Tetrathiafulvalenes acting as leaving groups: a route to bithiazoles.
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Crystallography, X-Ray↗
Biomedical subjects
Philippe Renaud
Publications and source records attributed to Philippe Renaud.
Radical amination with sulfonyl azides: a powerful method for the formation of C-N bonds.
A novel reaction for the introduction of an azide moiety by means of a mild radical process is currently under development. Sulfonyl azides are suitable azidating agents for nucleophilic radicals, such as secondary and tertiary alkyl radicals. More electrophilic radicals, such as enolate radicals, do not react with sulfonyl azides. This feature allowed the development of efficient intra- and intermolecular carboazidations of olefins. Due to the versatility of the azido group, this reaction has an important synthetic potential, as already demonstrated by the preparation of the core of several alkaloids, particularly those containing an amino-substituted quaternary carbon center, such as FR901483.
Journal Article↗
Thiophenol-mediated hydrogen atom abstraction: an efficient tin-free procedure for the preparation of cyclopentane derivatives.
[reaction: see text] An efficient procedure for running a cascade reaction involving 1,5-abstraction of a hydrogen atom followed by a radical cyclization is reported. Alkenyl radicals are generated from easily available terminal alkynes and thiophenol. This procedure eliminates the need of using the toxic tributyltin hydride and gives a greater amount of radical translocation products.
Journal Article↗
A convenient tin-free procedure for radical carboazidation and azidation.
The radical carboazidation of alkenes has been achieved in water with triethylborane as initiator. This efficient process is complete in 1 h at room temperature in an open system. These new tin-free carboazidation conditions are environmentally friendly and allow running reactions with an excess of either the alkene or the radical precursor. They are also suitable for simple radical azidation of alkyl iodides as well as for more complex cascade reactions involving annulation processes.
Journal Article↗
Radical carboazidation: expedient assembly of the core structure of various alkaloid families.
A procedure for one-pot intermolecular radical addition of 2-iodoesters to terminal alkenes followed by azidation of the radical adduct has been developed. This sequential reaction represents an alkene carboazidation process. Its efficacy is demonstrated by the two-step preparation of various lactams such as pyrrolidinones, pyrrolizidinones, and indolizidinones. An easy access to spirolactams bearing an amino-substituted quaternary carbon center is also described. These compounds are important building blocks for the synthesis of numerous alkaloids such as, for instance, FR901483.
Journal Article↗
Dielectric spectroscopy in a micromachined flow cytometer: theoretical and practical considerations.
We propose a model to determine the influence of different cell properties, such as size, membrane capacitance and cytoplasm conductivity, on the impedance spectrum as measured in a microfabricated cytometer. A dielectric sphere of equivalent complex permittivity is used as a simplified model to describe a biological cell. The measurement takes place between a pair of facing microelectrodes in a microchannel filled with a saline solution. The model incorporates various cell parameters, such as dielectric properties, size and position in the channel. A 3D finite element model is used to evaluate the magnitude of the electric field in the channel and the resultant changes in charge densities at the measurement electrode boundaries as a cell flows past. The charge density is integrated on the electrode surface to determine the displacement current and the channel impedance for the computed frequency range. The complete impedance model combines the finite element model, the electrode-electrolyte interface impedance and stray impedance, which are measured from a real device. The modeled dielectric complex spectra for various cell parameters are discussed and a measurement strategy for cell discrimination with such a system is proposed. We finally discuss the amount of noise and measurement fluctuations of the sensor.
Cell Physiological Phenomena↗
Superlattices of iron nanocubes synthesized from Fe[N(SiMe3)2]2.
The reaction of the metal-organic precursor Fe[N(SiMe3)2]2 with H2 in the presence of a long-chain acid and a long-chain amine in various proportions produces monodisperse zerovalent iron nanoparticles. These Fe particles display magnetic properties that match those of bulk iron as evidenced by magnetic and Mössbauer measurements. The nanoparticles adopt a cubic shape with edges of 7 nanometers and are incorporated into extended crystalline superlattices containing nanocubes in close proximity and with their crystallographic axes aligned. These superlattices are formed in solution, precipitate in high yield, and may be redissolved and redeposited as two-dimensional arrays.
Journal Article↗
Cell immersion and cell dipping in microfluidic devices.
Combining deflective dielectrophoretic barriers with controlled pressure driven liquid flows in microfluidic devices allows accurate handling of particles such as biological cells in suspensions. Working towards cell-based lab-on-a-chip applications, a platform permitting rapid testing of devices having different dielectrophoretic and fluidic subunits was developed. The performance of such a system is shown in the cases of (A) flooding a small number of immobilised cells with a dye and (B) transient buffer swapping of a large number of cells in flow. The transition times for moving cells from one reagent to the other are below 0.5 s in the case of flow-through cell dipping.
Biotechnology↗
A simple mechanism for reliable particle sorting in a microdevice with combined electroosmotic and pressure-driven flow.
Selective transport and sorting of particles in microfluidic devices by electroosmosis is complicated due to superposition of uncontrolled hydrodynamic pressure contributions on the electroosmotic force. In this paper, we present a microfluidic concept for the reliable and simple separation and sorting of particles in a microchip by electroosmosis combined with pressure-driven flow. The presented device allows fluid quantities to be switched and particles to be sorted within a channel manifold using only a single power supply with fixed voltage and an electric switch. Consequently, chip operation and fluid switching procedure are greatly simplified compared to a situation, in which several independent power sources are used for flow balancing, as is the common procedure. With the triple-T channel design presented, backpressure flow disturbing the electrokinetic fluid and particle separation process is eliminated by introducing controlled opposed hydrodynamic flow of buffer from side channels. This pressure-driven flow is generated on-chip by setting up differences in the reservoir pressures in a defined manner. A detailed flow analysis based on the equivalence of fluid flow and electric current is performed and the conditions for reliable chip function are worked out.
Cell Separation↗
Resistivity probing of multi-layered tissue phantoms using microelectrodes.
We present the use of an array of rectangular microelectrodes to discriminate between different resistivities in a thin, layered sample. Each electrode was 8 mm long and 200 nm thick. The electrode widths ranged from 20 to 500 microm. The electrodes were designed such that all pairs of consecutive electrodes had the same relative geometry, and therefore identical cell constants. A hydrogel-based tissue phantom, made by photopolymerization of 2-hydroxyethyl methacrylate (HEMA), was developed. By changing the hydrogel composition and the ionic strength of the storage medium, the resistivity of the hydrogels could be tuned between 100 omegam and 100 komegam. Using bipolar measurements, the tissue phantoms were characterized in the frequency range from 100 Hz to 30 MHz. The relative resistivity distribution of a three-layered structure composed of 120 microm sheets could be calculated and was shown to agree to within 7% of the bulk measurements. Potential clinical applications for this technique include probing of epithelial tissue and skin cancer screening.
Connective Tissue↗
Magnitude of fission product depositions from atmospheric nuclear weapon test fallout in France.
The external dose attributable to fallout from worldwide atmospheric nuclear testing, which represents about 40% of the total effective dose received before 2000, is dominated by specific fission products such as 95Zr, 104Ba, 106Ru, 103Ru, and 144Ce, which are far less well-documented than 90Sr and 137Cs. The depositions of these nuclides over France were calculated on the basis of activity measurements in air and rainwater samples collected from 1961 to 1977. These depositions were then compared to the same radionuclides activities measured in grass during that period. This study shows that the transfer and deposition processes occur in a very similar manner for all the studied radionuclides. Depositions calculated in this study, consistent in most cases with UNSCEAR estimates, constitute a good basis for the external dose assessment of nuclear weapon test fallout over Western Europe.
Air Pollutants, Radioactive↗
First steps toward noninvasive intraocular pressure monitoring with a sensing contact lens.
PURPOSE: To present a novel and minimally invasive approach to intraocular pressure (IOP) monitoring based on a sensing contact lens. METHODS: The key element of this measurement method is a soft contact lens with an embedded microfabricated strain gauge allowing the measurement of changes in corneal curvature correlated to variations in IOP. A prototype of this sensing contact lens was adapted and tested on enucleated porcine eyes. To verify the measurement principle of the device, the posterior chamber of the pig eyes was cannulated and connected to a syringe pump and a pressure sensor for precise control of IOP. The measurements of the contact lens were then compared to the ones from the pressure sensor, while pressure variations were induced through the cannula. RESULTS: Enucleated porcine eyes were stimulated with increasing and decreasing ramps of IOP. Measurements from the sensing contact lens and from the pressure sensor showed very good correlation, proving the high potential of this new measurement principle. In this study, a typical signal from the sensing contact lens obtained during the experiments is presented and discussed. CONCLUSIONS: The sensing contact lens shows the potential for continuously monitoring IOP in enucleated porcine eyes. The ultimate step will be the validation of the system and the reproducibility of results in humans. The device is placed in the same way as a corrective contact lens, no anesthesia is required, and vision remains almost unimpaired. This device would allow minimally invasive IOP monitoring over prolonged periods, regardless of the patient's position and activity, thus opening up new diagnostic and therapeutic methods for the management of glaucoma.
Animals↗
Unprecedented crystalline super-lattices of monodisperse cobalt nanorods.
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Journal Article↗
Diastereoselective radical-mediated hydrogen-atom abstraction.
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Journal Article↗
One-pot rhodium(i)-catalyzed hydroboration of alkenes: radical conjugate addition.
B-Alkylcatecholboranes, prepared by rhodium(I)-catalyzed hydroboration of alkenes, are suitable radical precursors for conjugate addition to activated olefins. This procedure proved to be particularly useful for the control of the regio- and chemoselectivity of such tandem processes. Enantioselective hydroboration has also been successfully coupled with radical chain reaction in a one-pot process.
Journal Article↗
Mapping of 137Cs deposition over eastern France 16 years after the Chernobyl accident.
We observed the relationship between present-day 137Cs surface activity and the rainfall in May 1986 to establish a relevant map of 137Cs deposition over eastern France. This study was performed in an area of the lower Rhône valley where clayey soils are assumed to trap caesium efficiently. Based on the rainwater/airborne activity ratio deduced from this relationship, we verified that present-day activities, measured in clayey soils of this type, are relatively representative of the initial depositions. The interlocked contaminated areas of the resulting map can be related to rainfall occurrences, as is the case for all countries affected by the Chernobyl fallout. This map can be reasonably compared with those obtained for countries bordering France in terms of both activity levels and extent of homogeneous activity areas. Lastly, we demonstrate that it would not be possible to produce a coherent map of initial fallout by extending the campaign over the whole of the eastern territory based on present-day soil activity measurements alone. Hence, only the relationship between 137Cs deposition and the rainfall of the first week of May 1986 can be used to construct a map depicting the Chernobyl fallout over eastern France.
Cesium Radioisotopes↗
Tin-free radical allylation of B-alkylcatecholboranes.
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Journal Article↗
Highly stereoselective radical cyclization of haloacetals controlled by the acetal center.
A systematic investigation of radical haloacetal cyclizations (Ueno-Stork reaction) where the acetal center is the unique stereogenic element is reported. This highly diastereoselective reaction can be used for the preparation of polysubstituted tetrahydrofurans and gamma-lactones. We report herein the full experimental details of reactions where up to three new chiral centers are created. To demonstrate the potential of this approach, short syntheses of (+)-eldanolide and of tricyclic acetals related to biologically active lignans have been achieved.
Journal Article↗