Activity coefficients at infinite dilution of organic compounds in 1-(meth)acryloyloxyalkyl-3-methylimidazolium bromide using inverse gas chromatography

Activity coefficients at infinite dilution, gammainfinity, of organic compounds in two new room-temperature ionic liquids (n-methacryloyloxyhexyl-N-methylimidazolium bromide (C10H17O2MIM)(Br) at 313.15 and 323.15 K and n-acryloyloxypropyl-N-methylimidazolium bromide(C6H11O2MIM)(Br)) were determined using inverse gas chromatography. Phase loading studies of the net retention volume per gram of packing as a function of the percent phase loading were used to estimate the influence of concurrent retention mechanisms on the accuracy of activity coefficients at infinite dilution of solutes in both ionic liquids. It was found that most of the solutes were retained largely by partition with a small contribution from adsorption and that n-alkanes were retained predominantly by interfacial adsorption on ionic liquids studied in this work. The solvation characteristics of the two ionic liquids were evaluated using the Abraham solvation parameter model.     

Sequential organocatalyzed Michael addition/[3 + 2]-heterocyclization for the stereoselective synthesis of fused-isoxazoline precursors of enantiopure cyclopentanoids

We propose an asymmetric synthesis of functionalized cyclopentanoids bearing up to four stereogenic centers from easily accessible nitroalkenes and unsaturated aldehydes. The overall sequence includes an enantioselective organocatalytic Michael addition and a [3 + 2]-heterocyclization between an in situ generated silylnitronate and the unactivated double bond. Finally, the fused isoxazoline can be further transformed to various cyclopentanoids.     

Fe2OCl6(2-) salt formed by electrochemical oxidation of ethylenedioxytetrathiafulvalenoquinone-1,3-dithiolemethide in the presence of FeCl4- ion with a silicon wafer electrode

Electrochemical oxidation of a bent donor molecule, ethylenedioxytetrathiafulvalenoquinone-1,3-dithiolmethide ( 2), in chlorobenzene (PhCl)/ethanol containing NBu 4FeCl 4 as a supporting electrolyte is performed using an undoped silicon wafer electrode. Black crystals of 2 6.Fe 2OCl 6.2PhCl are obtained that have a different molecular formula from that of 2 2.FeCl 4 crystals obtained previously using a platinum rod electrode. The new crystal has a structure composed of alternately stacked layers of 2 molecules and Fe 2OCl 6 (2-) ions, whose Fe-O-Fe bond is completely linear and for which the geometry around the Fe atom is almost tetrahedral. The electrical resistivity decreases with temperature until ca. 200 K, but below this temperature, it gently increases. The magnetic susceptibility (chi p) observed can be described by the sum of chi p obeying a Curie-Weiss law for the impurity spins and of chi p obeying a dimer model with a spin-exchange integral ( J approximately -180 K) in each Fe 2OCl 6 (2-) ion, which is also weakly coupled to neighboring Fe 2OCl 6 (2-) ions through an additional exchange interaction.     

Differential MRI diagnosis between brain abscesses and necrotic or cystic brain tumors using the apparent diffusion coefficient and normalized diffusion-weighted images

Magnetic Resonance Diffusion-Weighted Imaging (DWI) has been reported to be helpful for the differential diagnosis between abscesses and cystic/necrotic brain tumors. However the number of patients is still limited, and the sensitivity and specificity of the method remain to be confirmed. The primary purpose of this study was to investigate a larger sample of patients, all investigated under the same experimental conditions, in order to obtain statistically significant data. Moreover, there is no consensus about the appropriate values of b required to use to make an accurate diagnosis from DWI. The secondary purpose of this study was to determine the discriminating threshold b values for raw diffusion-weighted images and for normalized diffusion-weighted images. On the basis of 14 abscesses, 10 high-grade gliomas and 2 metastases, we show that the calculation of accurate Apparent Diffusion Coefficient (ADC) values gives a specificity rate of 100%. Without ADC calculation, we show that image normalization is required to make an accurate differential diagnosis, and we highlight the ability of DWI to discriminate between brain abscesses and cystic/necrotic brain tumors using normalized signal intensity at lower b values (503 s/mm(2)) than usual.     

Bacterial dioxygenase- and monooxygenase-catalysed sulfoxidation of benzo[b]thiophenes

Asymmetric heteroatom oxidation of benzo[b]thiophenes to yield the corresponding sulfoxides was catalysed by toluene dioxygenase (TDO), naphthalene dioxygenase (NDO) and styrene monooxygenase (SMO) enzymes present in P. putida mutant and E. coli recombinant whole cells. TDO-catalysed oxidation yielded the relatively unstable benzo[b]thiophene sulfoxide; its dimerization, followed by dehydrogenation, resulted in the isolation of stable tetracyclic sulfoxides as minor products with cis-dihydrodiols being the dominant metabolites. SMO mainly catalysed the formation of enantioenriched benzo[b]thiophene sulfoxide and 2-methyl benzo[b]thiophene sulfoxides which racemized at ambient temperature. The barriers to pyramidal sulfur inversion of 2- and 3-methyl benzo[b]thiophene sulfoxide metabolites, obtained using TDO and NDO as biocatalysts, were found to be ca.: 25-27 kcal mol(-1). The absolute configurations of the benzo[b]thiophene sulfoxides were determined by ECD spectroscopy, X-ray crystallography and stereochemical correlation. A site-directed mutant E. coli strain containing an engineered form of NDO, was found to change the regioselectivity toward preferential oxidation of the thiophene ring rather than the benzene ring.     

Stereoselective synthesis of enantiopure N-protected-3-arylpiperazines from keto-esters

An efficient method for a stereoselective synthesis of optically pure N-Boc-3-arylpiperazines has been developed. After optimization of the protecting group strategy and experimental conditions, compounds were obtained via a highly stereoselective synthesis in up to 45% overall yield. This is a practical route to optically pure piperazines for medicinal chemistry.     

New photochromic xerogels composites based on nitrosyl complexes

New photoswitchable hybrid materials based on mononitrosyl complexes with excellent optical properties have been obtained by sol–gel process. Inclusion in silica matrix prepared from tetramethoxysilane precursor leads to new materials in which the ruthenium complex [RuCl(NO)py₄](PF₆)₂·1/2H₂O (py = pyridine) is stabilized as crystalline nanoparticles with diameters between 2 and 15 nm. Photochromic properties are maintained and have been evidenced by infrared spectroscopy under irradiation (λ = 473 nm) at low temperature (T = 100 K). The reversible transfer from the ground state (GS) to the metastable state (MS1) is about 40% in the composite, which is close to the value observed on the most studied sodium nitroprusside (50% on pure material).     

Numerical Analysis of the Impact of Nanofluids and Vapor Grooves Design on the Performance of Capillary Evaporators

This paper discusses the impact of nanofluids and vapor grooves position on the performance of capillary evaporators. The phase change that occurs within the wick structure is simulated using a 2D transient mathematical model. The model combines Darcy’s law, Langmuir’s law, and energy equations to describe the heat and mass transfers inside the wick and the metallic wall. A comparison with experimental visualizations and numerical simulations is proposed. The analysis was performed for water and aluminum oxide nanoparticles with three volume concentrations of nanoparticles. Also, the effect of the vapor grooves configuration on the capillary evaporator performance is studied. The numerical results show that substituting water with nanofluids had a significant effect in reducing the evaporator temperature and the pressure drop in the whole loop. The present work has also shown that the contact between the metallic wall and the wick is an important element that must be taken into account in the design of the evaporator.