Separating points of measures on effect algebras

We prove the existence of separating points for every countable family of nonatomic σ-additive modular measures on a σ-complete lattice ordered effect algebra.      

Electron Transfer between Hydrogen‐Bonded Pyridylphenols and a Photoexcited Rhenium(I) Complex

Two pyridylphenols with intramolecular hydrogen bonds between the phenol and pyridine units have been synthesized, characterized crystallographically, and investigated by cyclic voltammetry and UV/Vis spectroscopy. Reductive quenching of the triplet metal‐to‐ligand charge‐transfer excited state of the [Re(CO)₃(phen)(py)]⁺ complex (phen=1,10‐phenanthroline, py=pyridine) by the two pyridylphenols and two reference phenol molecules is investigated by steady‐state and time‐resolved luminescence spectroscopy, as well as by transient absorption spectroscopy. Stern–Volmer analysis of the luminescence quenching data provides rate constants for the bimolecular excited‐state quenching reactions. H/D kinetic isotope effects for the pyridylphenols are on the order of 2.0, and the bimolecular quenching reactions are up to 100 times faster with the pyridylphenols than with the reference phenols. This observation is attributed to the markedly less positive oxidation potentials of the pyridylphenols with respect to the reference phenols (≈0.5 V), which in turn is caused by proton coupling of the phenol oxidation process. Transient absorption spectroscopy provides unambiguous evidence for the photogeneration of phenoxyl radicals, that is, the overall photoreaction is clearly a proton‐coupled electron‐transfer process.     

Lyapunov modular functions

We prove a Lyapunov type theorem for modular functions on complemented lattices.     

Singlet and Triplet State Properties and Singlet Oxygen Yield of an Amino-Acyl-Quinoxalinone Yellow Dye

Amino-acyl-quinoxalinone yellow dyes are cyclised analogues of the yellow azomethine dyes developed for, and still used in, silver halide colour photography. Unlike image azomethine dyes, which are rapidly deactivated in their excited states by torsion about the azomethine bond, amino-acyl-quinoxalinone dyes have an interesting photophysics because torsion is not possible due to their cyclised structure. We report results from studies on singlet and triplet state properties, and singlet oxygen yields, of the yellow dye, 7-diethylamino-3-(2,2-dimethyl-propionyl)-5-methyl-1-phenyl-1H-quinoxalin-2-one, in polar and nonpolar solvents. The dye photophysics is characterised by a weak fluorescence, with a solvent dependent emission yield (Φ_F?≈?0.002–0.004), and short singlet state lifetime (τ_expt?≈?20–50 ps), both increasing by a factor of ≈2 in going from polar acetonitrile to non-polar dioxane as solvent. DFT ZINDO calculations show a transition involving significant electron transfer from the diethyl-amino group into the carbonyl region of the molecule. In solution, in the presence of oxygen, the triplet state decays almost exclusively by oxygen quenching, and singlet oxygen is produced in high yield (Φ_??≈?0.5–0.55). The triplet state absorbs across the 450–750 nm region with maxima around 480 and 650 nm, and moderate molar absorption coefficients (ca. 6000–8000 M^?1 cm^?1). In a glass at 77 K, triplet decay gives a red phosphorescence, with λ_max?≈?640–650 nm, and a ?≈?0.25 s lifetime. If singlet oxygen yields are a good indication of triplet yields, then internal conversion and intersystem crossing occur with roughly equal efficiency.

     

Decreasing the oxidative potential of TiO(2) nanoparticles through modification of the surface with carbon: a new strategy for the production of safe UV filters

A safe UV filter may be obtained by inhibiting the photo-generation of free radicals through modification of the surface of TiO(2) nanoparticles with carbon.     

A biomimetic approach to the chemical inactivation of chrysotile fibres by lichen metabolites

Some lichens were recently reported to modify the surface state of asbestos. Here we report some new insight on the physico-chemical modifications induced by natural chelators (lichen metabolites) on two asbestos samples collected in two different locations. A biomimetic approach was followed by reproducing in the laboratory the weathering effect of lichen metabolites. Norstictic, pulvinic and oxalic acid (0.005, 0.5 and 50 mM) were put in contact with chrysotile fibres, either in pure form (A) or intergrown with balangeroite, an iron-rich asbestiform phase (B). Mg and Si removal, measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), reveals an incongruent dissolution for pure chrysotile (A), with Mg removal always exceeding that of Si, while chrysotile-balangeroite (B) follows a congruent dissolution pattern in all cases except in the presence of 50 mM oxalic acid. A much larger removal of Mg than Si in the solutions of 0.5 and 50 mM oxalic acid with chrysotile (A) suggests a structural collapse, which in the case of chrysotile-balangeroite (B) only occurs with 50 mM oxalic acid; in these cases both samples are converted into amorphous silica (as detected by X-ray diffraction (XRD)). Subsequent to incubation, some new phases (Fe(2)O(3), CaMg(CO(3))(2), Ca(C(2)O(4)) x H(2)O and Mg(C(2)O(4))2 x H(2)O), similar to those observed in the field, were detected by XRD and micro-Raman spectroscopy. The leaching effect of lichen metabolites also modifies the Fenton activity, a process widely correlated with asbestos pathogenicity: pure chrysotile (A) activity is reduced by 50 mM oxalic acid, while all lichen metabolites reduce the activity of chrysotile-balangeroite (B). The selective removal of poorly coordinated, highly reactive iron ions, evidenced by NO adsorption, accounts for the loss in Fenton activity. Such fibres were chemically close to the ones observed in the field. Chrysotile-rich rocks, colonised by lichens, could be exposed to a natural bioattenuation and considered as a transient environmental hazard.     

Zeolites as model solids for investigations on the role of iron at the solid-liquid interface in particulate toxicity

In order to investigate the molecular mechanism whereby iron in asbestos and in other iron containing fibres plays a crucial role in fibre induced carcinogenicity, two Fe²⁺-exchanged zeolites (Y and H-ZSM-5) have been prepared and used as model solids. Fe-Y was active both in free radical generation via hydrogen abstraction and in single strand DNA damage, but lost both these properties when oxidized by hydrogen peroxide. Fe-ZSM-5, on the other hand, was nearly inactive. Iron chelators and reductants (ascorbate, citrate and EDTA) enhance the activity in DNA single strand breaks. Moreover, they reactivate oxidized Fe-Y and activate Fe-ZSM-5. Iron is mobilized and Fe³⁺ is partially reduced to Fe²⁺. The most pronounced effect was found when citrate was present together with ascorbate. H-abstraction turns out to be a rather general reaction, occurring also with peptides as target molecules. In this case EPR spectra show that more than one type of radical moiety is generated.     

Tomographic PIV investigation of roughness-induced transition in a hypersonic boundary layer

The disagreement between free surface scalar experiments and the two-dimensional (2D) transport equation is discussed. An effective diffusivity coefficient, \(\kappa _{{\rm eff}}\) , is introduced and defined as the quotient between variance decay and mean gradient square. In all the experiments performed, \(\kappa _{{\rm eff}}\) is significantly larger than the scalar diffusivity, \(\kappa \) . Three mechanisms are identified as responsible for the differences between the quasi two-dimensional (Q2D) experiments and the 2D behaviour of a diffusive scalar. These are the vertical velocity gradients, the free surface divergence and the gravity currents induced by the scalar. These mechanisms, which affect the diffusive term in the 2D transport equation for large Péclet number ( \(Pe\gg 1\) ), are evaluated for steady and time-dependant laminar flows driven by electromagnetic body forces.     

A triarylamine-triarylborane dyad with a photochromic dithienylethene bridge

A molecular triad composed of a triarylamine donor, a triarylborane acceptor, and a photoisomerizable dithienylethene bridge has been synthesized and explored by cyclic voltammetry, UV-vis, and luminescence spectroscopy. The effects of irradiation with UV light and fluoride addition on the electrochemical and optical spectroscopic properties of the donor-bridge-acceptor molecule were investigated. Photoisomerization of the dithienylethene bridge affects the triarylboron reduction potential, but not the triarylamine oxidation potential. UV-vis experiments reveal that the association constant for fluoride binding at the triarylborane site is independent of the isomerization state of the bridge. Irradiation of a THF solution of our donor-bridge-acceptor molecule with UV light, followed by F(-) addition, leads to a different color of the sample than UV irradiation alone or F(-) addition alone.