Fluorescence lifetimes study of alpha-tocopherol and biological prenylquinols in organic solvents and model membranes

We have found that for biological prenyllipids, such as plastoquinol-9, alpha-tocopherol quinol, and alpha-tocopherol, the shortest fluorescence lifetimes were found in aprotic solvents (hexane, ethyl acetate) whereas the longest lifetimes were those of ubiquinonol-10 in these solvents. For all the investigated prenyllipids, fluorescence lifetime in alcohols increased along with an increase in solvent viscosity. In a concentrated hexane solution, the lifetimes of prenylquinols considerably decreased. This contrasts with methanol solutions, which is probably due to the self-association of these compounds in aprotic solvents. We have also found a correlation of the Stokes shift of prenyllipids fluorescence with the orientation polarizability of the solvents. Based on data obtained in organic solvents, measurements of the fluorescence lifetimes of prenyllipids in liposomes allowed an estimation of the relative distance of their fluorescent rings from the liposome membrane surface, and was found to be the shortest for alpha-tocopherol quinol in egg yolk phosphatidylcholine liposomes, and increased in the following order: alpha-tocopherol in dipalmitoyl phosphatidylcholine liposomes < alpha-tocopherol < plastoquinol-9 < ubiquinol-10 in egg-yolk phosphatidylcholine liposomes.     

Extrapolation algorithm for affine-convex feasibility problems

The convex feasibility problem under consideration is to find a common point of a countable family of closed affine subspaces and convex sets in a Hilbert space. To solve such problems, we propose a general parallel block-iterative algorithmic framework in which the affine subspaces are exploited to introduce extrapolated over-relaxations. This framework encompasses a wide range of projection, subgradient projection, proximal, and fixed point methods encountered in various branches of applied mathematics. The asymptotic behavior of the method is investigated and numerical experiments are provided to illustrate the benefits of the extrapolations.     

Mn–Co spinel protective–conductive coating on AL453 ferritic stainless steel for IT-SOFC interconnect applications

This paper presents research on the synthesis and properties of the Mn_1.5Co_1.5O₄ (MC) spinel powder, as well as its application for the preparation of a MC thick film on the AL453 steel to be used for metallic interconnect material in IT-SOFCs. In order to prepare the MC micropowder with excellent homogeneity of the chemical and phase compositions, EDTA gel processes were utilized. In order to improve the contact electrical resistance between an AL453 steel interconnect and the La_0.8Sr_0.2FeO₃ (LSF) cathode and protect the cathode from Cr poisoning, the surface of the AL453 steel was coated with a protective manganese cobaltite spinel matrix using screen printing in combination with an appropriate heat treatment. The oxidation of the AL453/MC composite layer carried out in the air–H₂O gas mixture at 1,073 K for 55 h showed that the spinel coating may serve as an effective barrier against outward Cr diffusion from the AL453 steel and, therefore, significantly inhibit the formation of volatile Cr vapors from the chromia scale. The contact ASR study of the interconnect–cathode interface in the AL453/MC/LSCM/LSF/LSCM/MC/AL453 system carried out in the range of 723?1,073 K in air showed a very large drop in ASR compared to the resistance of the AL453/LSCM/LSF/LSCM/AL453 system without the spinel coating.     

Facile method to synthesize platelet SBA-15 silica with highly ordered large mesopores

Highly ordered mesoporous SBA-15 silica with large pore diameter of 18 nm (nominal BJH pore diameter ~22 nm) and short pore length (~500 nm) was synthesized using a micelle expander 1,3,5-triisopropylbenzene in the absence of ammonium fluoride by employing short initial stirring time at 17 °C followed by static aging at low temperature. Scanning and transmission electron microscopies revealed that the material comprised of platelet particles in which large mesopores were nearly flawlessly arranged within uniform domains up to 3 μm in size. The platelet SBA-15 had the (100) interplanar spacing of 17 nm, high surface area (~470 m(2) g(-1)) and large pore volume (~1.6 cm(3) g(-1)). The hydrothermal treatment at 130 °C for 2 days was employed to eliminate constrictions from the pore channels. The control experiment showed that a sample prepared with prolonged stirring had very similar mesoporous properties, but the particle size was smaller and the domains were irregular, proving that the static conditions facilitate the formation of SBA-15 with platelet particle morphology. The absence of ammonium fluoride was also critical in attaining the platelet particle shape.     

Inter- and Intramolecular Relaxation in Molecular Liquids by Field Cycling 1H NMR Relaxometry

Field cycling ¹H nuclear magnetic resonance (NMR) relaxometry is applied to study rotational as well as translational dynamics in molecular liquids. The measured relaxation rates, $ T_{1}^{ - 1} \left( \omega \right) \equiv R_{1} \left( \omega \right) $ , contain intra- and intermolecular contributions, $ R_{{1,{\text{intra}}}}^{{}} \left( \omega \right) $ and $ R_{{ 1 , {\text{inter}}}}^{{}} \left( \omega \right) $ . The intramolecular part is mediated by rotational dynamics, the intermolecular part by translation as well as rotation. The rotational impact on the intermolecular relaxation (eccentricity effect) is due to the spins not located in the molecule’s center. The overall relaxation rate is decomposed into $ R_{{1,{\text{intra}}}}^{{}} \left( \omega \right) $ and $ R_{{ 1 , {\text{inter}}}}^{{}} \left( \omega \right) $ by isotope dilution experiments. It is shown that the eccentricity model (Ayant et al. in J. Phys. (Paris) 38:325, 1977) reproduces fairly well the bimodal shape of $ R_{{ 1 , {\text{inter}}}}^{{}} \left( \omega \right) $ for o-terphenyl and glycerol. As the relaxation contribution associated with translational dynamics dominates at lower frequencies, the overall relaxation rate shows a universal linear behavior when plotted versus square root of frequency. This allows determining the self-diffusion coefficient, D, in a model-independent way. It is demonstrated that the shape of NMR master curves comprising relaxation data for different temperatures, linked by frequency–temperature superposition, reflects the relative strength of translational and rotational contributions.     

Mechanism of Water Dynamics in Hyaluronic Dermal Fillers Revealed by Nuclear Magnetic Resonance Relaxometry

¹H spin−lattice nuclear magnetic resonance relaxation experiments were performed for five kinds of dermal fillers based on hyaluronic acid. The relaxation data were collected over a broad frequency range between 4 kHz and 40 MHz, at body temperature. Thanks to the frequency range encompassing four orders of magnitude, the dynamics of water confined in the polymeric matrix was revealed. It is demonstrated that translation diffusion of the confined water molecules exhibits a two-dimensional character and the diffusion process is slower than diffusion in bulk water by 3–4 orders of magnitude. As far as rotational dynamics of the confined water is concerned, it is shown that in all cases there is a water pool characterized by a rotational correlation time of about 4×10⁻⁹ s. In some of the dermal fillers a fraction of the confined water (about 10 %) forms a pool that exhibits considerably slower (by an order of magnitude) rotational dynamics. In addition, the water binding capacity of the dermal fillers was quantitatively compared.     

Chemical proprieties of the iron-quinone complex in mutated reaction centers of Rb. sphaeroides

We investigated type II bacterial photosynthetic reaction centers, which contain a quinone - iron complex (Q_A-Fe-Q_B) on their acceptor side. Under physiological conditions it was observed mainly in a reduced high spin state but its low spin ferrous states were also observed. Therefore, it was suggested that it might regulate the dynamical properties of the iron–quinone complex and the protonation and deprotonation events in its neighbourhood. In order to get insight into the molecular mechanism of the NHFe low spin state formation, we preformed M?ssbauer studies of a wild type of Rb. sphaeroides and its two mutated forms. Our M?ssbauer measurements show that the hydrophobicity of the Q_A binding site can be crucial for stabilization of the high spin ferrous state of NHFe.     

Structural characterization, thermal, dielectric, vibrational properties and molecular motions in

[C₃N₂H₅]₆[Bi₄Br₁₈] has been synthesized and characterized by the X-ray (at 293 and 110 K), calorimetric, dilatometric and dielectric measurements. At room temperature it crystallizes in the monoclinic space group, C2/m. A crystal structure consists of disordered imidazolium cations and ordered discrete tetramers of [Bi₄Br₁₈]^6-. This compound reveals a rich polymorphism in a solid state. It undergoes three solid–solid phase transitions: from phase I to II at 426/423 K (heating–cooling), II→III at 227 K and III→IV at 219.5/219 K. A clear dielectric relaxation process is found in the room temperature phase II. Infrared studies of the polycrystalline [C₃N₂H₅]₆[Bi₄Br₁₈] showed that the ν(N–H), δ(ring) and δ(C–H) modes of the imidazolium cations appeared to be very sensitive to the IV→III phase transition. ¹H NMR measurements confirmed a key role of the imidazolium cations in the phase transitions mechanisms at low temperatures.     

Study of the molecular tilt angle and the order parameter of a ferroelectric liquid crystal mixture using IR spectroscopy

We report measurements of the molecular tilt angle of a ferroelectric liquid crystal mixture (ZLI 3654), using infra-red spectroscopy, and of the optical tilt angle using polarizing microscopy. The molecular tilt angle is found to be approximately the same for different molecular vibrations. The second rank orientational order parameter for the axis of molecular vibrations of different groups of the molecule for homogeneously aligned samples have been determined as a function of temperature. The order parameter depends slightly on the sample thickness and is about 8 per cent higher for a lower thickness (∼ 7 μm) compared to a higher thickness (∼ 12 μm). The order parameter does not change significantly at the S_C*-S_A transition. The order parameter of S_C* is found to be unaffected by the application of a constant electric field. The order parameter for the alkyl chain is found to be about three times lower than for the molecular core.