Photophysical properties of polyacrylic acid with Ru (II) polypyridyl complexes

The nature of the conformational transition of the polymers with Ru (II) polypyridyl complexes covalently attached to poly(acrylic acid) (PAA) and poly(metacrylic acid) (PMAA) has been in studied in aqueous solutions at different pH values. The [PAA-Ru₄]⁸⁺ and [PMAA-Ru₄]⁸⁺ polymers has been investigated by means of the luminescence properties of the Ru(bpy)₃²⁺ moiety by steady-state and time-resolved luminescence spectroscopy. The pH markedly affects the luminescence spectra and quantum yields of both ruthenium-polyacid complexes in aqueous solution. Another feature investigated in this work was a comparative study of their luminescence quenching by acridinic dyes in solution. The analysis of the k_q values obtained indicates that the bimolecular quenching by acridinium and 9-aminoacridinium is more effective in the [PAA-Ru₄]⁸⁺ complex (6.4×10⁹ and 1.4×10⁹ M⁻¹ s⁻¹, respectively) compared to the [PMAA-Ru₄]⁸⁺ (2.6×10⁹ and 1.0×10⁹ M⁻¹ s⁻¹). Also, a similar behavior was evidenced for the Ru solely adsorbed onto pure PAA (9.0×10⁹ and 3.4×10⁹ M⁻¹ s⁻¹) and PMAA (1.8×10⁹ and 1.7×10⁹ M⁻¹ s⁻¹) in aqueous solution. The effect of enhancement of quenching rate constant in [PAA-Ru₄]⁸⁺ system could be ascribed to the higher density of Ru per polymer chain. The average number per chain is similar in both systems, but the molecular weight is lower for [PAA-Ru₄]⁸⁺. Furthermore, the larger hydrophilic environment provided by the PAA exposes the Ru probe to the outer surface of the polymer in solution.     

Possible direct physical detection of de Broglie waves

A modified version of the Mandel-Pfleegor experiment implies conflicting measurable predictions of the Copenhagen and statistical interpretations of quantum mechanics. Their detection would help to choose between the antagonistic positions of Bohr and Einstein in the Bohr-Einstein controversy.     

A Strategic Model for Intervention on the Portuguese Olive-Oil Market

A range of models are used in an attempt to explain the variability of the annual production of olive-oil in Portugal and to relate this time-series to economic factors. The effects of these variations on the demand of other edible oils and on the required imports of oil seeds is analysed and an integrated model is proposed to assess the relative merit of alternative governmental decisions.The trade-off between the financial support given to the Portuguese production of olive-oil and the improvement of the National Balance of Payments is also discussed.     

Consequences of the lumoton hypothesis

Lumotons with neutral current interactions are studied and their contributions to the e-p and p-p collisions are given. Their charged multiplicities in the electron-positron collisions are calculated and they are found to be outside of the experimental limits.     

Does Aliphatic Chain Length Influence Carbocyanines' Orientation in Supported Lipid Multilayers?

UV-Vis linear dichroism was used to study the orientation of 3,3'-dihexyloxacarbocyanine (DiOC6(3)) and 3,3'-dihexadecyloxacarbocyanine (DiOC16(3)) in supported multilayers of dipalmitoylphosphatidylcholine (DPPC) and dilauroylphosphatidylcholine (DLPC). Orientational probability density functions were similar for the two carbocyanines in both lipids. Multimodal distributions were found in all cases. The main peak is at 9 degrees-11 degrees relative to the bilayer normal axis, except for DiOC16(3) in DLPC multilayers (main peaks at 13 degrees and 90 degrees). Quenching studies revealed that the two carbocyanines are localized at the interface region of the membrane regardless of the lipid matrix they are inserted in. Combining these data with linear dichroism results lead to the conclusion that both the aliphatic chain length of carbocyanines and the lipid phase have little influence in the structural organization of these probes in lipidic bilayers. The partition constants of DiOC6 (3), K(p), were determined from fluorescence anisotropy measurements; the values obtained were K(p) (DPPC) = (2.39 +/- 0.05) x 10(3) and K(p) (DLPC) = (5.01 +/- 1.15) x 10(3).     

Study on thioridazine 5-sulfoxide epimerization and degradation by capillary electrophoresis

We present a method for the stereoselective analysis of thioridazine 5-sulfoxide (THD 5-SO) in human plasma based on liquid-liquid extraction with diethyl ether and chiral resolution of the stereoisomers by capillary electrophoresis using hydroxypropyl-beta-cyclodextrin and sulfated beta-cyclodextrin as chiral selectors. The method showed recovery rates of 85.5% for both THD 5-SO (slow-eluting, SE) enantiomers. The coefficients of variation observed in the precision studies, as well as the accuracy values, were below 10%. After validation, the method was used to study the stability and configurational changes of this THD metabolite. Our results showed that both enantiomers of THD 5-SO (SE) were stable under conditions of variation of temperatures (38 degrees C, 4 degrees C and -20 degrees C), pH (5.0, 7.0 and 8.5) and ionic strengths (0.2, 0.5 and 1.0 mol/L). The influence of light on the stability of the THD 5-SO (SE) stereoisomers was also studied using standard solutions prepared in methanol and an inversion in configuration was observed under UV light (254 and 366 nm).     

Shedding Light on the Enigmatic TcO2 ⋅ xH2O Structure with Density Functional Theory and EXAFS Spectroscopy**

The β-emitting ⁹⁹Tc isotope is a high-yield fission product in ²³⁵U and ²³⁹Pu nuclear reactors, raising special concern in nuclear waste management due to its long half-life and the high mobility of pertechnetate (TcO₄⁻). Under the conditions of deep nuclear waste repositories, Tc is retained through biotic and abiotic reduction of TcO₄⁻ to compounds like amorphous TcO₂ ⋅ xH₂O precipitates. It is generally accepted that these precipitates have linear (Tc(μ-O)₂(H₂O)₂)_n chains, with trans H₂O. Although corresponding Tc−Tc and Tc−O distances have been obtained from extended X-ray absorption fine structure (EXAFS) spectroscopy, this structure is largely based on analogy with other compounds. Here, we combine density-functional theory with EXAFS measurements of fresh and aged samples to show that, instead, TcO₂ ⋅ xH₂O forms zigzag chains that undergo a slow aging process whereby they combine to form longer chains and, later, a tridimensional structure that might lead to a new TcO₂ polymorph.     

Efficient Bayesian Inference for Multivariate Factor Stochastic Volatility Models

We discuss efficient Bayesian estimation of dynamic covariance matrices in multivariate time series through a factor stochastic volatility model. In particular, we propose two interweaving strategies to substantially accelerate convergence and mixing of standard MCMC approaches. Similar to marginal data augmentation techniques, the proposed acceleration procedures exploit nonidentifiability issues which frequently arise in factor models. Our new interweaving strategies are easy to implement and come at almost no extra computational cost; nevertheless, they can boost estimation efficiency by several orders of magnitude as is shown in extensive simulation studies. To conclude, the application of our algorithm to a 26-dimensional exchange rate dataset illustrates the superior performance of the new approach for real-world data. Supplementary materials for this article are available online.