Laurent Jouffret

Raman Spectroscopic and ESI-MS Characterization of Uranyl Peroxide Cage Clusters

Strategies for interpreting mass spectrometric and Raman spectroscopic data have been developed to study the structure and reactivity of uranyl peroxide cage clusters in aqueous solution. We demonstrate the efficacy of these methods using the three best-characterized uranyl peroxide clusters, {U24}, {U28}, and {U60}. Specifically, we show a correlation between uranyl-peroxo-uranyl dihedral bond angles and the position of the Raman band of the symmetric stretching mode of the peroxo ligand, develop methods for the assignment of the ESI mass spectra of uranyl peroxide cage clusters, and show that these methods are generally applicable for detecting these clusters in the solid state and solution and for extracting information about their bonding and composition without crystallization.

Correlations and differences between uranium(VI) arsonates and phosphonates.

Three new uranium arsonate compounds, UO(2)(C(6)H(5))(2)As(2)O(5)(H(2)O) (UPhAs-1), UO(2)(HO(3)AsC(6)H(4)AsO(3)H)(H(2)O)·H(2)O (UPhAs-2), and UO(2)(HO(3)AsC(6)H(4)NH(2))(2)·H(2)O (UPhAs-3) have been synthesized under mild hydrothermal conditions. UPhAs-1 is constructed from UO(7) pentagonal bipyramids that are chelated by the pyroarsonate moiety, [PhAs(O(2))OAs(O(2))Ph](2-), forming chains of layered uranyl polyhedra. Two of the phenylarsonic acids are condensed in situ to form the fused tetrahedra of the pyroarsonate moiety through a metal-mediated, thermally induced condensation process. The structure of UPhAs-2 consists of UO(7) pentagonal bipyramids that are chelated by phenylenediarsonate ligands, forming one-dimensional chains of uranyl polyhedra. UPhAs-3 consists of a rare UO(6) tetragonally distorted octahedron (D(4h)) that is on a center of symmetry and linked to two pairs of adjacent 4-aminophenylarsonate ligands. This linear chain structure is networked through hydrogen bonds between the lattice water molecules and the -NH(2) moiety. All three of these compounds fluoresce at room temperature, showing characteristic vibronically coupled charge-transfer based emission.

Homogeneous and Robust Polyproline Type I Helices from Peptoids with Nonaromatic α-Chiral Side Chains

Peptoids that are oligomers of N-substituted glycines represent a class of peptide mimics with great potential in areas ranging from medicinal chemistry to biomaterial science. Controlling the equilibria between the cis and trans conformations of their backbone amides is the major hurdle to overcome for the construction of discrete folded structures, particularly for the development of all-cis polyproline type I (PPI) helices, as tools for modulating biological functions. The prominent role of backbone to side chain electronic interactions (n → π*) and side chains bulkiness in promoting cis-amides was essentially investigated with peptoid aromatic side chains, among which the chiral 1-naphthylethyl (1npe) group yielded the best results. We have explored for the first time the possibility to achieve similar performances with a sterically hindered α-chiral aliphatic side chain. Herein, we report on the synthesis and detailed conformational analysis of a series of (S)-N-(1-tert-butylethyl)glycine (Ns1tbe) peptoid homo-oligomers. The X-ray crystal structure of an Ns1tbe pentamer revealed an all-cis PPI helix, and the CD curves of the Ns1tbe oligomers also resemble those of PPI peptide helices. Interestingly, the CD data reported here are the first for any conformationally homogeneous helical peptoids containing only α-chiral aliphatic side chains. Finally we also synthesized and analyzed two mixed oligomers composed of NtBu and Ns1tbe monomers. Strikingly, the solid state structure of the mixed oligomer Ac-(tBu)2-(s1tbe)4-(tBu)2-COOtBu, the longest to be solved for any linear peptoid, revealed a PPI helix of great regularity despite the presence of only 50% of chiral side chain in the sequence.

Linear Alkyl Diamine-Uranium-Phosphate Systems: U(VI) to U(IV) Reduction with Ethylenediamine

Mild-hydrothermal reactions in acidic medium using 1,3-diaminopropane, 1,4-diaminobutane, and 1,5-diaminopentane as structure directing agents led to three-dimensional (3D) uranyl phosphates (CH₂)₃(NH₃)₂{[(UO₂)(H₂O)][(UO₂)(PO₄)]₄} (C3U5P4), (CH₂)₄(NH₃)₂{[(UO₂)(H₂O)][(UO₂)(PO₄)]₄} (C4U5P4) and (CH₂)5(NH₃)₂{[(UO₂)(H₂O)][(UO₂)(PO₄)]₄} (C5U5P4). The structures of (C4U5P4) and (C5U5P4) were solved in the space group Cmc2₁ using single-crystal X-ray diffraction data. The compounds are isostructural to the corresponding uranyl vanadates and contain the same 3D inorganic framework built from uranyl-phosphate layers of uranophane-type anion topology pillared by [UO₆(H₂O)] pentagonal bipyramids. In neutral or basic medium the alkyl diamines decompose to give ammonium uranyl phosphate trihydrate. In the same conditions by using ethylenediamine, unexpected reduction of uranium(VI) to uranium(IV) occurs leading to the formation of (CH₂)₂(NH₃)₂[U(PO₄)₂] (C2UP2) single crystals. C2UP2 undergoes a reversible phase transition from triclinic to monoclinic symmetry at about 230 °C. The structure of the two forms results from the stacking of inorganic layers (∞)¹[U(PO₄)₂]²⁻, and organic layers containing ethylene diammonium ions, the two layers being linked by hydrogen bonds. Single crystals of (CH₂)₂(NH₃)₂[PO₃OH] (C2HP) are formed by evaporation of the solution after filtering of C2UP2 single crystals. The structure of C2HP contains infinite (∞)¹[PO₃OH]²⁻ chains connected by (CH₂)₂(NH₃)₂²⁺ ions through hydrogen bonds.

U(VI) oxygen polyhedra as pillars for building frameworks from uranophane-type layers

Solid state chemistry of uranyl-containing inorganic compounds has been enriched recently by a multiplication of papers dealing with two and three dimensional inorganic materials. This paper is a review of the compounds structurally based on uranophane–type layers in uranyl silicates, phosphates, arsenates and vanadates systems. Depending on the nature and size of the metallic or organic cation used as charge compensators or structure directing agents, various geometric isomers are obtained and described herein. The cations occupy either the interlayer space between uranophane-type sheets or different types of cavities created by a three dimensional inorganic framework built from uranophane layers pillared by U(VI) and oxygen polyhedra. The number of UO6 or UO7 pillars by [(UO2)(XO4)] structural block units of the layer give a series of compounds with the following general formula A2y/n{(UO2)1−y[(UO2)(XO4)]2} with y=0,1/3,1/2 and 1.

Topologically Diverse Shapes Accessible by Modular Design of Arylopeptoid Macrocycles

N-Substituted aromatic cyclooligoamides composed of different combinations of ortho-, meta-, and/or para-arylopeptoid residues carrying methoxyethyl side chains have been efficiently synthesized by macrocyclization of the corresponding linear oligomers. The study of the architectures of these macrocycles in solution and solid state has revealed that tetracyclic arylopeptoids adopt sequence-dependent shapes with different backbone amide conformations and side-chain orientations. Remarkably, despite the absence of intramolecular H-bonding ability, some of these arylopeptoid macrocycles show well-defined architectures in solution.

Click 1,2,3-triazole derived fluorescent scaffold by mesoionic carbene-nitrene cyclization: an experimental and theoretical study

We describe a set of three fluorescent mesoionic benzo[4,5]imidazo-3-ide-[1,2-c]-2-alkyl-1,2,3-triazol-2-ium compounds obtained through a simple, concise and efficient synthetic sequence featuring a copper-catalyzed carbene–nitrene cyclization. The compounds were characterized by fluorescence spectroscopy highlighting promising photophysical properties in terms of quantum yields and Stokes shifts. Experimental properties were rationalized by a computational DFT and TD-DFT approach with excellent agreement with structural and spectroscopic data.

Exploring the Conformation of Mixed Cis–Trans α,β-Oligopeptoids: A Joint Experimental and Computational Study

The synthesis and conformational preferences of a set of new synthetic foldamers that combine both the α,β-peptoid backbone and side chains that alternately promote cis- and trans-amide bond geometries have been achieved and addressed jointly by experiment and molecular modeling. Four sequence patterns were thus designed and referred to as cis-β- trans-α, cis-α- trans-β, trans-β- cis-α, and trans-α- cis-β. α- and β NtBu monomers were used to enforce cis-amide bond geometries and α- and β NPh monomers to promote trans-amides. NOESY and molecular modeling reveal that the trans-α- cis-β and cis-β- trans-α tetramers show a similar pattern of intramolecular weak interactions. The same holds for the cis-α- trans-β and trans-β- cis-α tetramers, but the interactions are different in nature than those identified in the trans-α- cis-β-based oligomers. Interestingly, the trans-α- cis-β peptoid architecture allows establishment of a larger amount of structure-stabilizing intramolecular interactions.

CCDC 1547795: Experimental Crystal Structure Determination

Related Article: Anca G. Coman, Codruta C. Paraschivescu, Anca Paun, Andreea Diac, Niculina D. Hădade, Laurent Jouffret, Arnaud Gautier, Mihaela Matache, Petre Ionita|2017|New J.Chem.|41|7472|doi:10.1039/C7NJ01698K

Synthesis of novel profluorescent nitroxides as dual luminescent-paramagnetic active probes

We describe herein the synthesis of new profluorescent nitroxides based on 2,5-disubstituted-1,3,4-oxadiazoles as fluorescent moieties and the 2,2,6,6-tetramethylpiperidine-N-oxyl radical (TEMPO) as paramagnetic probes. The synthesis and optical and electronic properties of the oxadiazole-based precursors of the profluorescent nitroxides, as well as the nitroxides and their reduced forms are also described. Physical investigations (i.e. absorption and emission spectroscopy, cyclic voltammetry) indicate a different luminescence behaviour function to the oxadiazole substituent. A linear response to reducing agents, i.e. sodium ascorbate, monitored by fluorescence spectroscopy, suggests the possibility of using the synthesized compounds as potent active probes in detection of various analytes of interest.