Mechanism of a secondary reaction during the coulometric determination of uranium in a mixture with iron

Summary The mechanism of a photochemical secondary reaction which takes place between iron and uranium during the coulometric determination of uranium is explained. As a result of this interfering effect lower uranium values are found. The appropriate working conditions to obtain reliable uranium measurements are indicated.We wish to thank Mr. H. L. Eschbach and Mr. V. Verdingh for their helpful comments when drafting this paper.     

Low mass πN enhancement in inelastic αp interaction

Evidence for an enhancement in the isospin $\text{I =}\text{1}\text{2}\text{π}\text{N}$ system at M = 1130 MeV/c² (Γ = 80 MeV/c²) has been found in the reaction αp → αx at an incident α-momentum of 4.00 and 5.08 GeV/c. A strong t-dependence of the cross section and a mass-slope correlation are seen as the main features of the data.     

Über die π-Elektronenstruktur dertrans-1,2-Di-(pyridyl)-äthylene, 3. Mitt.: Die SCF−MO−CI-Untersuchung

Zusammenfassung Mit dem SCF–MO-Verfahren in der -Variationsmethode wurde die -Elektronenstruktur dertrans-1,2-Di-(pyridyl)äthylene untersucht. Die Spektren werden berechnet, wobei man Wechselwirkung dereinzeln angeregten Singulett-Konfigurationen berücksichtigt. Die berechneten Übergangsenergien sind in guter Übereinstimmung mit gemessenen Werten.

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-Electron structure of trans-1,2-Di-(pyridyl)-ethylenes, III.: Application of the SCF–MO–CI method

The -electron structure oftrans-1,2-Di-(pyridyl)-ethylenes was studied by the SCF–MO-method in the variable -approximation. The electronic spectra were calculated using the singly excited singlet configurations for the CI treatment. The calculated transition energies are in good agreement with the experimental data.

     

Differential and channel cross sections for the reactions KL0p → KS0p and KL0p → Λ0π+ in the c.m. energy range 1605 to 1910 MeV

The differential and channel cross sections have been measured for the reactions K_L⁰p → K_S⁰p and K_L⁰p → Λ⁰π⁺ in nine energy intervals in the c.m. range 1605 to 1910 MeV. The regeneration reaction is a combination of the KN amplitudes (with I = 0 and 1) and the $\text{K}\text{N}$ amplitude (I = 1) and is very sensitive to the various KN phase-shift solutions, some of which show an exotic I = 0, P₁ resonance. Our results have been expressed in terms of frequency distributions and cross sections, normalised by the Λ⁰π⁺ reaction. These results have been compared with the predictions of various partial-wave analyses. Qualitatively we can eliminate the P₁ non-resonant solution, though no solution correctly predicts our results.     

Syntheses, X-ray structures, photochemistry, redox properties, and DFT calculations of interconvertible fac- and mer-[Mn(SPS)(CO)3] isomers containing a flexible SPS-based pincer ligand

The lithium salt of the anionic SPS pincer ligand composed of a central hypervalent lambda4-phosphinine ring bearing two ortho-positioned diphenylphosphine sulfide side arms reacts with [Mn(CO)5Br] to give fac-[Mn(SPS)(CO)3]. This isomer can be converted photochemically to mer-[Mn(SPS)(CO)3], with a very high quantum yield (0.80+/-0.05). The thermal backreaction is slow (taking ca. 8 h at room temperature), in contrast to rapid electrode-catalyzed mer-to-fac isomerization triggered by electrochemical reduction of mer-[Mn(SPS)(CO)3]. Both geometric isomers of [Mn(SPS)(CO)3] have been characterized by X-ray crystallography. Both isomers show luminescence from a low-lying 3IL (SPS-based) excited state. The light emission of fac-[Mn(SPS)(CO)3] is largely quenched by the efficient photoisomerization occurring probably from a low-lying Mn-CO dissociative excited state. Density functional theory (DFT) and time-dependent DFT calculations describe the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of fac- and mer-[Mn(CO)3(SPS)] as ligand-centered orbitals, largely localized on the phosphinine ring of the SPS pincer ligand. In line with the ligand nature of its frontier orbitals, fac-[Mn(SPS)(CO)3] is electrochemically reversibly oxidized and reduced to the corresponding radical cation and anion, respectively. The spectroscopic (electron paramagnetic resonance, IR, and UV-vis) characterization of the radical species provides other evidence for the localization of the redox steps on the SPS ligand. The smaller HOMO-LUMO energy difference in the case of mer-[Mn(CO)3(SPS)], reflected in the electronic absorption and emission spectra, corresponds with its lower oxidation potential compared to that of the fac isomer. The thermodynamic instability of mer-[Mn(CO)3(SPS)], confirmed by the DFT calculations, increases upon one-electron reduction and oxidation of the complex.     

First structural characterization of a protactinium(V) single oxo bond in aqueous media

The present work describes the first structural studies of protactinium(V) in sulfuric and hydrofluoric acid media using X-ray absorption spectroscopy. The results show unambiguously the absence of the trans-dioxo bond that characterizes the other early actinide elements such as U and Np. In concentrated sulfuric acid (13 M), Pa(V) is proved to exhibit a single oxo bond as postulated in the literature for species in more dilute media. In a 0.5 M HF medium, XANES and EXAFS spectra indicate the absence of any oxo bond: Pa(V) exists in the form of a pure fluoro complex.     

A reliable new three-dimensional potential energy surface for H(2)-Kr

An improved three-dimensional potential energy surface for the H(2)-Kr system is determined from a direct fit of new infrared spectroscopic data for H(2)-Kr and D(2)-Kr to a potential energy function form based on the exchange-Coulomb model for the intermolecular interaction energy. These fits require repetitive, highly accurate simulations of the observed spectra, and both the strength of the potential energy anisotropy and the accuracy of the new data make the "secular equation perturbation theory" method used in previous analyses of H(2)-(rare gas) spectra inadequate for the present work. To address this problem, an extended version of the "iterative secular equation" method was developed which implements direct Hellmann-Feynman theorem calculation of the partial derivatives of eigenvalues with respect to parameters of the Hamiltonian which are required for the fits.     

In-capillary non-covalent labeling of insulin and one gastrointestinal peptide for their analyses by capillary electrophoresis with laser-induced fluorescence detection

The potential of the commercially available dye sypro orange for in-capillary derivatization was evaluated for the detection of insulin and one gastrointestinal peptide (Arg-Arg-gastrin) by capillary electrophoresis with laser induced fluorescence (CE-LIF). The fluorescent emission intensity (lambda(ex) = 488 nm, lambda(em) = 610 nm) of this probe is very low in aqueous medium, and increases strongly in less polar solvent, e.g. methanol. The hydrophobic character of the two analyzed peptides is too low to induce sufficient interaction with the fluorescent probe for good sensitivity when the latter is alone in the background electrolyte. Thus, the potential of several neutral, zwitterionic, cationic and anionic surfactants to favor probe/peptide interactions has been evaluated. It was demonstrated that a borate buffer (pH 8.5) containing tetradecyltrimethylammonium bromide (TTAB) in sub-micellar conditions can be considered as the most suitable buffer for insulin CE-LIF analysis. In addition, the method showed a good linearity between insulin concentration and the peak area of the labeled insulin, allowing quantitative measurements. The sensitivity achieved so far is comparable with that achieved with UV absorption detection, but even at this level it is interesting for microchip analysis, in which fluorescence detection is much more commonly available than UV absorption detection.     

Effect of the polar headgroup of phospholipids on their interaction with actin

It is generally admitted that actin filaments are anchored to a membrane by membranar actin-binding-proteins. However, we found that actin may also interact directly with membrane phospholipids. The actin-phospholipid complex has been investigated at the air-water interface using a film balance technique. In order to probe the effect of the phospholipid headgroup on the actin-phospholipid interaction, we focus mainly on phospholipids that have the same acyl chain length but different headgroups. For all the phospholipids, the apparent area per molecule (the total surface divided by the number of lipid molecules) increases after the injection of the protein into the subphase, which suggests an intercalation of actin between the phospholipid molecules. This effect seems to be more important for DMPE and DMPS than for DMPG, suggesting that the headgroup plays an important role in this intercalation. The critical surface pressure associated to the liquid expanded-liquid condensed (LE-LC) phospholipid transition increases with the concentration of G-actin and thus suggests that G-actin acts as an impurity, simply competing as a surfactant at the air-water interface. On the other hand, F-actin affects the LE to LC transition of phospholipids differently. In this case, the LE to LC transition is broader and F-actin slightly decreases the critical surface pressure, which suggests that electrostatic interactions are involved.     

The Au(n) cluster probe in secondary ion mass spectrometry: influence of the projectile size and energy on the desorption/ionization rate from biomolecular solids

A Au-Si liquid metal ion source which produces Au(n) clusters over a large range of sizes was used to study the dependence of both the molecular ion desorption yield and the damage cross-section on the size (n = 1 to 400) and on the kinetic energy (E = 10 to 500 keV) of the clusters used to bombard bioorganic surfaces. Three pure peptides with molecular masses between 750 and 1200 Da were used without matrix. [M+H](+) and [M+cation](+) ion emission yields were enhanced by as much as three orders of magnitude when bombarding with Au(400) (4+) instead of monatomic Au(+), yet very little damage was induced in the samples. A 100-fold increase in the molecular ion yield was observed when the incident energy of Au(9) (+) was varied from 10 to 180 keV. Values of emission yields and damage cross-sections are presented as a function of cluster size and energy. The possibility to adjust both cluster size and energy, depending on the application, makes the analysis of biomolecules by secondary ion mass spectrometry an extremely powerful and flexible technique, particularly when combined with orthogonal time-of-flight mass spectrometry that then allows fast measurements using small primary ion beam currents.