Synthesis,structural characterization and catalytic potential of oxidovanadium(IV) and dioxidovanadium(V) complexes with thiazole-derived NNN-donor ligand

Reaction between the tridentate NNN donor ligand, (E)-2-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)benzo[d]thiazole (HL), and V₂O₅ in ethanol gave a new vanadium(V) complex, [VO₂L] (1), while the similar reaction by using [V^IVO(acac)₂] as the metal source gave two different types of crystals related to compounds [VO₂L] (1) and [V^IVO(acac)L] (2). The molecular structures of the complexes were determined by single-crystal X-ray diffraction and spectroscopic characterization was carried out by means of FT-IR, UV–vis and NMR experiments as well as elemental analysis. The oxidovanadium(IV) and dioxidovanadium(V) species were used as catalyst precursors for olefin oxidation in the presence of hydrogen peroxide (H₂O₂) as an oxidant. Under similar experimental conditions, the presence of 1 resulted in higher oxidation conversion than 2.     

The light Higgs window in the 2HDM at GigaZ

The sensitivity to a light Higgs boson in the general 2HDM (II), with a mass below 40 GeV, is estimated for a future Linear Collider operating with a very high luminosity at the Z peak (GigaZ). We consider possible Higgs boson production via the Bjorken process, the (hA) pair production, the Yukawa process , and the decay . Although the discovery potential is considerably extended compared to the current sensitivities, mainly from LEP, the existence of a h or A even with a mass of a few GeV cannot be excluded with two billion Z decays. The need to study the very light Higgs scenario at a Linear Collider running at several hundred GeV and the LHC is emphasized. Received: 18 September 2000 / Revised version: 22 December 2000 / Published online: 15 March 2001     

A semi-flexible attracting segment model of two-dimensional polymer collapse

Recently it has been shown that a two-dimensional model of self-attracting polymers based on attracting segments displays two phase transitions, a θ-like collapse between swollen polymers and a globular state and another between the globular state and a polymer crystal. On the other hand, the canonical model based on attracting monomers on lattice sites displays only one: the standard tricritical θ collapse transition. Here we consider the attracting segment model with the addition of stiffness and show that it displays the same phases as the canonical model.     

Nitrogen Pronucleophiles in the Self-Catalytic Michael Reaction

The self-catalytic Michael reaction of several nitrogen pronucleophiles with dicyclohexylammonium 2-diethylphosphonoacrylate and dicyclohexylammonium 2-cyanoacrylate proceeded highly efficiently at room temperature to give the corresponding 1,4-adducts.     

Synthesis and crystal structure of 1-(aminomethyl)vinylphosphonic acid

A highly efficient and versatile approach to the synthesis of 1-(aminomethyl)vinylphosphonic acid, a constituent of the antibiotic A53868A, is reported. In the crystal, molecules of the acid are linked by strong, linear, symmetric hydrogen bonds involving hydrogen atoms of the phosphonic group.     

An efficient approach to the synthesis of enantiomerically pure trans-1-amino-2-(hydroxymethyl)cyclopropanephosphonic acids

The synthesis of (1R,2S)- and (1S,2R)-1-amino-2-(hydroxymethyl)cyclopropanephosphonic acids was accomplished using different strategies. The (1R,2S)-stereoisomer could be efficiently obtained by the cyclopropanation of ethyl diethoxyphosphorylacetate with the cyclic sulfate derived from (S)-3-benzyloxy-1,2-propandiol as a key step. The (1S,2R)-stereoisomer was synthesized from a readily available (1S,5R)-3-oxabicyclo[3.1.0]hexan-2-on-1-phosphonate.     

The stability of small helical gold nanorods: a relativistic density functional study

Multistrand 7-1 helical Au(24), Au(32), and Au(40) structures with three, four, and five gold atoms in the central strand and 21, 28, and 35 gold atoms in the coaxial tube are investigated using relativistic density functional theory. We demonstrate that these helical gold nanorods are stable structures with a rather large HOMO-LUMO gap, a large binding energy per atom, a very large vertical dissociation energy, and an extremely large electron affinity. On the basis of the atomic charges and the nature of the frontier orbitals, they are also expected to have strong selective reactivity toward electrophiles and nucleophiles. Furthermore, we show that these helical Au(n) structures and, in particular, the helical Au(40) structure are competitive energetically and chemically with respect to alternate cage and compact Au(n) structures. We consider two fragmentations of the helical Au(40) structure and perform a density of states analysis to examine both charge transfer and electronic polarization.     

Organocatalytic Asymmetric Synthesis of Organophosphorus Compounds

240 Years have passed since the discovery of elemental phosphorus. During that time organophosphorus chemistry has emerged as an interesting and exciting field of research. Recently organophosphorus chemistry has been raised to a new level. Organophosphorus compounds have found applications in asymmetric organocatalysis for the synthesis of optically active compounds of synthetic or biological importance. The aim of this review article is to present recent contributions to this developing field of chemistry and to point out synthetic advantages of methodologies developed so far.