Large spontaneous polarization and clear hysteresis loop of a room-temperature hybrid ferroelectric based on mixed-halide [BiI3Cl2] polar chains and methylviologen dication

The search for hybrid organic-inorganic materials, which have the great advantage that they can be synthesized at moderate temperature (T < 200 °C), remains a great challenge in the field of ferroelectrics. Here, a room-temperature ferroelectric material with interesting characteristics, (MV)[BiI(3)Cl(2)] (MV(2+) = methylviologen), is reported. Its structure is based on polar inorganic chains resulting from a remarkable Cl/I segregation induced by methylviologen entities, which coincide with the fourfold polar axis of the tetragonal structure. Of great importance is that this room-temperature hybrid ferroelectric displays a clear electrical hysteresis loop with a large spontaneous polarization (>15 μC·cm(-2)).     

Spectroscopic detection of Saxitoxin: an alternative to mouse bioassay

Herein, we report the surface modification of quartz with a coumaryl-aza-crown-6 derivative to detect Saxitoxin using fluorescence enhancement through Photoinduced Electron Transfer and the sensitivity with this system approaches the limit of the mouse bioassay which is the current benchmark for Saxitoxin detection.     

Momentum-transport studies in high E x B shear plasmas in the National Spherical Torus Experiment

Experiments have been conducted at the National Sperical Torus Experiment (NSTX) to study both steady state and perturbative momentum transport. These studies are unique in their parameter space under investigation, where the low aspect ratio of NSTX results in rapid plasma rotation with ExB shearing rates high enough to suppress low-k turbulence. In some cases, the ratio of momentum to energy confinement time is found to exceed five. Momentum pinch velocities of order 10-40 m/s are inferred from the measured angular momentum flux evolution after nonresonant magnetic perturbations are applied to brake the plasma.     

Aggregation of chlorophylls in monolayers. Infrared study of chlorophyll a in a mono- and multilayer arrays

The nature of the interaction between adjacent chlorophyll a molecules in a mono- and multilayer is examined by infrared spectroscopy. The evidences suggest a different aggregation in the monolayer compared to the multilayer system. The monolayer state of chlorphylls may be a prerequisite to synthesize the energy trap in the photosynthetic unit.     

A dansylated peptide for the selective detection of copper ions

A new peptidyl fluorescent chemosensor for the selective detection of copper ions was studied.     

Rapid activation of the melibiose permease MelB immobilized on a solid-supported membrane

Rapid solution exchange on a solid-supported membrane (SSM) is investigated using fluidic structures and a solid-supported membrane of 1 mm diameter in wall jet geometry. The flow is analyzed with a new technique based on specific ion interactions with the surface combined with an electrical measurement. The critical parameters affecting the time course of the solution exchange and the transfer function describing the time resolution of the SSM system are determined. The experimental data indicate that solution transport represents an intermediate situation between the plug flow and the Hagen-Poiseuille laminar flow regime. However, to a good approximation the rise of the surface concentration can be described by Hagen-Poiseuille flow with ideal mixing at the surface of the SSM. Using an improved cuvette design, solution exchange as fast as 2 ms was achieved at the surface of a solid-supported membrane. As an application of the technique, the rate constant of a fast electrogenic reaction in the melibiose permease MelB, a bacterial ( Escherichia coli) sugar transporter, is determined. For comparison, the kinetics of a conformational transition of the same transporter was measured using stopped-flow tryptophan fluorescence spectroscopy. The relaxation time constant obtained for the charge displacement agrees with that determined in the stopped-flow experiments. This demonstrates that upon sugar binding MelB undergoes an electrogenic conformational transition with a rate constant of k approximately 250 s (-1).     

Complexes optiquement actifs de la serie du titanocene. Premiere filiation absolue entre les derives carbones et les complexes du titane a chiralite centro-metallee

Optically active titanocene complexes are synthesised starting from a fulvene asymmetric reduction. The optical purity is determined by analogy of these compounds with ferrocene derivatives.An absolute configuration is proposed for some titanium chiral complexes by reference to chiral ferrocene compounds.