David Flot

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CCDC 1970543: Experimental Crystal Structure Determination

Synthesis of unsymmetrical 1,8-naphthyridine-based ligands for the assembly of tri-and tetra-nuclear copper(ii) complexes

New Journal of Chemistry, 2020

Exploring copper(ii) coordination from a new unsymmetrical naphthyridine-based ligand leads to th... more

O2 Activation by Non-Heme Thiolate-Based Dinuclear Fe Complexes

Inorganic Chemistry, 2020

Iron centers featuring thiolates in their metal coordination sphere (as ligands or substrates) ar... more Iron centers featuring thiolates in their metal coordination sphere (as ligands or substrates) are well-known to activate dioxygen. Both heme and non-heme centers that contain iron-thiolate bonds are found in nature. Investigating the ability of iron-thiolate model complexes to activate O 2 is expected to improve the understanding of the key factors that direct reactivity to either iron or sulfur. We report here the structural and redox properties of a thiolate-based dinuclear Fe complex, [Fe II 2 (LS) 2 ] (LS 2-= 2,2′-(2,2′-bipyridine-6,6′-iyl)bis(1,1-diphenylethanethiolate)), and its reactivity with dioxygen, in comparison with its previously reported protonated counterpart, [Fe II 2 (LS)(LSH)] + . When reaction with O 2 occurs in the absence of protons or in the presence of 1 equiv of proton (i.e., from [Fe II 2 (LS)(LSH)] + ), unsupported μ-oxo or μ-hydroxo Fe III dinuclear complexes ([Fe III 2 (LS) 2 O] and [Fe III 2 (LS) 2 (OH)] + , respectively) are generated. [Fe III 2 (LS) 2 O], reported previously but isolated here for the first time from O 2 activation, is characterized by single crystal X-ray diffraction and Mossbauer, resonance Raman, and NMR spectroscopies. The addition of protons leads to the release of water and the generation of a mixture of two Fe-based "oxygen-free" species. Density functional theory calculations provide insight into the formation of the μ-oxo or μ-hydroxo Fe III dimers, suggesting that a dinuclear μ-peroxo Fe III intermediate is key to reactivity, and the structure of which changes as a function of protonation state. Compared to previously reported Mn-thiolate analogues, the evolution of the peroxo intermediates to the final products is different and involves a comproportionation vs a dismutation process for the Mn and Fe derivate, respectively.

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$Research paper thumbnail of Combined microdrop generation and microdiffraction for biopolymer hydration experiments$

Combined microdrop generation and microdiffraction for biopolymer hydration experiments

Fibre Diffraction Review, 2004

The article discusses instrumentation developed at the ESRF ID13 beamline for the study of rapid ... more The article discusses instrumentation developed at the ESRF ID13 beamline for the study of rapid biopolymer hydration reactions. An introduction into currently available optics and sample environments is provided and the use of a 0.7 µm beam is demonstrated for SAXS/WAXS patterns recorded from a starch granule. An inkjet system is described, which allows hydration of biopolymers locally with about

One-Pot Synthesis and Characterization of Soluble Poly(aryl ether−ketone)s Having Pendant Carboxyl Groups

Macromolecules, Jun 3, 2003

... Mikhail G. Zolotukhin,* Howard M. Colquhoun,* and Lionel G. Sestiaa. ... Howard M. Colquhoun,... more

Formation of crystalline macrocyclic phases during electrophilic precipitation–polycondensation syntheses of poly(arylene ether ketone)s

Polymer, Feb 1, 2004

Elongated crystalline particles formed as by-products during poly(arylene ether ketone) synthesis... more Elongated crystalline particles formed as by-products during poly(arylene ether ketone) synthesis by electrophilic precipitationpolycondensation of 4,4 0-diphenoxybenzophenone with terephthaloyl chloride or isophthaloyl chloride, thought previously to be polymerwhiskers, have now been identified as macrocyclic phases. Single crystal X-ray analysis of the needle-like particles formed in the reaction with terephthaloyl chloride, using the microdiffraction technique with synchrotron radiation, revealed that they consist of a macrocylic compound containing ten phenylene units, i.e. the [2 þ 2] cyclic dimer. An analogous structure has also been demonstrated for the corresponding macrocycle derived from the reaction of 4,4 0-diphenoxybenzophenone with isophthaloyl chloride. Chloroform extraction of the products of the two polycondensations dissolved the macrocyclic material (but not the linear polymer), and analysis of the extracts by MALDI-TOF mass spectrometry demonstrated the presence in both cases of homologous families of macrocyclic products. Higher yields of macrocycles were obtained under pseudo-high dilution conditions, enabling the [2 þ 2] cyclodimers from reactions of 4,4 0diphenoxybenzophenone with both terephthaloyl and isophthaloyl chloride to be isolated as pure compounds and fully characterised.

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Synthesis, electrical properties and thermal analysis of transition metal-doped Mg2TiO4 spinels

Solid State Ionics, Nov 1, 2000

The synthesis and characterization of Mg2TiO4 doped with different transition elements (Mn, Fe, C... more The synthesis and characterization of Mg2TiO4 doped with different transition elements (Mn, Fe, Co) are reported. Three different series of cubic spinel titanate are obtained by substitution of only one cation (Mg2−xMxTiO4, Mg2Ti1−xMxO4) or both cations (Mg2−x/2Ti1−x/2MxO4) for x=0.1 and their electrical properties have been compared. AC conductivity data have been measured in air between 500 and 1000°C, showing for

The Crystal Structure of the Extracellular Domain of the Inhibitor Receptor Expressed on Myeloid Cells IREM-1

Journal of Molecular Biology, Mar 1, 2007

The immune receptors expressed on myeloid cells (IREM) are type I transmembrane proteins encoded ... more The immune receptors expressed on myeloid cells (IREM) are type I transmembrane proteins encoded on human chromosome 17 (17q25.1), whose function is believed to be important in controlling inflammation. To date, three IREM receptors have been identified. IREM-1 functions as an inhibitory receptor, whereas IREM-2 and IREM-3 serve an activating function. Here, we report the crystal structure of IREM-1 extracellular domain at 2.6 Å resolution. The overall fold of IREM-1 resembles that of a V-type immunoglobulin domain, and reveals overall close homology with immunoglobulin domains from other immunoreceptors such as CLM-1, TREM-1, TLT-1 and NKp44. Comparing the surface electrostatic potential and hydrophobicity of IREM-1 with its murine homologous CLM-1, we observed unique structural properties for the complementary determining region of IREM-1, which suggests that they may be involved in recognition of the IREM-1 ligand. Particularly interesting is the structural conformation and physical properties of the antibody's equivalent CDR3 loop, which we show to be a structurally variable region of the molecule and therefore could be the main structural determinant for ligand discrimination and binding. In addition, the analysis of the IREM-1 structure revealed the presence of four structurally different cavities. Three of these cavities form a continuous hydrophobic groove on the IREM-1 surface, which point to a region of the molecule capable of accommodating potential ligands.

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$Research paper thumbnail of Structural Processes during Starch Granule Hydration by Synchrotron Radiation Microdiffraction$

Structural Processes during Starch Granule Hydration by Synchrotron Radiation Microdiffraction

Biomacromolecules, May 26, 2004

Starch granule hydration has been examined on the level of a single potato starch granule by stat... more Starch granule hydration has been examined on the level of a single potato starch granule by static and dynamic synchrotron radiation (SR) microdiffraction techniques. A cryofrozen, hydrated granule was mapped through a 5 µm SR-beam in order to investigate its internal organization. The edge of the granule showed fiber texture scattering due to radially oriented amylopectin helices. The variation of fiber texture across the granule center supports the model of concentric shells. The crystalline phase appears, however, to increase strongly toward the granule center due to a random amylopectin fraction, which could be related to crystallization of short-range ordered amylopectin during hydration. During gelatinization, the shell structure breaks down and remaining fiber-textured amylopectin domains belong probably to the swollen starch granule envelope. Hydration of a granule was initiated by a microdrop generator and followed in situ by SR-microdiffraction. A fast hydration process with a half time of about 7 s seems to reflect the porous nature of starch granules. The size of the hydrated domains suggests that this process is limited to the level of amylopectin side chain clusters. Longer hydration times are assumed to involve remaining short-range ordered amylopectin and results in larger domains.

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Synthesis and crystal structure of tris(2,3-triphenylenedioxy)cyclotriphosphazene: a new clathration system

CrystEngComm, 2011

ABSTRACT A new host compound TTPP (tris(2,3-triphenylenedioxy)cyclotriphosphazene), which is able... more ABSTRACT A new host compound TTPP (tris(2,3-triphenylenedioxy)cyclotriphosphazene), which is able to form a porous network, has been synthesized in five steps. When it crystallizes as a single component, TTPP exhibits a crystal structure with a monoclinic unit cell, the space groupP21/c (no. 14) and unit cell dimensions of a = 14.909(2) Å, b = 31.013(4) Å, c = 9.074(1) Å, β = 102.12(1)°. Co-crystallization of TTPP with 1,2,4-trichlorobenzene forms an inclusion crystal having a triclinic unit cell with a P space group (no. 2) and unit cell dimensions of a = 8.769(2) Å, b = 15.024(2) Å, c = 21.216(2) Å, α = 94.82(0)°, β = 99.98(0)°, γ = 98.23(1). The guest lies in two kinds of channel-like cavities with dimensions of 6.1 × 8.4 Å2 and 10.7 × 12.4 Å2 respectively. This represents the biggest porous network built up by spirocyclotriphosphazene derivatives to date.

New Asymmetric Approach to Natural Pyrrolizidines: Synthesis of (+)-Amphorogynine A, (+)-Amphorogynine D, and (+)-Retronecine

Journal of Organic Chemistry, Sep 21, 2005

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New Asymmetric Approach to Natural Pyrrolizidines: Synthesis of (+)-Amphorogynine A (Ia), (+)-Amphorogynine D (Ib), and (+)-Retronecine (II)

ChemInform, Feb 28, 2006

Three natural pyrrolizidines, (+)-amphorogynines A and D and (+)-retronecine, have been prepared ... more Three natural pyrrolizidines, (+)-amphorogynines A and D and (+)-retronecine, have been prepared from a common lactam intermediate. This central compound, in turn, was synthesized in diastereomerically enriched form through a highly selective [2 + 2]-cycloaddition of dichloroketene with a chiral enol ether, followed by Beckmann ring expansion and reduction. Subsequent stereocenters were then cleanly introduced through internal induction.

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Packing Polymorphism Affecting the Optoelectronic Properties of a π-Conjugated Organic Compound

Crystal Growth & Design, Jun 11, 2021

Benzothieno[3,2-b]benzothiophene (BTBT) derivatives are widely employed as hole transport materia... more Benzothieno[3,2-b]benzothiophene (BTBT) derivatives are widely employed as hole transport materials in organic field-effect transistors. The electronic properties of these Supporting Information. Crystal structure data of BTBT-C5OH-I and BTBT-C5OH-II, packing similarities between BTBT-C5OH-I and BTBT-C5OH-II and other structures in the Cambridge Structural Database, photomicrographs of crystals of polymorph I and II, thermal expansion data of BTBT-C5-OH-I, atomic displacement plots for the low-temperature structures of I and II with atom labelling, unusual geometric observations (Mogul analysis), 6-molecules clusters for polymorph I and II used for the promolecular NCI calculations, electron density variation between BTBT-C5-OH isolated subunits (DFT calculations). Crystallographic Information Framework (CIF) files for all structural models reported in this paper have been deposited at the Cambridge Structural Database under the numbers CCDC 2059375, 2060594-2060599. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/structures" AUTHOR INFORMATION

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Effect of Monoelectronic Oxidation of an Unsymmetrical Phenoxido-Hydroxido Bridged Dicopper(II) Complex

Inorganic Chemistry, Sep 18, 2018

A (μ-hydroxido, μ-phenoxido)Cu II Cu II complex 1 has been synthesized using an unsymmetrical lig... more A (μ-hydroxido, μ-phenoxido)Cu II Cu II complex 1 has been synthesized using an unsymmetrical ligand bearing an N,N-bis(2-pyridyl)methylamine (BPA) moiety coordinating one copper and a dianionic bis-amide moiety coordinating the other copper(II) ion. Electrochemical mono-oxidation of the complex in DMF occurs reversibly at 213 K at E 1/2 = 0.12 V vs Fc + /Fc through a metal-centered process. The resulting species (complex 1 +) is only stable at low temperature and has been spectroscopically characterized by UV−vis−NIR cryo-spectroelectrochemical and EPR methods. DFT and TD-DFT calculations, consistent with experimental data, support the formation of a Cu II Cu III phenoxido-hydroxido complex. Lowtemperature chemical oxidation of 1 by NOSbF 6 yields a tetranuclear complex 2(SbF 6)(NO 2) which displays two binuclear Cu II Cu II subunits. The X-ray crystal structure of 2(SbF 6)(NO 2) evidences that the nitrogen of the terminal amide group is protonated and the coordination of the amide occurs via the O atom. The bis-amide moiety appears to be a non-innocent proton acceptor along the redox process. Alternatively, protonation of complex 1 leads to the complex 2(ClO 4) 2 , as evidenced by X-ray crystallography, cyclic voltammetry, and 1 H NMR.

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Expression, crystallization and X-ray data collection from microcrystals of the extracellular domain of the human inhibitory receptor expressed on myeloid cells IREM-1

Acta crystallographica, Feb 13, 2007

IREM-1 is an inhibitory receptor involved in the functional regulation of myeloid cells. The expr... more IREM-1 is an inhibitory receptor involved in the functional regulation of myeloid cells. The expression, in vitro folding, purification, crystallization and X-ray data collection of the Ig-V like domain of IREM-1 are reported. X-ray data were collected from a microcrystal (300 Â 10 Â 10 mm) at 100 K and a diffraction pattern was obtained to 2.6 Å resolution on microfocus beamline ID23-2 at the ESRF. The crystal belongs to space group P3 1 21, with unit-cell parameters a = b = 54.23, c = 72.02 Å , = = 90, = 120. Assuming the presence of one molecule per asymmetric unit, V M (the Matthews coefficient) was calculated to be 1.96 Å 3 Da À1 and the solvent content was estimated to be 37.27%. Determination of the IREM-1 structure will provide insights into its structural requirements for ligand discrimination and binding.

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Structure of Synthetic K-rich Birnessite Obtained by High-Temperature Decomposition of KMnO<sub>4</sub>. I. Two-Layer Polytype from 800 °C Experiment

Chemistry of Materials, Nov 6, 2003

The structure of a synthetic potassium birnessite (KBi) obtained as a finely dispersed powder by ... more The structure of a synthetic potassium birnessite (KBi) obtained as a finely dispersed powder by thermal decomposition of KMnO 4 at 800°C was for the first time studied by single crystal X-ray diffraction (XRD). It is shown that KBi has a two-layer cell with a = 2.840(1) Å, and c = 14.03(1) Å, and space group P6 3 /mmc. In contrast to the structure model proposed by Kim et al., 1 the refined model demonstrates the sole presence of Mn 4+ in the octahedral layers, the presence of 0.12 vacant layer sites per octahedron being responsible for the layer charge deficit. This layer charge deficit is compensated for 1) by the presence of 1 / 36 interlayer Mn 3+ above or below vacant layer octahedra sharing three O layer with neighboring Mn layer octahedra to form a triple-corner surface complex (VI TC sites), and 2) by the presence of interlayer K in prismatic cavities located above or below empty tridentate cavities, sharing three edges with neighboring Mn layer octahedra (VI TE sites). As compared to the structure model proposed by Kim et al., 1 this VI TE site is shifted from the center of the prismatic cavity towards its edges. A complementary powder XRD study confirmed the structure model of the main defect-free KBi phase and allowed to determine the nature of stacking disorder in a defective accessory KBi phase admixed to the defect-free KBi.

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Microcrystallography with an X-ray waveguide

Journal of Applied Crystallography, Oct 1, 2000

A waveguide microdiffraction setup is described for an undulator beamline at the European Synchro... more A waveguide microdiffraction setup is described for an undulator beamline at the European Synchrotron Radiation Facility. The composite optics consists of a waveguide, which con®nes the beam vertically, and a horizontally focusing multilayer mirror. A beam size of about 0.1 Â 3 mm (vertical Â horizontal) at ! = 0.095 nm has been obtained. The sample stage comprises a three-axis gantry with micrometre precision and a three-axis piezo-scanner with about 0.1 mm repeatability. Diffraction experiments are demonstrated for selected inorganic and polymeric samples. Possibilities for scanning diffractometry and small-angle scattering experiments are discussed.

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Hybrid π-conjugated organosilica materials: semiconductors for fully covalent transistors or photovoltaic applications

HAL (Le Centre pour la Communication Scientifique Directe), Oct 16, 2017

International audienc

Synthesis and electrical characterisation of different doped magnesium titanates

Ionics, May 1, 1998

ABSTRACT

Molecular machines in energy transduction, cellular signaling and defense processes

Within this BAG we are focussing mainly on three topics: 1.) proteins that use the energy of ligh... more Within this BAG we are focussing mainly on three topics: 1.) proteins that use the energy of light, ATP, GTP or NADH to perform essential biological functions, either embedded in the membrane or in the cytosol 2.) proteins of different essential signaling or metabolic processes in plants like the ethylene pathway or the nitrogen metabolism 3.) proteins involved in the immune system of prokaryotic bacteria and plants or associated with diseases like cancer or developmental disorders

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