Foam films in the presence of functionalized gold nanoparticles

Dry aqueous foams made of anionic surfactant (SDS) and spherical gold nanoparticles are studied by small angle X-ray scattering and by optical techniques. To obtain stable foams, the surfactant concentration is well above the critical micelle concentration. The specular reflectivity signal obtained on a very thin film (thickness 20 nm) shows that functionalized nanoparticles (17 nm typical size) are trapped within the film in the form of a single monolayer. In order to isolate the film behavior, investigations are made on a single film confined in a tube. The film thinning according to the ratio of functionalized nanoparticle and SDS micelles (1:1, 1:10, 1:100) is mainly governed by the structural arrangement of SDS micelles. In thick films, nanoparticles tend to form aggregates that disappear during drainage. In particular self-organization of nanoparticles (with different surface charge) inside the film is not detected.     

Ultrafast fluorescence studies of dye sensitized solar cells

Time-resolved fluorescence spectra from the RuN719 dye exhibit very short lifetimes (<30 fs) in solutions, on non-injecting substrates and on injecting ones. This reveals <10 fs intramolecular energy redistribution competing with the injection. We conclude that injection proceeds on a sub-10 fs time scale from non-thermalized levels of the dye.     

Hexanuclear copper(II) cages built on a central {μ3-O···H···μ3-O} moiety, 1,3-bis(dimethylamino)-2-propanolato and capping R-phosphonates: crystal structures, magnetic behavior, and DFT studies

The syntheses, structural characterization, and magnetic behavior of two new hexanuclear copper(II) complexes derived from R-phosphonic acids and 1,3-bis(dimethylamino)-2-propanol (Hbdmap) with formulas [Cu(6)(μ-bdmap)(3)(μ(3)-Ph-PO(3))(2)(μ(3)-O···H···μ(3)-O)(ClO(4))(2)(H(2)O)]·5H(2)O (1) and [Cu(6)(μ-bdmap)(3)(μ(3)-t-Bu-PO(3))(2)(μ(3)-O···H···μ(3)-O)(μ(1,3)-dca)(dca)(H(2)O)]·6H(2)O (2) (Ph-H(2)PO(3) = phenylphosphonic acid, t-Bu-H(2)PO(3) = tert-butylphosphonic acid, dca = dicyanamide) are reported. Compounds 1 and 2 are hexanuclear 3.111 R-phosphonate(2-)/1,3-bis(dimethylamino)-2-propanolato(1-) cages including in the center the [μ(3)-O···H···μ(3)-O](3-) unit. The temperature dependence of the magnetic properties of 1 and 2 clearly indicates an overall strong antiferromagnetic coupling confirmed by DFT calculations.     

Aggregation of [Cu(II)4] building blocks into [Cu(II)8] clusters or a [Cu(II)4]infinity chain through subtle chemical control

Coordination complexes of the ligand H3L [1,3-bis(3-oxo-3-phenylpropionyl)-2-hydroxy-5-methylbenzene] with Cu(II) are reported. Clusters showing various nuclearities or modes of supramolecular organization have been prepared by slightly changing the reaction conditions and have been crystallographically characterized. The reaction of H3L with one equivalent of Cu(OAc)2 in DMF yields the dinuclear complex [Cu2(HL)2(dmf)2] (1). Reaction in MeOH of H3L with an increased amount of metal, in the form of Cu(NO3)2, and excess strong base (nBu4NOH) affords the cluster [Cu8(L)2(OMe)8(NO3)2] (2). Complex 2 is a dimer of two linear [Cu4] arrays bridged by methoxide ligands, where the polynucleating ligand is fully deprotonated. The [Cu4]2 clusters are linked to each other by NO3- bridges to form one-dimensional coordination polymers. The link between [Cu8] units and their relative spatial positioning can be modified by changing the anion of the Cu(II) salt, as demonstrated by the synthesis of the cluster polymers [Cu8(L)2(OMe)8Cl2] (3) and [Cu8(L)(OMe)7.86Br2.14] (4), where only NO3- has been replaced by Cl- or Br-, respectively. Similarly, when ClO4- is used, compound [Cu8(L)2(OMe)8(ClO4)2(MeOH)4] (5) can be isolated. It contains independent [Cu8] units. A slight change in the stoichiometry of the reaction leading to 2 affords the related complex catena-[Cu4(L)(OMe)3(NO3)2(H2O)0.36] (6). This polymer contains essentially the same [Cu4] moiety as 2, albeit organized in a completely different arrangement. Each [Cu4] unit in 6 is linked by OMe- ligands to two such equivalent groups to form an infinite chain. Magnetic susceptibility measurements reveal weak antiferromagnetic exchange between Cu(II) centers in 1 (J = -0.73 cm(-1)) and strong antiferromagnetic coupling within [Cu4] chains in 2, 5, and 6 (most negative J values of -113.8 and -177.3 cm(-1) for 2 and 6, respectively).     

About diastereoselective oxidations of ferrocenyl amino alcohols

Oxidation of some 2-(N,N-dimethylaminomethyl)ferrocenylalkylcarbinols by MnO₂ is totally diastereoselective: only one diastereomer is oxidized. A study was performed to highlight the influential factors of this phenomenon. Several ferrocenyl alcohols have been studied. First, two diastereomers of the ferrocenyl amino alcohol bearing a deuterium as an R group have been synthesized and oxidized. The good reactivity of both diastereomers displayed the importance of the size of the alkyl group, which needs to be bulkier than a deuterium. The synthesis and the oxidation of endo- and exo-α-hydroxy [4](1,2)ferrocenophane enabled the elimination of the hypothesis involving the spatial position of the hydroxy group, while the two diastereomers were oxidized. The replacement of the dimethylamino group by a methoxy or a methyl, the oxidation of these compounds, and the study of the preferential conformation of each diastereomer showed clearly the influence of an intramolecular hydrogen bond. So,the diastereoselectivity was shown to depend on the steric bulk of the alkyl group and on the presence of a strong intramolecular hydrogen bond between the hydroxy group and the nitrogen.     

Designed Topology and Site‐Selective Metal Composition in Tetranuclear [MM′⋅⋅⋅M′M] Linear Complexes

The ligand 1,3‐bis[3‐oxo‐3‐(2‐hydroxyphenyl)propionyl]benzene (H₄L), designed to align transition metals into tetranuclear linear molecules, reacts with M^II salts (M=Ni, Co, Cu) to yield complexes with the expected [MM???MM] topology. The novel complexes [Co₄L₂(py)₆] ( 2 ; py=pyridine) and [Na(py)₂][Cu₄L₂(py)₄](ClO₄) ( 3 ) have been crystallographically characterised. The metal sites in complexes 2 and 3 , together with previously characterised [Ni₄L₂(py)₆] ( 1 ), favour different coordination geometries. These have been exploited for the deliberate synthesis of the heterometallic complex [Cu₂Ni₂L₂(py)₆] ( 4 ). Complexes 1 , 2 , 3 and 4 exhibit antiferromagnetic interactions between pairs of metals within each cluster, leading to S=0 spin ground states, except for the latter cluster, which features two quasi‐independent S=1/2 moieties within the molecule. Complex 4 gathers the structural and physical conditions, thus allowing it to be considered as prototype of a two‐qbit quantum gate.     

Ferromagnetic versus antiferromagnetic exchange interactions in tetrathiafulvalene-based 3d/4f heterobimetallic complexes

(TTF-salphen)M compounds (TTF-salphen(2-)=4,5-bis(propylthio)tetrathiafulvalene-N,N'-phenylenebis(salicylideneimine) dianion; M=Cu(II) and Ni(II)) have been treated with Ln(hfac)(3)·2H(2)O precursors (hfac(-)=1,1,1,5,5,5-hexafluoroacetylacetonate anion; Ln=Gd(III), Tb(III), and Dy(III)) to elaborate unprecedented 3d/4f TTF-based heterobimetallic complexes of formula [(TTF-salphen)MLn(hfac)(3)]. All the structures of these compounds have been resolved by X-ray diffraction on single crystals. The structures of these complexes are formed by a TTF-salphen(2-) ligand coordinated to the 3d metal ions in the inert tetradentate N(2)O(2) site. The Ln(hfac)(3) fragment is coordinated to the (TTF-salphen)M one through the two phenolate bridges. Even if the complexes are similar in both Cu(II) and Ni(II) families, the crystal packing is different. In the first case, dimers of TTF-salphen(2-) donors constitute the organic network. In the other case, a reminiscent organic network is observed with S···S contacts. The photophysical properties of [(TTF-salphen)CuDy(hfac)(3)] (3) in chloroform solution highlight the redshift of the TTF→salphen charge transfer (400 cm(-1)) relative to the analogue excitations in (TTF-salphen)Cu, which attest to the stability of these structures in solution. Static magnetic measurements have allowed us to quantify the ferromagnetic interactions (J=+1.29 cm(-1)) between Cu(II) and Gd(III) in the [(TTF-salphen)CuGd(hfac)(3)] complex. Finally, an empirical method that consists of the comparisons of the magnetic properties of [(TTF-salphen)CuTb(hfac)(3)] with [(TTF-salphen)NiTb(hfac)(3)] and [(TTF-salphen)CuDy(hfac)(3)] with [(TTF-salphen)NiDy(hfac)(3)] has established that ferromagnetic interactions take place between Cu(II) and Tb(III) ions, whereas unusual antiferromagnetic interactions have been identified between Cu(II) and Dy(III) ions.     

Violet-to-blue tunable emission of aryl-substituted dispirofluorene-indenofluorene isomers by conformationally-controllable intramolecular excimer formation

Two series of DiSpiroFluorene-IndenoFluorene (DSF-IF) positional isomers, namely dispiro[2,7-diarylfluorene-9',6,9',12-indeno[1,2-b]fluorenes], (1,2-b)-DSF-IFs 1 and dispiro[2,7-diarylfluorene-9',6,9',12-indeno[2,1-a]fluorenes], (2,1-a)-DSF-IFs 2 have been synthesized. These violet-to-blue fluorescent emitters possess a 3π-2spiro architecture, which combines via two spiro links two different indenofluorene cores, that is, (1,2-b)-IF or (2,1-a)-IF and 2,7-substituted-diaryl-fluorene units. Due to their different geometric profiles, the two families of positional isomers present drastically different properties. The marked difference observed between the properties of (1,2-b)-DSF-IF (1) and (2,1-a)-DSF-IF (2) is discussed in terms of intramolecular π-π interactions occurring in (2,1-a)-DSF-IF (2) leading to conformationally-controllable intramolecular excimer formation. Indeed, the original geometry of the (2,1-a)-DSF-IF (2) family, with face-to-face "aryl-fluorene-aryl" moieties, leads to remarkable excimer emission through intramolecular π-π interactions in the excited state. Furthermore, the emission wavelengths can be gradually modulated by the control of the steric hindrance between the adjacent substituted phenyl rings. Thus, through a comparative and detailed study of the (1)H NMR, electrochemical and photophysical properties of DSF-IFs 1 and 2, we have evidenced the intramolecular π-π interactions occurring between the two "aryl-fluorene-aryl" moieties in the ground state and in the excited state. These properties have been finally correlated to the spectacular conformational change modeled by density functional theory (DFT) calculations. Indeed, the two "aryl-fluorene-aryl" moieties switch from a staggered conformation in the ground state to an eclipsed conformation in the first excited state.     

Oxidation of Zn(Cys)4 zinc finger peptides by O2 and H2O2: products, mechanism and kinetics

The reactivity of a series of Zn(Cys)(4) zinc finger model peptides towards H(2)O(2) and O(2) has been investigated. The oxidation products were identified by HPLC and ESI-MS analysis. At pH<7.5, the zinc complexes and the free peptides are oxidised to bis-disulfide-containing peptides. Above pH 7.5, the oxidation of the zinc complexes by H(2)O(2) also yields sulfinate- and sulfonate-containing overoxidised peptides. At pH 7.0, monitoring of the reactions between the zinc complexes and H(2)O(2) by HPLC revealed the sequential formation of two disulfides. Several techniques for the determination of the rate constant for the first oxidation step corresponding to the attack of H(2)O(2) by the Zn(Cys)(4) site have been compared. This rate constant can be reliably determined by monitoring the oxidation by HPLC, fluorescence, circular dichroism or absorption spectroscopy in the presence of excess ethyleneglycol bis(2-aminoethyl ether)tetraacetic acid. In contrast, monitoring of the release of zinc with 4-(2-pyridylazo)resorcinol or of the thiol content with 5,5'-dithiobis(2-nitrobenzoate) did not yield reliable values of this rate constant for the case in which the formation of the second disulfide is slower than the formation of the first. The kinetic measurements clearly evidence a protective effect of zinc on the oxidation of the cysteines by both H(2)O(2) and O(2), which points to the fact that zinc binding diminishes the nucleophilicity of the thiolates. In addition, the reaction between the zinc finger and H(2)O(2) is too slow to consider zinc fingers as potential sensors for H(2)O(2) in cells.     

Annelated Pyridines as Highly Nucleophilic and Lewis Basic Catalysts for Acylation Reactions

New heterocyclic derivatives of 9‐azajulolidine have been synthesized and characterized with respect to their nucleophilicity and Lewis basicity. The Lewis basicity of these bases as quantified through their theoretically calculated methyl‐cation affinities correlate well with the experimentally measured reaction rates for addition to benzhydryl cations. All newly synthesized pyridines show exceptional catalytic activities in benchmark acylation reactions, which correlate only poorly with Lewis basicity or nucleophilicity parameters. A combination of Lewis basicity with charge and geometric parameters in the framework of a three‐component quantitative structure–activity relationship (QSAR) model is, however, highly predictive.