Mono N,C,N-pincer complexes of titanium, vanadium and niobium. Synthesis, structure and catalytic activity in olefin polymerisation

Transmetallation of 4,4'-bis{(2,6-bis[(dimethylamino)methyl]phenylgold)diphenyl-phosphino}biphenyl (3) with MCl(4) (M = Ti, NbCl, V) in benzene gave the corresponding transition metal pincer complexes (4) and insoluble 4,4'-bis[P-(chloro gold(I))diphenylphosphino]biphenyl (2), which can be quantitatively recovered and recycled. Interestingly, 3 did not react with TiCl(3). However, reaction of 2,6-bis[(dimethylamino)methyl]phenyllithium (1) with TiCl(3) resulted in formation of the novel diaryltitanium(IV) compound 5 (16% yield), comprising one N,C,N-mer bound NCN-pincer ligand and a second NCN-pincer ligand that is rearranged from a 1,2,6-isomer to a 1,2,4 one. The latter NCN-ligand is dianionic and is bidentate bonded; one of the CH(2)NMe(2) substituents (para to C'(ipso)) is non-coordinated, while the second CH(2)NMe(2) group, after C-H activation of one of the Me groups, is η(2)-C,N-bonded to the titanium centre trans to C(ipso) of the mer-NCN ligand. The new NCN-pincer metal complexes 2,6-bis[(dimethylamino)methyl]phenylTiCl(3) (4a) and 2,6-bis[(dimethylamino)methyl]-phenylVCl(2) (4d) gave, after immobilization on MgCl(2)-based supports, very high activity in ethene polymerisation.     

Observers and Locality in Everett Quantum Field Theory

A model for measurement in collapse-free nonrelativistic fermionic quantum field theory is presented. In addition to local propagation and effectively-local interactions, the model incorporates explicit representations of localized observers, thus extending an earlier model of entanglement generation in Everett quantum field theory (Rubin in Found. Phys. 32:1495–1523, 2002). Transformations of the field operators from the Heisenberg picture to the Deutsch-Hayden picture, involving fictitious auxiliary fields, establish the locality of the model. The model is applied to manifestly-local calculations of the results of measurements, using a type of sudden approximation and in the limit of massive systems in narrow-wavepacket states. Detection of the presence of a spin-1/2 system in a given spin state by a freely-moving two-state observer illustrates the features of the model and the nonperturbative computational methodology. With the help of perturbation theory the model is applied to a calculation of the quintessential “nonlocal” quantum phenomenon, spin correlations in the Einstein-Podolsky-Rosen-Bohm experiment.     

The dynamics of a forced coupled network of active elements

This paper presents the derivation and analysis of mathematical models motivated by the experimental induction of contour phosphenes in the retina. First, a spatially discrete chain of periodically forced coupled oscillators is considered via reduction to a chain of scalar phase equations. Each isolated oscillator locks in a 1:2 manner with the forcing so that there is intrinsic bistability, with activity peaking on either the odd or even cycles of the forcing. If half the chain is started on the odd cycle and half on the even cycle (“split state”), then with sufficiently strong coupling, a wave can be produced that can travel in either direction due to symmetry. Numerical and analytic methods are employed to determine the size of coupling necessary for the split state solution to destabilize such that waves appear. Taking a continuum limit, we reduce the chain to a partial differential equation. We use a Melnikov function to compute, to leading order, the speed of the traveling wave solution to the partial differential equation as a function of the form of coupling and the forcing parameters and compare our result to the numerically computed discrete and continuum wave speeds.     

Diamidopyrazoles: A New Class of Anion Receptors

The synthesis of a series of 3,5-diamidopyrazoles is reported. The anion binding properties of these systems were examined via ¹H NMR, UV/Vis and ITC titration techniques. Target compound 2a acts as a selective receptor for phosphate and sulfate anions in DMSO, whereas N-methylated 2b and the unmethylated species 4d show no appreciable binding affinity. Insights into the binding events occurring in solution came from the solid state structures of compounds 2a and 4a, 4b, and 4d, which were deduced from single crystal X-ray diffraction analyses.     

A paracrine requirement for hedgehog signalling in cancer

Ligand-dependent activation of the hedgehog (Hh) signalling pathway has been associated with tumorigenesis in a number of human tissues. Here we show that, although previous reports have described a cell-autonomous role for Hh signalling in these tumours, Hh ligands fail to activate signalling in tumour epithelial cells. In contrast, our data support ligand-dependent activation of the Hh pathway in the stromal microenvironment. Specific inhibition of Hh signalling using small molecule inhibitors, a neutralizing anti-Hh antibody or genetic deletion of smoothened (Smo) in the mouse stroma results in growth inhibition in xenograft tumour models. Taken together, these studies demonstrate a paracrine requirement for Hh ligand signalling in the tumorigenesis of Hh-expressing cancers and have important implications for the development of Hh pathway antagonists in cancer.     

Method of analytic continuation for the inverse spherical mean transform in constant curvature spaces

The following problem arises in thermoacoustic tomography and has intimate connection with PDEs and integral geometry. Reconstruct a function f supported in an n-dimensional ball B given the spherical means of f over all geodesic spheres centered on the boundary of B. We propose a new approach to this problem, which yields explicit reconstruction formulas in arbitrary constant curvature space, including euclidean space ? ⁿ , the n-dimensional sphere, and hyperbolic space. The main idea is analytic continuation of the corresponding operator families. The results are applied to inverse problems for a large class of Euler-Poisson-Darboux equations in constant curvature spaces of arbitrary dimension.     

Rearrangements of cyclopropenes into five-membered aromatic heterocycles: mechanistic aspect

This review covers rearrangements of cyclopropenes into aromatic five-membered heterocyclic compounds, namely furans and pyrroles; accompanied by small ring cleavage proceeding in the presence of catalytic amounts of transition metals, Lewis acids, or under UV irradiation.     

Unexpected formation of a Sc3C2@C80 bisfulleroid derivative

The reaction of tetrazine 1 with Sc(3)C(2)@C(80) exclusively affords the open-cage derivative 2 instead of the expected C(2)-inserted derivative 3 bearing a four-membered ring, as previously obtained for C(60). The structure of 2 has been firmly established by NMR spectroscopy and theoretical calculations. EPR spectroscopy shows that a single Sc atom of the Sc(3)C(2) cluster gets located within the bulge created by the bridging addend, which is a first step toward release of the internal metal atoms.     

A distal enhancer and an ultraconserved exon are derived from a novel retroposon

Hundreds of highly conserved distal cis-regulatory elements have been characterized so far in vertebrate genomes. Many thousands more are predicted on the basis of comparative genomics. However, in stark contrast to the genes that they regulate, in invertebrates virtually none of these regions can be traced by using sequence similarity, leaving their evolutionary origins obscure. Here we show that a class of conserved, primarily non-coding regions in tetrapods originated from a previously unknown short interspersed repetitive element (SINE) retroposon family that was active in the Sarcopterygii (lobe-finned fishes and terrestrial vertebrates) in the Silurian period at least 410 million years ago (ref. 4), and seems to be recently active in the 'living fossil' Indonesian coelacanth, Latimeria menadoensis. Using a mouse enhancer assay we show that one copy, 0.5 million bases from the neuro-developmental gene ISL1, is an enhancer that recapitulates multiple aspects of Isl1 expression patterns. Several other copies represent new, possibly regulatory, alternatively spliced exons in the middle of pre-existing Sarcopterygian genes. One of these, a more than 200-base-pair ultraconserved region, 100% identical in mammals, and 80% identical to the coelacanth SINE, contains a 31-amino-acid-residue alternatively spliced exon of the messenger RNA processing gene PCBP2 (ref. 6). These add to a growing list of examples in which relics of transposable elements have acquired a function that serves their host, a process termed 'exaptation', and provide an origin for at least some of the many highly conserved vertebrate-specific genomic sequences.     

Symbiosis insights through metagenomic analysis of a microbial consortium

Symbioses between bacteria and eukaryotes are ubiquitous, yet our understanding of the interactions driving these associations is hampered by our inability to cultivate most host-associated microbes. Here we use a metagenomic approach to describe four co-occurring symbionts from the marine oligochaete Olavius algarvensis, a worm lacking a mouth, gut and nephridia. Shotgun sequencing and metabolic pathway reconstruction revealed that the symbionts are sulphur-oxidizing and sulphate-reducing bacteria, all of which are capable of carbon fixation, thus providing the host with multiple sources of nutrition. Molecular evidence for the uptake and recycling of worm waste products by the symbionts suggests how the worm could eliminate its excretory system, an adaptation unique among annelid worms. We propose a model that describes how the versatile metabolism within this symbiotic consortium provides the host with an optimal energy supply as it shuttles between the upper oxic and lower anoxic coastal sediments that it inhabits.