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131.
Gibasiewicz K Szrajner A Ihalainen JA Germano M Dekker JP van Grondelle R 《The journal of physical chemistry. B》2005,109(44):21180-21186
Almost all photosystem I (PSI) complexes from oxygenic photosynthetic organisms contain chlorophylls that absorb at longer wavelength than that of the primary electron donor P700. We demonstrate here that the low-energy pool of chlorophylls in the PSI-LHCI complex from the green alga Chlamydomonas reinhardtii, containing five to six pigments, is significantly blue-shifted (A(max) at 700 nm at 4 K) compared to that in the PSI core preparations from several species of cyanobacteria and in PSI-LHCI particles from higher plants. This makes them almost isoenergetic with the primary donor. However, they keep the other characteristic features of "red" chlorophylls: clear spectral separation from the bulk chlorophylls, big Stokes shift revealing pronounced electron-phonon coupling, and large homogeneous and inhomogeneous broadening of approximately 170 and approximately 310 cm(-1), respectively. 相似文献
132.
Tatiana Murakhtina Jasper Heuft Evert Jan Meijer Daniel Sebastiani 《Chemphyschem》2006,7(12):2578-2584
A combined experimental and ab initio study is presented of the 1H NMR chemical shift distribution of aqueous hydrogen chloride solution as a function of acid concentration, based on Car-Parrinello molecular dynamics simulations and fully periodic NMR chemical-shift calculations. The agreement of computed and experimental spectra is very good. From first-principles calculations, we can show that the individual contributions of Eigen and Zundel ions, regular water molecules, and the chlorine solvation shell to the NMR line are very distinct and almost independent of the acid concentration. From the computed instantaneous NMR distributions, it is further possible to characterize the average variation in hydrogen-bond strength of the different complexes. 相似文献
133.
Jan Budziski 《International journal of quantum chemistry》1985,28(6):853-860
A modified form of the Neumann expansion in terms of products of orthogonal polynomials for the inverse interelectronic distance r112 is proposed. This expansion has been applied in order to derive a unified analytical formula for two-center and two-electron integrals over Slater-type orbitals. The results are equivalent to those given recently by Yasui and Saika, but the expansion itself can be used for building up a realistic algorithm for evaluation of three- and four-electron integrals determined by using correlated variational wave functions. 相似文献
134.
Horváth-Szabó G Czarnecki J Masliyah JH 《Journal of colloid and interface science》2002,253(2):427-434
Equilibrium liquid crystal (LC) layer on an interface between crude oils and water was observed at high pH. This layer is composed mainly of sodium naphthenates produced in situ at the water/oil interface. Transient LC layer was also evolved at the interface of aqueous phase of sodium hydroxide solutions and oleic phase of naphthenic acid (NA) solutions as result of a chemical reaction between NaOH and NA. This chemical reaction causes transport process resulting in a disturbance of the interface. Optical observation of this interface disturbance reviled that the interface covered with LC shows considerably lower flexibility as compared to LC free interface. The LC layer eventually dissolves in the water phase at low oil-to-water ratio, while at high oil-to-water ratio it can form an equilibrium phase, which spreads spontaneously at the oil-water interface. 相似文献
135.
Diastereopure monofluorinated cyclopropanoid nucleosides were synthesized for biological studies. As key intermediates cis- and trans-(+/-)-[1-fluoro-2-(acetoxymethyl)cyclopropyl]methanol were prepared starting from diastereopure fluorinated cyclopropanecarboxylates. The latter were synthesized by copper(i)-catalyzed cyclopropanation of [small alpha]-fluorostyrene with ethyl diazoacetate. After reduction and O-acetylation the diastereomeric (2-fluoro-2-phenylcyclopropyl)methyl acetates were obtained. Oxidative degradation using RuO(4) and reduction of the formed carboxyl group with borane gave the fluorinated alcohols, which were coupled with different nucleobases. After deprotection, the corresponding cyclopropanoid nucleosides of adenine, cytosine, guanine, thymine and uracil were obtained. Antiviral tests revealed for the cis-configured guanosine a low, but specific activity against HSV-1 and HSV-2. In addition low affinities of the adenine derivatives to adenosine receptors were detected. 相似文献
136.
Piotr Michorczyk Piotr Kutrowski Lucjan Chmielarz Jan Ogonowski 《Reaction Kinetics and Catalysis Letters》2004,82(1):121-130
Different Fe-containing catalysts (pure Fe2O3, Fe2O3 supported on active carbon or g-Al2O3, and hydrotalcite derived Mg-Fe oxides) were examined in the dehydrogenation of propane performed in an Ar or CO2 atmosphere at 873 K. A promoting effect of carbon dioxide was found for the Fe2O3 and Fe2O3/AC samples. The catalytic results are discussed in terms of redox properties of the catalysts determined by temperature-programmed
reduction (TPR).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
137.
Berezkin Victor G. Mardanov Robert G. Moiseew Aleksey A. Malinowska Irena Różyło Jan K. 《平面色谱法杂志一现代薄层色谱法》2002,15(5):377-379
JPC – Journal of Planar Chromatography – Modern TLC - 相似文献
138.
Studies on the photooxidation mechanism of polymers. I. Photolysis and photooxidation of polystyrene
A new mechanism has been proposed for the photooxidation of polystyrene as film and in benzene. The initial stage of the photooxidative degradation may involve reactions of singlet oxygen with polystyrene molecules. Singlet oxygen may be formed in the reaction between excited benzene ring in polystyrene molecule and molecular oxygen. The addition of singlet oxygen quenchers such as 1,3-cyclohexadiene or β-carotene reduces the rate of polymer degradation in benzene solution. The mechanisms of the photolysis of polystyrene as film and in benzene solution, in vacuo and in the presence of oxygen, are discussed and interpretations proposed. The pronounced yellowing of polystyrene during the photooxidation process is interpreted as a reaction involving benzene ring-opening photooxidation in polystyrene molecule. These results were obtained by comparing ultraviolet and infrared spectra in experiments of photooxidation of pure liquid benzene and polystyrene film. 相似文献
139.
Summary The calculation of vibrational states using a gradient extremal path is discussed. Gradient extremal paths are defined by local criteria, which lead to stable solutions. This has certain advantages in comparison with a steepest-descent path, which is often difficult to determine accurately. For cases where a reaction path formalism is applicable, a path based on the gradient extremal concept gives results in close agreement with those obtained using traditional steepest-descent methods. We present algorithms for carrying out such calculations and also give some numerical results. 相似文献
140.