Photoionization of highly charged ions using an ECR ion source and undulator radiation

Photoionization of Xe4+ to Xe7+ ions was studied by combining an electron cyclotron resonance ion source with synchrotron radiation. Multiconfiguration Dirac-Fock calculations were performed to interpret the data. Many autoionization lines were measured and identified, resulting from excitation of a 4d electron into nf and np orbitals followed by Auger decay of the excited states. Continuum photoionization is negligible for the higher members of the isonuclear series.     

A bootstrap estimation scheme for chemical compositional data with nondetects

The bootstrap method is commonly used to estimate the distribution of estimators and their associated uncertainty when explicit analytic expressions are not available or are difficult to obtain. It has been widely applied in environmental and geochemical studies, where the data generated often represent parts of whole, typically chemical concentrations. This kind of constrained data is generically called compositional data, and they require specialised statistical methods to properly account for their particular covariance structure. On the other hand, it is not unusual in practice that those data contain labels denoting nondetects, that is, concentrations falling below detection limits. Nondetects impede the implementation of the bootstrap and represent an additional source of uncertainty that must be taken into account. In this work, a bootstrap scheme is devised that handles nondetects by adding an imputation step within the resampling process and conveniently propagates their associated uncertainly. In doing so, it considers the constrained relationships between chemical concentrations originated from their compositional nature. Bootstrap estimates using a range of imputation methods, including new stochastic proposals, are compared across scenarios of increasing difficulty. They are formulated to meet compositional principles following the log‐ratio approach, and an adjustment is introduced in the multivariate case to deal with nonclosed samples. Results suggest that nondetect bootstrap based on model‐based imputation is generally preferable. A robust approach based on isometric log‐ratio transformations appears to be particularly suited in this context. Computer routines in the R statistical programming language are provided. Copyright © 2014 John Wiley & Sons, Ltd.     

Far‐field patterns of solutions of the perturbed Dirac equation

The purpose of the paper is to study the asymptotic behavior at infinity of solutions of a perturbed Dirac equation in called k‐monogenic. Every such solution is a solution of the Helmholtz equation with values in a complex Clifford algebra. The main goal is to use the far‐field pattern to characterize the radiating (outgoing) k‐monogenic functions among the radiating solutions of the Helmholtz equation. It will be shown that an algebraic condition characterizes these far‐field patterns. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and Fungicidal Activity of Hydrated Geranylated Phenols against Botrytis cinerea

Botrytis cinerea is a ubiquitous fungus that affects hundreds of plants, resulting in economic losses to the horticulture and fruit industry. The search for new antifungal agents is a matter of current interest. Thus, in this work a series of geranylated phenols in which the side alkyl chain has been hydrated have been synthesized, and their activity against B. cinerea has been evaluated. The coupling of phenol and geraniol has been accomplished under microwave irradiation obtaining the highest reaction yields in the shortest reaction times. Hydration of the side chain was carried out in dioxane with p-toluenesulfonic acid polymer-bound as the catalyst. All synthesized compounds were tested against B. cinerea using the growth inhibition assay and EC₅₀ values were determined. The results show that activity depends on the number and nature of functional groups in the phenol ring and hydration degree of the geranyl chain. The most active compound is 1,4-dihydroquinone with one hydroxyl group attached at the end of the alkyl chain. Results from a molecular docking study suggest that hydroxyl groups in the phenol ring and alkyl chain are important in the binding of compounds to the active site, and that the experimental antifungal activity correlates with the number of H-bond that can be formed in the binding site.     

MMX polymer chains on surfaces

Fibres of [Ru(2)Br(micro-O(2)CEt)4]n polymer have been isolated on different surfaces under specific conditions, and morphologically characterised by AFM and STM, showing an unexpected helical internal structure.     

Counterion and composition effects on discotic nematic lyotropic liquid crystals II. Ion exchange and molecular dynamics

The static fluorescence quenching of pyrene by bromide, at the interface of mixed TTAC/TTAB discotic nematic lyotropic liquid crystals, allowed an estimation of the equilibrium constant for the exchange of chloride by bromide. The affinity of the interface for bromide is much higher than for chloride (K(Br-/Cl-) = 13.2). For a molecular level understanding of the experimental results of this and the preceding paper, 20 ns molecular dynamics (MD) simulations were calculated for samples with TTAB/TTAC molar percent ratios 100/0 (A), 50/50 (B) and 0/100 (C). The increment in the concentration of chloride induces a wider distribution of ammonium headgroups along the axis normal to the bilayer surface, increasing the width of the interface. The charge density profile of simulation B shows that the concentration of bromide is higher than the concentration of chloride in the vicinity the ammonium headgroups. The short range contribution to the electrostatic energy from the ammonium-ammonium repulsion is 291.7 kJ/mol for TTAC and 195.6 kJ/mol for TTAB, and the short range ammonium-halide interaction is -6166 kJ/mol for TTAC and -6607 kJ/mol for TTAB, from simulations A and C, respectively. These results are in agreement with a more neutralized TTAB interface. Consistently, the electric dipole moments of water are significantly more aligned with the larger electric field of the TTAB interface.     

Thermodynamic and Kinetic Study of the Interaction between Alkylpyridinium Ions and Pyrene Derivatives in Aqueous Solution

Abstract— The kinetics of fluorescence quenching of pyrene and three of its derivatives by a series of n -alkylpyridinium ions has been studied. The quenching process is diffusion controlled for all the systems studied, independent of the charge in the aromatic molecule and the size of the alkyl chain in the pyridinium ions. Pyrensulfonate, PS, and pyranine form ground-state complexes with these quenchers. The association constants were determined by using a kinetic scheme where both dynamic and static quenching were included. A linear relationship between the free energy change and number of carbon atoms was found for PS, and a methylene contribution equal to -1.1 kJ/mol was determined from the slope. A similar correlation was established for pyranine, but a slope change was observed when the alkyl chain has more than 10 carbon atoms. From the initial slope, an incremental free energy of -0.35 kJ/mol was obtained. The ground-state complex formation is determined mainly by an electrostatic interaction, but there is a hydrophobic effect on the value of the measured association constants.