Single crystal EPR study of the dinuclear Cu(II) complex [Cu(tda)(phen)](2)·H(2)tda (tda = thiodiacetate, phen = phenanthroline): influence of weak interdimeric magnetic interactions

We report powder and single crystal EPR measurements of [Cu(tda)(phen)](2)·H(2)tda (tda = thiodiacetate, phen = phenanthroline) at 9.7 GHz. This compound consists of centrosymmetric copper(II) ion dimers, weakly ferromagnetically exchange-coupled (J = +3.2 cm(-1)), in which the dimeric units are linked by hydrophobic chemical paths involving the phen molecules. EPR revealed that the triplet spectra are collapsed by interdimeric exchange interactions mediated by that chemical path. Analysis and simulation of the single crystal EPR spectra were performed using Anderson's exchange narrowing model, together with statistical arguments. This approach allowed us to interpret the spectra modulated by the interdimeric interactions in situations of weak, intermediate, and strong exchange. We evaluated an interdimeric exchange constant J' = 0.0070(3) cm(-1), indicating that hydrophobic paths can transmit weak exchange interactions between centers at relatively long distances of the order of ～10 ?.     

Aqua(oxydiacetato‐κ3O,O′,O′′)(pyridine‐3‐carboxamide‐κN1)copper(II) sesquihydrate

In the monomeric title compound, [Cu(C₄H₄O₅)(C₆H₆N₂O)(H₂O)]·1.5H₂O, the Cu^II cation is bound in a square‐pyramidal coordination to a tridentate oxydiacetate (ODA) ligand, a monodentate pyridine‐3‐carboxamide (p3ca) ligand and one aqua ligand, where the two organic ligands form the basal plane and the water O atom occupies the unique apical site. The ODA ligand presents a slight out‐of‐plane puckering in its central ether O atom, while the p3ca ligand is essentially planar. The availability of efficient donors and acceptors for hydrogen bonding results in the formation of strongly linked hydrogen‐bonded bilayers parallel to (101), with an interplanar distance of 3.18 (1) Å and a stacking separation between the bilayers of 3.10 (1) Å, both of them governed by extended π–π interactions. The disordered nature of the solvent water molecules around inversion centres is discussed. The monoaqua compound is compared with the octahedral diaqua analogue, [Cu(C₄H₄O₅)(C₆H₆N₂O)(H₂O)₂], reported recently [Perec & Baggio (2009). Acta Cryst. C 65 , m296–m298].     

Ultraviolet Radiation in the Rhône River Lenses of Low Salinity and in Marine Waters of the Northwestern Mediterranean Sea: Attenuation and Effects on Bacterial Activities and Net Community Production

The high content in nutrients of freshwater outflows induces highly productive and buoyant plumes spreading over marine waters (MW). As a consequence, the growth of organisms developing in these low‐salinity waters (LSW) might be potentially affected by UV‐R (280–400 nm). This study investigated the penetration of UV‐R and its impact on net community production (NCP) and bacterial protein (B_PROTS) and DNA (B_DNAS) synthesis in mesotrophic‐LSW formed from the Rhône River and in oligotrophic MW of the Northwestern Mediterranean Sea (Gulf of Lions) in May 2006. High concentrations of chlorophyll a (up to 8 μg L^?1) measured in the LSW (<37.8 psu, 0–10 m) were the main factor influencing the diffuse attenuation coefficients (K_d) of both UV‐R and photosynthetically active radiation (PAR). The mean ratio of the K_d measured between the LSW and the MW increased with wavelength from 2.4 at 305 nm to 2.9 at 380 nm and 3.1 for PAR indicating more similarity in the UV region. NCP was severely inhibited by UV‐R at the surface of the LSW, whereas no effect was measured in the surrounding MW. In contrast, B_PROTS and B_DNAS were affected deeper by UV‐R in the MW (up to 8 m depth) compared to the LSW where inhibition was only observed at the surface. Differences in response of bacteria in LSW and MW are largely explained by differences in UV‐R transparency; however, transplant experiments indicate that bacterial assemblages from the MW were also more sensitive to UV‐R than those present in the LSW. We also observed that higher activity of bacteria after nutrient additions increased their sensitivity to UV‐R during the day, but favored their recovery during the night incubation period for both LSW and MW. Results suggest that riverine and nutrient inputs may alter the effects of UV‐R on microbial activity by attenuating the UV‐R penetration and by modifying the physiology of bacteria.     

Quenching of molecular fluorescence on the surface of monolayer-protected gold nanoparticles investigated using place exchange equilibria

The insertion of fluorescently labeled thiols into the protecting self-assembled monolayer on the surface of gold nanoparticles through place exchange reactions and the effects of this insertion on the photophysical properties of the fluorophores are investigated. Analysis of solution-phase fluorescence data using a dynamic equilibrium model yields the equilibrium constant for the place exchange equilibrium, as well as the relative fluorescence brightness of the fluorophores on the particle surface. In all cases we find a significant quenching of the fluorescence, and potential reasons for this quenching are discussed. In the case of these relatively small particles (4.5 nm diameter), the quenching appears to be mainly related to enhanced nonradiative deactivation pathways. The place exchange equilibrium constant reveals a reduced affinity of the fluorescently labeled thiols for insertion into the nonfluorescent alkylthiol monolayer (K(eq) approximately 0.2) compared to unlabeled alkylthiols.     

Synthesis, fluorescence, and two-photon absorption of a series of elongated rodlike and banana-shaped quadrupolar fluorophores: a comprehensive study of structure-property relationships

An extensive series of push-push and pull-pull derivatives was prepared from the symmetrical functionalization of an ambivalent core with conjugated rods made from arylene-vinylene or arylene-ethynylene building blocks, bearing different acceptor or donor end-groups. Their absorption and photoluminescence, as well as their two-photon-absorption (TPA) properties in the near infrared (NIR) region, were systematically investigated to derive structure-property relationships and to lay the guidelines for both spectral tuning and amplification of molecular TPA in the target region. Whatever the nature of the core or of the connectors, push-push systems were found to be more efficient than pull-pull systems, and planarization of the core (fluorene versus biphenyl) always leads to an increase in the TPA cross sections. In contrast, increasing the conjugation length as well as replacement of a phenylene moiety by a thienylene moiety in the conjugated rods did not necessarily lead to increased TPA responses. The present study also demonstrated that the topology of the conjugated rods can dramatically influence the TPA properties. This is of particular interest in terms of molecular engineering for specific applications, as both TPA properties and photoluminescence characteristics can be considerably affected. Thus, it becomes possible to optimize the transparency/TPA and fluorescence/TPA efficiency trade-offs for optical limiting in the red-NIR region (700-900 nm) and for two-photon-excited fluorescence (TPEF) microscopy applications, respectively.     

Synthetic,Optical and Theoretical Study of Alternating Ethylenedioxythiophene–Pyridine Oligomers: Evolution from Planar Conjugated to Helicoidal Structure towards a Chiral Configuration

A series of alternating 3,4‐ethylenedioxythiophene–alkynylpyridine oligomers (DA)_n with increased solubility are synthesized and their photophysical properties and nonlinear optical properties are investigated. Their quadratic polarizabilities are determined from hyper‐Rayleigh scattering experiments to obtain information on their conformations in solution. These chromophores, based on the alternation of electron‐rich (D) and electron‐deficient (A) moieties, exhibit optical properties that arise from the combination of dipolar and helicoidal features in the (DA)_n homologue series where n=1–4. The transition from dipolar conjugated planar structures (n=1, 2) to helicoidal structures (n=3, 4) is clearly evidenced by results from symmetry‐sensitive second‐order nonlinear optical experiments. This suggests an approach towards highly efficient chiral chromophores for second‐order nonlinear optics. Interestingly, this structural evolution also has significant impact on the photophysical properties: both absorption and fluorescence emission show bathochromic and hyperchromic shifts with increasing number of repeating units in the dipolar planar derivatives (n=1–2) but show saturation effects in the helicoidal structures (n=2–4). In addition, the helicoidal structures show sizeable two‐photon absorption at 700–750 nm (40–100 GM) for compounds lacking either electron‐donating or electron‐withdrawing substituents.     

Computing a molecule in its environment: A mathematical viewpoint

This article is the sequel of a previous survey where we presented the mathematical results rigorously known on the models used in quantum chemistry to simulate an isolated molecular system. The emphasis here is on the models that take into account the environment of the molecule, namely, the models of the condensed phase and the models of interaction with electromagnetic fields. Some related issues are also dealt with. A bibliography of more than 150 references are provided. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 71: 227–250, 1999     

Development and validation of methods for the trace determination of phthalates in sludge and vegetables

A routine method which is simple, quick and precise has been set up and validated for phthalate analysis in environmental samples (tomato plants and sewage sludges). Six phthalates have been studied simultaneously: dimethylphthalate, diethylphthalate, di-n-butylphthalate, n-butylbenzylphthalate, di-2-ethyl-hexyl phthalate (DEHP) and di-n-octylphthalate. Optimization of sample, solvent extraction uses a Soxtec apparatus and extract purification with an a solid-phase extraction cartridge allows between 90 and 110% recovery of phthalates. Precise, sensitive and selective identification and quantifying of analytes is by GC-MS in the single ion monitoring mode. This protocol allows analytes with concentrations as low as 10 microg/kg dry matter (DM) to be determined from small (1-2 g DM) samples. This analytical method has been applied to the phthalate transfer study for agricultural recycling of sludges, where phthalate bioavailability has been studied in aquiculture using two types of experiments. Tomatoes have been grown in containers where the trace organics have been directly introduced as pure substances, and in a second experiment under the same growth conditions, sewage sludge has replaced the pure substances. Transfer of these trace organics has been followed into the various parts of the tomato plant and in general only the DEHP is worthy of note although its percentage transfer remains very low even in an experiment designed to maximize this.     

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.     

Portable single-sided NMR measurements at variable temperatures: Implementation of a thermo-controlled device and application to the heating of bread dough

A temperature control unit was implemented to vary the temperature of samples studied on a commercial Mobile Universal Surface Explorer nuclear magnetic resonance (MOUSE-NMR) apparatus. The device was miniaturized to fit the maximum MOUSE sampling depth (25 mm). It was constituted by a sample holder sandwiched between two heat exchangers placed below and above the sample. Air was chosen as the fluid to control the temperature at the bottom of the sample, at the interface between the NMR probe and the sample holder, in order to gain space. The upper surface of the sample was regulated by the circulation of water inside a second heat exchanger placed above the sample holder. The feasibility of using such a device was demonstrated first on pure water and then on several samples of bread dough with different water contents. For this, T1 relaxation times were measured at various temperatures and depths and were then compared with those acquired with a conventional compact closed-magnet spectrometer. Discussion of results was based on biochemical transformations in bread dough (starch gelatinization and gluten heat denaturation). It was demonstrated that, within a certain water level range, and because of the low magnetic field strength of the MOUSE, a linear relationship could be established between T1 relaxation times and the local temperature in the dough sample.