Based on the crystal structure and spectral properties of C-phycocyanin (C-PC) from cyanobacteria, models for complexes with 2 and 3 C-PC hexamer disks were built and the energy transfer dynamic properties were studied by the use of stochastic computer simulation approach. In addition, an experimental parameter of 0.056 ps-1, corresponding to a time constant of 18 ps, derived from the previous time-resolved measurement, was used for simulation of the energy transfer process from the three terminal symmetrically equivalent β84 chromophores of the core-linked disk to an α84 chromophore of the allophycocyanin (APC) core. The simulation showed: (1) The disk-to-disk energy transfer can be as fast as several picoseconds. (2) The energy transfer efficiencies from the first disk to the core would depend on the length of the rod (i.e. the number of disks). Efficiencies of 0.95, 0.87, and 0.75 were found for the rods with 1, 2 and 3 hexamer disks, respectively. (3) The energy transfer along a rod in a native phycobilisome (PBS) is probably very close to the one-way manner. It is the core of PBS that makes the excitation energy be transferred fast in a nearly one-way manner. and Jie Xie, Jing-quan Zhao, Chenghang Peng.
The paper reports the results of studying the kinetics of DGEBA reactions with maleic anhydride catalyzed by N, N-dimethyl aniline (DMA). This stuffs are used as phot oelastic model materials. The origination of monoester was studied separately on a model reaction of maleic anhydride with isopropyl alcohol. The subsequent reaction of epox y groups with monoester was examined on a system of epoxy resin and isopropyl maleic monoester. The curing process depends significantly on the content of hydroxyl groups in the system., František Kolář and Jaroslava Svítilová., and Obsahuje bibliografické odkazy
Measurements of ryanodine receptor (RyR) activity during dynamic changes of calcium concentration have suggested that RyR has at least four calcium binding sites, and that activation transpires as an increase in the activity within the high open probability H-mode. Binding of several Ca2+ ions within the H-mode should manifest itself in the steady-state RyR activity by the presence of multiple closed times. However, previously only two closed times were detected in the H-mode of RyR activity. Here we recorded steady-state activity of single cardiac RyRs with high temporal resolution and compared it to data simulated under the same conditions using our previously published model of RyR gating. At a 10 kHz resolution, the closed time histograms of both experimental and simulated data had three exponential components. The closed times of simulated data were not significantly different from those obtained experimentally. After filtering at 2 kHz, only two exponential closed time components with time constants not significantly different from those previously published could be detected in both experimental and simulated records. The conformity of the steady-state experimental data to the model derived from the dynamic data provides further support for the idea that RyRs need binding of multiple Ca2+ ions to open., M. Dura, I. Zahradník, A. Zahradníková., and Obsahuje bibliografii
Measurements of the gasification rate of chars from lignite with admixtures by steam or CO2 showed that the admixtures of polymers, celluloses and wood reduce reactivity of resulting chars. The decrease of reactivity significantly manifests itself at both 800 °C and 900 °C. This is caused mainly by lower inner surface area which resists the gasification reactions. This negative phenomenon can be compensated by addition of magnetite, which acts as Fe-catalyst of the reactions of chars with steam as well as CO2 and accelerates the gasification. Through the isoconversional analysis, it was proven that the presence of magnetite significantly lowers the effective activation energy of these reactions, thus accelerating their course. The measurements of the reaction rate showed that it leads to a two- or three-fold acceleration of gasification., Pavel Straka., and Obsahuje bibliografii
The variable fluorescence at the maximum Fm of the fluorescence induction (Kautsky) curve is known to be substantially suppressed shortly after light adaption due to nonphotochemical qE quenching. The kinetic pattern of the dark decay at Fm consists of three components with rates ~20, ~1, and ~0.1 s-1, respectively. Light adaptation has no or little effect on these rate constants. It causes a decrease in the ratio between the amplitudes of the slow and fast one with negligible change in the small amplitude of the ultra-slow component. Results add to evidence for the hypothesis that the dark-reversible decrease in variable fluorescence accompanying light adaptation during the P-S phase of the fluorescence induction curve is due to an alteration in nonphotochemical qE quenching caused by changes in the trans-thylakoid proton motive force in response to changes in the proton conductance gH+ of the
CF0-channel of the CF0·CF1·ATPase., W. J. Vredenberg., and Obsahuje bibliografické odkazy
The paper deals with the use of the luminiscence phenomenon of epoxy resins to obtain an estimation of basic technological variables such as the storage temperature of the mixed resin and an estimation of the end of the crosslinking reaction in the state of the material that allows manipulation with the product. To obtain a description of the curing reaction kinetics, it was necessary to measure the fluorescence spectra over time and to create a mathematical model. From the processed data we obtained the value of the highest storage temperature for a particular epoxy system (EPOXY 1200 + P11), when the reaction stops t = -0.7 °C and we also determined the potential barrier value for the given chemical reaction w0 = 158 meV. The obtained results are an interesting possibility to use a non-contact optical method for controlling the curing processes in the production of composite products (e.g. aircraft wings in an autoclave) and their automation. and Článek se zabývá využitím jevu luminiscence u epoxidových pryskyřic k získání odhadu základních technologických veličin, jako jsou teplota skladování zamíchané pryskyřice a odhad ukončení síťovací reakce ve stavu materiálu, který umožňuje manipulaci s výrobkem. Kzískání popisu kinetiky vytvrzovací reakce bylo nutno naměřit fluorescenční spektra v závislosti na čase a následně vytvořit matematický model. Ze zpracovaných dat jsme pro konkrétní epoxidový systém (EPOXY 1200+P11) získali hodnotu nejvyšší skladovací teploty t=-0,7 °C, kdy se reakce zastaví, a navíc jsme určili hodnotu potenciálové bariéry pro danou chemickou reakci w0 = 158 meV. Získané výsledky jsou zajímavou možností využití nekontaktní optické metody pro řízení vytvrzovacích postupů při výrobě kompozitových výrobků (například křídel letadel v autoklávu) a jejich automatizaci.
Dependence of ATP hydrolysis kinetics by the chloroplast coupling factor (CF1) on medium viscosity was studied at varying temperatures. For samples with oxidized and reduced CF1 γ-subunit, this dependence was shown to be described by Cramers’ relationship k - (η/ηo)-n, where k is the reaction rate constant, η/ηo is the medium/water viscosity ratio, and 0 < n < 1. Transition of the γ-subunit from its reduced to oxidized state was accompanied by increasing n value, which is indicative of increasing friction losses between certain enzyme sections and the solution. The increased medium viscosity produced no effect on the reaction activation energy which appeared to be almost the same for the both enzyme states. The molecular mechanisms responsible for CF1 activity loss in viscous media are discussed., A.N. Malyan., and Obsahuje bibliografii