The cyclodimerisation of 3-methyl-2-butenenitrile

3-Methyl-2-butenenitrile (1) cyclodimerised on treatment with lithium diisopropylamide in dimethoxyethane at temperatures between ?78°C and 0°C to 3-amino-4-cyano-1,5,5-trimethyl-1,3-cyclohexadiene (2) the structure of which was established by acid hydrolysis to the known 4-cyano-1,5,5-trimethyl-1-cyclohexene-3-one (3).     

Novel carbohydrate-appended metal complexes for potential use in molecular imaging

Seven discrete sugar-pendant diamines were complexed to the {M(CO)(3)}(+) ((99m)Tc/Re) core: 1,3-diamino-2-propyl beta-D-glucopyranoside (L(1)), 1,3-diamino-2-propyl beta-D-xylopyranoside (L(2)), 1,3-diamino-2-propyl alpha-D-mannopyranoside (L(3)), 1,3-diamino-2-propyl alpha-D-galactopyranoside (L(4)), 1,3-diamino-2-propyl beta-D-galactopyranoside (L(5)), 1,3-diamino-2-propyl beta-(alpha-D-glucopyranosyl-(1,4)-D-glucopyranoside) (L(6)), and bis(aminomethyl)bis[(beta-D-glucopyranosyloxy)methyl]methane (L(7)). The Re complexes [Re(L(1)-L(7))(Br)(CO)(3)] were characterized by (1)H and (13)C 1D/2D NMR spectroscopy which confirmed the pendant nature of the carbohydrate moieties in solution. Additional characterization was provided by IR spectroscopy, elemental analysis, and mass spectrometry. Two analogues, [Re(L(2))(CO)(3)Br] and [Re(L(3))(CO)(3)Br], were characterized in the solid state by X-ray crystallography and represent the first reported structures of Re organometallic carbohydrate compounds. Conductivity measurements in H(2)O established that the complexes exist as [Re(L(1)-L(7))(H(2)O)(CO)(3)]Br in aqueous conditions. Radiolabelling of L(1)-L(7) with [(99m)Tc(H(2)O)(3)(CO)(3)](+) afforded in high yield compounds of identical character to the Re analogues. The radiolabelled compounds were determined to exhibit high in vitro stability towards ligand exchange in the presence of an excess of either cysteine or histidine over a 24 h period.     

Efficient calculation of SAMPL4 hydration free energies using OMEGA,SZYBKI, QUACPAC,and Zap TK

Several submissions for the SAMPL4 hydration free energy set were calculated using OpenEye tools, including many that were among the top performing submissions. All of our best submissions used AM1BCC charges and Poisson–Boltzmann solvation. Three submissions used a single conformer for calculating the hydration free energy and all performed very well with mean unsigned errors ranging from 0.94 to 1.08 kcal/mol. These calculations were very fast, only requiring 0.5–2.0 s per molecule. We observed that our two single-conformer methodologies have different types of failure cases and that these differences could be exploited for determining when the methods are likely to have substantial errors.     

Conical parametric scattering of a single extraordinary beam in BaTiO3 crystal

In this paper, the parametric scattering of a single extraordinary polarized beam of laser in BaTiO₃ photorefractive crystal has been investigated experimentally and theoretically. The resulting pattern consists of beam fanning, isotropic ring, and anisotropic one. Among all parts of scattering pattern, isotropic ring has not been studied as much as beam fanning and anisotropic ring, and there still are some differences in reports about it. Therefore, the study has mainly focused on this part. In this experimental configuration, isotropic ring is just visible in positive angles although the other parts of parametric scattering pattern can be visible from behind and in front of the crystal. In addition to steady state pattern in forward and backward directions, its transient behavior with the rotation of crystal has been studied. The results of experiments have been analyzed carefully, and their theoretical explanations have been presented based on the standard theory of parametric scattering in photorefractive crystals. It has been shown that this configuration corresponds to the so called parametric B-process scattering.     

De-excitation processes near the surface of ion bombarded SiO2 and Si

Ion bombardment induced secondary ion and optical excitation from oxide coated Si has been studied as the oxide layer is eroded away. By comparing ion and photon yields, a model for the role of resonant and Auger electron transitions in the neutralisation and de-excitation of the sputtered atoms and ions has been suggested.     

The energy spectra of secondary ions emitted during ion bombardment

Secondary ion energy spectra have been measured for singly charged ions emitted from targets irradiated with 43 keV A⁺ ions. Targets studied include the 3d transition metals (Sc, Ti, V, Cr, Fe, Ni) Cu and Zn, Zr, Al and Si and the compounds SiO₂, Al₂O₃, NaCl, KCl. Energy spectra were measured in the energy range 1–600 eV. In several cases a peak in the energy spectrum in the region around 200 eV has been found. This is in addition to the usual low energy peaks in the region of 5–10 eV. In many cases the low energy peak was observed to decay steadily with irradiation time or to increase with oxygen pressure. In the case of the cleanest Zn spectrum, only the high energy peak can be detected. The data are discussed in relation to current models of secondary ion emission. We conclude that, in general, elemental metal targets which are clean are characterised by the high energy peak in the secondary ion energy spectrum. The slower ions emitted have been neutralised by electron exchange processes. The low energy peaks in unclean, partially clean, oxide coated or compound targets (NaCl, KCl) arise because the neutralisation of the slower ions is either not as efficient or is not possible. The secondary ion emission model of Blaise and Slodzian could account for the emission of ions from most targets.     

Spatial organization,predictability, and determinism in ventricular fibrillation

The degree of spatial organization of ventricular fibrillation (VF) is a fundamental dynamical property of the arrhythmia and may determine the success of proposed therapeutic approaches. Spatial organization is closely related to the dimension of VF, and hence to its predictability and controllability. We have explored several techniques to quantify spatial organization during VF, to predict patterns of activity, and to see how spatial organization and predictability change as the arrhythmia progresses. Epicardial electrograms recorded from pig hearts using rectangular arrays of unipolar extracellular electrodes (1 mm spacing) were analyzed. The correlation length of VF, the number of Karhunen-Loeve modes required to approximate data during VF, the number, size and recurrence of wavefronts, and the mean square error of epicardial potential fields predicted 0.256 seconds into the future were all estimated. The ability of regularly-timed pacing stimuli to capture areas of fibrillating myocardium during VF was confirmed by a significant increase in local spatial organization. Results indicate that VF is neither "low-dimensional chaos" (dimension <5) nor "random" behavior (dimension= infinity ), but is a high-dimensional response with a degree of spatial coherence that changes as the arrhythmia progresses. (c) 1998 American Institute of Physics.     

Anion-templated calix[4]arene-based pseudorotaxanes and catenanes

We present the rational design and anion-binding properties of the first anion-templated pseudorotaxanes and catenanes in which the "wheel" component is provided by a calix[4]arene macrobicyclic unit. The designs and syntheses of two new calix[4]arene macrobicycles, 2 and 3, are presented, and the abilities of these new species both to bind anions and to undergo anion-dependent pseudorotaxane formation are demonstrated. Furthermore, it is shown that performing ring-closing metathesis reactions on some of these pseudorotaxane assemblies gives novel catenane species 14 and 15, in which the yield of interlocked molecule obtained is critically dependent on the presence of a suitable anion template, namely, chloride. Exchange of the chloride anion in catenane 14 a for hexafluorophosphate gives catenane 14 d, which contains a unique anion-binding domain defined by the permanently interlocked hydrogen-bond-donating calix[4]arene macrobicycle and pyridinium macrocycle fragments. The anion-binding properties of this domain are presented, and shown to differ from non-interlocked components.