Search results for "molecule"

Theoretical characterization of iron and manganese porphyrins for catalyzed saturated alkane hydroxylations

1997

Abstract The theoretical characterization of porphin (H2Por), iron and manganese porphyrins MIII(Por) and their chlorine derivatives MIII(Por)Cl has been carried out. This work represents a first step for modelling catalyzed saturated alkane hydroxylations. The chlorine atom is responsible for the existence of a dipole moment of 1.2–2.0 D in the MIII(Por)Cl molecules and for a negative value of the mean quadrupole moment (−16–(−14)DA). The charge of the metal atom (1.8–2.2 e) is rather varied (to 2.1–2.6 e) and the effective polarizability (2.8–2.9 A3) is increased (to 3.5–3.6 A3) by the addition of the chlorine atom. Starting from the porphin molecule, the presence of the metal atom decrea…

Linear chain surfactants at a planar interface: a comparative Monte Carlo study of several lattice models

1993

Linear chain surfactants in a densely packed arrangement (such as alkane chains in lipid monolayers in the “uniform tilt” structures) are described by a crude coarse-grained model where the endgroups grafted on the interface form a regular lattice and the chains are described by the bond fluctuation model with chains containing N = 4 effective monomers only. Square-well interactions between the monomers are studied for both the attractive and repulsive case for three choices of the interaction range. None of these models exhibits a structure with uniform tilt. For attractive interactions the last bond has a strong tendency to fold back thus leading to a very high density close to the interf…

1988

Deviations in the determination of the unperturbed dimensions of polymers arising in ternary polymer systems (solvent (1)/solvent (2)/polymer) can be explained by the inaccurate use of an interaction parameter independent of polymer molecular weight. On this basis, a new formalism for the calculation of the second virial coefficient from intrinsic viscosity is proposed. This formalism was tested (and compared with well established formalisms) for all ternary polymer systems with simultaneous intrinsic viscosity and second virial coefficient data in the literature.

Functionalization of CnH2n+2Alkanes: Supercritical Carbon Dioxide Enhances the Reactivity towards Primary Carbon-Hydrogen Bonds

2015

The functionalization of the primary sites of alkanes is one of the more challenging areas in catalysis. In this context, a novel effect has been discovered that is responsible for an enhancement in the reactivity of the primary C-H bonds of alkanes in a catalytic system. The copper complex Cu(NCMe) (=hydrotris{[3,5-bis(trifluoromethyl)-4-bromo]-pyrazol-1-yl}borate) catalyzes the functionalization of CnH2n+2 with ethyl diazoacetate upon inserting the CHCO2Et unit into C-H bonds. In addition, the selectivity of the reaction toward the primary sites significantly increased relative to that obtained in neat alkane upon using supercritical carbon dioxide as the reaction medium. This was attribu…

Bis(3,5-dimethylpyrazol-1-ato) zirconium complexes as precursors for ethylene polymerisation upon activation with MAO: Syntheses, characterisation an…

2007

Abstract The bis(3,5-dimethylpyrazol-1-ato) zirconium complex [Zr(η2-3,5-Me2Pz)2(NMe2)2(NHMe2)2] (2) is obtained by treatment of [Zr(NMe2)4] with 2 equiv. of 3,5-dimethylpyrazole 1. The reaction of the [ZrCl4(THF)2] adduct with 2 equiv. of the potassium salt of 1 affords the dichloro derivative [Zr(η2-3,5-Me2Pz)2Cl2]n (3), while reaction with 4.1 equiv. of 1 in the presence of 2.1 equiv. of NEt3 affords the dichloro pyrazole adduct [Zr(η2-3,5-Me2Pz)2Cl2(η1-3,5-Me2PzH)2] (4). Treatment of [Zr(CH2Ph)4] with 2 equiv. of 1 gives the dibenzyl complex [Zr(η2-3,5-Me2Pz)2(CH2Ph)2] (5) via alkane elimination. Compound 4 presents fluxional behaviour in CDCl3 solution, which was studied and quantified…

Supramolecular Aggregates in Vacuum: Positively Mono-Charged Sodium Alkanesulfonate Clusters

2010

The formation and structural features of positively mono-charged aggregates of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and sodium methane—(MetS), butane—(ButS) and octane—(OctS) sulfonate molecules in the gas phase have been investigated by electrospray ionization mass spectrometry, energy-resolved mass spectrometry and density functional theory (DFT) calculations. The experimental results show that the center-of-mass collision energy required to dissociate 50% of these mono-charged aggregates scantly depends on the length of the alkyl chain as well as on the aggregation number. This, together with the large predominance of mono-charged species in the mass spectra, was rationalized i…

A Highly Active System for the Metal-Free Aerobic Photocyanation of Tertiary Amines with Visible Light: Application to the Synthesis of Tetraponerine…

2015

A highly efficient metal-free catalytic system for the aerobic photocyanation of tertiary amines with visible light is reported. The use of air as terminal oxidant offers an improved safety profile compared with pure oxygen, the used compact fluorescent lamp (CFL) light sources are highly economical, and no halogenated solvents are required. This system not only proves to be effective for a wide variety of trialkylamines, pharmaceuticals, and alkaloids but remarkably also allows the lowest catalyst loading (0.00001 mol% or 0.1 ppm) ever reported for an organic dye. Bruylants reactions and C-alkylation/decyanations were performed on the obtained α-aminonitriles to demonstrate the postfunctio…

Effects of Parietaria judaica pollen extract on human microvascular endothelial cells

2008

Abstract Pollinosis from Parietaria judaica is one of the main causes of allergy in the Mediterranean area. The present study is designed to assess if P. judaica pollens contain bioactive compounds able to elicit a functional response in endothelial cells. We have demonstrated that addition of pollen extract to human lung microvascular endothelial cells (HMVEC-L) induces a modification of cell morphology, actin cytoskeletal rearrangements and an increase in endothelial cell permeability. We further showed that the treatment of endothelial cells with pollen extract causes an increase of E-selectin and VCAM-1 protein levels as well as an increase of IL-8 production. The stimulation of cell–ce…

Comparative chemistry of 18-electron Mo(II) and 17-electron Mo(III) compounds containing only carbon-based ligands

1998

International audience; The chemical reactivity of various kinetically stable isomers of compound CpMo(η3-C3H5)(η4-C4H6), 1, and its oxidation product [1]+, as well as the bis-allyl Mo(III) complex CpMo(η3-C3H5)2, 2, and the bis-diene Mo(II) complex [CpMo(η4-C4H6)2]+, 3, is reviewed. The inertness toward isomerization processes of the allyl and butadiene ligands in the Mo(II) complexes has allowed a study of the relative reactivity toward both electrophilic and nucleophilic addition processes as a function of coordination mode. The dependence of various reaction pathways on the metal oxidation state has also been investigated. Of particular interest is the discovery that the electronically …

Recent advances in the synthesis of functionalised monofluorinated compounds.

2018

Over the past few years, we have tackled the synthesis of interesting monofluorinated organic molecules, such as: dihydronaphthalene derivatives, β-fluoro sulfones and related carbonyl compounds, fluorohydrins and allylic alcohols. Overall, a wide range of modern synthetic techniques are covered in this feature article including transition-metal, photo- and organocatalysis, nucleophilic and electrophilic fluorinations, chiral auxiliaries and enantioselective catalysis.