment, on the structure
and luminescence properties of the fabricated materials are presented and discussed. 相似文献
The new ternary intermetallic title compounds, namely trilanthanum undeca(zinc/magnesium), La3(Zn0.874Mg0.126)11, (I), and tricerium undeca(zinc/magnesium), Ce3(Zn0.863Mg0.137)11, (II), are isostructural and crystallize in the orthorhombic La3Al11 structure type. These three phases belong to the same structural family, the representative members of which may be derived from the tetragonal BaAl4 structure type by a combination of internal deformation and multiple substitution. Compared to the structure of La3Al11, in (I), a significant decrease of 11.9% in the unit‐cell b axis and an increase in the other two directions, of 3.6% along a and 5.2% along c, are observed. Such an atypical deformation is caused by the closer packing of atoms in the unit cell due to atom shifts that reflect strengthening of metallic‐type bonding. This structural change is also manifested in a significant difference in the coordination around the smaller atoms at the 8l Wyckoff position (site symmetry m). The Al atom in La3Al11 is in a tricapped trigonal prismatic environment (coordination number 9), while the Zn atoms in (I) and (II) are situated in a tetragonal antiprism with two added atoms (coordination number 10). 相似文献
The x-ray emission in laser-plasma accelerators can be a powerful tool to understand the physics of relativistic laser-plasma interaction. It is shown here that the mapping of betatron x-ray radiation can be obtained from the x-ray beam profile when an aperture mask is positioned just beyond the end of the emission region. The influence of the plasma density on the position and the longitudinal profile of the x-ray emission is investigated and compared to particle-in-cell simulations. The measurement of the x-ray emission position and length provides insight on the dynamics of the interaction, including the electron self-injection region, possible multiple injection, and the role of the electron beam driven wakefield. 相似文献
Digital image correlation may be useful in many different fields of science, one of which is medicine. In this paper, the authors present the results of research aimed at detecting skin micro-shifts caused by pulsation of the veins. A novel technique using digital image correlation (DIC) and filtering the resulting shifts map to detect pulsating veins was proposed. After applying the proposed method, the veins in the forearm were visualized. The proposed technique may be used in the diagnosis of venous stenosis and may also contribute to reducing the number of adverse events during blood collection. The great advantage of the proposed method is the lack of the need to have specialized equipment, only a typical mobile phone camera is needed to perform the test. 相似文献
Ethanol extracts of two types of pepper (sweet and hot) were separated into fractions with increasing lipophilicity. After drying the extracts and fractions, their chemical composition, anti-radical activity in the DPPH radical system, and cytotoxic activity against PC-3 and HTC-116 cells were determined. A detailed qualitative analysis of the fractions was performed with the LC-QTOF-MS method. It was found that the chemical composition of pepper fractions did not always reflect their biological activity. The highest antiradical activity was detected in the fraction eluted with 40% methanol from sweet pepper. The highest total content of phenolic compounds was found in an analogous fraction from hot pepper, and this fraction showed the strongest cytotoxic effect on the PC-3 tumour line. The LC-MS analysis identified 53 compounds, six of which were present only in sweet pepper and four only in hot pepper. The unique chemical composition of the extracts was found to modulate their biological activity, which can only be verified experimentally. 相似文献
To be or not to be solvated is the decisive parameter that controls the photoinduced hydrogen‐atom transfer in diastereomeric ketone/phenol dyads. A kinetic solvent effect that refers to hydrogen bonding between the phenol and the solvent is suggested to be the main source of the stereoselective discrimination in the hydrogen transfer (see figure).
The recent reduction of laser pulse duration down to the attosecond regime offers unprecedented opportunities to investigate ultrafast changes in the electron density before nuclear motion sets in. Here, we investigate the hole dynamics in the Caffeine molecule that is induced by an ionizing XUV pulse of 6 fs duration using the approximate time-dependent density functional theory method TD-DFTB. In order to account for ionization in a localized atomic orbital basis we apply a complex absorbing potential to model the continuum. Propagation of the time-dependent Kohn–Sham equations allows us to extract the time-dependent hole density taking the pulse shape explicitly into account. Results show that the sudden ionization picture, which is often used to motivate an uncorrelated initial state, fails for realistic pulses. We further find a strong dependence of the hole dynamics on the polarization of the laser field. Notwithstanding, we observe fs charge migration between two distant functional groups in Caffeine even after averaging over the molecular orientation. 相似文献
One can approximate numerically the solution of the initial value problem using single or multistep methods. Linear multistep methods are used very often, especially combinations of explicit and implicit methods. In floating-point arithmetic from an explicit method (a predictor), we can get the first approximation to the solution obtained from an implicit method (a corrector). We can do the same with interval multistep methods. Realizing such interval methods in floating-point interval arithmetic, we compute solutions in the form of intervals which contain all possible errors. In this paper, we propose interval predictor-corrector methods based on conventional Adams-Bashforth-Moulton and Nyström-Milne-Simpson methods. In numerical examples, these methods are compared with interval methods of Runge-Kutta type and methods based on high-order Taylor series. It appears that the presented methods yield comparable approximations to the solutions. 相似文献