The determination of organochlorine compounds and petroleum hydrocarbons in a seaweed sample: results of a world-wide intercomparison exercise

A seaweed sample (Fucus sp.) was prepared, homogenised and distributed to laboratories worldwide as the IAEA-140 intercomparison material for the analysis of organochlorine compounds and petroleum hydrocarbons. A total of 80 laboratories from 51 countries reported results for this sample. The data sets reported by laboratories were evaluated statistically and the mean concentration values could be computed with 95% confidence limits for a large number of analytes. The accuracy of the analytical performance of each laboratory has been introduced by using Z-scores. The spread of results reported generally indicates that the accurate determination of many persistent organic pollutants, such as hexachlorobenzene, lindane, Aroclors or fluoranthene, is still difficult for many laboratories. The final results of this intercomparison exercise enable individual participants to assess their performance and, where necessary, to introduce appropriate modifications in their analytical procedures. Furthermore, as a series of statistical criteria was fulfilled for a number of compounds, the sample IAEA-140 can now be used as a reference material for quality control in the determination of chlorinated compounds and petroleum hydrocarbons in environmental samples.     

Mild Synthesis of Amino‐Poly(ethylene glycol)s. Application to Steric Stabilization of Clays

The hydroxyl end groups of poly(ethylene glycol) (PEG) have been transformed easily and quantitatively into amino groups via the Mitsunobu reaction. Phthalimide was alkylated with PEGs and the hydrazinolysis of the resulting phthalimido‐PEGs gave the amino compounds in high yields. Quaternization of the amino groups leads to hydrophilic polymer chains bearing a positive charge on one or two ends, depending on the chosen PEG. Such products can be used to protect sterically, negatively charged particles such as clays.

     

Luminescence of Eu3+ and Tb3+ Complexes of Two Macrobicyclic Ligands Derived from a Tetralactam Ring and a Chromophoric Antenna

Two macrobicyclic ligands derived from an 18‐membered tetralactam ring and 2,2′‐bipyridine or 2,6‐bis(pyrazol‐1‐yl)pyridine moieties, 1 and 2 , respectively, form stable complexes with Gd^III, Eu^III, and Tb^III ions in aqueous solution. The ligand‐based luminescence is retained in the Gd^III cryptates, whereas this radiative deactivation is quenched in the Eu^III and Tb^III cryptates by ligand‐to‐metal energy transfer, resulting in the usual metal‐centered emission spectra. Singlet‐ and triplet‐state energies, emission‐decay lifetimes, and luminescence yields were measured. [Tb⊂ 1 ]³⁺ cryptate shows a long luminescence lifetime (τ=1.12 ms) and a very high metal luminescence quantum yield (Φ=0.25) in comparison with those reported in the literature for Tb³⁺ complexes sensitized by a bipyridine chromophore. By comparison to [Ln⊂ 1 ]³⁺, [Ln⊂ 2 ]³⁺ presents markedly lower luminescence properties, due to worse interaction between the 2,6‐bis(pyrazol‐1‐yl)pyridine unit and the metal ion. Moreover, the luminescent metal and the triplet ligand energy levels of [Eu⊂ 2 ]³⁺ do not match. The effects of H₂O molecules coordinated to the metal centre and of thermally activated decay processes on nonradiative deactivation to the ground‐state are also reported.     

The expected discounted penalty function under a risk model with stochastic income

Quantities of interest in ruin theory are investigated under the general framework of the expected discounted penalty function, assuming a risk model where both premiums and claims follow compound Poisson processes. Both a defective renewal equation and an integral equation satisfied by the expected discounted penalty function are established. Some implications that these equations have on particular quantities such as the discounted deficit and the probability of ultimate ruin are illustrated. Finally, the case when premiums have Erlang(n,β) distribution and the distribution of the claims is arbitrary is investigated in more depth. Throughout the paper specific examples where claims and premiums have particular distributions are provided.     

trans-cis Photoisomerization of the styrylpyridine Ligand in [Re(CO)3(2,2'-bipyridine)(t-4-styrylpyridine)]+: role of the metal-to-ligand charge-transfer excited states

The trans-cis isomerization of the styrylpyridine carbon-carbon double bond induced by visible light irradiation in fac-[Re(CO)(3)(bpy)(stpy)](+) (bpy = 2,2'-bipyridine; stpy = t-4-styrylpyridine) has been investigated by means of quantum-chemical methods. The structures of the various cis and trans conformers of [Re(CO)(3)(bpy)(stpy)](+) have been optimized at the density functional theory (DFT) level. Three rotational conformers for the most stable trans isomer lie within 2.3 kJ mol(-1) each other. The energy difference between the cis and trans isomers is 27.0 kJ mol(-1). The electronic spectroscopy of the most stable conformers has been investigated by time-dependent DFT (TD-DFT) and complete active space self-consistent field/CAS second order perturbation theory (CASSCF/CASPT2) calculations. The lowest absorption bands are dominated by metal-to-ligand charge-transfer (MLCT, d(Re)-->pi*(bpy)) transitions calculated at about 25,000 cm(-1) and by a strong intraligand (1)IL (pi(stpy)-->pi*(stpy)) transition in the near UV region. On the basis of CASSCF potential energy curves (PECs) calculated as a function of the torsion angle of the C=C bond of the styrylpyridine ligand, it is shown that the role of the low-lying MLCT states is important in the photoisomerization mechanism. In contrast to the free organic ligand, in which the singlet mechanism is operational via the (1)IL (S(1)) and electronic ground (S(0)) states, coordination to the rhenium steers the isomerization to the triplet PEC corresponding to the (3)IL state. From the (3)IL(t) (t = trans) the system evolves to the perpendicular intermediate (3)IL(p) (p = perpendicular) following a 90 degrees rotation around the styrylpyridine C=C bond. The metal center acts as a photosensitizer because of the presence of photoactive MLCT states under visible irradiation. The position of the crossing between the (3)IL and electronic ground state PEC determines the quantum yield of the isomerization process.     

Immobilization of Protein A on SAMs for the elaboration of immunosensors

Binary mixtures of 11-mercaptoundecanoic acid (MUA) and other thiols of various lengths and terminal functions were chemisorbed on gold-coated surfaces via S–Au bonds to form mixed self-assembled monolayers (SAMs). Several values of the mole fraction of MUA in the thiol mixtures were tested and the structure and composition of the resulted thin films were characterized by X-ray photoelectron spectroscopy (XPS) and polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS). The results made it clear that co-adsorption of MUA with thiols of similar chain length led to well-ordered monolayers whereas the co-adsorption of MUA with shorter thiols yielded less crystalline-like thin films, but with more reactive carboxylic acid terminal groups. This criterion appeared decisive for efficient covalent binding of Staphylococcus aureus Protein A (PrA), a protein that displays high affinity for the constant fragment (Fc) of antibodies of the IgG type from various mammal species. The ability of immobilized Protein A to recognize and bind a model IgG appeared to be optimal for the mixed SAM of MUA and the short-chain, ω-hydroxythiol 6-mercaptohexanol in the proportion 1–3.     

Well-defined carboxyl-terminated alkyl monolayers grafted onto H-Si(111): packing density from a combined AFM and quantitative IR study

This work demonstrates that well-defined mixed carboxyl-terminated/methyl-terminated alkyl monolayers can be prepared in one step on H-terminated Si(111) via direct photochemical hydrosilylation of undecylenic acid and 1-decene mixtures. As evidenced by AFM imaging and IR spectroscopy, a final rinse in hot acetic acid leaves the functionalized surface atomically smooth and perfectly free of physisorbed contaminants while unwanted material remains atop the monolayer with most other common solvents. The compositional surface chemistry was determined from a truly quantitative IR (ATR geometry) study in the range of 900-4000 cm(-)(1). Results prove that neither surface oxidation nor grafting through the carboxyl end groups occurs. Monolayers are fairly dense for such bulky end groups, with a total molecular surface density of approximately 2.7 10(14) cm(-)(2) corresponding to a surface coverage of 0.35 (maximum theoretical value approximately 0.5). Careful analysis of the CH- and COOH-related IR bands reveals that the composition of the grafted layers is richer in acid chains than the starting grafting mixture. A simple model is presented that shows that the grafting kinetics is about twice as fast for undecylenic acid as for 1-decene. Complementary electrochemical impedance measurements indicate the excellent electronic properties of the interface with a very low density of gap states. They also show that the acid terminal groups promote the penetration of water in the outer part of the organic film.     

Photochemistry of CH3Mn(CO)5: a multiconfigurational ab initio study

The electronic spectroscopy of CH3Mn(CO)5 has been investigated by means of ab initio multiconfigurational MS-CASPT2/CASSCF calculations. The absorption spectrum is characterized by a series of Metal-Centered (MC) excited states in the UV energy domain (below 290 nm) that could be responsible for the observed photoreactivity starting at 308 nm. The upper part of the spectrum is overcrowded between 264 and 206 nm and dominated by a high density of Metal-to-Ligand-Charge-Transfer (MLCT) states corresponding mainly to 3d(Mn) --> pi*(CO) excitations. A non-negligible contribution of Metal-to-sigma-Bond-Charge-Transfer (MSBCT) states corresponding to 3d(Mn) --> sigma*(Mn-CH3) excitations is also present in the theoretical spectrum of CH3Mn(CO)5. However, in contrast to other transition metal hydrides and methyl substituted (HMn(CO)5, HCo(CO)4, and CH3Co(CO)4) these MSBCT transitions do not participate to the lowest bands of the spectrum as main contributions. The photochemistry of CH3Mn(CO)5, namely the loss of a CO ligand vs. the metal-methyl bond homolysis, is investigated by means of MS-CASPT2 states correlation diagrams. This study illustrates the complexity of the photodissociation mechanism of this class of molecules, which involves a large number of nearly degenerate electronic states with several channels for fragmentation.     

Broad-bandwidth shot-noise-limited class-A operation of a monomode semiconductor fiber-based ring laser

We demonstrate the operation of a monomode semiconductor laser with a relative intensity noise limited by the shot-noise floor, -156 dB/Hz for a typical detected photocurrent of 1 mA, over a large frequency range from 50 MHz to 18 GHz. We achieve direct control of photon lifetime to turn an initially class-B laser into a relaxation-oscillation-free class-A one while preserving strict single-mode operation. Finally, we confirm experimentally that the laser operation in the desired class-A regime allows a dramatic filtering out of the relative intensity noise.     

Control of the evolution of iron peroxide intermediate in superoxide reductase from Desulfoarculus baarsii. Involvement of lysine 48 in protonation

Superoxide reductase is a nonheme iron metalloenzyme that detoxifies superoxide anion radicals O(2)(?-) in some microorganisms. Its catalytic mechanism was previously proposed to involve a single ferric iron (hydro)peroxo intermediate, which is protonated to form the reaction product H(2)O(2). Here, we show by pulse radiolysis that the mutation of the well-conserved lysine 48 into isoleucine in the SOR from Desulfoarculus baarsii dramatically affects its reaction with O(2)(?-). Although the first reaction intermediate and its decay are not affected by the mutation, H(2)O(2) is no longer the reaction product. In addition, in contrast to the wild-type SOR, the lysine mutant catalyzes a two-electron oxidation of an olefin into epoxide in the presence of H(2)O(2), suggesting the formation of iron-oxo intermediate species in this mutant. In agreement with the recent X-ray structures of the peroxide intermediates trapped in a SOR crystal, these data support the involvement of lysine 48 in the specific protonation of the proximal oxygen of the peroxide intermediate to generate H(2)O(2), thus avoiding formation of iron-oxo species, as is observed in cytochrome P450. In addition, we proposed that the first reaction intermediate observed by pulse radiolysis is a ferrous-iron superoxo species, in agreement with TD-DFT calculations of the absorption spectrum of this intermediate. A new reaction scheme for the catalytical mechanism of SOR with O(2)(?-) is presented in which ferrous iron-superoxo and ferric hydroperoxide species are reaction intermediates, and the lysine 48 plays a key role in the control of the evolution of iron peroxide intermediate to form H(2)O(2).