1H NMR detection of immobilized water molecules within a strong distal hydrogen-bonding network of substrate-bound human heme oxygenase-1

Solution 1H NMR is used to probe the environments of the donor protons of eight strong hydrogen bonds on the distal side of the heme substrate in the cyanide-inhibited, substrate-bound complex of human heme oxygenase, hHO. It is demonstrated that significant magnetization transfer from the bulk water signal to the eight labile protons does not result from chemical exchange, but from direct nuclear Overhauser effect due to the dipolar interaction of these labile protons with "ordered" water molecules. The enzyme labile proton to water proton distances are estimated at approximately 3 A. It is proposed that the role of the strong hydrogen-bonding network is to immobilize numerous water molecules which both stabilize the activated hydroperoxy species and funnel protons to the active site.     

Speckle detection for 3D ultrasound

Positioning accuracy of 3D ultrasound slice planes can be enhanced by speckle decorrelation of the B-scans. A suitable method requires accurate identification of zones of non-specular reflection in the image, a feature of parenchymal tissue. This has traditionally been achieved with statistics such as signal-to-noise ratios and measures of autocorrelation curves. Co-occurrence matrices and structural approaches have also been applied to ultrasound images. In this paper we assess the performance of these methods when only B-scan display data is available. We also report improved results with in vivo images using a proposed structural algorithm that detects speckle kernels. All detection algorithms yielded detection error rates between 28% and 38%, suggesting that user intervention may be required for clinically useful performance.     

Proliferation dynamics of germinative zone cells in the intact and excitotoxically lesioned postnatal rat brain

Background  

The forebrain subventricular zone (SVZ)-olfactory bulb pathway and hippocampal subgranular zone (SGZ) generate neurons into adulthood in the mammalian brain. Neurogenesis increases after injury to the adult brain, but few studies examine the effect of injury on neural and glial precursors in the postnatal brain. To characterize the spatio-temporal dynamics of cell proliferation in the germinative zones, this study utilized a model of postnatal damage induced by NMDA injection in the right sensorimotor cortex at postnatal day 9.     

Complexation of thorium(IV) with acetate at variable temperatures

The complexation between Th(IV) and acetate in 1.05 mol kg(-1) NaClO4 was studied at variable temperatures (10, 25, 40, 55 and 70 degrees C). The formation constants of five successive complexes, Th(Ac)j(4-j)+ where Ac = CH3COO- and j = 1-5, and the molar enthalpies of complexation were determined by potentiometry and calorimetry. Extended X-ray absorption fine structure spectroscopy (EXAFS) provided additional information on the complexes in solution. The effect of temperature on the stability of the complexes is discussed in terms of the electrostatic model.     

Transformations of cyclic nonaketides by Aspergillus terreus mutants blocked for lovastatin biosynthesis at the lovA and lovC genes

Two mutants of Aspergillus terreus with either the lovC or lovA genes disrupted were examined for their ability to transform nonaketides into lovastatin 1, a cholesterol-lowering drug. The lovC disruptant was able to efficiently convert dihydromonacolin L 5 or monacolin J 9 into 1, and could also transform desmethylmonacolin J 15 into compactin 3. In contrast, the lovA mutant has an unexpectedly active beta-oxidation system and gives only small amounts of 1 upon addition of the immediate precursor 9, with most of the added nonaketide being degraded to heptaketide 22. Similarly, the lovA mutant does not accumulate the polyketide synthase product 5 and rapidly degrades any 5 added as a precursor via two cycles of beta-oxidation and hydroxylation at C-6 to give 20. The possible involvement of epoxides 21a and 21b in the biosynthesis of 1 was also examined, but their instability in fermentation media and fungal cells will require purified enzymes to establish their role.     

Enhanced accuracy by post-processing for finite element methods for hyperbolic equations

We consider the enhancement of accuracy, by means of a simple post-processing technique, for finite element approximations to transient hyperbolic equations. The post-processing is a convolution with a kernel whose support has measure of order one in the case of arbitrary unstructured meshes; if the mesh is locally translation invariant, the support of the kernel is a cube whose edges are of size of the order of only. For example, when polynomials of degree are used in the discontinuous Galerkin (DG) method, and the exact solution is globally smooth, the DG method is of order in the -norm, whereas the post-processed approximation is of order ; if the exact solution is in only, in which case no order of convergence is available for the DG method, the post-processed approximation converges with order in , where is a subdomain over which the exact solution is smooth. Numerical results displaying the sharpness of the estimates are presented.

     

Large intrinsic birefringence in zinc-blende based artificial semiconductors

A new attempt to solve the phase matching problem for semiconductor-based frequency conversion devices, based on the implementation of intrinsic birefringence in artificial materials, is discussed. The first results concerning the growth and characterization of ultrashort period superlattices are presented. To cite this article: J.-M. Jancu et al., C. R. Physique 8 (2007).     

Structure and conformational analysis of CFC-113 by density functional theory calculations and FTIR spectroscopy

Altitude-resolved volume mixing ratio profiles of CFC-113 have recently become available on a global scale with the Atmospheric Chemistry Experiment (ACE) satellite mission. However, the accuracy of the retrieval is currently limited by the uncertainties on the spectroscopic parameters of CFC-113. This paper reports on the geometrical structure, harmonic frequencies and intensities in the mid-infrared region of the two conformers of CFC-113 and the evaluation of whether theoretical calculations reproduce measurements. The calculations are performed using density functional theory at the B3LYP/6-311+G(3df) level. The molecular geometry parameters, the enthalpy difference and the potential barrier between conformers are calculated. The harmonic frequency of the normal modes of vibration are presented and accurately compared to experimental data. Overtones and combination bands are assigned in the 1200-2500 cm⁻¹ region.