Alkoxy- and amidocarbonylation of functionalised aryl and heteroaryl halides catalysed by a Bedford palladacycle and dppf: a comparison with the primary Pd(II) precursors (PhCN)2PdCl2 and Pd(OAc)2

The versatility of a Bedford-type palladacycle , namely [{Pd(micro-Cl){kappa2-P,C-P(OC6H(2)-2,4-tBu2)(OC6H(3)-2,4-tBu2)2}}2], as a primary Pd source, in combination with the ligand bis-1,1'-(diphenylphosphino)ferrocene (dppf) has been established in carbonylation reactions of aryl and heteroaryl bromides with methanol, piperidine and related nucleophiles. Palladacycle has been compared with other primary Pd sources, e.g. (PhCN)2PdCl2 and Pd(OAc)2. The efficacy of the carbonylation processes appear to be linked to the [Pd] concentration, substrate : catalyst ratio, CO pressure and reaction temperature. In amidocarbonylation, double carbonylation is observed for certain organohalides. In the case of 2,5-dibromopyridine, regioselective amination (Hartwig-Buchwald type) also occurs as a side-reaction.     

Eta(1)-2-pyrone metal carbonyl complexes as CO-releasing molecules (CO-RMs): a delicate balance between stability and CO liberation

An evaluation of the CO releasing ability of iron(II) and molybdenum(II) complexes has facilitated the discovery of the most rapid CO releaser, namely [Mo(CO)(3)(eta(5)-C(5)H(5))(eta(1)-{O}-C{=O}-O-CMe=CH-COMe=CBr)]BF(4) (CORM-F10), reported to date. The rate of CO release is related to the overall solution phase stability of the transition metal carbonyl complex. The cytotoxicity and vasodilatory properties of CORM-F10 have been determined.     

A memory of chirality approach to the stereoselective synthesis of 4-hydroxy-alpha-methylprolines

To extend the memory of chirality (MOC) methodology to structurally more diverse compounds, the synthesis of 4-hydroxy-alpha-methylprolines was undertaken. Yield and selectivity were very good, with an unexpected reversal in selectivity observed for the cyclization of one adduct with an unprotected hydroxyl.     

Restrictions of bounded linear operators: Closed range

Let be a bounded linear operator on a Banach space and let be a subspace of which is a Banach space and invariant. Denote by the restriction of to This paper explores the questions:

If the range of is closed, under what conditions is the range of closed?

If the range of is closed, under what conditions is the range of closed?

     

Quality issues in proficiency testing

 Proficiency testing is a means of assessing the ability of laboratories to competently perform specific tests and/or measurements. It supplements a laboratory's own internal quality control procedure by providing an additional external audit of their testing capability and provides laboratories with a sound basis for continuous improvement. It is also a means towards achieving comparability of measurement between laboratories. Participation is one of the few ways in which a laboratory can compare its performance with that of other laboratories. Good performance in proficiency testing schemes provides independent evidence and hence reassurance to the laboratory and its clients that its procedures, test methods and other laboratory operations are under control. For test results to have any credibility, they must be traceable to a standard of measurement, preferably in terms of SI units, and must be accompanied by a statement of uncertainty. Analytical chemists are coming to realise that this is just as true in their field as it is for physical measurements, and applies equally to proficiency testing results and laboratory test reports. Recent approaches toward ensuring the quality and comparability of proficiency testing schemes and the means of evaluating proficiency test results are described. These have led to the drafting of guidelines and subsequently to the development of international requirements for the competence of scheme providers. Received: 2 January 1999 · Accepted: 7 April 1999     

Bifurcation from Discrete Rotating Waves

Discrete rotating waves are periodic solutions that have discrete spatiotemporal symmetries in addition to their purely spatial symmetries. We present a systematic approach to the study of local bifurcation from discrete rotating waves. The approach centers around the analysis of diffeomorphisms that are equivariant with respect to distinct group actions in the domain and the range. Our results are valid for dynamical systems with finite symmetry group, and more generally, for bifurcations from isolated discrete rotating waves in dynamical systems with compact symmetry group.     

A Note on Characterizing the k-OPTNeighborhood Via Group Theory

Group theory can be used to model and synthesize the neighborhood of Traveling Salesman tours reachable through k-OPT exchanges. A primary concept is that a dihedral group action partitions the sets of cut arcs so that k-OPT exchanges of orbital elements are conjugate. Also presented is a method to produce all k-OPT exchanges for a given set of cut arcs.     

Position magnifying sensor

This paper describes the application of multiple beam shearing interferometry to a position magnifying sensor. A multiple beam shearing interferometer (MBSI) with a shear plate wedged in the vertical direction produces sharp multiple beam fringes. When the lateral displacement of a point source (which gives rise to the input beam of the MBSI) or its image occurs in the horizontal direction, these fringes move vertically in a magnified manner. This characteristic was used in a position magnifying sensor to detect the displacement of a point image. The advantages of the sensor include a large displacement magnification (more than a hundred times) and a large working distance.     

Atomic force microscopy of Au deposition from aqueous HF onto Si(111)

Non-contact atomic force microscopy (AFM) was employed following emersion to examine Au nanoclusters deposited from aqueous mixtures of HF and 10⁻⁴ M KAu(CN)₂ onto Si(111). As the HF concentration is increased, the growth rates both parallel and perpendicular to the substrate of the approximately oblate Au hemispheroids increase. AFM images were obtained for times at which previously reported in situ second harmonic generation signals from the interface reach a maximum. At the time when the second harmonic enhancement is maximized during deposition from 0.500 (5.00) M HF, the Au nanoclusters have an average diameter of 94 (109) nm and an average height of 3.6 (9.5) nm. These cluster diameters can be understood qualitatively by the shift of the plasmon resonance due to depolarization as the cluster size increases, causing the resonant second harmonic enhancement at 532 nm to pass through a maximum at cluster diameters in the range 90–110 nm.     

Overlapping Associating Fluids with Directional Bonds in a Bulk and Near a Hard Wall: Monte Carlo Study

Two models have been used in these Monte Carlo simulations: the original model with an angular-dependent associative interaction and a model with an angular-averaged potential, which is better suited for simulation and computationaly more efficient. We show that in the homogeneous case under the same conditions, both models yield a nearly identical interparticle structure, but with a slightly different degree of dimerization. This causes differences between these models in the local density distribution of monomers and dimers when an inhomogeneity is present, though the resulting local total density distribution is found to be the same. The theoretical predictions based on Wertheim's theory of association are always closer to the simulation data for the model with the angular-averaged potential.