Molecular multifunctionality preservation upon surface deposition for a chiral single-molecule magnet

International audienceThe synthesis and characterization of a chiral, enneanuclear Mn(III)-based, Single-Molecule Magnet, [Mn9O4(Me-sao)6(L)3(MeO)3(MeOH)3]Cl (1; Me-saoH2 = methylsalicylaldoxime, HL = lipoic acid) is reported. Compound 1 crystallizes in the orthorhombic P212121 space group and consists of a metallic skeleton describing a defect super-tetrahedron missing one vertex. The chirality of the [MnIII9] core originates from the directional bridging of the Me-sao2− ligands via the –N–O– oximate moieties, which define a clockwise (1ΔΔ) or counter-clockwise (1ΛΛ) rotation in both the upper [MnIII3] and lower [MnIII6] subunits. Structural integrity and retention of chirality upon dissolution and upon deposition on (a) gold nanoparticles, 1@AuNPs, (b) transparent Au(111) surfaces, 1ΛΛ@t-Au(111); 1ΔΔ@t-Au(111), and (c) epitaxial Au(111) on mica surfaces, 1@e-Au(111), was confirmed by CD and IR spectroscopies, mass spectrometry, TEM, XPS, XAS, and AFM. Magnetic susceptibility and magnetization measurements demonstrate the simultaneous retention of SMM behaviour and optical activity, from the solid state, via dissolution, to the surface deposited species

Hélice moléculaire multiporphyrinique à squelette polypeptidique (Vers la propagation intramoléculaire d'un signal)

La photosynthèse fait appel à des antennes collectrices constituées de pigments chlorophylliens capables d'absorber des photons et d'acheminer leur énergie le long du groupe de pigments vers le centre réactionnel où sera transformer l'énergie photonique en énergie chimique nécessaire à la croissance des plantes. Il est possible de modéliser ces systèmes naturels et l'effet d'antenne qui s'y produit en synthétisant des architectures moléculaires où on multiplie le nombre de chromophores récepteurs de photons autour d'un centre accepteur d'énergie. Nous avons réalisé la synthèse d'oligopeptides fonctionnalisés par des porphyrines, obtenues par oligomérisation d'un nouvel amino-acide dérivé de la L-lysine et fonctionnalisé par une porphyrine. Un octa- et un hexadéca-peptide ont notamment été synthétisés. La chiralité imposée par l'hélicité de la chaîne polypeptidique est ressentie par les porphyrines qui adoptent, d'un pas de l'hélice à l'autre, une conformation parallèle détectée en Dichroïsme Circulaire par la présence d'un couplage excitonique. Une telle conformation, correspondant à un positionnement éclipsé des porphyrines, favorise en effet un couplage excitonique susceptible de favoriser une migration d'états excités. La série des oligopeptides a été métallée au Zn (II) dans le but d'examiner l'effet du degré d'oligomérisation de ces architectures moléculaires sur leur capacité de complexation. Nous avons pu montrer que la coordination de DABCO est favorisée au fur et à mesure de l'élévation du degré d'oligomérisation, probablement grâce à la préorganisation conformationnelle observée notamment pour l'octamère. Enfin, nous nous sommes intéressés à la synthèse de nouveaux systèmes porphyriniques encore plus sophistiqués destinés à concentrer l'énergie photonique vers le cœur de la molécule constitué par une porphyrine base libre. A cet effet, une penta- et une nona-porphyrine linéaires, constituées respectivement de deux dipeptides de Zn (II) ou deux tétrapeptides de Zn (II) reliés à une porphyrine base libre centrale de type A2B2 trans, ont été élaborées. Un transfert d'énergie a été mis en évidence depuis les porphyrines de Zn (II) vers la porphyrine base libre centrale dans les deux multi-porphyrines synthétisées. L'effet d'antenne escompté est donc bien observé.Photosynthesis needs collecting antennas made up of chlorophyllian pigments able to absorb photons and to forward their energy along the group of pigments to the reactional center where will be to transform the photonic energy into chemical energy necessary to the growing up of plants. It is possible to model these natural systems and the antenna effect which produced there by synthesizing molecular architectures where we multiplie the number of chromophoric receivers of photons around a center acceptor of energy. We have realised the synthesis of oligopeptides functionalized by the porphyrins, obtained by oligomerisation of a new amino-acid derived from L-lysin and functionalized by a porphyrin. A octa- and a hexadeca-peptide were synthesized. The chirality imposed by the helicity of the polypeptide chain is felt by porphyrins which adopt, of one step of the helical to the other, a parallel conformation detected in Circular Dichroism (CD) by the presence of an excitonic coupling. Such conformation, corresponding to an eclipsed positioning of porphyrins, favourise an excitonic coupling to support a migration of excited states. The series of the oligopeptides were metallated with Zn (II) with an aim of examining the effect of the degree of oligomerisation of these molecular architectures on their capacity of complexation. We could show that the coordination of DABCO is favoured progressively with the rise in the degree of oligomerisation, probably thanks to the conformational preorganisation observed in particular for the octamer. Finally, we were interested in the synthesis of new porphyrins systems more sophisticated even intended to concentrate the photonic energy towards the core of the molecule consisted by a free base porphyrin. For this effect, a linear penta- and nona-porphyrin, respectively made up of two dipeptides from Zn (II) or two Zn tétrapeptides (II) connected to a central free base porphyrin of the type A2B2 trans, were elaborated. A energy transfer was highlighted since Zn porphyrins (II) towards the central free base porphyrin in the two synthesized multi-porphyrins. The antenna effect discounted is observed.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

S2- and S1-states properties of zinc porphyrin polypeptides

International audienc

Chirality and spatially pre-organized multi-porphyrinoids

International audienc

Multiple photosynthetic reaction centres using zinc porphyrinic oligopeptide–fulleropyrrolidine supramolecular complexes

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Noise-Induced Cochlear Damage Involves PPAR Down-Regulation through the Interplay between Oxidative Stress and Inflammation

The cross-talk between oxidative stress and inflammation seems to play a key role in noise-induced hearing loss. Several studies have addressed the role of PPAR receptors in mediating antioxidant and anti-inflammatory effects and, although its protective activity has been demonstrated in several tissues, less is known about how PPARs could be involved in cochlear dysfunction induced by noise exposure. In this study, we used an in vivo model of noise-induced hearing loss to investigate how oxidative stress and inflammation participate in cochlear dysfunction through PPAR signaling pathways. Specifically, we found a progressive decrease in PPAR expression in the cochlea after acoustic trauma, paralleled by an increase in oxidative stress and inflammation. By comparing an antioxidant (Q-ter) and an anti-inflammatory (Anakinra) treatment, we demonstrated that oxidative stress is the primary element of damage in noise-induced cochlear injury and that increased inflammation can be considered a consequence of PPAR down-regulation induced by ROS production. Indeed, by decreasing oxidative stress, PPARs returned to control values, reactivating the negative control on inflammation in a feedback loop

Review-Two Different Multiple Photosynthetic Reaction Centers Using Either Zinc Porphyrinic Oligopeptide-Fulleropyrrolidine or Free-Base Porphyrinic Polypeptide-Li+@C 60 Supramolecular Complexes

International audienceAn overview of two successful examples of photosynthetic reaction center models combined with light-capturing antenna chromophores is presented. In the first example, supramolecular complexes are formed between flexible zinc porphyrinic oligopeptides and fulleropyrrolidine bearing either a pyridine or imidazole functionalized C 60 via a coordination bond plus π−π interactions. The excited energy migration occurs between porphyrin units followed by charge separation. The charge separation (CS) lifetimes of the supramolecular oligopeptide complexes have been elongated by increasing the generation of the porphyrins, enabling us to attain the longest lifetime (0.84 ms) for the P(ZnP) 8-ImC 60 supramolecular system in PhCN solution at 298 K, ever reported for supramolecular complexes. In the second example, free-base porphyrin polypeptides (P(H 2 P) n ; n = 4 and 8) form supramolecular complexes with Li + @C 60 in PhCN, in which the binding is much stronger than C 60. Efficient energy migration occurs between porphyrins in P(H 2 P) n. The triplet CS states derived from 3 Li+@C 60 had long lifetimes due to spin-forbidden back electron transfer. The triplet CS lifetime becomes longer upon increasing the number of H 2 P due to the charge migration among porphyrins. The present study provides valuable insight into the energy and electron transfer processes leading to long-lived charge separated states in artificial photosynthetic antenna-reaction center models