Biology-oriented synthesis of stereochemically diverse natural-product-derived compound collections by iterative allylations on a solid support

A strategy aiming at the introduction of stereocenters into polymer-bound natural-product-derived and -inspired compound collections is presented. Treatment of immobilized aldehydes with Brown's pinene-derived allylboranes results in the stereoselective formation of homoallylic alcohols with up to 89 % ee (ee=enantiomeric excess). Subsequent iterative ozonolysis-allylation sequences with up to three allylations on a solid support give access to 1,3-polyols with different relative configurations. Esterification with acryloyl chloride and final ring-closing metathesis yields alpha,beta-unsaturated delta-lactones with multiply oxygenated side chains, a substructure found in a group of natural products with a broad range of biological activity. The flexibility of the approach is exemplified by the parallel synthesis of all eight diastereomers of cryptocarya diacetate on a solid support. The individual isomers are obtained in overall yields of 40-60 % over 10 steps and with 63-85 % diastereoselectivity for the major isomer.     

On the Growth of Positive Definite Double Sequences Which Are not Moment Sequences

For every a > 1, there is a function f : N²₀ → R, which is positive semidefinite but not a moment sequence, such that |f(m, n)| ≥ m+ n^a(m+n) for all (m, n). The constant 1 is the best possible.     

Segmentation of Stochastic Images using Stochastic Extensions of the Ambrosio-Tortorelli and the Random Walker Model

We discuss methods based on stochastic PDEs for the segmentation of images with uncertain gray values resulting from measurement errors and noise. Our approach yields a reliable precision estimate for the segmentation result, and it allows us to quantify the robustness of edges in noisy images and under gray value uncertainty. The ansatz space for such images identifies gray values with random variables. For their discretization we utilize generalized polynomial chaos expansions and the generalized spectral decomposition method. This leads to the stochastic generalization of the Ambrosio-Tortorelli approximation of the Mumford-Shah functional. Moreover, we present the extension of the random walker segmentation for our stochastic images, which is based on an identification of the graph weights with random variables. We demonstrate the performance of the methods on a data set obtained from a digital camera as well as real medical ultrasound data. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of loading and particle size on the oxygen reaction in CGO impregnated Pt electrodes

Porous platinum electrodes impregnated with Gd _x Ce_1−x O_2−δ (CGO) are investigated to characterise how nano-sized CGO grains affect the oxygen reaction. Impedance measurements were performed at temperatures between 450 and 750 °C and at oxygen partial pressures of 0.2 and 5 × 10⁻⁵ bar for electrodes with various CGO loadings and electrodes annealed at various temperatures. The morphology was characterised by scanning electron microscopy and the CGO grain size was determined from X-ray diffraction peak broadening. The results showed that the polarisation resistance decreased with increasing CGO loading and increasing annealing temperature. CGO facilitates transport of oxygen ions thereby increasing the effective triple-phase boundary.     

2-(2-Methoxyphenyl)-1,3-dimethyl-1H-benzoimidazol-3-ium iodide as a new air-stable n-type dopant for vacuum-processed organic semiconductor thin films

2-(2-Methoxyphenyl)-1,3-dimethyl-1H-benzoimidazol-3-ium iodide (o-MeO-DMBI-I) was synthesized and employed as a strong n-type dopant for fullerene C(60), a well-known n-channel semiconductor. The coevaporated thin films showed a maximum conductivity of 5.5 S/cm at a doping concentration of 8.0 wt% (14 mol%), which is the highest value reported to date for molecular n-type conductors. o-MeO-DMBI-I can be stored and handled in air for extended periods without degradation and is thus promising for various organic electronic devices.     

New luminescence measurement facilities in retrospective dosimetry

This paper gives a review of recent developments in luminescence measurement facilities on the Risø TL/OSL reader including radio-luminescence (RL), exo-electron and violet stimulation attachments, and a method for characterising and if necessary correcting for beta irradiation source non-uniformity.We first describe improvements to the existing RL option to allow near infra-red detection (NIR) during irradiation by the built-in ⁹⁰Sr/⁹⁰Y beta source. The RL optical signal is collected by a liquid light guide through an F34-901 interference filter and detection is based on a dedicated thermoelectrically cooled NIR sensitive PMT (detection window peak at 855 nm, FWHM 27 nm). Software and electronics have been modified to allow standard TL and OSL measurements in the same sequence as RL measurements. Together with a new bleaching source based on a high-power UV LED (395 nm; 700 mW/cm²), this facility has been used to measure natural doses in feldspar using the decaying NIR RL signal.Secondly, we present a method for mapping radiation field of the built-in ⁹⁰Sr/⁹⁰Y β-source and estimating grain-location specific dose-rates. This is important for the accuracy of single grain results, when radiation field is spatially non-uniform across the sample area. We document the effect of this correction method and further investigate on the effect of lifting the source to achieve a better dose-rate uniformity.Finally we summarise two recently-developed novel facilities to help investigate (i) the time scales involved in OSL processes (time-resolved exo-electron detection) and (ii) extending the age range (violet stimulated signals from deep quartz OSL traps).     

New amine-templated zinc phosphates with a temperature-induced increase of structural dimensionality

Three new amine-templated zinc phosphates, [C4N2H14][Zn(HPO4)2].H2O, AU-I, [C4N2H14][Zn2(H(0.5)PO4)2(H2PO4)], AU-II, and [C4N2H14][Zn5(H2O)(PO4)4], AU-III, are prepared by hydrothermal synthesis using an organic amine, N,N'-dimethylethylendiamine CH3NHCH2CH2NHCH3, as structure-directing agent. The three materials are prepared from the same reaction mixture, 1Zn(CH3CO2)2:3.05H3PO4:2.25CH3NHCH2CH2NHCH3:138H2O (pH = 5.1), AU-I at RT, AU-II at 60 degrees C, and AU-III at 170 degrees C. The materials are built from corner-sharing ZnO4 and PO4 tetrahedra forming chains, layers, or framework structures for AU-I to III, respectively, and are linked together by hydrogen bonds via the diprotonated amine ions. The complete hydrogen-bond scheme is resolved for these new compounds and reveals some interesting phenomena, for example, a hydrogen shared between two phosphate groups in AU-II, thereby forming H(0.5)PO4 groups. Furthermore, the water molecules are different; that is, in AU-I they act as hydrogen-bond donor and acceptor, whereas they act as ligand in AU-III with coordination to Zn. The structures of the compounds are determined by single-crystal X-ray diffraction analysis. AU-I, [C4N2H14][Zn(HPO4)2].H2O, crystallizes in the triclinic space group P-1, a = 8.215(2), b = 8.810(3), c = 8.861(3) A, alpha = 88.001(4) degrees , beta = 89.818(5) degrees , and gamma = 89.773(5) degrees , Z = 2. AU-II, [C4N2H14][Zn2(H(0.5)PO4)2(H2PO4)], is monoclinic, P2/n, a = 11.7877(4), b = 5.2093(2), c = 12.2031(4) A, beta = 98.198(1) degrees , Z = 2. AU-III, [C4N2H14][Zn5(H2O)(PO4)4], crystallizes in the orthorhombic space group Pna2(1) with lattice parameters, a = 20.723(2), b = 5.2095(6), c = 17.874(2) A, Z = 4. The phase stability investigated by systematic hydrothermal synthesis is presented, and the materials are further characterized by 31P solid-state MAS NMR, for example, by determination of 31P chemical shift anisotropies for AU-III, while the thermal behavior is investigated by thermogravimetry (TG).     

Remarkable supramolecular catalysis of glycoside hydrolysis by a cyclodextrin cyanohydrin

(6AR,6DR)-6A,6D-di-C-cyano-beta-cyclodextrin (3) was synthesized and shown to catalyze hydrolysis of nitrophenyl glycosides with the reaction following Michaelis-Menten kinetics. At pH 7.4 and 25 degrees C, hydrolysis of 4-nitrophenyl-beta-glucopyranoside (2) was catalyzed with KM = 15 mM, kcat = 8.2 x 10-6 s-1, and kcat/kuncat = 1217. Catalysis was observed with concentration of 3 as low as 10 muM. Hydrolysis of the corresponding alpha-glucoside, alpha-galactoside, alpha-mannoside, and 2-nitrophenyl-beta-galactoside was also catalyzed by 3, with kcat/kuncat ranging from 283 to 2147. A series of analogues of 3 was prepared and investigated for catalysis of the hydrolysis of 2: (6AR,6DR)-6A,6D-di-C-propyl-beta-cyclodextrin (9) was not catalytic, while 6A,6D-di-C-cyano-6A,6D-dideoxy-beta-cyclodextrin (12) had a low catalytic activity (kcat/kuncat = 4). A kcat/kuncat = 48 was found for 6A,6D-dialdehydo-beta-cyclodextrin dihydrate (11). It was proposed that 3 acts by general acid catalysis on the bound substrate.     

Hoeffding's inequalities: A counterexample

A sequence : ₀ satisfiesHoeffding's inequality of order n if wheneverX ₁,...,X _n are independent nonnegative integer-valued elementary random variables and are independent identically distributed nonnegative integer-valued elementary random variables, the common distribution of which is the average of those ofX ₁,...,X _n. We show that for each integerm greater than 2 there exists a sequence satisfying Hoeffding's inequality of every order greater thanm but not that of orderm. This answers a question raised by Berg, Christensen, and Ressel.     

FCC Rolling Textures Reviewed in the Light of Quantitative Comparisons between Simulated and Experimental Textures

The crystallographic texture of metallic materials has a very strong effect on the properties of the materials. In the present article, we look at the rolling textures of fcc metals and alloys, where the classical problem is the existence of two different types of texture, the “copper-type texture” and the “brass-type texture.” The type of texture developed is determined by the stacking fault energy of the material, the rolling temperature and the strain rate of the rolling process. Recent texture simulations by the present authors provide the basis for a renewed discussion of the whole field of fcc rolling texture. We simulate the texture development with a model which allows us to vary the strength of the interaction between the grains and to vary the scheme for the calculation of the lattice rotation in the individual grains (type CL/MA or PR/PSA). For the deformation pattern we focus on {111}<110> slip without or with deformation twinning, but we also consider slip on other slip planes and slip by partial dislocations. We consistently make quantitative comparison of the simulation results and the experimental textures by means of a scalar correlation factor. We find that the development of the copper-type texture is best simulated with {111}<110> slip combined with type CL/PR lattice rotation and relatively strong interaction between the grains — but not with the full-constraint Taylor model and neither with the classical relaxed-constraint models. The development of the brass-type texture is best simulated with {111}<110> slip combined with PR/PSA lattice rotation and weak interaction between the grains. The possible volume effect of deformation twins on the formation of the brass-type texture is a controversial question which we discuss on the basis of our simulations as seen together with other investigations.