Development of a reference solution for the pH of seawater

A method that uses a Harned cell to perform potentiometric pH measurements has been optimized and applied to an aqueous solution of simulated seawater that contains sodium perchlorate, sodium sulfate, sodium hydrogen carbonate and boric acid and has an ionic strength I of 0.57 mol kg⁻¹. The standard metrological approach developed for the measurement of pH in low ionic strength aqueous solutions was maintained, but a few modifications were necessary, and measurement procedures and calculations were modified ad hoc from those adopted in conventional protocols. When determining the standard potential of the cell, E°, NaClO₄ salt was added to a 0.01 mol/kg HCl solution to attain the same ionic strength as the test solution and to investigate possible specific effects related to the high levels and the nature of the background electrolyte. An appropriate value of γ _±HCl (0.737) was then selected from the literature, based on a realistic value for I. Finally, in order to convert the acidity function at zero chloride molality into pH, a suitable value of γ _Cl (0.929) was calculated. As a result, we obtained pH = 8.18 (T = 25 °C) with an associated expanded uncertainty U = 0.01 (coverage factor k = 2). The aim was to establish a sound basis for the pH measurement of seawater by identifying the critical points of the experimental and theoretical procedure, and to discuss further possible developments that would be useful for achieving a reference solution.     

Structural and photophysical characterization of multichromophoric pyridylporphyrin-rhenium(i) conjugates

Four porphyrin-Re(I) conjugates, in which a pyridylporphyrin chromophore is directly coordinated to the electron-acceptor fragment [ fac-Re(CO) 3(bipy)] (+), were prepared: the dimeric and pentameric compounds [ fac-Re(CO) 3(bipy)(4'MPyP)](CF 3SO 3) ( 1) (4'MPyP = 4'-monopyridylporphyrin) and [ fac-{Re(CO) 3(bipy)} 4(mu-4'TPyP)](CF 3SO 3) 4 ( 2) (4'TPyP = 4'-tetrapyridylporphyrin), and the corresponding compounds with 3' rather than 4' porphyrins, [ fac-Re(CO) 3(bipy)(3'MPyP)](CF 3SO 3) ( 3) and [ fac-{Re(CO) 3(bipy)} 4(mu-3'TPyP)](CF 3SO 3) 4 ( 4). These adducts proved to be very stable in solution and were also structurally characterized in the solid state by X-ray crystallography. A detailed photophysical study was performed on the zincated adducts of the conjugates 1- 3, labeled 5, 6, and 7, respectively. In all adducts the typical fluorescence of the zinc-porphyrin unit was reduced in intensity and lifetime by the presence of the peripheral rhenium-bipy fragment(s) (heavy-atom effect). For the dyads 5 and 7 the photoinduced charge transfer process from the zinc-porphyrin to the Re(I)-bipy unit is only slightly exoergonic. Ultrafast spectroscopy experiments showed no evidence for electron transfer quenching in the dyads as such, whereas the addition of pyridine (that binds axially to zinc and thus affects the porphyrin redox potential) led to a moderately efficient photoinduced electron transfer process. In perspective, an appropriate functionalization of the bipy ligand and/or of the porphyrin chromophore might improve the thermodynamics and, thus the efficiency, of the photoinduced electron transfer process.     

Structural and collisional relaxations in liquids and supercritical fluids

The dynamic structure factor S(Q,omega) of both associated (water and ammonia) and simple fluids (nitrogen and neon) has been determined by high-resolution inelastic x-ray scattering in the 2-14 nm(-1) momentum transfer range. A line-shape analysis with a generalized hydrodynamic model was used to study the involved relaxation process and to characterize its strength and time scale. We observe that in the liquid phase such a process is governed by rearrangements of intermolecular bonds, whereas in the supercritical region it assumes a collisional nature.     

Entire solutions of quasilinear elliptic systems on Carnot groups

We prove general a priori estimates of the solutions of a class of quasilinear elliptic systems on Carnot groups. As a consequence, we obtain several nonexistence theorems. The results are new even in the Euclidean setting.     

Numerical Experiments in Complex Hæmodynamic Flows. Non-Newtonian Effects

Numerical experiments for non-trivial flows, close to realistic situations in hæmodynamics, are described and interpreted. Two geometries have been selected: an axisymmetric corrugated tube (with periodic boundary conditions) and a 3D bifurcation with an obstructed end (anastomosis). Results concern sensitivity of errors associated to the time-step size and mesh refinement, but essentially consist of the quantitative estimation of non-Newtonian effects based on Casson's rheological model, treated in retarded form. The time-step lag of such effects is the main reason for evaluating the sensitivity of errors. Due to the high computational cost characterizing the problems to be faced, we expect that the present results will be useful when real geometries should be modeled. The main conclusions are that non-Newtonian effects may be relevant (especially for secondary flows) and that, in most cases, for the same level of errors the use of Casson's law does not generate excessive additional computational costs. Thus, within this strategy, the user can accurately solve the problem using this rheological model without having to worry if the non-Newtonian effects are important or not.     

Asymmetric dihydroxylation of drim-7-en-11-ol: synthesis of diastereomerically pure driman-7α,8α,11-triol and its elaboration into novel chlorinated norlabdanic compounds

The asymmetric dihydroxylation of drim-7-en-11-ol was studied in detail and diastereomerically pure driman-7α,8α,11- and driman-7β,8β,11-triols were prepared. Further elaboration of driman-7α,8α,11-triol afforded 14,15-bisnorlabd-7α,8α-isopropylidenedioxy-11,13-dione from which a novel chlorinated bisnorlabdanic compound (14,15-bisnorlabd-12-ene-12-chloro-8α,13-epoxy-7α-ol-11-one) and an unusual dichloro-derivative, 13,14,15,16-tetranorlabd-12-dichloro-7α-acetoxy-8α-ol-11-one, were obtained.     

Finite Element Modeling of Liquid Deuterium Flow and Heat Transfer in a Cold-neutron Source

A finite element simulation of flow and heat transfer in the moderator cell of a cold-neutron source (CNS), in which liquid deuterium subject to internal heat generation is flowing, is reported. The numerical scheme consists of a stabilized equal-order method. A time-accurate approach is adopted to resolve the large-scale eddies of the flow, with a Smagorinsky's model for the subgrid-scale effects. The thermal coupling follows a staggered strategy, with SUPG-type upwinding. A specific wall-law is developed that accounts for the correct partition of the heat deposited at the wall by radiation between the liquid deuterium and the helium gas flowing at the outer side of the wall. The average flow and thermal structure are presented. The turbulent fluctuations are both illustrated in physical space and decomposed into spectral components. The wavenumber spectrum suggests that adequate resolution of the large-scale eddies has been attained with just 200,000 nodes, while a DNS analysis would have required at least 1010 nodes. Usefulness of the approach in the design process of the CNS is highlighted.     

New Procedure for the Determination of 3-Nitrotyrosine in Plasma by GC–ECD

A method suitable for the determination of 3-nitrotyrosine, a well known marker of nitro-oxidative stress, in plasma by GC–ECD has been investigated. After deproteinisation, SPE and LC separation, 3-nitrotyrosine was derivatised by a single-step procedure to the corresponding N-heptafluorobutyryl heptafluorobutyl ester and analysed. The precision and reliability of the procedure were assured by using 4-nitrophenylalanine as internal standard and a diverter valve to protect the detector. The method was applied to the analysis of volunteers’ plasma samples.     

Interaction between aspergillic acid and iron(III): A potentiometric,UV–Vis,H NMR and quantum chemical study

The complex formation equilibria of aspergillic acid with iron(III) were studied by potentiometric and spectrophotometric methods. The ligand was prepared by a biosynthetic route and its purity checked by MS and ¹H NMR spectroscopies. Some structural features of the ligand are discussed on the basis of NMR results. The iron(III) coordination model is compared with those of two other cyclic hydroxamates, 1-hydroxy-2-pyridinone and 1,4-dihydroxy-2-pyridinone, and its features are discussed on the basis of quantum chemical calculations.