CEC for Studying the Retention and Separation of Pesticides on a Humic Acid Stationary Phase

A humic acid stationary phase is evaluated for studying by capillary electrochromatography (CEC) the binding of four pesticides with humic acid (HA), the main organic component in soil. It was demonstrated that the humic acid capillary was stable in terms of efficiency and retention during a long period of time. It appeared that HA has a lower affinity for neutral than for charged pesticides. The influence of the mobile phase constitution on the pesticide retention was also investigated in order to provide valuable information about the binding mechanism. The results suggest that the interactions of the pesticides during CEC are solely based on chromatographic mechanisms and that electrophoresis only plays a minor role. As well, it was shown that the HA stationary phase was able to separate these pesticides by CEC with a low analysis time. This HA capillary column could soon become attractive to determining the risk assessment of pesticides.     

Inducing spin crossover in metallo-supramolecular polyelectrolytes through an amphiphilic phase transition

A phase transition in an amphiphilic mesophase is explored to deliberately induce mechanical strain in an assembly of tightly coupled metal ion coordination centers. Melting of the alkyl chains in the amphiphilic mesophase causes distortion of the coordination geometry around the central transition metal ion. As a result, the crystal field splitting of the d-orbital subsets decreases resulting in a spin transition from a low-spin to a high-spin state. The diamagnetic-paramagnetic transition is reversible. This concept is demonstrated in a metallo-supramolecular coordination polyelectrolyte-amphiphile complex self-assembled from ditopic bis-terpyridines, Fe(II) as central transition metal, and dialkyl phosphates as amphiphiles. The magnetic properties are studied in a Langmuir-Blodgett multilayer. The modularity of this concept provides extensive control of structure and function from molecular to macroscopic length scales and gives access to a wide range of new molecular magnetic architectures such as nanostructures, thin films, and liquid crystals.     

Perchloro-2,5,8-triazaphenalenyl radical

[reaction: see text] The unusually stable perchloro-2,5,8-triazaphenalenyl radical 1 and its twisted dechlorinated dimer 2 were synthesized and characterized by ESR spectroscopy and X-ray crystallography. The X-ray structure of dimer 2 shows that the double bond connecting the two triazaphenalene systems is strongly twisted. Dimer 2 has a dramatic color shift from the solid state to solution, which may be due to a change of the twisting angle between both states.     

Synthesis of highly functionalised spiro-indoles by a halogen atom transfer radical cyclization

The halogen atom transfer radical cyclization (HATRC) has been evaluated on N-(indolylmethyl)trichloroacetamides under Cu(I)Cl catalysis using nitrogen containing ligands. The ring closure leads to the formation of 3,3-spiro-3H-indoles in moderate to good yields by a 5-exo-mechanism. Derivatives with an N-electron withdrawing substituent also lead to a 5-exo-trig and not to a 6-endo-trig cyclization.     

A new organometallic heteropolytungstate related to [Sb2W22O74(OH)2](12-): synthesis and structural characterisation of the bis-{Ru(p-cymene)}(2+)-containing anion [Sb2W20O70{Ru(p-cymene)}2](10-)

The easy synthesis of [Sb2W20O70{Ru(p-cymene)}2](10-) by the reaction between the organometallic precursor [Ru(p-cymene)Cl2]2 and [Sb2W20O70]14-, formed in situ, confirms the importance of the organometallic route to well defined ruthenium(+II)-substituted heteropolytungstates.     

Digital holographic microscopy: a noninvasive contrast imaging technique allowing quantitative visualization of living cells with subwavelength axial accuracy

We have developed a digital holographic microscope (DHM), in a transmission mode, especially dedicated to the quantitative visualization of phase objects such as living cells. The method is based on an original numerical algorithm presented in detail elsewhere [Cuche et al., Appl. Opt. 38, 6994 (1999)]. DHM images of living cells in culture are shown for what is to our knowledge the first time. They represent the distribution of the optical path length over the cell, which has been measured with subwavelength accuracy. These DHM images are compared with those obtained by use of the widely used phase contrast and Nomarski differential interference contrast techniques.     

Time evolution of second-order nonlinear profiles induced within thermally poled silica samples

The second-order nonlinear profile induced within thermally poled Infrasil silica samples is characterized as a function of the duration of the poling process. For poling durations shorter than 5 min the spatial distribution of the chi(2) susceptibility exhibits a triangular shape. This observation, as well as the maximum value of the electric field recorded during poling (1.9 x 10(9) V/m), is in excellent agreement with charge migration models that involve a single charge carrier. It is shown that for higher poling durations the nonlinear profiles tend to flatten; in that case the charge injection mechanisms cannot be neglected. For another point of view, the experimental method introduced herein has allowed us to determine the mobility of the rapid charge carrier involved in the poling process: micro = 1.5 x 10(-15) m2 V(-1) s(-1) at 250 degrees C.     

Evidence of thermal effects in a high-power Er3+-Yb3+ fiber laser

We analyze the influence of heat generation caused by nonradiative transitions in a high-power 1.55 microm double-clad erbium-ytterbium fiber laser on the Stark level population. At strong pumping rates, 1 microm lasing can start as a result of parasitic reflections. We present a model that allows us to simulate the effect of self-generated heat on the Stark level population by using the MacCumber relation. Heat generation plays a significant role and improves the 1.5 microm laser's efficiency by increasing the 1 microm lasing threshold.