Copolymers dispersions designed to shaping of ceramic materials

Journal of Thermal Analysis and Calorimetry - To study the effect of ionic liquids (ILs) of the microstructure on the surface of the coal, four ILs ([Emim][BF4], [Bmim][BF4], [Bmim][NO3], and...     

The photoinduced triplet of flavins and its protonation states

The photogenerated triplet states of riboflavin and flavin mononucleotide (FMN) have been examined by time-resolved electron paramagnetic resonance (EPR) spectroscopy at low temperature (T = 80 K). Because of the high time resolution of the utilized EPR instrumentation, the triplets are for the first time observed in the nonequilibrated electron-spin polarized state and not in their equilibrated forms with the population of the triplet sublevels governed by Boltzmann distribution. The electron-spin polarization pattern directly reflects the anisotropy of the intersystem crossing from the excited singlet-state precursor. Spectral analysis of the resulting enhanced absorptive and emissive EPR signals yields the zero-field splitting parameters, |D| and |E|, and the zero-field populations of the triplet at high accuracy. These parameters are sensitive probes for the protonation state of the flavin's isoalloxazine ring, as becomes evident by a comparison of the spectra recorded at different pH values of the solvent. The three protonation states of the flavins can furthermore be distinguished by the kinetics of the transient EPR signals, which are dominated by spin-lattice relaxation. The fastest decays are observed for the protonated FMN and riboflavin triplets, followed by the deprotonated flavin triplets. Slow decays are measured for the triplet states of neutral FMN and riboflavin. Because proton transfer is found to be slow on the time scale of spin-polarized triplet detection by transient EPR, the pH-dependent spin-relaxation and zero-field splitting parameters offer a novel approach to probe the protonation state of flavins in their singlet ground state through the characterization of their triplet-state properties.     

Deep inelastic Compton process and large QCD corrections

The reactions \(\bar vD \to \mu ^ + n\pi ^ - (p_s )\) and \(\bar vD \to \mu ^ + p\pi (n_s )\) have been studied at antineutrino energies varying from 5 to 200 GeV. The cross sections for these reactions were determined from 545 and 300 selected events for each channel respectively. The first reaction was used for the study of the decay properties of the Δ resonance that dominates this channel. The experimental results have been compared with the theoretical predictions of Rein and Sehgal [9] and of Fogli and Nardulli [10]. Using the first model we obtained for the axial form factor parameterM _a =1.01±0.05 GeV/c². With this value the model is in agreement with the experimentaldσ/dQ ² distributions forQ ²>0.25 GeV² and with the distributions of the invariant hadronic massW. The isospin structure of the one-pion production has been investigated and compared with the results of other experiments.     

Synergistic effects in multicomponent electrocatalysts: the Pb-Ir-O system

The ionic interactions were studied in aqueous solutions of Na(3)IrCl(6) + Pb(NO(3))(2) in order to develop a facilitated electrosynthesis of iridium-based catalytic surfaces. Spectroscopic studies indicated that ion pair charge-transfer complexes [IrCl(6)(3-)]-Pb(II) (K = 6 x 10(3)) and [Ir(H(2)O)Cl(5)(2-)]-Pb(II) (K = 2 x 10(3)) were formed in fresh and aged solutions, respectively. Electrochemical studies showed that interactions between the Ir(H(2)O)Cl(5)(2-) and Pb(II) species lead to synergistic lowering of the overpotential that was necessary for nucleation and growth of mixed metal oxide PbIrOx on the surface of glassy carbon electrodes. The Ir:Pb stoichiometry of the PbIrOx surface films was the same (1:1) as that of the high-temperature phase of Pb-Ir-O pyrochlore. Compared to IrOx, the PbIrOx films displayed enhanced catalytic activity toward the electrooxidation of carbohydrates. This was ascribed to synergism that involved retention of carbohydrate molecules at the Pb(II) sites of a PbIrOx film and oxidation at the adjacent Ir(IV) sites. The synergistic electroplating utilizing interactions between the partially aquated transition metal complex and posttransition metal ion represents a new synthetic route to highly homogeneous and reactive films of mixed metal oxides.     

Photophysical properties of tyrosine and its simple derivatives in organic solvents studied by time-resolved fluorescence spectroscopy and global analysis

Photophysical properties of tyrosine and its derivatives with free and blocked functional groups were studied by steady state and time-resolved fluorescence spectroscopy and global analysis in organic solvents, such as methanol, 2-propanol, tetrahydrofuran (THF), and dimethylsulfoxide (DMSO). The mono-exponential fluorescence intensity decays were observed for all tyrosine derivatives in THF and DMSO solutions, whereas in alcohols some derivatives have bi-exponential decays. The rotamer population calculated from 1H nuclear magnetic resonance spectroscopy in DMSO does not correspond to the pre-exponential factors obtained from fluorescence spectroscopy. Moreover in the case of DMSO, the strong interaction of this solvent with the hydroxyl group of the fluorophore's phenol ring causes substantial changes in the fluorescence and nonradiative rate constants of tyrosine derivatives compared with those of tyrosine with a blocked hydroxyl group, Tyr(Me). The steady state and time-resolved fluorescence measurements in pure organic solvents and water-organic solvent mixtures indicate that the fluorescence quenching of the phenol chromophore of tyrosine by an acetyl or amide group or both depends on the polarity of the solvent used as well as the ability of the solvent to form hydrogen bonds with functional groups of tyrosine.     

Electrochemical sensing platform based on the carbon nanotubes/redox mediators-biopolymer system

A new electrochemical sensing platform was developed that relied on synergy between carbon nanotubes (CNT) and redox mediators that were co-immobilized in the biopolymer chitosan (CHIT). To demonstrate the concept, the redox mediator Toluidine Blue O (TBO) and CNT were integrated in CHIT and used for the determination of a reduced form of nicotinamide adenine dinucleotide (NADH). As compared to CHIT-TBO, the CHIT-TBO/CNT films displayed large amplification of a current due to the TBO-mediated oxidation of NADH at -0.10 V. This was discussed in terms of the TBO/CNT synergy that resulted in the improved charge propagation through the CHIT-TBO/CNT matrix.     

A note on attractors with finite fractal dimension

Conditions for the finite fractal dimension of precompact invariantsets are formulated and exponential attractors for discreteand continuous dynamical systems are constructed.     

On the reaction mechanism of adduct formation in LOV domains of the plant blue-light receptor phototropin

The blue-light sensitive photoreceptor, phototropin, is a flavoprotein which regulates the phototropism response of higher plants. The photoinduced triplet state and the photoreactivity of the flavin-mononucleotide (FMN) cofactor in two LOV domains of Avena sativa, Adiantum capillus-veneris, and Chlamydomonas reinhardtii phototropin have been studied by time-resolved electron paramagnetic resonance (EPR) and UV-vis spectroscopy at low temperatures (T < or = 80 K). Differences in the electronic structure of the FMN as reflected by altered zero-field splitting parameters of the triplet state could be correlated with changes in the amino acid composition of the binding pocket in wild-type LOV1 and LOV2 as well as in mutant LOV domains. Even at cryogenic temperatures, time-resolved EPR experiments indicate photoreactivity of the wild-type LOV domains, which was further characterized by UV-vis spectroscopy. Wild-type LOV1 and LOV2 were found to form an adduct between the FMN cofactor and the functional cysteine with a yield of 22% and 68%, respectively. The absorption maximum of the low-temperature photoproduct of wild-type LOV2 is red-shifted by about 15 nm as compared with the FMN C(4a)-cysteinyl adduct formed at room temperature. In light of these observations, we discuss a radical-pair reaction mechanism for the primary photoreaction in LOV domains.     

Laser flash photolysis of carboxymethylcellulose in an aqueous solution

Laser flash photolysis with excitation at 248 nm was used to study photochemically derived changes of carboxymethylcellulose (CMC) in aqueous solutions. Transient absorption spectra of solutions after photolysis revealed a broad band with a maximum of approximately 720 nm, which could be ascribed to the signal of the hydrated electron. The interaction of the hydrated electron with CMC was slow (<10⁷ dm³ mol^?1 s^?1), but the OH radical, formed by the decomposition of H₂O₂, reacted with CMC at a high rate constant (9.5–11.0 × 10⁸ dm³ mol^?1 s^?1). The rate constant of the reactions of CMC with hydroxyl radicals depended on the conformation of the macromolecules, which was determined by the pH of the solution. Transient absorption was recorded at a wavelength shorter than 370 nm for CMC solutions photolyzed in the presence of H₂O₂. As a result of OH attack, long‐lived radicals were formed on CMC. The recombination of macroradicals led to the formation of crosslinking bonds between side‐chain groups, and as a result of it an insoluble gel arose in low‐pH solutions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 505–518, 2005     

Pomeron dominance in a triple-Regge representation of inclusive Δ++ production in K−p and π−p reactions

Data are presented on the reactions K^?p → Δ⁺⁺ + anything at 10 and 16 GeV/c and π^?p → Δ⁺⁺ + anything at 16 GeV/c. In the K^?p reaction, scaling is observed between 10 and 16 GeV/c in the variable M²/s. The scaling occurs at relatively low values of M in marked contrast to the reaction π⁺p → Δ⁺⁺ + anything. This result can be explained by duality arguments on a triple Regge picture, since the exchanged reggeon-incident particle scattering is exotic. Comparison of the π^?p reaction, which is similarly exotic, with the K^?p reaction at the same energy gives further evidence for factorization in pomeron-dominated inclusive reactions.