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281.
Three-dimensional cubic mesoporous molecular sieves of FDU-1 containing niobium: dependence of niobium source on structural properties 总被引:1,自引:0,他引:1
The introduction of niobium into the FDU-1 structure has been studied. The evolution of the NbFDU-1 pore structure was deliberated using nitrogen adsorption at 77 K and X-ray diffraction. The influence of the niobium source on the structural properties and the incorporation of niobium species into the walls of FDU-1 molecular sieve were evaluated with the aforementioned techniques and thermogravimetry. The prepared materials retained a 3D cubic Fm3m structure typical of FDU-1 materials. 相似文献
282.
Reaction of 5,10,15,20-tetraphenyl-2-aza-21-carbaporphyrinatonickel(II) with dihalomethanes in the presence of a proton scavenger gives a 2,21'-CH2-linked dimer of Ni(II) inverted porphyrins with the yield reaching 90% and its 2,2'-linked isomer as a minor product. 相似文献
283.
The nature of the interaction of isocyanic acid (HNCO) with the active centers at the ideal anatase TiO2 (1 0 1) surface were studied using ab initio density functional theory (DFT) method with a cluster model. Two types of adsorption of isocyanic acid are found to be likely at (1 0 1) surface – dissociative and molecular adsorption. Only molecular adsorption of HNCO leads to the direct weakening and further splitting of the NC bond, which is a necessary step for the hydrolysis of isocyanic acid. During molecular adsorption of HNCO, an energetically stable intermediate surface complex is created with an adsorption energy of −1.33 eV, in which the HNCO skeleton is changing due to new strong bonds between C–Os and N–Tis. Based on the existence of this intermediate complex a probable reaction pathway for the hydrolysis of HNCO over the ideal anatase (1 0 1) surface was developed. A surface oxygen vacancy was formed after the decomposition of the intermediate complex and CO2 desorption. Afterwards, water adsorbs at the oxygen vacancy site and NH3 is successively formed. The HNCO hydrolysis over TiO2 was found to be energetically favorable with global energy gain of about −2.08 eV. 相似文献
284.
The influence of pH on the spectral forms of negatively and positively charged porphyrin dyes: tetrakis(4-sulfonatophenyl)porphyrin (TPPS4) and tetra(4-N, N, N, N-trimethylanilinium) porphyrin (TAP) in the presence of dopa melanin is investigated. The interaction between dyes and dopa melanin is shown to be dependent on the kind of dye spectral forms and on environmental pH. The creation of different forms, deactivation of their electronic excited states, and their interaction with dopa melanin have been monitored by absorption, fluorescence, and photoacoustic spectroscopy in the pH range of 2–9. This article demonstrates that the TAP–dopa melanin complex is destroyed at the lowest pH because of competition between positively charged peripheral groups of TAP and protons, which interact with negative centers of dopa melanin. Otherwise, dopa melanin affects photothermal and fluorescence properties of monomeric dications (TAP and TPPS4) rather weakly. It has also been suggested that the aggregated dicationic of TPPS4 can serve as an acceptor in the energy transfer from dopa melanin. Presented results seem to be applicable to a photodynamic therapy of cancer. 相似文献
285.
286.
Poplewskaa I Kramarz R Piatkowski W Seidel-Morgenstern A Antos D 《Journal of chromatography. A》2007,1173(1-2):58-70
The adsorption behavior of two amino acids, i.e., l,d-threonine and l,d-methionine has been investigated on the chiral stationary phase (CSP)column packed with teicoplanin bonded to a silica support. The study has been performed under non-linear conditions of adsorption isotherm for various types of organic modifiers (methanol, ethanol, propan-2-ol and acetonitrile) in the reversed-phase mode. A heterogeneous adsorption mechanism of amino acids has been identified that was strongly affected by the nature of organic modifier. Generally, isotherm non-linearity and retention decreased with decrease of the modifier content in the mobile phase exhibiting a minimum at water-rich mobile phases. These trends were suggested to result from a combined effect of the mobile as well as the adsorbed phase composition. To determine the composition of the adsorbed phase the excess adsorption of modifiers in aqueous solutions has been measured and their binary adsorption equilibria have been quantified and compared. Strongly non-ideal behavior of solvents in the mobile phase and the adsorbed phase has been accounted for by activity coefficients. The fraction of the modifiers in the adsorbed phase decreased in the sequence: methanol, ethanol, propan-2-ol and acetonitrile. 相似文献
287.
Izabela Petrykiewicz 《Comptes Rendus Mathematique》2014,352(4):273-276
The aim of this note is to present results concerning the differentiability of some Fourier series arising from Eisenstein series. Sine series exhibit different behaviours with respect to differentiability than the series with cosine function. The precise results are given for the series related to Eisenstein series of weight 2, whereas for the series arising from Eisenstein series of higher weight we conjecture the results. 相似文献
288.
Mohesh Moothanchery Izabela Naydenova Vincent Toal 《Applied Physics A: Materials Science & Processing》2011,104(3):899-902
We studied the shrinkage in acrylamide-based photopolymer by measuring the Bragg detuning of transmission diffraction gratings
recorded at different slant angles and at different intensities. Transmission diffraction gratings of spatial frequency 1000
lines/mm were recorded in an acrylamide-based photopolymer film having 60±5 μm thickness. We have obtained the grating thickness
and the final slant angles from the Bragg curve and hence calculated the shrinkage caused by holographic recording. The shrinkage
of the material was evaluated for three different recording intensities 1, 5 and 10 mW/cm2, while the total exposure energy was kept constant at 80 mJ/cm2. From the experimental results it can be seen that the shrinkage of the material is higher for recording with lower intensities
and the corresponding values are 1.9%, 1.3% and 1%. 相似文献
289.
Izabela Tworowska Wojciech Dabkowski Jan Michalski 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6-7):1855-1858
Oligonucleotides containing 3'- S -P(S) and 5'- S -P(S) fragments in the deoxy-series are available only by tedious multistep procedures. We have developed a novel and efficient methodology based on ring opening of anhydronucleosides by phosphorus dithioacids. This approach allows efficient synthesis of modified dinucleotides of the ribo-series. 相似文献
290.
A method has been developed for retrieving the complete angular selectivity profile of transmission holographic gratings in one step. The method is applied to study in real time the shrinkage and changes in the effective optical thickness of a slanted holographic grating recorded in an acrylamide-based photopolymer. It can form the basis of a holographic sensor of analytes that cause a thickness change in the holographic medium. It can also be useful for the study and optimization of holographic recording materials and for quality control during production of holographic optical elements. 相似文献