Electrochemical fabrication and characterization of thin films of redox-active molecular wires based on extended Rh-Rh bonded chains

An original electrochemical synthesis of {[Rh4(mu-OOCCH3)4(phen)4]2+}n (1) molecular wire films from a solution of binuclear bridged Rh complexes [Rh2(mu-OOCCH3)2(phen)2(X)2](Y)2 (X = H2O, Y = BF4(-) (2a) and X = CH3CN, Y = BF4(-) (2b)) in MeCN electrolyte is reported. UV-vis spectroscopy and quartz crystal microbalance electrochemical coupled techniques have been used to demonstrate the electrosynthesis process. The resulting polymetallic compound has been characterized on the basis of its physicochemical properties, which have been compared with those of a chemically synthesized sample. Furthermore, according to EPR, 1H NMR and electrochemical behaviour, the mechanism of the oxidation of this polymetallic wire, containing mixed valent rhodium centers and alternatively acetate bridged Rh-Rh bonds, has been investigated in detail.     

A tetranuclear organorhenium(i) complex of the 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-p-quinodimethane radical anion, TCNQF4 (-)

The radical complex {(mu(4)-TCNQF4)[Re(CO)(3)(bpy)](4)}(PF(6))(3), as prepared and isolated from the reaction between TCNQF4 and [Re(CO)(3)(bpy)(MeOH)](PF(6)), was studied electrochemically and by IR vibrational spectroscopy, UV-Vis-NIR absorption spectroscopy, and by EPR at 9.5, 190 and 285 GHz. The isotropic g factor of 2.0058, the detectable g anisotropy, and the (185,187)Re EPR hyperfine coupling of 0.95 mT for four equivalent metal nuclei support predominant, but not exclusive, spin localisation at the bridging ligand. Nitrile and metal carbonyl stretching frequencies as well as the typically structured near infrared absorption band lend further support to (TCNQF4 (-))(Re(I))(4) as the most appropriate oxidation state formulation. In comparison to the non-radical complex {(mu(4)-TCNQ)[Re(CO)(3)(bpy)](4)}(PF(6))(4) an X-ray structure analysis of {(mu(4)-TCNQF4)[Re(CO)(3)(bpy)](4)}(PF(6))(3) shows a marginally more twisted (ReNCCCNRe)(C(6)X(4))(ReNCCCNRe) configuration and a different up/down arrangement of the [Re(CO)(3)(bpy)](+) groups. This first isolation, electrochemical, structural and spectroscopic characterisation of a discrete tetranuclear radical complex of a TCNQ-type ligand suggests a link between the stability of such materials and the rather small structural changes on ligand-based electron transfer.     

Generalized fast marching method: applications to image segmentation

In this paper, we propose a segmentation method based on the generalized fast marching method (GFMM) developed by Carlini et al. (submitted). The classical fast marching method (FMM) is a very efficient method for front evolution problems with normal velocity (see also Epstein and Gage, The curve shortening flow. In: Chorin, A., Majda, A. (eds.) Wave Motion: Theory, Modelling and Computation, 1997) of constant sign. The GFMM is an extension of the FMM and removes this sign constraint by authorizing time-dependent velocity with no restriction on the sign. In our modelling, the velocity is borrowed from the Chan–Vese model for segmentation (Chan and Vese, IEEE Trans Image Process 10(2):266–277, 2001). The algorithm is presented and analyzed and some numerical experiments are given, showing in particular that the constraints in the initialization stage can be weakened and that the GFMM offers a powerful and computationally efficient algorithm.     

Artificial metalloenzyme for enantioselective sulfoxidation based on vanadyl-loaded streptavidin

Nature's catalysts are specifically evolved to carry out efficient and selective reactions. Recent developments in biotechnology have allowed the rapid optimization of existing enzymes for enantioselective processes. However, the ex nihilo creation of catalytic activity from a noncatalytic protein scaffold remains very challenging. Herein, we describe the creation of an artificial enzyme upon incorporation of a vanadyl ion into the biotin-binding pocket of streptavidin, a protein devoid of catalytic activity. The resulting artificial metalloenzyme catalyzes the enantioselective oxidation of prochiral sulfides with good enantioselectivities both for dialkyl and alkyl-aryl substrates (up to 93% enantiomeric excess). Electron paragmagnetic resonance spectroscopy, chemical modification, and mutagenesis studies suggest that the vanadyl ion is located within the biotin-binding pocket and interacts only via second coordination sphere contacts with streptavidin.     

Methyl proton contacts obtained using heteronuclear through-bond transfers in solid-state NMR spectroscopy

A two-dimensional proton-mediated carbon-carbon correlation experiment that relies on through-bond heteronuclear magnetization transfers is demonstrated in the context of solid-state NMR of proteins. This new experiment, dubbed J-CHHC by analogy to the previously developed dipolar CHHC techniques, is shown to provide selective and sensitive correlations in the methyl region of 2D spectra of crystalline organic compounds. The method is then demonstrated on a microcrystalline sample of the dimeric protein Crh (2 x 10.4 kDa). A total of 34 new proton-proton contacts involving side-chain methyl groups were observed in the J-CHHC spectrum, which had not been observed with the conventional experiment. The contacts were then used as additional distance restraints for the 3D structure determination of this microcrystalline protein. Upon addition of these new distance restraints, which are in large part located in the hydrophobic core of the protein, the root-mean-square deviation with respect to the X-ray structure of the backbone atom coordinates of the 10 best conformers of the new ensemble of structures is reduced from 1.8 to 1.1 A.     

Structural and luminescent properties of micro- and nanosized particles of lanthanide terephthalate coordination polymers

Reaction in water between rare earth ions (Ln = Y, La-Tm, except Pm) and the sodium salt of terephthalic acid leads to a family of lanthanide-based coordination polymers of general formula [Ln2(C8H4O4)3(H2O)4] n with Ln = La-Tm or Y. The isostructurality of the compounds with the previously reported Tb-containing polymer is ascertained on the basis of their X-ray powder diffraction diagrams. The coordination water molecules can be reversibly removed without destroying the crystal structure for compounds involving one of the lighter lanthanide ions (La-Eu). For compounds involving one of the heavier lanthanide ions (Tb-Tm) or yttrium, a structural change occurs during the drying process. X-ray diffraction data show this new anhydrous phase corresponding to the linking of pairs of Er(III) ions through mu-carboxylate bridges. Porosity profiles calculated for the anhydrous phases of Tb(III) and Er(III) show the presence of channels with very small sections. The luminescent properties of all the compounds have been recorded and the two most luminescent polymers, namely, the europium- and the terbium-containing ones, have been studied in more detail. Tb(III)-containing compounds display large quantum yields, up to 43%. Polyvinylpyrrolidone nanoparticles doped with [Ln2(C8H4O4)3(H2O)4] n (Ln = Eu, Tb, Er) have also been synthesized and characterized. The encapsulation of the coordination polymers results in somewhat reduced luminescence intensities and lifetime, but the nanoparticles can be dispersed in water and remain unchanged in this medium for more than 20 h.     

A Computational and Experimental Approach Linking Disorder,High‐Pressure Behavior,and Mechanical Properties in UiO Frameworks

Whilst many metal–organic frameworks possess the chemical stability needed to be used as functional materials, they often lack the physical strength required for industrial applications. Herein, we have investigated the mechanical properties of two UiO‐topology Zr‐MOFs, the planar UiO‐67 ([Zr₆O₄(OH)₄(bpdc)₆], bpdc: 4,4′‐biphenyl dicarboxylate) and UiO‐abdc ([Zr₆O₄(OH)₄(abdc)₆], abdc: 4,4′‐azobenzene dicarboxylate) by single‐crystal nanoindentation, high‐pressure X‐ray diffraction, density functional theory calculations, and first‐principles molecular dynamics. On increasing pressure, both UiO‐67 and UiO‐abdc were found to be incompressible when filled with methanol molecules within a diamond anvil cell. Stabilization in both cases is attributed to dynamical linker disorder. The diazo‐linker of UiO‐abdc possesses local site disorder, which, in conjunction with its longer nature, also decreases the capacity of the framework to compress and stabilizes it against direct compression, compared to UiO‐67, characterized by a large elastic modulus. The use of non‐linear linkers in the synthesis of UiO‐MOFs therefore creates MOFs that have more rigid mechanical properties over a larger pressure range.     

A Simple Primary Amide for the Selective Recovery of Gold from Secondary Resources

Waste electrical and electronic equipment (WEEE) such as mobile phones contains a plethora of metals of which gold is by far the most valuable. Herein a simple primary amide is described that achieves the selective separation of gold from a mixture of metals typically found in mobile phones by extraction into toluene from an aqueous HCl solution; unlike current processes, reverse phase transfer is achieved simply using water. Phase transfer occurs by dynamic assembly of protonated and neutral amides with [AuCl₄]^? ions through hydrogen bonding in the organic phase, as shown by EXAFS, mass spectrometry measurements, and computational calculations, and supported by distribution coefficient analysis. The fundamental chemical understanding gained herein should be integral to the development of metal‐recovery processes, in particular through the use of dynamic assembly processes to build complexity from simplicity.     

Monitoring ssDNA Binding to the DnaB Helicase from Helicobacter pylori by Solid‐State NMR Spectroscopy

DnaB helicases are bacterial, ATP‐driven enzymes that unwind double‐stranded DNA during DNA replication. Herein, we study the sequential binding of the “non‐hydrolysable” ATP analogue AMP‐PNP and of single‐stranded (ss) DNA to the dodecameric DnaB helicase from Helicobacter pylori using solid‐state NMR. Phosphorus cross‐polarization experiments monitor the binding of AMP‐PNP and DNA to the helicase. ¹³C chemical‐shift perturbations (CSPs) are used to detect conformational changes in the protein upon binding. The helicase switches upon AMP‐PNP addition into a conformation apt for ssDNA binding, and AMP‐PNP is hydrolyzed and released upon binding of ssDNA. Our study sheds light on the conformational changes which are triggered by the interaction with AMP‐PNP and are needed for ssDNA binding of H. pylori DnaB in vitro. They also demonstrate the level of detail solid‐state NMR can provide for the characterization of protein–DNA interactions and the interplay with ATP or its analogues.