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

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

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

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

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

Crystal and molecular structure of 1-picryl-2-phenyl-2-(4-picrylamidophenyl)-diazenium betaine: analogy between a picramido group and an oxygen atom

International audienceThe title compound is formed by a non-trivial reaction involving two molecules of the stable free radical 2,2-diphenyl-1-picryl-hydrazyl and one molecule of N-methoxy-picramide. We could now perform an X-ray diffraction experiment on a single crystal and can fully confirm the betaine structure which has a central quino-noid ring with alternating long and short bonds