Synthesis and bioactivity of labelled germination stimulants for the isolation and identification of the strigolactone receptor

Strigolactones are highly potent germination stimulants for seeds of the parasitic weeds Striga and Orobanche spp. The induction of seed germination is thought to proceed via a receptor-mediated mechanism. Isolation and purification of the strigolactone receptor by affinity chromatography using immobilized avidin or streptavidin requires a biotin labelled strigolactone analogue. For this purpose biotin has been attached, directly as well as indirectly, via a hydrophilic linker to the amino function of optically active amino-GR24. Using the same amino substituted synthetic stimulant GR24, labelled stimulants have been prepared which may be suitable for the identification of the receptor by means of fluorescence correlation spectroscopy, scanning force microscopy or photoaffinity techniques. Bioassays of the labelled stimulants reveal that the germination activity on seeds of Striga hermonthica is retained. Crystal data for the diastereoisomer (+)-8 are reported.     

Cruciform pi-systems for molecular electronics applications

This study details a modular and general synthesis of a new class of molecules consisting of cruciform pi-systems. The key to synthesizing these molecules was an unprecedented double Staudinger cyclization. Once formed, these rigid compounds assemble into ordered monolayer films on metal and metal oxide surfaces to orient their conjugated, bis-phenyloxazole subunits upright. This surface orientation is enforced by the external phenyl substituents that are out of the ring plane, thus preventing the prone conformation.     

Meshfree Extrapolation with Application to Enhanced Near-Boundary Approximation with Local Lagrange Kernels

Foundations of Computational Mathematics - The paper deals with the problem of extrapolating data derived from sampling a $$C^m$$ function at scattered sites on a Lipschitz region $$\varOmega $$ in...     

Following photoinduced dynamics in bacteriorhodopsin with 7-fs impulsive vibrational spectroscopy

Sub-10-fs laser pulses are used to impulsively photoexcite bacteriorhodopsin (BR) suspensions and probe the evolution of the resulting vibrational wave packets. Fourier analysis of the spectral modulations induced by transform-limited as well as linearly chirped excitation pulses allows the delineation of excited- and ground-state contributions to the data. On the basis of amplitude and phase variations of the modulations as a function of the dispersed probe wavelength, periodic modulations in absorption above 540 nm are assigned to ground-state vibrational coherences induced by resonance impulsive Raman spectral activity (RISRS). Probing at wavelengths below 540 nm-the red edge of the intense excited-state absorption band-uncovers new vibrational features which are accordingly assigned to wave packet motions along bound coordinates on the short-lived reactive electronic surface. They consist of high- and low-frequency shoulders adjacent to the strong C=C stretching and methyl rock modes, respectively, which have ground-state frequencies of 1008 and 1530 cm-1. Brief activity centered at approximately 900 cm-1, which is characteristic of ground-state HOOP modes, and strong modulations in the torsional frequency range appear as well. Possible assignments of the bands and their implication to photoinduced reaction dynamics in BR are discussed. Reasons for the absence of similar signatures in the pump-probe spectral modulations at longer probing wavelengths are considered as well.     

Quantitative structure-activity relationship analysis of β-amyloid aggregation inhibitors

Inhibiting the aggregation process of the β-amyloid peptide is a promising strategy in treating Alzheimer’s disease. In this work, we have collected a dataset of 80 small molecules with known inhibition levels and utilized them to develop two comprehensive quantitative structure–activity relationship models: a Bayesian model and a decision tree model. These models have exhibited high predictive accuracy: 87% of the training and test sets using the Bayesian model and 89 and 93% of the training and test sets, respectively, by the decision tree model. Subsequently these models were used to predict the activities of several new potential β-amyloid aggregation inhibitors and these predictions were indeed validated by in vitro experiments. Key chemical features correlated with the inhibition ability were identified. These include the electro-topological state of carbonyl groups, AlogP and the number of hydrogen bond donor groups. The results demonstrate the feasibility of the developed models as tools for rapid screening, which could help in the design of novel potential drug candidates for Alzheimer’s disease.     

An achiral manganese salen catalyst encapsulated in a peptidic phosphonate homochiral solid for the enantioselective formation of diols by consecutive epoxidation and hydration reactions

An insoluble, porous, amorphous, homochiral material based on a polypeptide titanium-phosphonate scaffold with an encapsulated achiral Mn(III)-salen was prepared and characterized. Consecutive epoxidation and hydration of styrene and its derivatives by aqueous hypochlorite in THF showed the highly enantioselective (>99%) formation of styrene diol derivatives.     

On The Potential of Dynamic Nuclear Polarization Enhanced Diamonds in Solid‐State and Dissolution 13C NMR Spectroscopy

Dynamic nuclear polarization (DNP) is a versatile option to improve the sensitivity of NMR and MRI. This versatility has elicited interest for overcoming potential limitations of these techniques, including the achievement of solid‐state polarization enhancement at ambient conditions, and the maximization of ¹³C signal lifetimes for performing in vivo MRI scans. This study explores whether diamond's ¹³C behavior in nano‐ and micro‐particles could be used to achieve these ends. The characteristics of diamond's DNP enhancement were analyzed for different magnetic fields, grain sizes, and sample environments ranging from cryogenic to ambient temperatures, in both solution and solid‐state experiments. It was found that ¹³C NMR signals could be boosted by orders of magnitude in either low‐ or room‐temperature solid‐state DNP experiments by utilizing naturally occurring paramagnetic P₁ substitutional nitrogen defects. We attribute this behavior to the unusually long electronic/nuclear spin‐lattice relaxation times characteristic of diamond, coupled with a time‐independent cross‐effect‐like polarization transfer mechanism facilitated by a matching of the nitrogen‐related hyperfine coupling and the ¹³C Zeeman splitting. The efficiency of this solid‐state polarization process, however, is harder to exploit in dissolution DNP‐enhanced MRI contexts. The prospects for utilizing polarized diamond approaching nanoscale dimensions for both solid and solution applications are briefly discussed.     

Surface-modified hemispherical polystyrene/polybutyl methacrylate composite particles

Micrometer-sized polystyrene/poly(n-butyl methacrylate) composite particles of hemisphere morphology and narrow size distribution were prepared by a process of single-step swelling of uniform polystyrene template microspheres with emulsion droplets of the monomer n-butyl methacrylate containing the initiator benzoyl peroxide in the presence, or absence, of the co-swelling agent toluene. Butyl methacrylate was then polymerized at 73 degrees C within the template microspheres. Surface and bulk characterization of the particles were performed by methods such as FTIR, elemental analysis, XPS, advancing contact angle, light microscope, SEM, and cross-sectional TEM. Selective surface functionalization of the poly(n-butyl methacrylate) phase of the composite particles was performed by carrying out a similar swelling and polymerization process in the presence of a water-soluble vinylic monomer such as acrylamide.     

Seamless image stitching by minimizing false edges.

Various applications such as mosaicing and object insertion require stitching of image parts. The stitching quality is measured visually by the similarity of the stitched image to each of the input images, and by the visibility of the seam between the stitched images. In order to define and get the best possible stitching, we introduce several formal cost functions for the evaluation of the stitching quality. In these cost functions the similarity to the input images and the visibility of the seam are defined in the gradient domain, minimizing the disturbing edges along the seam. A good image stitching will optimize these cost functions, overcoming both photometric inconsistencies and geometric misalignments between the stitched images. We study the cost functions and compare their performance for different scenarios both theoretically and practically. Our approach is demonstrated in various applications including generation of panoramic images, object blending and removal of compression artifacts. Comparisons with existing methods show the benefits of optimizing the measures in the gradient domain.     

Kinetic bromine isotope effect: example from the microbial debromination of brominated phenols

The increasing use of kinetic isotope effects for environmental studies has motivated the development of new compound-specific isotope analysis techniques for emerging pollutants. Recently, high-precision bromine isotope analysis in individual brominated organic compounds was proposed, by the coupling of gas chromatography to a multi-collector inductively coupled plasma mass spectrometer using strontium as an external spike for instrumental bias correction. The present study, for the first time, demonstrates an application of this technique for determining bromine kinetic isotope effects during biological reaction, focusing on the reductive debromination of brominated phenols under anaerobic conditions. Results show bromine isotope enrichment factors (ε) of ?0.76?±?0.08, ?0.46?±?0.19, and ?0.20?±?0.06?‰ for the debromination of 4-bromophenol, 2,4-dibromophenol, and 2,4,6-tribromophenol, respectively. These values are rather low, yet still high enough to be obtained with satisfying certainty. This further implies that the analytical method may be also appropriate for future environmental applications.