Approaches to new fluoride ion sources

Fluoride ion sources have been surveyed and perfluoroalkyl anions and hindered amine/HF adducts prepared and investigated as reagents. The perfluoroalkyl anions (I) and (II) have been used in an attempt to fluorinate various organic compounds such as alkyl halides, alkyl tosylates, aryl halides and acetyl chloride. The following new compounds have been synthesised and identified by glc-mass spec and, where possible, (^19)F nmr. These arose from reaction of the substrate with the perfluoroalkyl anion rather than with F(^-). Preliminary work on hindered amine bases, particularly proton sponge and tri-n-octylamine, with HF was undertaken, these being studied as possible soluble fluoride ion sources. Solid adducts were obtained in most cases from ether solutions and they were shown to behave as fluoride ion sources under various conditions

Accurate measurement of ^{13}C - ^{15}N distances with solid-state NMR

Solid-state NMR technique for measureing distances between hetero-nuclei in static powder samples is described. It is based on a two-dimensional single-echo scheme enhanced with adiabatic cross-polarization. As an example, the results for intra-molecular distances in $\alpha$-crystalline form of glycine are presented. The measured NMR distances ^13 C(2) - ^15 N and ^13 C(1) - ^15 N are 1.496 $\pm$ 0.002 \AA and 2.50 $\pm$ 0.02 \AA, respectively.Comment: 12 page

Self-induced water intoxication : a case report

CITATION: Emsley, R. A. & Taljaard, J. J. F. 1988. Self-induced water intoxication : a case report. South African Medical Journal, 74:80-81.The original publication is available at http://www.samj.org.zaA 19-year-old female schizophrenic with self-induced water intoxication is described. Factors of pathogenic significance included primary polydipsia and non-maximal urinary diluting capacity.Publisher’s versio

Fidelity enhancement by logical qubit encoding

We demonstrate coherent control of two logical qubits encoded in a decoherence free subspace (DFS) of four dipolar-coupled protons in an NMR quantum information processor. A pseudo-pure fiducial state is created in the DFS, and a unitary logical qubit entangling operator evolves the system to a logical Bell state. The four-spin molecule is partially aligned by a liquid crystal solvent, which introduces strong dipolar couplings among the spins. Although the system Hamiltonian is never fully specified, we demonstrate high fidelity control over the logical degrees of freedom. In fact, the DFS encoding leads to higher fidelity control than is available in the full four-spin Hilbert space.Comment: 10 pages, 2 figure

Quantum information processing using strongly-dipolar coupled nuclear spins

Dipolar coupled homonuclear spins present challenging, yet useful systems for quantum information processing. In such systems, eigenbasis of the system Hamiltonian is the appropriate computational basis and coherent control can be achieved by specially designed strongly modulating pulses. In this letter we describe the first experimental implementation of the quantum algorithm for numerical gradient estimation on the eigenbasis of a four spin system.Comment: 5 pages, 5 figures, Accepted in PR

New determination of structure parameters in strong field tunneling ionization theory of molecules

In the strong field molecular tunneling ionization theory of Tong et al. [Phys. Rev. A 66, 033402 (2002)], the ionization rate depends on the asymptotic wavefunction of the molecular orbital from which the electron is removed. The orbital wavefunctions obtained from standard quantum chemistry packages in general are not good enough in the asymptotic region. Here we construct a one-electron model potential for several linear molecules using density functional theory (DFT). We show that the asymptotic wavefunction can be improved with an iteration method and after one iteration accurate asymptotic wavefunctions and structure parameters are determined. With the new parameters we examine the alignment-dependent tunneling ionization probabilities for several molecules and compare with other calculations and with recent measurements, including ionization from inner molecular orbitals

The new-generation antipsychotics -integrating the neuropathology and pharmacology of schizophrenia

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