Highly reactive equivalents of allylidenetriphenylphosphoranes for the stereospecific synthesis of 1,3-dienes by cis-olefination of hindered aldehydes

Ylides derived from 3-dimethylaminopropyltriphenylphosphonium salts react smoothly and stereospecifically with even hindered aldehydes to form $\text{Z}$-olefins which are easily converted to 1,3-dienes.     

A characterization of the smallest eigenvalue of a graph

It is well known that the smallest eigenvalue of the adjacency matrix of a connected d-regular graph is at least ? d and is strictly greater than ? d if the graph is not bipartite. More generally, for any connected graph G = (V, E), consider the matrix Q = D + A where D is the diagonal matrix of degrees in the graph G and A is the adjacency matrix of G. Then Q is positive semidefinite, and the smallest eigenvalue of Q is 0 if and only if G is bipartite. We will study the separation of this eigenvalue from 0 in terms of the following measure of nonbipartiteness of G. For any S ? V, we denote by e_min(S) the minimum number of edges that need to be removed from the induced subgraph on S to make it bipartite. Also, we denote by cut(S) the set of edges with one end in S and the other in V ? S. We define the parameter Ψ as. The parameter Ψ is a measure of the nonbipartiteness of the graph G. We will show that the smallest eigenvalue of Q is bounded above and below by functions of Ψ. For d-regular graphs, this characterizes the separation of the smallest eigenvalue of the adjacency matrix from ?d. These results can be easily extended to weighted graphs.     

Determination of biogenic halogenated methyl-phenyl ethers (halogenated anisoles) in the picogram m−3 range in air

Halogenated anisoles (methyl-phenyl ethers) appear to be ubiquitous organic trace compounds in the environment. An analytical method is presented for analyzing the altogether 134 congeners of chloro-, bromo- and mixed bromochloro-anisoles on an isomer-specific basis in air. High volume sampling (20 m(3) per hour) is carried out by adsorption, using a mixture of silica gel 60 and ENVI-Carb. The preseparation of the anisoles is achieved by NP-LC on Florisil (a magnesium silicate). The interference by volatile n-alkyl nitrates in the electron-capture detection can be avoided by a LC-preseparation on a carboneous phase. The isomer-specific separation and detection is performed by HRGC-ECD and HRGC-MS-SIM. A structure-specific systematic numbering of the 134 congeners of the chloro-, bromo- and bromochloro-anisoles is suggested. The retention data are given of 16 chloroanisoles, 10 bromoanisoles and 27 bromo-chloroanisoles on three stationary phases with different polarity.     

Palladium catalyzed carbonylative generation of potent,pyridine-based acylating electrophiles for the functionalization of arenes to ketones

We describe here the design of a palladium catalyzed route to generate aryl ketones via the carbonylative coupling of (hetero)arenes and aryl- or vinyl-triflates. In this, the use of the large bite angle Xantphos ligand on palladium provides a unique avenue to balance the activation of the relatively strong C(sp²)–OTf bond with the ultimate elimination of a new class of potent Friedel–Crafts acylating agent: N-acyl pyridinium salts. The latter can be exploited to modulate reactivity and selectivity in carbonylative arene functionalization chemistry, and allow the efficient synthesis of ketones with a diverse array of (hetero)arenes.

A palladium catalyzed approach to the overall carbonylative functionalization of arenes to form ketones with aryl- and vinyl-triflates is described.     

Colloidal TiO2 nanocrystals/MEH-PPV nanocomposites: photo(electro)chemical study

An extensive optical and photoelectrochemical study of blended systems composed of organic-capped TiO(2) nanocrystals with either a spherical or rodlike morphology and a conjugated polymer, MEH-PPV, is presented. The absorption and emission properties of the heterojunctions have been characterized both in solution and in thin films. The blended structures deposited onto conductive substrates have been employed as active layers in photoelectrochemical systems. The investigation has been focused on the photoinduced charge transfer and recombination processes at the interface between the two components, as a function of the nanocrystal shape and surface coating, and of the film thickness. The presence of a large number of interfaces available for charge transfer is believed to play a fundamental role in enhancing the photoelectrochemical performances of the dispersed heterojunctions. The reported results suggest that such MEH-PPV/TiO(2) heterojunctions may be exploited as potential active layers in future photovoltaic and photoelectrochemical devices.     

Systematic coarse-graining of nanoparticle interactions in molecular dynamics simulation

A recently developed multiscale coarse-graining procedure [Izvekov, S.; Voth, G. A. J. Phys. Chem. B 2005, 109, 2469] is extended to derive coarse-grained models for nanoparticles. The methodology is applied to C(60) and to carbonaceous nanoparticles produced in combustion environments. The coarse-graining of the interparticle force field is accomplished applying a force-matching procedure to data obtained from trajectories and forces from all-atom MD simulations. The CG models are shown to reproduce accurately the structural properties of the nanoparticle systems studied, while allowing for MD simulations of much larger self-assembled nanoparticle systems.