Pluronics‐Stabilized Gold Nanoparticles: Investigation of the Structure of the Polymer–Particle Hybrid

Hybrid gold–polymer nanoparticles are obtained by self‐assembly of amphiphilic copolymers (Pluronics) in solutions containing preformed gold nanoparticles (diameter ca. 12 nm). Dynamic light scattering, TEM, cryo‐TEM, and small‐angle neutron scattering experiments with contrast variation are used to characterize the structure of the gold–polymer particles. Five Pluronics (F127, F68, F88, F108, P84) with different molecular weights and hydrophilic/hydrophobic balances are investigated. Gold nanoparticles are individually embedded within globules of polymer, even under conditions for which Pluronics micelles do not form in solution. The hybrid particles are several tens of nanometers in size (larger than micelles of the corresponding Pluronics), and the size can be tuned by changing the temperature.     

Solvation of Co(III)-cysteinato complexes in water: a DFT-based molecular dynamics study

Structural, dynamical, and vibrational properties of complexes made of metal cobalt(III) coordinated to different amounts of cysteine molecules were investigated with DFT-based Car-Parrinello molecular dynamics (CPMD) simulations in liquid water solution. The systems are composed of Co(III):3Cys and Co(III):2Cys immersed in liquid water which are modeled by about 110 explicit water molecules, thus one of the biggest molecular systems studied with ab initio molecular simulations so far. In such a way, we were able to investigate structural and dynamical properties of a model of a typical metal binding site used by several proteins. Cobalt, mainly a toxicological agent, can replace the natural binding metal and thus modify the biochemical activity. The structure of the surrounding solvent around the metal-ligands complexes is reported in detail, as well as the metal-ligands coordination bonds, using radial distribution functions and electronic analyses with Mayer bond orders. Structures of the Cocysteine complexes are found in very good agreement with EXAFS experimental data, stressing the importance of considering the surrounding solvent in the modeling. A vibrational analysis is also conducted and compared to experiment, which strengthens the reliability of the solvent interactions with the Cocysteine complexes from our molecular dynamics simulations, as well as the dynamics of the systems. From this preliminary analysis, we could suggest a vibrational fingerprint able to distinguish Co(III):2Cys from Co(III):3Cys. Our simulations also show the importance of considering a quantum explicit solvent, as solute-to-solvent proton transfer events have been observed.     

Ruthenium-SYNPHOS-catalyzed asymmetric hydrogenations: an entry to highly stereoselective synthesis of the C15-C30 subunit of dolabelide A

An efficient construction of the C15-C30 segment of the cytotoxic macrolide dolabelide A is described. The synthesis relies on ruthenium-SYNPHOS-mediated asymmetric hydrogenation reactions of beta-keto esters to generate the C19, C21, and C27 hydroxyl-bearing stereocenters with very high levels of enantio- and diastereoselectivity.     

Synthesis of 2-Azanorbornanes via Strain-Release Formal Cycloadditions Initiated by Energy Transfer

Rigid bicycles are becoming more popular in the pharmaceutical industry because they allow for expansion to new and unique chemical spaces. This work describes a new strategy to construct 2-azanorbornanes, which can act as rigid piperidine/pyrrolidine scaffolds with well-defined exit vectors. To achieve the synthesis of 2-azanorbornanes, new strain-release reagent, azahousane, is introduced along with its photosensitized strain-release formal cycloaddition with alkenes. Furthermore, new reactivity between a housane and an imine is disclosed. Both strategies lead to various substituted 2-azanorbornanes with good selectivities.     

Photodetachment of Deprotonated R-Mandelic Acid: The Role of Proton Delocalization on the Radical Stability

The photodetachment and stability of R-Mandelate, the deprotonated form of the R-Mandelic acid, was investigated by observing the neutral species issued from either simple photodetachment or dissociative photodetachment in a cold anions set-up. R-Mandalate has the possibility to form an intramolecular ionic hydrogen-bond between adjacent hydroxyl and carboxylate groups. The potential energy surface along the proton transfer (PT) coordinate between both groups (O⁻…H⁺…⁻OCO) features a single local minima, with the proton localized on the O⁻ group (OH…⁻OCO). However, the structure with the proton localized on the ⁻OCO group (O⁻…HOCO) is also observed because it falls within the extremity of the vibrational wavefunction of the OH…⁻OCO isomer along the PT coordinate. The stability of the corresponding radicals, produced upon photodetachment, is strongly dependent on the position of the proton in the anion: the radicals produced from the OH…⁻OCO isomer decarboxylate without barrier, while the radicals produced from the O⁻…HOCO isomer are stable.     

Stoichiometries and thermodynamic stabilities for aqueous sulfate complexes of U(VI)

The formation constants of UO2SO4 (aq), UO2(SO4)2(2-), and UO2(SO4)3(4-) were measured in aqueous solutions from 10 to 75 degrees C by time-resolved laser-induced fluorescence spectroscopy (TRLFS). A constant enthalpy of reaction approach was satisfactorily used to fit the thermodynamic parameters of stepwise complex formation reactions in a 0.1 M Na(+) ionic medium: log 10 K 1(25 degrees C) = 2.45 +/- 0.05, Delta r H1 = 29.1 +/- 4.0 kJ x mol(-1), log10 K2(25 degrees C) = 1.03 +/- 0.04, and Delta r H2 = 16.6 +/- 4.5 kJ x mol(-1). While the enthalpy of the UO2(SO4)2(2-) formation reaction is in good agreement with calorimetric data, that for UO2SO4 (aq) is higher than other values by a few kilojoules per mole. Incomplete knowledge of the speciation may have led to an underestimation of Delta r H1 in previous calorimetric studies. In fact, one of the published calorimetric determinations of Delta r H1 is here supported by the TRLFS results only when reinterpreted with a more correct equilibrium constant value, which shifts the fitted Delta r H1 value up by 9 kJ x mol(-1). UO2(SO 4) 3 (4-) was evidenced in a 3 M Na (+) ionic medium: log10 K3(25 degrees C) = 0.76 +/- 0.20 and Delta r H3 = 11 +/- 8 kJ x mol(-1) were obtained. The fluorescence features of the sulfate complexes were observed to depend on the ionic conditions. Changes in the coordination mode (mono- and bidentate) of the sulfate ligands may explain these observations, in line with recent structural data.     

Acid-base-driven interconversion between a mononuclear complex and supramolecular coordination polymers in a terpyridine-functionalized dioxocyclam ligand

A polytopic cyclam-bis-terpyridine ligand has been used to accomplish an acid-base-triggered formation of either a mononuclear neutral complex or metallopolymers with Cu(2+) ions. A controlled interconversion between these two forms was achieved through the reversible displacement of a Cu(2+) cation from the macrocycle to the terpyridine units.     

Solvation of UCl6(2-) anionic complex by MeBu3N(+), BuMe2Im(+), and BuMeIm(+) cations

The complexes [MeBu 3N] 2[UCl 6] and [BuMe 2Im] 2[UCl 6] were characterized in the solid state and in solution of [MeBu 3N][Tf 2N], [BuMe 2Im][Tf 2N], and [BuMeIm][Tf 2N] room-temperature ionic liquids using single-crystal XRD, EXAFS, electrochemistry, UV-visible absorption spectroscopy, and NMR. In the solid state and in solution, the existence of hydrogen bonding between the UCl 6 (2-) complex and the ionic liquid cations was revealed by these techniques. The MeBu 3N (+) cation interacts with UCl 6 (2-) via the protons on the alpha-carbon atoms of nitrogen. The protons of the imidazolium ring account for the interaction between the BuMe 2Im (+) cation and the UCl 6 (2-) anion. For the BuMeIm (+) cation the major interaction was confirmed between the most acidic proton on C(2) and the chlorides of UCl 6 (2-). The experimental results also show that the intensity of the interaction between the UCl 6 (2-) anion and the cation varies with the ionic liquid cation in the following order: MeBu 3N (+) approximately BuMe 2Im (+) < BuMeIm (+).     

Nickel(II) chain with alternating end-on/end-to-end single azido bridges: a combined structural, magnetic, and theoretical study

The reaction of a tridentate Schiff base LH (L-: 1,1,1-trifluoro-7-(dimethylamino)-4-methyl-5-aza-3-hepten-2-onato) with a Ni(II) salt in the presence of azide salt has led to a new alternating end-on (EO)/end-to-end (EE) azido-bridged Ni(II) chain of formula {[Ni2(micro1,1-N3)(micro1,3-N3)(L)2(MeOH)2]}n. Its originality lies in the presence of single EE and EO coordination modes for the azide. It crystallizes in the C2/c space group, a=21.570(7) A, b=10.79(1) A, c=16.154(5) A, beta=120.81(2) degrees, Z=4. The chain can be viewed as {Ni2(N3)(L)2(MeOH)2}+ dimeric units linked to each other in a zigzag pattern by the other azide. Magnetic susceptibility and magnetization measurements have been performed and revealed that the chain can magnetically be depicted as isolated {Ni2(N3)} units exhibiting antiferromagnetic interaction (JAF approximately -37 cm(-1)). Ab initio calculations confirmed the efficient magnetic coupling through the EE bridge and vanishingly small EO {Ni2(micro1,1-N3)} interactions.     

Hyperbranched polyamidoamine as stabilizer for catalytically active nanoparticles in water

Poly(amidoamine) hyperbranched polymers (HYPAM) were successfully used to synthesize platinum nanoparticles of ca. 1.8 nm and to stabilize these particles in water. Furthermore these hyperbranched-stabilized platinum nanoparticles proved to be effective and robust for hydrogenation reaction in water.