Probing the Local Magnetic Structure of the [FeIII(Tp)(CN)3]− Building Block Via Solid-State NMR Spectroscopy,Polarized Neutron Diffraction,and First-Principle Calculations

The local magnetic structure in the [Fe^III(Tp)(CN)₃]⁻ building block was investigated by combining paramagnetic Nuclear Magnetic Resonance (pNMR) spectroscopy and polarized neutron diffraction (PND) with first-principle calculations. The use of the pNMR and PND experimental techniques revealed the extension of spin-density from the metal to the ligands, as well as the different spin mechanisms that take place in the cyanido ligands: Spin-polarization on the carbon atoms and spin-delocalization on the nitrogen atoms. The results of our combined density functional theory (DFT) and multireference calculations were found in good agreement with the PND results and the experimental NMR chemical shifts. Moreover, the ab-initio calculations allowed us to connect the experimental spin-density map characterized by PND and the suggested distribution of the spin-density on the ligands observed by NMR spectroscopy. Interestingly, significant differences were observed between the pseudo-contact contributions of the chemical shifts obtained by theoretical calculations and the values derived from NMR spectroscopy using a simple point-dipole model. These discrepancies underline the limitation of the point-dipole model and the need for more elaborate approaches to break down the experimental pNMR chemical shifts into contact and pseudo-contact contributions.     

How to broaden the light reflection band in cholesteric liquid crystals? A new approach based on polymorphism

Cholesteric liquid crystals (CLCs) may selectively reflect light when the helicoidal pitch is of the order of the wavelength of the incident beam propagating along the helix axis. The reflection bandwidth is dependent on the birefringence and is limited to a few tens of nanometers, which is insufficient for applications such as white-on-black reflective displays. Recent studies have shown that CLC polymer networks with a pitch gradient induce a broadening of the reflection bandwidth over several hundreds of nanometers. Most related processes rely on photocrosslinking reactions with a UV-gradient in a mixture made of chiral and achiral monomers with different UV-reactivities. Here a new experimental route exploiting the polymorphism of the mixture is presented. The basic concept lies in a thermally-induced pitch variation simultaneously carried out with the UV-crosslinking reaction. The optical behaviour is investigated in parallel with the cross-sectional microstructure as observed by transmission electron microscopy.     

Terminal Alkynes as One-Carbon Donors in [5+1] Heteroannulation: Synthesis of Pyridines via Ynimine Intermediates and Application in the Total Synthesis of Anibamine B

Transition-metal-catalyzed [4+2] heteroannulation of α,β-unsaturated oximes and their derivatives with alkynes has been developed into a powerful strategy for the synthesis of pyridines. It nevertheless lacks regioselectivity when unsymmetrically substituted alkynes are used. We report herein the unprecedented synthesis of polysubstituted pyridines by a formal [5+1] heteroannulation of two readily accessible building blocks. A copper-catalyzed aza-Sonogashira cross-coupling between β,γ-unsaturated oxime esters and terminal alkynes affords ynimines, which, without isolation, undergo an acid-catalyzed domino reaction involving ketenimine formation, 6π-electrocyclization and aromatization to afford pyridines. Terminal alkynes served as a one-carbon donor to the pyridine core in this transformation. Di- through pentasubstituted pyridines are accessible with complete regioselectivity and excellent functional-group compatibility. The first total synthesis of anibamine B, an indolizinium alkaloid with potent antiplasmodial activity, was accomplished featuring this reaction as a key step.     

Revisiting Prussian Blue Analogues with Solid‐State MAS NMR Spectroscopy: Spin Density and Local Structure in [Cd3{Fe(CN)6}2]⋅15 H2O

No legendary Prussian order! The distribution of vacancies in Prussian blue analogues is not random, and the spin density on the Cd²⁺ ion varies depending on the number of paramagnetic ions in its surroundings. This conclusion follows from ¹¹³Cd solid‐state magic‐angle spinning NMR studies of [Cd₃{Fe/Co(CN)₆}₂]?15 H₂O, where the presence of small but significant spin density on the observed ¹¹³Cd nucleus leads to improved spectral resolution.

     

Influence of homocysteine on the physical structure and molecular mobility of elastin network in cultured arteries

The thermal and dielectric properties of the elastin network were investigated in arteries cultured with physiological and pathological concentrations of homocysteine, an aminoacid responsible of histological impairments in human arteries. The glass transition of this amorphous protein was investigated by Differential Scanning Calorimetry (DSC). To explore the molecular dynamics of the elastin network in the nanometer range, we used Thermally Stimulated Currents (TSC), a dielectric technique running at low frequency and measuring the dipolar reorientations in proteins subjected to a static electrical field. Combining TSC and DSC experiments with determination of the activation parameters of relaxation times reveals the molecular mobility of the proteins. The major differences in the relaxation behavior of elastin between arteries cultured with physiological and pathological concentrations of homocysteine are discussed.     

CAD-based calibration and shape measurement with stereoDIC

A new calibration procedure is proposed for a stereovision setup. It uses the object of interest as the calibration target, provided the observed surface has a known definition (e.g., its CAD model). In a first step, the transformation matrices needed for the calibration of the setup are determined assuming that the object conforms to its CAD model. Then the 3D shape of the surface of interest is evaluated by deforming the a priori given freeform surface. These two steps are performed via an integrated approach to stereoDIC. The measured 3D shape of a machined Bézier patch is validated against data obtained by a coordinate measuring machine. The feasibility of the calibration method’s application to large surfaces is shown with the analysis of a 2-m² automotive roof panel.