Fast X‐ray powder diffraction on I11 at Diamond

The commissioning and performance characterization of a position‐sensitive detector designed for fast X‐ray powder diffraction experiments on beamline I11 at Diamond Light Source are described. The detecting elements comprise 18 detector‐readout modules of MYTHEN‐II silicon strip technology tiled to provide 90° coverage in 2θ. The modules are located in a rigid housing custom designed at Diamond with control of the device fully integrated into the beamline data acquisition environment. The detector is mounted on the I11 three‐circle powder diffractometer to provide an intrinsic resolution of Δ2θ? 0.004°. The results of commissioning and performance measurements using reference samples (Si and AgI) are presented, along with new results from scientific experiments selected to demonstrate the suitability of this facility for powder diffraction experiments where conventional angle scanning is too slow to capture rapid structural changes. The real‐time dehydrogenation of MgH₂, a potential hydrogen storage compound, is investigated along with ultrafast high‐throughput measurements to determine the crystallite quality of different samples of the metastable carbonate phase vaterite (CaCO₃) precipitated and stabilized in the presence of amino acid molecules in a biomimetic synthesis process.     

Mössbauer study of the microscopic surrounding of co atoms implanted in si and ge below the full amorphization limit

Mössbauer spectroscopy on ⁵⁷Co implanted into Si and Ge at doses between 10¹¹ and 10¹⁵ atoms/cm² supports the single track amorphization model. Calculations based on linear cascade theory do not give quantitative agreement with the experiment.     

Molecular dynamics of cryptophane and its complexes with tetramethylammonium and neopentane using a continuum solvent model

Time scales currently obtainable in explicit–solvent molecular dynamics simulations are inadequate for the study of many biologically important processes. This has led to increased interest in the use of continuum solvent models. For such models to be used effectively, it is important that their behavior relative to explicit simulation be clearly understood. Accordingly, 5 ns stochastic dynamics simulations of a derivative of cryptophane-E alone, and complexed with tetramethylammonium and neopentane were carried out. Solvation electrostatics were accounted for via solutions to the Poisson equation. Nonelectrostatic aspects of solvation were incorporated using a surface area-dependent energy term. Comparison of the trajectories to those from previously reported 25 ns explicit–solvent simulations shows that use of a continuum solvent model results in enhanced sampling. Use of the continuum solvent model also results in a considerable increase in computational efficiency. The continuum solvent model is found to predict qualitative structural characteristics that are similar to those observed in explicit solvent. However, some differences are significant, and optimization of the continuum parameterization will be required for this method to become an efficient alternative to explicit–solvent simulation. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 956–970, 1999     

A double mesogen based on linked p‐ter­phenyl units

The structure of bis(4,4′′‐decyl­oxy‐p‐ter­phenyl‐2′‐yl­methyl) carbonate, C₇₉H₁₁₀O₇, (I), has been determined at 123 K. It is a new type of twin mesogen. No two adjacent aromatic rings are coplanar and the four decyl­oxy side chains are maximally extended. Molecules of the compound are packed along the crystallographic a axis. The molecular arrangement is a precursor of a smectic A phase.     

Carbon-13 NMR spectroscopy of hop bitter substances

The ¹³C NMR spectra of the most important hop bitter substances are analysed. All individual carbon atoms are assigned, except the oxygen bonded sp² carbon atoms. Most assignments are made partly by comparison with analogous compounds and partly by reference to literature data. Cross-correlations with the ¹H NMR shifts are made for two main products and confirm the correctness of the assignments. All data are in agreement with the known structures.     

Synthesis of Novel Polyphosphate Analogues of Inositol 1,4,5-Trisphosphate

Abstract

The synthesis of novel polyphosphate mimics of inositol 1,4,5-trisphosphate, including ring-contracted and conformationally restricted analogues is reported.