Exciton Coupling in Redox-Active Salen based Self-Assembled Metallacycles

The incorporation of a redox-active nickel salen complex into supramolecular structures was explored via coordination-driven self-assembly with homobimetallic ruthenium complexes (bridged by oxalato or 5,8-dihydroxy-1,4-naphthoquinato ligands). The self-assembly resulted in the formation of a discrete rectangle using the oxalato complex and either a rectangle or a catenane employing the larger naphthoquinonato complex. The formation of the interlocked self-assembly was determined to be solvent and concentration dependent. The electronic structure and stability of the oxidized metallacycles was probed using electrochemical experiments, UV-Vis-NIR absorption, EPR spectroscopy and DFT calculations, confirming ligand radical formation. Exciton coupling of the intense near-infrared (NIR) ligand radical intervalence charge transfer (IVCT) bands provided further confirmation of the geometric and electronic structures in solution.     

Towards a new class of ferroelectric liquid crystal molecules for nonlinear optical applications

The synthesis of a new molecule specifically designed to exhibit both ferroelectric and nonlinear optical properties is presented. This molecule possesses an optically active phenyl sulphinic group, which introduces a dipole moment directly linked to the chromophore group, with a nitro group in the meta -position. The rest of the molecule comprises a tolane and a benzoate group. Such a structure results in an enantiotropic smectic C*-smectic A phase sequence in its polymorphism. A first measurement of the spontaneous polarization shows a high value. The polymorphism of the racemic homologous molecule possessing the nitro group in the ortho-position is also presented, and also shows the smectic C-smectic A phase sequence.     

α-NH2 Determination from Biological Infrared Spectra

The use of Mid-infrared spectroscopy for the analysis of food products has only recently developped with the advent of Fourier Transformed spectroscopy and other techniques like Attenuated Total Reflectance, diffused reflection combined to the use of powerful micro-computers. We have recently reported to use a combination of multidimensional statistical analysis and Mid-FTIR spectroscopy for the quantitative determination of sugars in a biological sample. In this paper we have evaluated the use of such a method for the quantitative measurement of α-amino groups from ammo-acids, peptides and proteins. The spectral region where the characteristic absorption bands of such groups are located, ranges between 1200 cm-1 and 1900 cm-1. Water features a major absorption band in this region (1500–1700 cm-1). This superimpose with amide I and II bands.

The standard deviation for each and every wavelength, calculated for all the spectra of the calibration set, show the existence of two absorption bands in the 1500–1900 cm-1 region which means that the observed variations in this zone are not only due to water but are also due to two peaks centered at 1650 cm-1 and 1540 cm-1 (with a hollow at 1600 cm-1) that are characteristic of protids.

The contribution of the first four axes of the PCA, axes 5, 1, 4 and 2, to the total inertia percentage are 2. 37%, 53. 36%, 3. 92% and 28. 82% respectively. The correlation coefficient between the major axis, axis 5, and the chemical values of α-NH₂ is 0. 311 and the second axis, axis 1, increases this value to 0. 541. The first 10 axes were used to establish the prediction equation; the correlation coefficient value is very high: 0. 978.

Good predictions were obtained; mean and standard deviation associated to the predicted concentrations of α-NH₂content, valued 0 g/ml and 0. 12 g/ml respectively. Hence, we have established the possibility of determining, from a MIR spectra, the α-NH₂ content.     

Effect of thermal transformation and stability on the flammability of PAN precursors-based carbon fibres

Journal of Thermal Analysis and Calorimetry - During the development of the carbon fibres and oxidized fibres, the aim was to get a material with extraordinary mechanical properties. Nowadays, it...     

Mechanistic Aspects of the Palladium-Catalyzed Suzuki-Miyaura Cross-Coupling Reaction

The story of C−C bond formation includes several reactions, and surely Suzuki-Miyaura is among the most outstanding ones. Herein, a brief historical overview of insights regarding the reaction mechanism is provided. In particular, the formation of the catalytically active species is probably the main concern, thus the preactivation is in competition with, or even assumes the role of the rate determining step (rds) of the overall reaction. Computational chemistry is key in identifying the rds and thus leading to milder conditions on an experimental level by means of predictive catalysis.     

The α2‐polymorph of salicylidene­aniline

N‐Salicylideneaniline (SA), C₁₃H₁₁NO, belongs to the large family of aromatic Schiff bases. It is of particular importance owing to its reversible photoreactivity. SA forms two photochromic polymorphs, both with two non‐coplanar benzene rings. In addition, we have recently discovered a planar polymorph, named the β‐polymorph, which will be discussed in a subsequent paper. We report here the structure of the α₂‐polymorph in the orthorhombic crystal system. This compound exhibits a strong intra­molecular O—H⋯N hydrogen bond and the dihedral angle between the two rings varies with temperature.     

Speciation of adsorbates on surface of solids by infrared spectroscopy and chemometrics

Speciation, i.e. identification and quantification, of surface species on heterogeneous surfaces by infrared spectroscopy is important in many fields but remains a challenging task when facing strongly overlapped spectra of multiple adspecies. Here, we propose a new methodology, combining state of the art instrumental developments for quantitative infrared spectroscopy of adspecies and chemometrics tools, mainly a novel data processing algorithm, called SORB-MCR (SOft modeling by Recursive Based-Multivariate Curve Resolution) and multivariate calibration. After formal transposition of the general linear mixture model to adsorption spectral data, the main issues, i.e. validity of Beer–Lambert law and rank deficiency problems, are theoretically discussed. Then, the methodology is exposed through application to two case studies, each of them characterized by a specific type of rank deficiency: (i) speciation of physisorbed water species over a hydrated silica surface, and (ii) speciation (chemisorption and physisorption) of a silane probe molecule over a dehydrated silica surface. In both cases, we demonstrate the relevance of this approach which leads to a thorough surface speciation based on comprehensive and fully interpretable multivariate quantitative models. Limitations and drawbacks of the methodology are also underlined.