Donor-substituted triaryl-1,3,5-triazinanes-2,4,6-triones: octupolar NLO-phores with a remarkable transparency-nonlinearity trade-off

International audienceWe report in this letter the measurement of the hyperpolarizabilities of a series of donor-substituted triaryl-1,3,5-triazinanes-2,4,6-triones by hyper Rayleigh scattering (HRS). A remarkable transparency-nonlinearity trade-off is evidenced for these octupolar NLO-phores which might be accessed in a straightforward synthetic way and in a few steps from commercial isocyanates

Photoisomerisation in Aminoazobenzene-Substituted Ruthenium(II) Tris(bipyridine) Complexes: Influence of the Conjugation Pathway.

International audienceTransition-metal complexes containing stimuli-responsive systems are attractive for applications in optical devices, photonic memory, photosensing, as well as luminescence imaging. Amongst them, photochromic metal complexes offer the possibility of combining the specific properties of the metal centre and the optical response of the photochromic group. The synthesis, the electrochemical properties and the photophysical characterisation of a series of donor-acceptor azobenzene derivatives that possess bipyridine groups connected to a 4-dialkylaminoazobenzene moiety through various linkers are presented. DFT and TD-DFT calculations were performed to complement the experimental findings and contribute to their interpretation. The position and nature of the linker (ethynyl, triazolyl, none) were engineered and shown to induce different electronic coupling between donor and acceptor in ligands and complexes. This in turn led to strong modulations in terms of photoisomerisation of the ligands and complexes

Nonlinear optical properties of intriguing Ru σ-acetylide complexes and the use of a photocrosslinked polymer as a springboard to obtain SHG active thin films

This work reports on the design, synthesis and photo-physical properties of two ruthenium σ-alkynyl complexes. It is shown that, despite similar optical absorption features recorded in solution, the introduction of a benzaldehyde moiety leads to an improved non-linear optical (NLO) response as measured by Electric Field Induced Second Harmonic (EFISH) generation and Third Harmonic Generation (THG) at 1.907 μm, both related to the second order hyperpolarizability. These structure–property relationships are rationalized based on few state modelling. Complex 2 is subsequently processed to afford composite films that demonstrate a χ2 of 1.4 pm V−1, quite remarkable given the ease of film processing implemented in this work

Methyl Viologens of Bis-(4'-pyridylethynyl)arenes - Structures, Photophysical and Electrochemical Studies, and their Potential Application in Biology

A series of bis-(4'-pyridylethynyl)arenes (arene = benzene, tetrafluorobenzene, and anthracene) were synthesized and their bis-N-methylpyridinium compounds were investigated as a class of π-extended methyl viologens. Their structures were determined by single crystal X-ray diffraction, and their photophysical and electrochemical properties (cyclic voltammetry), as well as their interactions with DNA/RNA were investigated. The dications showed bathochromic shifts in emission compared to the neutral compounds. The neutral compounds showed very small Stokes shifts, which are a little larger for the dications. All of the compounds showed very short fluorescence lifetimes (< 4 ns). The neutral compound with an anthracene core has a quantum yield of almost unity. With stronger acceptors, the analogous bis-N-methylpyridinium compound showed a larger two-photon absorption cross-section than its neutral precursor. All of the dicationic compounds interact with DNA/RNA ; while the compounds with benzene and tetrafluorobenzene cores bind in the grooves, the one with an anthracene core intercalates as a consequence of its large, condensed aromatic linker moiety, and it aggregates within the polynucleotide when in excess over DNA/RNA

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

DFT study of two-photon absorption of octupolar molecules

International audienceThe two-photon absorption (TPA) properties of octupolar molecules based on a triphenyl-isocyanurate cyclotrimer, a 1,3,5-triphenyl-benzene or a triphenyl-triazine core were theoretically investigated using DFT and TD-DFT computations. These compounds are very promising regarding their potential application especially for optical limitation. These systems, which exhibit a threefold axis, contain three arms with a terminal electron donating group linked in 1, 3 and 5 positions to the central C 3 N 3 O 3 isocyanurate, benzene or triazine ring. The SAOP functional and a DZP basis set were selected for the TPA computations. The so-computed TPA energies and cross sections are in good agreement with the observed data. Increasing the strength of the donor terminal group enhances the TPA cross-section values. The compound with triazine core presents the highest two photon cross-section value compared to the values found for the isocyanurate or the 1,3,5-phenyl core as central ring. Furthermore, this study brings to light a cooperative enhancement of the TPA property between the three arms attached to the isocyanurate ring

In Situ Calculation of the Rotation Barriers of the Methyl Groups of Tribromomesitylene Crystals: Theory Meets Experiment

The computation of the rotation barriers of the methyl groups (Me) of tribromomesitylene (TBM) crystals has been carried out. Experimentally, the barriers of the three Me groups of TBM are found to be high and different. These groups do not experience the same hindering environment in the crystal state. For an isolated TBM molecule, the three barriers are equal and very low. We found that a cluster of 21 TBM molecules permits the reproduction of the crystal symmetry and structure of the bulk, with a central molecule surrounded by six molecules in the same plane and seven other molecules in two planes above and below. DFT computations including dispersion corrections have been carried out using the ONIOM procedure. The Me groups of the central TBM molecule were rotated step by step to determine the conformations of lowest and highest energy for each Me, thus allowing estimation of the rotation barriers as the difference between these energies. In doing so, we found the following barrier values, namely 105, 173, and 205 cm−1, whereas the experimental values were 111, 180 and 200 cm−1

How to drive imine-enamine tautomerism of pyronic derivatives of biological interest - A theoretical and experimental study of substituent and solvent effects

International audienceAn investigation of the tautomerism of five series of aminated pyronic compounds of pharmacological interest was carried out using NMR experiments and standard quantum mechanical B3LYP/6-311+G** calculations. The obtained results indicate that among four possible tautomers, imine and enamine forms are the two predominating ones in the gas phase as well as in solution. Depending on the nature of the substituting group, the enamine or the imine form is the most stable tautomer, the calculations being in agreement with experiment. The calculated equilibrium constants in the gas phase and in solution show that the enamine form is stabilized by polar solvents, in all cases. NBO analysis explains well the predominance of a form over another one when changing a substituting group. We give indications on how to favour the imine form which is preferred for synthesis purposes

Couloir prothétique et gérodontologie : traitement simple pour une stabilité optimum

Le processus du vieillissement s’accompagne le plus souvent, au niveau buccal, d’un rétrécissement du couloir prothétique en rapport avec l’importance de la résorption osseuse et l’envahissement des éléments périphériques; la situation devient, de ce fait, défavorable pour la réalisation prothétique. Le recours à la piézographie en prothèse complète permet de mieux respecter la physiologie buccale du sujet âgé tout en assurant un maximum de stabilité prothétique. La piézographie relève en effet quatre défis: restituer au visage son aspect naturel et harmonieux, proposer un plan d’occlusion, rechercher une dimension verticale d’occlusion, conforter une relation intermaxillaire apte à assurer la fonction masticatoire. Un protocole rationnel, ergonomique et individualisé s’avère particulièrement adapté aux cas difficiles, permettant ainsi de bien définir le volume prothétique dévolu à l’emplacement des dents artificielles. C’est ce que nous allons essayer d’illustrer, à travers deux cas clinique