Photosystem 2 effective fluorescence cross-section of cyanobacterium Synechocystis sp. PCC6803 and its mutants

The effective fluorescence cross-section of photosystem 2 (PS2) was defined by measurements of chlorophyll a fluorescence induction curves for the wild type of the unicellular cyanobacterium Synechocystis sp. PCC6803, C-phycocyanin deficient mutant (CK), and mutant that totally lacks phycobilisomes (PAL). It was shown that mutations lead to a strong decrease of the PS2 effective fluorescence cross-section. For instance, the effective fluorescence cross-section of PS2 for wild type, CK and PAL mutants excited at λ(ex)=655 nm were found to be 896, 220 and 83 ?(2) respectively. Here we present an estimation of energy transfer efficiency from phycobilisomes to the pigment-protein complexes of PS2. It was shown that the PS2 fluorescence enhancement coefficient reaches a maximum value of 10.7 due to the energy migration from phycobilisomes. The rate constant of energy migration was found to be equal to 1.04 × 10(10) s(-1).     

Tailoring (bio)chemical activity of semiconducting nanoparticles: critical role of deposition and aggregation

The impact of deposition and aggregation on (bio)chemical properties of semiconducting nanoparticles (NPs) is perhaps among the least studied aspects of aquatic chemistry of solids. Employing a combination of in situ FTIR and ex situ X-ray photoelectron spectroscopy (XPS) and using the Mn(II) oxygenation on hematite (α-Fe(2)O(3)) and anatase (TiO(2)) NPs as a model catalytic reaction, we discovered that the catalytic and sorption performance of the semiconducting NPs in the dark can be manipulated by depositing them on different supports or mixing them with other NPs. We introduce the electrochemical concept of the catalytic redox activity to explain the findings and to predict the effects of (co)aggregation and deposition on the catalytic and corrosion properties of ferric (hydr)oxides. These results offer new possibilities for rationally tailoring the technological performance of semiconducting metal oxide NPs, provide a new framework for modeling their fate and transport in the environment and living organisms, and can be helpful in discriminating between weakly and strongly adsorbed species in spectra.     

A note on Poisson brackets for orthogonal polynomials on the unit circle

The connection of orthogonal polynomials on the unit circle to the defocusing Ablowitz–Ladik integrable system involves the definition of a Poisson structure on the space of Verblunsky coefficients. In this paper, we compute the complete set of Poisson brackets for the monic orthogonal and the orthonormal polynomials on the unit circle, as well as for the second kind polynomials and the Wall polynomials. This answers a question posed by Cantero and Simon (J Approx Theory 158(1):3–48, 2009), for the case of measures with finite support. We also show that the results hold for the case of measures with periodic Verblunsky coefficients.     

3,5‐Bis(arylidene)piperid‐4‐ones Containing 1,3,2‐Oxazaphosphorinane Moieties: Synthesis and Antitumor Activity

Two novel series of phosphorus‐substituted 3,5‐bis(arylidene)piperid‐4‐ones bearing 1,3,2‐oxazaphosphorinane cycle either directly attached to the piperidone core through the P N bond (diamidophosphates 4 ) or connected with it via thiocarbamoyl linker (thioureas 5 ) were obtained by the phosphorylation of NH precursors with 2‐oxo‐1,3,2‐oxazaphosphorinane chloride or the reaction of the former ones with the corresponding cyclic isothiocyanate. According to the results of cytotoxicity screening against human carcinoma cell lines (A549, CaOv3, KB), thioureas 5 were more active than the diamidophosphates 4 bearing the same arylidene rings, with compounds with electron‐withdrawing side groups displaying IC₅₀ in the micromolar range of 1.2–7 μM. © 2013 Wiley Periodicals, Inc. Heteroatom Chem 24:191–199, 2013; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21082     

Polycyanurate–Organically Modified Montmorillonite Nanocomposites: Structure–Dynamics–Properties Relationships

Polycyanurate‐modified montmorrilonite (PCN‐MMT) nanocomposites were synthesized by polymerization of dicyanate ester of bisphenol A in the presence of MMT dispersed by ultrasound. Techniques of IR spectroscopy, WAXD, and TEM were applied to study polymerization kinetics and structure of the nanocomposites prepared, whereas their dynamics and thermal/mechanical properties over the ?30 to 420°C range were studied by using DSC, laser‐interferometric creep rate spectroscopy (CRS), and dielectric relaxation spectroscopy (DRS) techniques. It was shown that a small amount of MMT additive acts as a catalyst of polymerization and results in the formation of complicated intercalated/exfoliated structures, as well as strongly modifies the dynamics in the PCN network. Pronounced dynamic heterogeneity was observed for PCN/MMT nanocomposites. Along with the main PCN glass transition, two new glass transitions, at much higher and much lower temperatures, were revealed as a consequence of constrained dynamics in matrix interfacial nanolayers and due to incomplete local cross‐linking in the PCN matrix, respectively. In addition, increased sub‐T _g mobility was observed in these nanocomposites. A two‐fold rise of modulus of elasticity as well as increasing thermal stability and arising microplasticity at low temperatures, promoting, obviously, improved crack resistance in a brittle PCN network, were found for the PCN‐MMT nanocomposites.     

X‐ray harmonics rejection on third‐generation synchrotron sources using compound refractive lenses

A new method of harmonics rejection based on X‐ray refractive optics has been proposed. Taking into account the fact that the focal distance of the refractive lens is energy‐dependent, the use of an off‐axis illumination of the lens immediately leads to spatial separation of the energy spectrum by focusing the fundamental harmonic at the focal point and suppressing the unfocused high‐energy radiation with a screen absorber or slit. The experiment was performed at the ESRF ID06 beamline in the in‐line geometry using an X‐ray transfocator with compound refractive lenses. Using this technique the presence of the third harmonic has been reduced to 10^?3. In total, our method enabled suppression of all higher‐order harmonics to five orders of magnitude using monochromator detuning. The method is well suited to third‐generation synchrotron radiation sources and is very promising for the future ultimate storage rings.     

Kinetics and mechanism of the growth of gold nanoparticles by reduction of tetrachloroauric acid by hydrazine in Triton N-42 reverse micelles

The kinetics of the growth of gold nanoparticles during the reduction of tetrachloroauric acid by hydrazine in dispersed aqueous solution encapsulated by reverse micelles of Triton N-42 surfactant (with decane as dispersion medium) was studied by means of spectrophotometry. According to DLS data, at a set value of solubilization capacity V _s/V _o = 0.005 initial micelles have an aqueous core hydrodynamic diameter d _c = 3.6±0.2 nm. The final particles obtained after full reduction of Au^III have a metallic core of defect-free single-crystalline gold with a narrow size distribution and average core diameter d _Au = 7.7 ± 1.4 nm as shown by TEM. The rate of the particle growth is limited by the rate of gold reduction. The process kinetics corresponds to the model consisting of two stages of reduction Au^III → Au^I → Au⁰. The stages involve the formation and redox decay of the intermediate complexes Au(N₂H₄)Cl₃ and Au(N₂H₄)Cl, and each stage proceeds via two routes: (1) homogeneous in the dispersed aqueous phase, and (2) heterogeneous on the particle surfaces. Reactions taking route (2) are autocatalytic because they proceed with participation of the surface atoms of particles as the final products of Au^III reduction. The dependencies of observed rate constants on reagent concentrations, temperature, and solubilization capacity of the micellar solution are studied.     

Study of As-Sb-Se chalcogenide glasses by NQR and EPR spectroscopy methods

In this paper experimental results obtained by both ⁷⁵As NQR and EPR spectroscopy are presented for the three-component system As-Sb-Se. The ⁷⁵As NQR spectra of glasses of structures (As₂Se₃)_0.78 (Sb₂Se₃)_0.22, (As₂Se₃)_0.75 (Sb₂Se₃)_0.25, (As₂Se₃)_0.5 (Sb₂Se₃)_0.5 have broad lines with two Sb-NQR lines (corresponding to the Sb₂Se₃ units) and two ⁷⁵As-NQR lines (corresponding to the As₂Se₃ units). Differences in the EPR spectra of the different glasses arise because of the different amounts of arsenic and antimony in their structure.     

Synthesis of new tetrahydropyrido[1,2-a]benzimidazoles based on recyclization of N-arylitaconimides with 2-cyanomethylbenzimidazole

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