Optimal cubature on the sphere and other orientation averaging schemes

We propose an orientation averaging scheme which we call optimal cubature on the sphere to be used in light scattering computations. The cubature points are optimally arranged on the sphere to produce non-biased and fast convergence in scattering problems requiring numerical orientation averaging. We will compare performance against other possible schemes.     

Efficient Conversion of Light to Chemical Energy: Directional,Chiral Photoswitches with Very High Quantum Yields

Photochromic systems have been used to achieve a number of engineering functions such as light energy conversion, molecular motors, pumps, actuators, and sensors. Key to practical applications is a high efficiency in the conversion of light to chemical energy, a rigid structure for the transmission of force to the environment, and directed motion during isomerization. We present a novel type of photochromic system (diindane diazocines) that converts visible light with an efficiency of 18 % to chemical energy. Quantum yields are exceptionally high with >70 % for the cis–trans isomerization and 90 % for the back‐reaction and thus higher than the biochemical system rhodopsin (64 %). Two diastereomers (meso and racemate) were obtained in only two steps in high yields. Both isomers are directional switches with high conversion rates (76–99 %). No fatigue was observed after several thousands of switching cycles in both systems.     

A homogeneous quenching resonance energy transfer assay for the kinetic analysis of the GTPase nucleotide exchange reaction

A quenching resonance energy transfer (QRET) assay for small GTPase nucleotide exchange kinetic monitoring is demonstrated using nanomolar protein concentrations. Small GTPases are central signaling proteins in all eukaryotic cells acting as a “molecular switches” that are active in the GTP-state and inactive in the GDP-state. GTP-loading is highly regulated by guanine nucleotide exchange factors (GEFs). In several diseases, most prominently cancer, this process in misregulated. The kinetics of the nucleotide exchange reaction reports on the enzymatic activity of the GEF reaction system and is, therefore, of special interest. We determined the nucleotide exchange kinetics using europium-labeled GTP (Eu-GTP) in the QRET assay for small GTPases. After GEF catalyzed GTP-loading of a GTPase, a high time-resolved luminescence signal was found to be associated with GTPase bound Eu-GTP, whereas the non-bound Eu-GTP fraction was quenched by soluble quencher. The association kinetics of the Eu-GTP was measured after GEF addition, whereas the dissociation kinetics could be determined after addition of unlabeled GTP. The resulting association and dissociation rates were in agreement with previously published values for H-Ras^Wt, H-Ras^Q61G, and K-Ras^Wt, respectively. The broader applicability of the QRET assay for small GTPases was demonstrated by determining the kinetics of the Ect2 catalyzed RhoA^Wt GTP-loading. The QRET assay allows the use of nanomolar protein concentrations, as more than 3-fold signal-to-background ratio was achieved with 50 nM GTPase and GEF proteins. Thus, small GTPase exchange kinetics can be efficiently determined in a HTS compatible 384-well plate format.

Detector-Based Calibration Method for High-Accuracy Solar UV Measurements

A novel method for calibrating the absolute responsivity of solar UV spectroradiometers has been developed and tested. The method is based on calibrated filter radiometers constructed from a detector, a precision aperture, a band-pass filter and devices for temperature stabilization. The filter radiometers utilize a trap detector with very low reflectance. The filter and the detector can therefore be characterized separately. As an example the detector-based calibration is compared at 312 nm wavelength with lamp-based calibration by measuring the irradiance of a deuterium lamp with both the filter radiometer and the lamp-calibrated spectroradiometer. The agreement between the results is at the level of 1%, well within the estimated uncertainties of both methods.     

Studies on the reaction of 2-aminoacetophenone with thiophosgene

The reaction of 3- and 4-aminoacetophenone with thiophosgene in a chloroform-water-calcium carbonate mixture at room temperature results in good yields of the related, known isothiocyanates. At first, however, we failed in all our attempts to produce 2-isothiocyanatoacetophenones with this reaction. Closer inspection of the reaction showed, that the product distribution depends upon the concentration of hydrogen ions pro-ducted and on the reaction time. When the reaction was followed with thin-layer chromatography, it was observed that the isothiocyanates formed first. In the further course of the reaction, they were converted to the 4-methylene-2-oxo-3,1-benzothiazines by the action of protons. The final products of the reaction were the 4-(3,1-benzothiazin-4-yl)-methylene-3,1-benzothiazines, formed from the monomer in a dimerization process. Depending upon the time the protons were removed from the reaction mixture, different products could be isolated.     

Unification constraints in composite models

We consider unification constraints on composite models with special emphasis on two-loop effects due to relatively large metacolor coupling. Two classes of models are discussed. The first consists of those which do not have gaugedSU(2) _W and the second of those which include technicolor and gaugedSU(2) _W . The outcome is that in each specific composite model the two-loop contributions can affect noticeably several important quantities, such as the grand unified mass or the weak mixing angle. We find also that it may not be possible to have a unified composite model based on the symmetryG _MC ×SU(3) _c × U(1) _em with low (<10⁶ GeV) metacolor mass scale.     

Utilization of cascade chemo-bio catalysis for the synthesis of R -1-phenylethyl acetate

Liquid phase tert-butylation of m-cresol was carried out using 12-tungstosilicic acid supported on neutral alumina by varying different parameters. The reaction has also been carried out by using calcined samples under optimized conditions. The present catalyst shows an excellent activity of 93.2%, conversion of 100% selectivity for the o-isomer, an important industrial product.