The first synthetic receptor for the RGD sequence

[structure: see text] The combination of an optimized arginine receptor unit with a semirigid linker carrying a strategically placed primary ammonium group leads to the first synthetic RGD receptor. It binds to the free RGD peptide as well as to cyclo(RGDfV) in water with association constants around 1000 M(-1). RGD mimetics such as benzamidine 6 are not recognized, rendering the new host a prototype of a new class of receptors selective for the true RGD sequence in peptides.     

Method of Gaussian equivalent representation: a new technique for reducing the sign problem of functional integral methods

We report on the specific features of the sign problem in the classical auxiliary field methodology and the strategies employed for its alleviation. In particular, we focus on a new technique based on the method of Gaussian equivalent representation of Efimov and Nogovitsin [Physica (Amsterdam) 234A, 506 (1996)]] with which we could ameliorate the convergence properties significantly. We believe that this technique can also provide an interesting possibility to reduce the sign problem of other methods of computer simulation based on a functional integral approach.     

Nonlocal dynamics of spontaneous imbibition fronts

We have studied spontaneous imbibition fronts generated by capillary rise between two roughened glass plates, the separation d of which varied between 10 and 50 microm. Perfect agreement with Washburn's law was obtained. We have determined the roughness exponent chi of the fronts, and found chi=0.81+/-0.01 for small length scales. Above a certain crossover length xi, it reached chi=0.58+/-0.04, as predicted by the quenched noise Kardar-Parisi-Zhang equation. The crossover length is found to scale with the plate separation as sqrt[d], as predicted by recent models which properly include nonlocal dynamics effects on the front. We believe this to be the first clear identification of crossover from nonlocal to local dynamics.     

The influence of hyperoxia on regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV) and cerebral blood flow velocity in the middle cerebral artery (CBFVMCA) in human volunteers

Conflicting results reported on the effects of hyperoxia on cerebral hemodynamics have been attributed mainly to methodical and species differences. In the present study contrast-enhanced magnetic resonance imaging (MRI) perfusion measurement was used to analyze the influence of hyperoxia (fraction of inspired oxygen (FiO2) = 1.0) on regional cerebral blood flow (rCBF) and regional cerebral blood volume (rCBV) in awake, normoventilating volunteers (n = 19). Furthermore, the experiment was repeated in 20 volunteers for transcranial Doppler sonography (TCD) measurement of cerebral blood flow velocity in the middle cerebral artery (CBFV(MCA)). When compared to normoxia (FiO2 = 0.21), hyperoxia heterogeneously influenced rCBV (4.95 +/- 0.02 to 12.87 +/- 0.08 mL/100g (FiO2 = 0.21) vs. 4.50 +/- 0.02 to 13.09 +/- 0.09 mL/100g (FiO2 = 1.0). In contrast, hyperoxia diminished rCBF in all regions (68.08 +/- 0.38 to 199.58 +/- 1.58 mL/100g/min (FiO2 = 0.21) vs. 58.63 +/- 0.32 to 175.16 +/- 1.51 mL/100g/min (FiO2 = 1.0)) except in parietal and left frontal gray matter. CBFV(MCA) remained unchanged regardless of the inspired oxygen fraction (62 +/- 9 cm/s (FiO2 = 0.21) vs. 64 +/- 8 cm/s (FiO2 = 1.0)). Finding CBFV(MCA) unchanged during hyperoxia is consistent with the present study's unchanged rCBF in parietal and left frontal gray matter. In these fronto-parietal regions predominantly fed by the middle cerebral artery, the vasoconstrictor effect of oxygen was probably counteracted by increased perfusion of foci of neuronal activity controlling general behavior and arousal.     

Dynamical response of modulated Nd-doped kilometric fibre lasers

The response to pump-power modulation of Nd-doped fibre lasers with lengths in the kilometre range is reported. The timescales involved are close to those of subcritical regimes so that the transient relaxation oscillations are strongly damped. Furthermore, no competing effects (antiphase dynamics) occur between the two polarization eigenstates of the laser. Simple rate equations are shown to predict these behaviours. The experimental side of this study furnishes a definite demonstration of the importance of timescales in the dynamical properties of nonlinear and nonautonomous physical systems.     

Solvent influence on photochemical isomerizations: Photophysics of DODCI

We have studied the photophysics of DODCI dissolved in a series of polar solvents. Through measurements of the temperature dependence of the photoisomer quantum yield, fluorescence lifetime and fluorescence quantum yields we clarify the kinetic mechanism for nonradiative decay. By measuring the isomerization rate as a function of temperature at constant viscosity we are able to separate the innuence of internal barriers and solvent viscous drag. The apparent activation energy observed in solutions is less than the sum of the internal and viscosity activation energies. This is shown to be consistent with the full Kramer's rate expression for diffusive barrier crossing. We also establish the temperature dependence of a second “direct” internal conversion process which does not lead to photoisomer formation and dominates the nonradiative decay of DODCI at low temperatures or in a rigid matrix.     

Bridging the gap between homogeneous and heterogeneous catalysis: ortho/para H(2) conversion, hydrogen isotope scrambling, and hydrogenation of olefins by Ir(CO)Cl(PPh(3))(2)

Some transition metal complexes are known to catalyze ortho/para hydrogen conversion, hydrogen isotope scrambling, and hydrogenation reactions in liquid solution. Using the example of Vaska's complex, we present here evidence by NMR that the solvent is not necessary for these reactions to occur. Thus, solid frozen solutions or polycrystalline powdered samples of homogeneous catalysts may become heterogeneous catalysts. Comparative liquid- and solid-state studies provide novel insight into the reaction mechanisms.