Biomimetic cycloaddition approach to tropolone natural products via a tropolone ortho-quinone methide

[reaction: see text] A study toward a possible biomimetic hetero Diels-Alder reaction is reported between humulene and a novel tropolone ortho-quinone methide. A suitable tropolone ortho-quinone methide precursor has been prepared from 3-methyl-2-furoate. Heating the ortho-quinone methide precursor gave a tropolone ortho-quinone methide, which in the presence of humulene underwent a hetero Diels-Alder reaction to give a deoxy analogue of epolone B.     

Aquachlorobis[4,4,5,5‐tetramethyl‐2‐(2‐pyridyl)‐4,5‐dihydro‐1H‐imidazol‐1‐oxyl 3‐oxide‐κ2O1,N2]nickel(II) nitrate methanol disolvate monohydrate

The title complex, [NiCl(C₁₂H₁₆N₃O₂)₂(H₂O)]NO₃·2CH₄O·H₂O, was obtained from a methano­lic solution of Ni(NO₃)₂·6H₂O, 2‐pyridyl nitro­nyl nitro­xide (2‐NITpy) and (NEt₄)₂[CoCl₄]. The equatorial coordination sites of the octahedral Ni^II centre are occupied by two chelating radical ligands, with the axial positions occupied by the Cl^? and water ligands. The H₂O—Ni—Cl axis of the complex lies along a crystallographic twofold axis, so that only half the cation is present in the asymmetric unit. The Ni—Cl bond length [2.3614 (17) Å] is significantly shorter than distances typical of octahedral Ni^II centres [2.441 (5) Å]. However, with only one nitrate anion per formula unit, the oxidation state of the metal must be assigned as Ni^II. The 2‐NITpy ligands bend away from the equatorial plane, forming a hydro­phobic region around the Cl atoms. Conversely, the ligated water mol­ecule forms moderately strong hydrogen bonds with the disordered methanol solvent mol­ecules, which in turn form interactions with the water of crystallization and the disordered nitrate anion. These interactions combine to give hydro­philic regions throughout the crystal structure.     

X-band Electron Spin Relaxation Times for Four Aromatic Radicals in Fluid Solution and Comparison with Other Organic Radicals

X-band electron spin relaxation times of BDPA (1:1 α,γ-bisdiphenylene-β-phenylallyl), galvinoxyl 2,6-di-tert-butyl-α-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-p-tolyloxy, DPPH (2,2-diphenyl-1-picrylhydrazyl) and thianthrene radicals in fluid solution were measured by electron spin echo and inversion recovery at ambient temperature. Tumbling correlation times are estimated to be in the range of 20–30 ps. In this fast tumbling regime T ₁ ~ T ₂. Relaxation times are compared with previously reported values for symmetrically substituted triarylmethyl, semiquinone, and nitroxide radicals. The concentration dependence of spin lattice relaxation for neutral BDPA in toluene is about 10³ times greater than for anionic trityl radicals in water. T ₁ decreases in the order carbon-center BDPA > galvinoxyl > DPPH > thianthrene. The dominant relaxation mechanisms are proposed to be a local mode for BDPA, spin rotation, local mode and modulation of anisotropic proton hyperfine coupling for galvinoxyl, modulation of anisotropic nitrogen hyperfine for DPPH, and spin rotation plus modulation of anisotropic proton hyperfine coupling for thianthrene.     

Field-cycled PEDRI imaging of free radicals with detection at 450 mT

This paper describes the design, construction and use of a field-cycled proton-electron double-resonance imaging (FC-PEDRI) system for the detection and imaging of free radicals. The unique feature of this imager is its use of a 450-mT detection magnetic field in order to achieve good image quality and sensitivity. The detection magnetic field is provided by a superconducting magnet, giving high stability and homogeneity. Field cycling is implemented by switching on and off the current in an internal, coaxial, resistive secondary magnet that partially cancels the superconducting magnet's field at the sample; the secondary magnet is actively shielded to avoid eddy currents. EPR irradiation takes place at approximately 5 mT, following which the field is switched to 450 mT in 40 ms for NMR signal detection. Full details of the imager's subsystems are given, and experiments to image the distribution of stable free radical contrast agents in phantoms and in anesthetized rats are described.     

Bayesian wavelet-based analysis of functional magnetic resonance time series

Wavelet methods for image regularization offer a data-driven alternative to Gaussian smoothing in functional magnetic resonance (fMRI) analysis. Their impact has been limited by the difficulties in integrating regularization in the wavelet domain and inference in the image domain, precluding the probabilistic decision on which areas are activated by a task. Here we present an integrated framework for Bayesian estimation and regularization in wavelet space that allows the usual voxelwise hypothesis testing. This framework is flexible, being an adaptation to fMRI time series of a more general wavelet-based functional mixed-effect model. Through testing on a combination of simulated and real fMRI data, we show evidence of improved signal recovery, without compromising test accuracy in image space.     

Developed smectics: when exact solutions agree

In the limit where the bending modulus vanishes, we construct layer configurations with arbitrary dislocation textures by exploiting a connection between uniformly spaced layers in two dimensions and developable surfaces in three dimensions. We then show how these focal textures can be used to construct layer configurations with finite bending modulus.     

A phase I, randomized study of combined IL-2 and therapeutic immunisation with antiretroviral therapy

Background  

Fully functional HIV-1-specific CD8 and CD4 effector T-cell responses are vital to the containment of viral activity and disease progression. These responses are lacking in HIV-1-infected patients with progressive disease. We attempted to augment fully functional HIV-1-specific CD8 and CD4 effector T-cell responses in patients with advanced chronic HIV-1 infection.     

High-spectral-resolution coherent anti-Stokes Raman scattering with interferometrically detected broadband chirped pulses

To achieve high-spectral-resolution multiplex coherent anti-Stokes Raman scattering (CARS), one typically uses a narrowband pump pulse and a broadband Stokes pulse. This is to ensure a correspondence between anti-Stokes and vibrational frequencies. We obtain high-resolution CARS spectra of isopropanol, using a broadband chirped pump pulse and a broadband Stokes pulse, by detecting the anti-Stokes pulse with spectral interferometry. With the temporally resolved anti-Stokes signal, we can remove the chirp of the anti-Stokes pulse and restore high spectral resolution while also rejecting nonresonant scattering.