CoI-Catalyzed Barbier Reactions of Aromatic Halides with Aromatic Aldehydes and Imines

The reductive Barbier coupling of aromatic halides and electrophiles has been achieved using a CoBr₂/1,10-phenanthroline catalytic system and over stoichiometric amounts of zinc. The reaction displayed a broad scope of substrates, including (hetero)aryl chlorides as pro-nucleophiles and aldehydes or imines as electrophiles, leading to diarylmethanols and diarylmethylamines in moderate to excellent yields, respectively.     

Tandem CH Activation/Arylation Catalyzed by Low‐Valent Iron Complexes with Bisiminopyridine Ligands

Tandem C?H activation/arylation between unactivated arenes and aryl halides catalyzed by iron complexes that bear redox‐active non‐innocent bisiminopyridine ligands is reported. Similar reactions catalyzed by first‐row transition metals have been shown to involve substrate‐based aryl radicals, whereas our catalytic system likely involves ligand‐centered radicals. Preliminary mechanistic investigations based on spectroscopic and reactivity studies, in conjunction with DFT calculations, led us to propose that the reaction could proceed through an inner‐sphere C?H activation pathway, which is rarely observed in the case of iron complexes. This bielectronic noble‐metal‐like behavior could be sustained by the redox‐active non‐innocent bisiminopyridine ligands.     

Effects of anionic additives on the rheological behavior of aqueous calcium montmorillonite suspensions

Three different experimental measurements, namely, rheology, particle sizing, and x-ray diffraction (XRD), were used to study the effect of anionic additives on the properties of bentonite suspensions. The three additives were sodium carboxymethylcellulose, xanthan gum, and sodium dodecyl sulfate. Flow curves were obtained from shear stress–shear rate measurements, and the viscoelastic properties were determined from oscillatory and transient measurements. Mineralogical data were evaluated by XRD and the particle size analysis performed by light scattering technique. The presence of the surfactant modifies the face-to-face interactions and yields changes of the mixtures rheological behavior at low deformation rates. Polymers act by coating each clay particle and prevent their agglomeration. Therefore, the additives are responsible for the mechanisms of destructuration and structure reorganization as well as the mixtures viscous and viscoelastic behavior.     

Differentiation of heterocyclic regioisomers: a combined tandem mass spectrometry and computational study of N-acridin-4-ylbenzylamide and N-acridin-2-yl-benzylamide

Electrospray ionization (ESI) tandem mass spectrometry (MS/MS) has been used to differentiate two positional isomers of acridine derivatives, N-acridin-4-ylbenzylamide and N-acridin-2-ylbenzylamide. The study revealed that the isomeric ion structures produced by these heterocycles could be distinguished upon collision-induced dissociations (CID). In particular, the loss of a water molecule was shown to be a regiospecific reaction of the protonated N-acridin-4-ylbenzylamide, in which the location of the benzylamide substituent with respect to the acridinic nitrogen greatly assists proton migration by allowing the creation of intramolecular hydrogen bonds. To a lesser extent, the two isomers could also be distinguished by the difference in the abundance of the benzoyl cation in the MS/MS spectra of the [M+H]+ ions, as this ion is produced with a much higher rate from N-acridin-4-ylbenzylamide. Calculations based on quantum-mechanical models have been performed to evaluate the stability of the ion structures and to support mechanisms proposed for these two dissociation reactions.     

Inclusion complexes of a nucleotide analogue with hydroxypropyl-beta-cyclodextrin

Bis(tbutyl-S-acyl-2-thioethyl)-AraCMP (UA911) is a mononucleotide prodrug developed to overcome some of the cellular resistance to cytotoxic deoxynucleosides analogues. Its use for in vivo studies is limited due to its poor solubility in water. Thus, 2-hydroxypropyl-beta-cyclodextrin (HP-β-CD) was proposed to solubilize UA911 in water, in order to obtain concentrations needed for in vivo experiments. A molar ratio of HP-β-CD: UA911 of 3:1 was sufficient to obtain complete solubilization of the prodrug. The corresponding inclusion complex was characterized by differential scanning calorimetry and ¹H NMR spectroscopy study provided a definitive proof of the formation of the inclusion complex. The complex retained its cytotoxic activity as shown by in vitro cell survival assays on murine leukemia cells, and was evaluated in vivo. HP-β-CD is therefore suitable for the preparation of adequate solutions for the study of the antitumoral activity of nucleotide prodrugs such as UA911.     

A model for vibrational properties of the atomic interface in A/B fcc metals

The motivation of this theoretical work is to introduce a model calculation for the elastic waves scattering and coherent phonon transport at an atomic nanojunction between face-centered cubic (fcc) leads. The model system A/B consists of two perfect semi-infinite fcc leads A and B, oriented in the same direction and joined by an atomic interface. It is applied to the system Cu/Ni and its inverse Ni/Cu. A theoretical approach based on the matching method is used to study the dynamics of the system A/B.     

Unsteady rheometry: can we characterize weak gels with a controlled stress rheometer?

This paper is concerned with the influence of apparatus inertia effects in controlled stress rheometry. As evidenced on creep experiments, the coexistence of apparatus inertia and viscoelasticity leads to a coupling frequency. For weak gels, this coupling frequency is typically between 1 and 100 Hz. Therefore, frequency sweeps around and above this coupling frequency also corresponds to an effective shear stress sweep evolution due to a non-trivial resonant effect. In other words, frequency sweep experiments are not made at constant shear stress. The detailed modelling and analysis of this inertia effect on a typical weak gel shows a clear and fundamental limitation for its characterization using a controlled stress rheometer. Also, alternative approaches to standard rheometer software analysis are proposed to take this coupling effect into account. This paper was presented at the 3rd Annual Rheology Conference, AERC 2006, April 27-29, 2006, Crete, Greece.     

Microstructural characterization and recrystallization kinetics of cold rolled copper

The recrystallization kinetics in pure copper deformed by cold rolling is mainly investigated by differential scanning calorimetry (DSC) under non-isothermal conditions. DSC curves show exothermic peaks corresponding to the stored energy released during recrystallization process. Variation of the heating rate and application of different methods allowed us to calculate two kinetic parameters of recrystallization: (i) the activation energy of the process was calculated using three different methods and (ii) the Avrami exponent was estimated using the Matusita method. On other hand, the microstructural evolution during recrystallization and grain growth of cold rolled copper were investigated at a temperature of 450 °C by scanning electron microscopy (SEM) and electron back scattered diffraction (EBSD).     

1H and 13C NMR signal assignments of some new N,N′‐diacyl proflavine derivatives

The complete ¹H and ¹³C NMR signal assignments of 23 new N,N′‐diacyl proflavine derivatives were achieved using one‐ and two‐dimensional experiments (DEPT, HMQC and HMBC). Copyright © 2009 John Wiley & Sons, Ltd.