Organometallic reactivity: the role of metal-ligand bond energies from a computational perspective

The association and dissociation of ligands plays a vital role in determining the reactivity of organometallic catalysts. Computational studies with density functional theory often fail to reproduce experimental metal-ligand bond energies, but recently functionals which better capture dispersion effects have been developed. Here we explore their application and discuss future challenges for computational studies of organometallic catalysis.     

Chiral palladacycles based on resorcinol monophosphite ligands: the role of the meta-hydroxyl in ligand C-H activation and catalysis

The reactions of a range of chiral resorcinol monophosphite ligands with [PdCl(2)(NCMe)(2)] was investigated in order to establish whether the meta-hydroxyl function was involved in the orthometallation processes. These ligands underwent facile orthopalladation at room temperature in the presence of Et(3)N, whilst the equivalent hydroxyl-free analogues needed more forcing conditions to induce orthometallation. When the hydroxyl function was replaced by a similar sized methyl group no orthometallation occurred, even on heating. Furthermore the hydroxyl group influences both the structure and isomerism in the resultant palladacycles via hydrogen bonding to adjacent chloride ligands. Similarly, the hydroxyl function leads to higher enantiocontrol in the asymmetric allylation of benzaldehyde with allyl tributyltin. Representative examples of the ligands and the palladium complexes obtained were characterised by single crystal X-ray diffraction.     

Tuning ligand structure in chiral bis(phosphite) and mixed phosphite-phosphinite PCP-palladium pincer complexes

A range of chiral resorcinol bis(phosphite) and phosphite-phosphinite ligands were produced and their propensity to form palladium PCP-pincer complexes examined. The ease of base-assisted C-H palladation of the ligands falls in the order bis(phosphinite) > phosphite-phosphinite > bis(phosphite). The catalytic activity of the complexes in the asymmetric allylation of benzaldehyde with allyl tributyltin was examined and it was found that, contrary to expectations, ligands with 3,3'-disubstituted BINOL residues show poorer activity and stereoselectivity than unsubstituted BINOL analogues. In addition the order of activity of the pincer complexes was established as bis(phosphite) > phosphite-phosphinite > bis(phosphinite). Crystal structures of representative examples of a 3,3'-disubstituted BINOL, mono- and bis(phosphite) ligands based on 2,4-di-tert-butyl resorcinol and Pd complexes of two of the chiral complexes are presented.     

Tissue-Specific stem cell differentiation in an in vitro airway model

The respiratory tract is the primary site of exposure to airborne compounds, with the bronchial epithelium providing one of the first lines of defence. A growing need exists for an accurate in vitro model of the bronchial epithelium. Here, normal human bronchial epithelial (NHBE) cells cultured at an air/liquid interface create a fully differentiated, in-vivo-like model of the human bronchial epithelium. Developmental characterisation includes (i) trans-epithelial electrical resistance, (ii) morphology and (iii) bronchial cell specific stains/markers. It is concluded that the basal/progenitor cells create a pseudo-stratified, mucociliary NHBE model containing basal, serous, Clara, goblet and ciliated cells, reflective of the normal human bronchial epithelium (days 24-33 ALI culture).     

Structural Stability of Discontinuous Galerkin Schemes

The goal of this work is to determine classes of traveling solitary wave solutions for a differential approximation of a discontinuous Galerkin finite difference scheme by means of an hyperbolic ansatz. It is shown that spurious solitary waves can occur in finite-difference solutions of nonlinear wave equation. The occurence of such a spurious solitary wave, which exhibits a very long life time, results in a non-vanishing numerical error for arbitrary time in unbounded numerical domain. Such a behavior is referred here to have a structural instability of the scheme, since the space of solutions spanned by the numerical scheme encompasses types of solutions (solitary waves in the present case) that are not solutions of the original continuous equations. This paper extends our previous work about classical schemes to discontinuous Galerkin schemes (David and Sagaut in Chaos Solitons Fractals 41(4):2193?C2199, 2009; Chaos Solitons Fractals 41(2):655?C660, 2009).     

A finite‐volume scheme for the multidimensional quantum drift‐diffusion model for semiconductors

A finite‐volume scheme for the stationary unipolar quantum drift‐diffusion equations for semiconductors in several space dimensions is analyzed. The model consists of a fourth‐order elliptic equation for the electron density, coupled to the Poisson equation for the electrostatic potential, with mixed Dirichlet‐Neumann boundary conditions. The numerical scheme is based on a Scharfetter‐Gummel type reformulation of the equations. The existence of a sequence of solutions to the discrete problem and its numerical convergence to a solution to the continuous model are shown. Moreover, some numerical examples in two space dimensions are presented. © 2010 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 27: 1483–1510, 2011     

Investigation of the interface in silica-encapsulated liposomes by combining solid state NMR and first principles calculations

In the context of nanomedicine, liposils (liposomes and silica) have a strong potential for drug storage and release schemes: such materials combine the intrinsic properties of liposome (encapsulation) and silica (increased rigidity, protective coating, pH degradability). In this work, an original approach combining solid state NMR, molecular dynamics, first principles geometry optimization, and NMR parameters calculation allows the building of a precise representation of the organic/inorganic interface in liposils. {(1)H-(29)Si}(1)H and {(1)H-(31)P}(1)H Double Cross-Polarization (CP) MAS NMR experiments were implemented in order to explore the proton chemical environments around the silica and the phospholipids, respectively. Using VASP (Vienna Ab Initio Simulation Package), DFT calculations including molecular dynamics, and geometry optimization lead to the determination of energetically favorable configurations of a DPPC (dipalmitoylphosphatidylcholine) headgroup adsorbed onto a hydroxylated silica surface that corresponds to a realistic model of an amorphous silica slab. These data combined with first principles NMR parameters calculations by GIPAW (Gauge Included Projected Augmented Wave) show that the phosphate moieties are not directly interacting with silanols. The stabilization of the interface is achieved through the presence of water molecules located in-between the head groups of the phospholipids and the silica surface forming an interfacial H-bonded water layer. A detailed study of the (31)P chemical shift anisotropy (CSA) parameters allows us to interpret the local dynamics of DPPC in liposils. Finally, the VASP/solid state NMR/GIPAW combined approach can be extended to a large variety of organic-inorganic hybrid interfaces.     

OH�� Radical Production Induces Direct Enhancement of the Amylo?d �� Protein/Chondroitin Sulfate Binding: Inhibition by Potentially Radical Scavengers, a Biochromatographic and Thermodynamic Model

??-Amyloid (A??) is a major component of the senile plaques characteristic of Alzheimer disease (AD). Chondroitin sulfate (CS) and glycoaminoglycan (GAG) are also localized throughout the senile plaques in AD. In previous studies, the interaction of the A?? protein with CS immobilized on a chromatographic support and the role of aluminum and copper cations was studied using a molecular chromatographic approach [1, 2]. Here, we demonstrated the direct implication of OH· radical formation on this binding via a novel analytical procedure. The binding of A?? amyloid on CS was accompanied by an OH· radical uptake. The A?¨CCS complex was stabilized by the OH· radical via the creation of about one to two hydrogen bonds. The addition in the medium of a radical scavenger allowed decreasing the A??/CS association and thus confirmed the positive role of these compounds in amyloidosis.     

New Triterpenoid and Ergostane Glycosides from the Leaves of Hydrocotyle umbellata L.

Two new triterpenoid glycosides, together with two new ergostane glycosides, umbellatosides A–D ( 1 – 4 , resp.), have been isolated from the leaves of Hydrocotyle umbellata L. Their structures were established by 2D‐NMR spectroscopic techniques (¹H,¹H‐COSY, TOCSY, NOESY, HSQC, and HMBC) and mass spectrometry as 3β,22β‐dihydroxy‐3‐O‐[α‐L ‐rhamnopyranosyl‐(1→2)‐β‐D ‐glucuronopyranosyl]olean‐12‐en‐28‐oic acid 28‐O‐β‐D ‐glucopyranosyl ester ( 1 ), 3‐O‐[α‐L ‐rhamnopyranosyl‐(1→2)‐β‐D ‐glucuronopyranosyl]oleanolic acid 28‐O‐β‐D ‐glucopyranosyl ester ( 2 ), (3β,11α,26)‐ergosta‐5,24(28)‐diene‐3,11,26‐triol 3‐O‐(β‐D ‐glucopyranosyl)‐11‐O‐(α‐L ‐rhamnopyranosyl)‐26‐O‐β‐D ‐glucopyranoside ( 3 ), and (3β,11α,21,26)‐ergosta‐5,24(28)‐diene‐3,11,21,26‐tetrol 3‐O‐(β‐D ‐glucopyranosyl)‐11‐O‐(α‐L ‐rhamnopyranosyl)‐26‐O‐β‐D ‐glucopyranoside ( 4 ).     

Aerosol-assisted self-assembly of hybrid Layered Double Hydroxide particles into spherical architectures

Over the last decade, the use of nanocellulose in advanced technological applications has been promoted both due the excellent properties of this material in combination with its renewability. In this study, multilayered thin films composed of nanofibrillated cellulose (NFC), polyvinyl amine (PVAm) and silica nanoparticles were fabricated on polydimethylsiloxane (PDMS) using a layer-by-layer adsorption technique. The multilayer build-up was followed in situ by quartz crystal microbalance with dissipation, which indicated that the PVAm-SiO(2)-PVAm-NFC system adsorbs twice as much wet mass material compared to the PVAm-NFC system for the same number of bilayers. This is accompanied with a higher viscoelasticity for the PVAm-SiO(2)-PVAm-NFC system. Ellipsometry indicated a dry-state thickness of 2.2 and 3.4 nm per bilayer for the PVAm-NFC system and the PVAm-SiO(2)-PVAm-NFC system, respectively. Atomic force microscopy height images indicate that in both systems, a porous network structure is achieved. Young's modulus of these thin films was determined by the Strain-Induced Elastic Buckling Instability for Mechanical Measurements (SIEBIMM) technique. The Young's modulus of the PVAm/NFC films was doubled, from 1 to 2 GPa, upon incorporation of silica nanoparticles in the films. The introduction of the silica nanoparticles lowered the refractive index of the films, most probably due to an increased porosity of the films.