Biomimetic self-assembling acylphthalocyanines

International audienceWe synthesized a series of biomimetic self-assembling phthalocya-nines equipped with carbonyl groups as recognition motifs, a central zinc atom and diverse solubilizing alkyl chains mimicking for the first time with these robust pigments the natural chlorosomal bacterio-chlorophylls. Upon self-assembly a very broad and red-shifted Q-band absorption extending to over 900 nm is put into evidence

Meso-Ester Corroles

International audienceDedicated to Professor Mieczysław Józef Mąkosza on the occasion of his 80th birthday. Abstract: The introduction of ester groups on the 5 and 15 meso positions of corroles stabilizes them against oxidation and induces a red-shift of their absorption and emission spectra. These effects are studied through the photophysical and electrochemical characterization of up to sixteen different 5,15-diester corroles where the third meso position is free or occupied by an aryl group, a long alkyl chains or an ester moiety. The single crystal X-ray structure analysis of five 5,15-diestercorroles and Density Functional Theory (DFT) and Time Dependant Density Functional Theory (TD-DFT) calculations, show that the strong electron withdrawing character of the 5,15 ester substituents is reinforced by their π-overlapping with the macrocycle aromatic system. The crystal packings of corroles 2, 4, 6, 9 and 15 feature short distances between chromophores that are stacked into columns thanks to the low steric hindrance of meso ester groups. This close packing is partially due to intermolecular interactions involving inner hydrogen and nitrogen atoms and thereby stabilizing a single and identical corrole tautomeric form

1,3,5,7-Tetra-tert-butyl-4-aza- und 1,3,5,7-Tetra-tert-4-phospha-s-indacen

s-Indacen 1 [1], ein tricyclisches, nichtalternierendes [4n]π-System, war wiederholt Gegenstand theoretischer und experimenteller Untersuchungen. Formal läßt sich 1 als durch zwei σ-Bindungen gestortes [12]Annulen und somit als antiaromatische Verbindung auffassen. Dementsprechend legten bisherige Rechnungen [2 -4] fur 1 einen Grundzustand mit lokalisierten Doppelbindungen und den C2h-symmetrischen π-Bindungsisomeren 1A und 1B nahe

Preferential pathways for light-trapping involving β-ligated chlorophylls

AbstractThe magnesium atom of chlorophylls (Chls) is always five- or six-coordinated within chlorophyll–protein complexes which are the main light-harvesting systems of plants, algae and most photosynthetic bacteria. Due to the presence of stereocenters and the axial ligation of magnesium the two faces of Chls are diastereotopic. It has been previously recognized that the α-configuration having the magnesium ligand on the opposite face of the 17-propionic acid moiety is more frequently encountered and is more stable than the more seldom β-configuration that has the magnesium ligand on the same face [T.S. Balaban, P. Fromme, A.R. Holzwarth, N. Krauβ, V.I. Prokhorenko, Relevance of the diastereotopic ligation of magnesium atoms in chlorophylls in Photosystem I, Biochim. Biophys. Acta (Bioenergetics), 1556 (2002) 197–207; T. Oba, H. Tamiaki, Which side of the π-macrocycle plane of (bacterio)chlorophylls is favored for binding of the fifth ligand? Photosynth. Res. 74 (2002) 1–10]. In photosystem I only 14 Chls out of a total of 96 are in a β-configuration and these occupy preferential positions around the reaction center. We have now analyzed the α/β dichotomy in the homodimeric photosystem II based on the 2.9 Å resolution crystal structure [A. Guskov, J. Kern, A. Gabdulkhakov, M. Broser, A. Zouni, W. Saenger, Cyanobacterial photosystem II at 2.9 Å resolution: role of quinones, lipids, channels and chloride, Nature Struct. Mol. Biol. 16 (2009) 334–342] and find that out of 35 Chls in each monomer only 9 are definitively in the β-configuration, while 4 are uncertain. Ab initio calculations using the approximate coupled-cluster singles-and-doubles model CC2 [O. Christiansen, H. Koch, P. Jørgensen, The second-order approximate coupled cluster singles and doubles model CC2, Chem. Phys. Lett. 243 (1995) 409–418] now correctly predict the absorption spectra of Chls a and b and conclusively show for histidine, which is the most frequent axial ligand of magnesium in chlorophyll–protein complexes, that only slight differences (<4 nm) are encountered between the α- and β-configurations. Significant red shifts (up to 50 nm) can, however, be encountered in excitonically coupled β–β-Chl dimers. Surprisingly, in both photosystems I and II very similar “special” β–β dimers are encountered at practically the same distances from P700 and P680, respectively. In purple bacteria LH2, the B850 ring is composed exclusively of such tightly coupled β-bacteriochlorophylls a. A statistical analysis of the close contacts with the protein matrix (<5 Å) shows significant differences between the α- and β-configurations and the subunit providing the axial magnesium ligand. The present study allows us to conclude that the excitation energy transfer in light-harvesting systems, from a peripheral antenna towards the reaction center, may follow preferential pathways due to structural reasons involving β-ligated Chls

Bottom-up synthesis of porphyrin based graphene nanoribbons and nanomeshes

International audienceThe outstanding properties of graphene strongly inspire the scientific community at both the fundamental and applicative levels for high performance electronics, low power spintronics, renewable energy, composites materials and biomedicine. However, along this way several key scientific issues have to be addressed and one of the main challenges is the control and modification of graphene electronic properties, and notably the controlled opening of a sizable bandgap. This can be achieved by quantum confinement, by means of the fabrication of nano-objects with a precise control of the topology, edge-effects... As a consequence, two main graphene forms have emerged for electronic applications, Graphene NanoRibbons (GNR) and Graphene NanoMeshes (GNM). For the last decade, a great attention has been paid to the fabrication of GNRs and GNMs using conventional top-down approach (lithography, etching, thermal treatments). However, this approach does not allow manipulating the material at the atomic scale. In order to truly control the morphology and the composition of the materials and of its edges, the bottom-up approach is the relevant way to proceed. Recently, graphene incorporating porphyrin molecules have been designed either by the groups of Barth and Fischer. Here we report on the synthesis of porphyrin derivatives that can lead to nitrogen doped GNR and GNM. The strategy we applied was to design building blocks based on porphyrins with halogens connectors and polymerize them on metallic surface under Scanning Tunnelling Microscope (STM). We succeeded in the synthesis of two original porphyrins with reasonable yield. The first one is a tetrabromoanthracenyl porphyrin (BrTAP, Fig. 1) with four connectors for the formation of a 2D nanostructure and a second, a bis-bromoanthracenylporphyrin (BrBAP) with two connectors GNR. Preliminary STM image for BrTAP on Ag (111) is shown Fig. 1 and other catalytic surfaces are under investigation to form GNR and GNM

Absorption shifts of diastereotopically ligated chlorophyll dimers of photosystem I

The light-harvesting chlorophyll (Chl) molecules of photosynthetic systems form the basis for light-driven energy conversion. In biological environments, the Chl chromophores occur in two distinct diastereotopic configurations, where the alpha and beta configurations have a magnesium-ligating histidine residue and a 17-propionic acid moiety on the opposite side or on the same side of the Chl ring, respectively. Although beta-ligated Chl dimers occupy conserved positions around the reaction center of photosystem I (PSI), the functional relevance of the alpha/beta configuration of the ligation is poorly understood. We employ here correlated ab initio calculations using the algebraic-diagrammatic construction through second order (ADC(2)) and the approximate second-order coupled cluster (CC2) methods in combination with the reduced virtual space (RVS) approach in studies of the intrinsic excited-state properties of alpha-ligated and beta-ligated Chl dimers of PSI. Our ab initio calculations suggest that the absorption of the alpha-ligated reaction-center Chl dimer of PSI is redshifted by 0.13-0.14 eV in comparison to the beta-ligated dimers due to combined excitonic coupling and strain effects. We also show that time-dependent density functional theory (TDDFT) calculations using range-separated density functionals underestimate the absorption shift between the alpha- and beta-ligated dimers. Our findings may provide a molecular starting point for understanding the energy flow in natural photosynthetic systems, as well as a blueprint for developing new molecules that convert sunlight into other forms of energy.Peer reviewe

High-flexibility combinatorial peptide synthesis with laser-based transfer of monomers in solid matrix material

Laser writing is used to structure surfaces in many different ways in materials and life sciences. However, combinatorial patterning applications are still limited. Here we present a method for cost-efficient combinatorial synthesis of very-high-density peptide arrays with natural and synthetic monomers. A laser automatically transfers nanometre-thin solid material spots from different donor slides to an acceptor. Each donor bears a thin polymer film, embedding one type of monomer. Coupling occurs in a separate heating step, where the matrix becomes viscous and building blocks diffuse and couple to the acceptor surface. Furthermore, we can consecutively deposit two material layers of activation reagents and amino acids. Subsequent heat-induced mixing facilitates an in situ activation and coupling of the monomers. This allows us to incorporate building blocks with click chemistry compatibility or a large variety of commercially available non-activated, for example, posttranslationally modified building blocks into the array’s peptides with >17,000 spots per cm²

Auto-assemblage de porphyrines équipées d'un radical organique stable

Un auto-assemblage de porphyrines possédant le radical organique stable a été réalisé dans le but de créer un nouveau type d aimant moléculaire. La synthèse mène à la formation du complexe de zinc de la 10,20-bis(3,5-di-tert-butyl-4-hydroxyphényl)porphyrine, substitué aux positions 3 par un alcool acétyl et en 13 par un acyle. Ces deux groupes dirige l auto-assemblage tandis qu une oxydation génère un phénoxyle. Des métalloporphyrines plus simples ont été utilisées pour étudier l oxydation et les interactions hyperfines, en électrochimie ou en RPE. La comparaison des résultats de la spectroélectrochimie et des spectres UV-visible de l oxydation montre qu une même espèce est générée. De plus, ces spectres comparés aux voltamogrammes prouvent que deux phénoxyles sont très probablement générés. Le complexe de zinc a été utilisé pour montrer la présence de phénoxyle en RPE, avec une quantification du signal en fonction du nombre d équivalent d oxydant. Le complexe de cuivre sert, en RPE, à déterminer les interactions présentent autour et entre les unités paramagnétiques. Une interaction hyperfine entre le cuivre et le phénoxyle n a pas été démontrée. Enfin, le phénomène d auto-assemblage a été caractérisé en UV-visible. Les porphyrines oxydées sont ajoutées dans du n-heptane et des oligomères sont immédiatement visibles. En RPE, un couplage magnétique entre les phénoxyles n a pas été détecté. L auto-assemblage de porphyrines a donc été réalisé sans toutefois obtenir un couplage magnétique.The self-assembly of porphyrins bearing stable organic radicals were realised with the aim to create a new type of molecular magnet. The synthesis lead to the zinc complex of the 1,10-bis(3,5-di-tert-butyl-4-hydroxyphenyl)porphyrin, substituted with two groups that direct the self-assembly, an acetyl alcohol at the position 3 and an acyl at the position 13. The meso substituant gives after oxidation a phenoxyl. Two simpler complexes were made with zinc and copper to study the oxidation or the hyperfine interactions, using electrochemistry and EPR. The comparison between the results of the spectroelectrochemistry and the UV-visible spectra of the oxidation proves that the same specie is generated. Moreover, these spectra and the electrochemistry allow concluding that two phenoxyls per porphyrin were generated. The zinc complex was used to show the phenoxyl formation by a quantification of the EPR signal functions of the number of oxidant equivalent. The copper complex was used in EPR to determine the interactions present around and between the paramagnetic units. A hyperfine coupling between the copper and the phenoxyl was not detected. Finally, the self-assembly was observed by UV-visible. The oxidized porphyrins were added in n-heptan and the oligomers were immediately visible. In EPR, a magnetic coupling between the phenoxyl was not detected. The self-assembly of paramagnetic porphyrins was realised but no magnetic coupling were detected because of the steric hindrance of the phenoxyls.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF