Site-specific C content by quantitative isotopic C Nuclear Magnetic Resonance spectrometry: A pilot inter-laboratory study

Isotopic ¹³C NMR spectrometry, which is able to measure intra-molecular ¹³C composition, is of emerging demand because of the new information provided by the ¹³C site-specific content of a given molecule. A systematic evaluation of instrumental behaviour is of importance to envisage isotopic ¹³C NMR as a routine tool. This paper describes the first collaborative study of intra-molecular ¹³C composition by NMR. The main goals of the ring test were to establish intra- and inter-variability of the spectrometer response. Eight instruments with different configuration were retained for the exercise on the basis of a qualification test. Reproducibility at the natural abundance of isotopic ¹³C NMR was then assessed on vanillin from three different origins associated with specific δ¹³C_i profiles. The standard deviation was, on average, between 0.9 and 1.2‰ for intra-variability. The highest standard deviation for inter-variability was 2.1‰. This is significantly higher than the internal precision but could be considered good in respect of a first ring test on a new analytical method. The standard deviation of δ¹³C_i in vanillin was not homogeneous over the eight carbons, with no trend either for the carbon position or for the configuration of the spectrometer. However, since the repeatability for each instrument was satisfactory, correction factors for each carbon in vanillin could be calculated to harmonize the results.     

An Efficient Procedure for the Synthesis of p-Anisidine Phenylglyoxal Imine from Acetophenone

An efficient procedure for the oxidation of acetophenone to phenylglyoxal and its subsequent in situ conversion to the title compound is described herein.     

The synthesis of luminescent lanthanide-based chemosensors for the detection of zinc ions

Herein, we report the synthesis of two lanthanide-based chemosensors, Tb-5 and Eu-6, designed to sense free zinc ions (Zn²⁺) in aqueous solutions. The Tb-5 complex features a bis(2-pyridinylmethyl)amine moiety as a zinc(II)-responsive lanthanide-sensitising ‘antenna’, while Eu-6 incorporates a quinoline-based moiety for this purpose. Luminescence enhancements of 210% and 340% are observed upon addition of Zn²⁺ ions to Tb-5 and Eu-6, respectively. Both sensors are selective for Zn²⁺ ions over several other cations of environmental significance.     

Synthesis and biological evaluation of the osteoblast proliferating cyclic peptides dianthins G and H

The first synthesis and osteoblast proliferative activity of the naturally occurring cyclic peptides dianthins G and H is described. The greater potency of naturally occurring dianthin G over dianthin H at physiological concentrations mirrored the osteoblast proliferative activity observed for synthetic dianthins G and H. Six alanine-scan analogues of the more potent dianthin G were also synthesised and osteoblast assays revealed that four of the six residues can be further modified for improved activity. We also confirmed by variable temperature ¹H NMR spectroscopic analysis that the sets of major and minor signals observed for dianthins G and H in DMSO-d₆ are in fact due to cis–trans rotational isomers of the proline ring.     

X-ray microfluorescence (μXRF) imaging of Aspergillus nidulans cell wall mutants reveals biochemical changes due to gene deletions

We used synchrotron X-ray fluorescence to create the first semiquantitative, submicron resolution, element distribution maps of P, S, K, and Ca, in situ, in fungal samples. Data collection was performed at the European Synchrotron Radiation Facility beam line ID21, Grenoble, France. We studied developing hyphae, septa, and conidiophores in Aspergillus nidulans, comparing wild type and two cell wall biosynthesis gene deletion strains. The latter encode sequential enzymes for biosynthesis of galactofuranose, a minor wall carbohydrate. Each gene deletion caused hyphal morphogenesis defects, and reduced both colony growth and sporulation 500-fold. Elemental imaging has helped elucidate biochemical changes in the phenotype induced by the gene deletions that were not apparent from morphological examination. Here, we examined S as a proxy for protein content, P for nucleic acid content, as well as Ca and K, which also have important metabolic roles. Element distributions in wild-type fungi reflect biological aspects already known or expected from other types of analysis; however, the application of X-ray fluorescence (XRF) imaging reveals aspects of gene deletion phenotypes that were not previously available. We have demonstrated that deleting a dispensable gene involved in galactose metabolism (ugeA) and one involved in biosynthesis of a minor cell wall component (ugmA) led to changes in hyphal elemental distribution that may have resulted from compromised wall composition.     

Lensless diffractive imaging using tabletop coherent high-harmonic soft-X-ray beams

We present the first experimental demonstration of lensless diffractive imaging using coherent soft x rays generated by a tabletop soft-x-ray source. A 29 nm high harmonic beam illuminates an object, and the subsequent diffraction is collected on an x-ray CCD camera. High dynamic range diffraction patterns are obtained by taking multiple exposures while blocking small-angle diffraction using beam blocks of varying size. These patterns reconstruct to images with 214 nm resolution. This work demonstrates a practical tabletop lensless microscope that promises to find applications in materials science, nanoscience, and biology.     

Fitting of deuterium quadrupole echo spectra with multiple motional models

Dynamic information is generally extracted from deuterium quadrupole echo spectra by matching a spectrum calculated for a particular motional model to the experimental spectrum. In this work, a set of computer programs has been written to facilitate fitting of calculated spectra to experimental spectra that represent from one to five motional models. The fitting program requires pre-calculated libraries of spectra for the models of interest, and accomplishes the fitting either by a systematic method or by simulated annealing. The systematic method is convenient for fitting with one or two motional models, but the simulated annealing method is faster for two or more models, if the libraries are made up of hundreds of spectra. The parameter Q, with the standard deviation of the spectral points estimated as the standard deviation of the baseline noise, provides a stringent measure of goodness of fit. Acceptable fits of experimental data as judged by this criterion have not been found, even in the case of ring flip motion in phenylalanine-d(5) in which the fit may be judged acceptable by eye. An example of fitting with isotropic and methyl rotation motional models of alanine-d(3), which have distinct spectral patterns, shows that it is possible to obtain reasonably accurate estimates of the relative amounts of deuterium representing the different models, even from poorly fitted spectra.     

Diagnostic cellular organization features extracted from autofluorescence images

Depth-resolved NADH autofluorescence images are shown to differentiate between normal and precancerous engineered tissues. An inverse power law behavior of the power spectral density (PSD) of these images is observed, indicating a self-affine organization of mitochondrial NADH at length scales 1-10 microm. Power exponents of the PSD functions vary significantly with tissue depth and precancerous state, giving insight into the morphological changes associated with precancerous lesions and providing substantial potential for noninvasive clinical diagnosis of squamous epithelial lesions and tumors.     

[UIII{N(SiMe2tBu)2}3]: A Structurally Authenticated Trigonal Planar Actinide Complex

We report the synthesis and characterization of the uranium(III) triamide complex [U^III(N**)₃] [ 1 , N**=N(SiMe₂tBu)₂^?]. Surprisingly, complex 1 exhibits a trigonal planar geometry in the solid state, which is unprecedented for three‐coordinate actinide complexes that have exclusively adopted trigonal pyramidal geometries to date. The characterization data for [U^III(N**)₃] were compared with the prototypical trigonal pyramidal uranium(III) triamide complex [U^III(N“)₃] (N”=N(SiMe₃)₂^?), and taken together with theoretical calculations it was concluded that pyramidalization results in net stabilization for [U^III(N“)₃], but this can be overcome with very sterically demanding ligands, such as N**. The planarity of 1 leads to favorable magnetic dynamics, which may be considered in the future design of U^III single‐molecule magnets.     

Probing Relaxation Dynamics in Five-Coordinate Dysprosium Single-Molecule Magnets

A new family of five-coordinate lanthanide single-molecule magnets (Ln SMMs) [Dy(Mes*O)₂(THF)₂X] (Mes*=2,4,6-tri-tert-butylphenyl; X=Cl, 1 ; Br, 2 ; I, 3 ) is reported with energy barriers to magnetic reversal >1200 K. The five-coordinate Dy^III ions have distorted square pyramidal geometries, with halide anions on the apex, and two Mes*O ligands mutually trans- to each other, and the two THF molecules forming the second trans- pair. These geometrical features lead to a large magnetic anisotropy in these complexes along the trans-Mes*O direction. QTM and Raman relaxation times are enhanced by varying the apex halide from Cl to Br to I, or by dilution in a diamagnetic yttrium analogue.