Incorporation of manganese complexes into xylanase: new artificial metalloenzymes for enantioselective epoxidation.

Here we report the best artificial metalloenzyme to date for the selective oxidation of aromatic alkenes; it was obtained by noncovalent insertion of Mn(III)-meso-tetrakis(p-carboxyphenyl)porphyrin [Mn(TpCPP), 1-Mn] into a host protein, xylanase 10A from Streptomyces lividans (Xln10A). Two metallic complexes-N,N'-ethylene bis(2-hydroxybenzylimine)-5,5'-dicarboxylic acid Mn(III) [(Mn-salen), 2-Mn] and 1-Mn-were associated with Xln10A, and the two hybrid biocatalysts were characterised by UV-visible spectroscopy, circular dichroism and molecular modelling. Only the artificial metalloenzyme based on 1-Mn and Xln10A was studied for its catalytic properties in the oxidation of various substituted styrene derivatives by KHSO(5): after optimisation, the 1-Mn-Xln10A artificial metalloenzyme was able to catalyse the oxidation of para-methoxystyrene by KHSO(5) with a 16 % yield and the best enantioselectivity (80 % in favour of the R isomer) ever reported for an artificial metalloenzyme.

Selective oxidation of aromatic sulfide catalyzed by an artificial metalloenzyme: new activity of hemozymes.

Two new artificial hemoproteins or "hemozymes", obtained by non covalent insertion of Fe(III)-meso-tetra-p-carboxy- and -p-sulfonato-phenylporphyrin into xylanase A from Streptomyces lividans, were characterized by UV-visible spectroscopy and molecular modeling studies, and were found to catalyze the chemo- and stereoselective oxidation of thioanisole into the S sulfoxide, the best yield (85 +/- 4%) and enantiomeric excess (40% +/- 3%) being obtained with Fe(III)-meso-tetra-p-carboxyphenylporphyrin-Xln10A as catalyst in the presence of imidazole as co-catalyst.

Various strategies for obtaining artificial hemoproteins: from "hemoabzymes" to "hemozymes".

The design of artificial hemoproteins that could lead to new biocatalysts for selective oxidation reactions of organic compounds presents a huge interest especially in pharmacology, both for a better understanding of the metabolic profile of drugs and for the synthesis of enantiomerically pure molecules that could be involved in the design of drugs. The present results show that the so-called "host-guest strategy" that involves the non-covalent incorporation of anionic water-soluble iron-porphyrins into xylanase A from Streptomyces lividans, a low cost protein, leads to such an artificial hemoprotein that is able to perform the stereoselective oxidation of sulfides.

Chronic corticosterone elevation and sex-specific augmentation of the hypoxic ventilatory response in awake rats.

Perinatal stress disrupts normal development of the hypothalamo-pituitary-adrenal (HPA) axis. Adult male (but not female) rats previously subjected to a stress such as neonatal maternal separation (NMS) are characterized by chronic elevation of plasma corticosterone (Cort) levels and an abnormally elevated hypoxic ventilatory response through mechanisms that remain unknown. The present study tested the hypothesis that a chronic increase of plasma Cort levels alone augments the ventilatory response to hypoxia in adult rats. Three groups of Sprague-Dawley male and female rats were used (control, placebo and Cort implants). Rats subjected to chronic Cort elevation received a subcutaneous Cort implant (300 mg) 14 days prior to ventilatory measurements, whereas sham-operated rats received placebo implants. Controls received no treatment. Plasma Cort levels and body weight profiles were measured to assess protocol efficiency. Whole body plethysmography was used to measure ventilatory activity and metabolic indices during normoxia and following a 20 min period of moderate hypoxia (12% O(2)). Male rats implanted with Cort showed a ventilatory response to hypoxia higher than placebo-treated rats; this effect was mainly due to a larger tidal volume response. In females, Cort treatment increased the breathing frequency response but the effect on minute ventilation was not significant. Taken together, these data show that chronic elevation of Cort alone increases the ventilatory response to hypoxia, but in a sex-specific manner. These data raise important questions regarding the mechanisms underlying the sexual dimorphism of this effect and the potential link between HPA axis dysfunction and respiratory disorders related to abnormal ventilatory chemoreflex.

Developmental changes in central O2 chemoreflex in Rana catesbeiana: the role of noradrenergic modulation.

The in vitro brainstem preparation from Rana catesbeiana shows a functional central O(2) chemoreflex. Acute brainstem exposure to hypoxic superfusate elicits lung burst frequency responses that change over the course of development. Based on studies suggesting that brainstem noradrenergic neurons are involved in this reflex, we tested the following two hypotheses in vitro: (1) activation of adrenoceptors is necessary for the expression of the fictive lung ventilation response to hypoxia, and (2) changes in fast, Cl(-)-dependent neurotransmission (GABA/glycine) contribute to developmental changes in noradrenergic modulation. Experiments were performed on preparations from pre-metamorphics tadpoles (TK stages V-XIII) and adult bullfrogs. Acute exposure to hypoxic superfusate (98% N(2), 2% CO(2)) increased fictive lung ventilation frequency in the pre-metamorphic group, whereas a decrease was observed in adults. Buccal burst frequency was unchanged by hypoxia. Noradrenaline (NA; 5 micromol l(-1)) bath application mimicked both fictive breathing responses and application of the alpha(1)-antagonist prazosine (0.5 micromol l(-1)) blocked the lung burst response to hypoxia in both groups. Blocking GABA(A)/glycine receptors with a bicuculine/strychnine mixture (1.25 micromol l(-1)/1.5 micromol l(-1), respectively) or activation of GABA(B) pre-synaptic autoreceptors with baclofen (0.5 micromol l(-1)) prevented the lung burst response to hypoxia and to the alpha(1)-agonist phenylephrine (25 micromol l(-1)) in both stage groups. We conclude that NA modulation contributes to the central O(2) chemoreflex in bullfrog, which acts via GABA/glycine pathways. These data suggest that maturation of GABA/glycine neurotransmission contributes to the developmental changes in this chemoreflex.

Combined magnetic resonance and bioluminescence imaging of live mice.

We perform combined magnetic resonance and bioluminescence imaging of live mice for the purpose of improving the accuracy of bioluminescence tomography. The imaging is performed on three live nude mice in which tritium-powered light sources are surgically implanted. High-resolution magnetic resonance images and multispectral, multiview bioluminescence images are acquired in the same session. An anatomical model is constructed by segmenting the magnetic resonance images for all major tissues. The model is subsequently registered with nonlinear transformations to the 3-D light exittance (exiting intensity) surface map generated from the luminescence images. A Monte Carlo algorithm, along with a set of tissue optical properties obtained from in vivo measurements, is used to solve the forward problem. The measured and simulated light exittance images are found to differ by a factor of up to 2. The greatest cause of this moderate discrepancy is traced to the small errors in source positioning, and to a lesser extent to the optical properties used for the tissues. Discarding the anatomy and using a homogeneous model leads to a marginally worse agreement between the simulated and measured data.

Using metamaterial yokes in NMR measurements.

Swiss rolls are one instance of metamaterials, and can be described as an effective medium with a complex, anisotropic magnetic permeability. It has been shown that bundles of Swiss rolls can guide the magnetic flux in magnetic resonance measurements and increase the coupling between the nuclear spins and the receiver coil. Here, we investigate, with a numerical model, whether Swiss rolls can boost the detected signal in a NMR experiment, where the rolls could provide a low-reluctance return path for the magnetic flux when shaped in a yoke encircling the sample. The system consisting of the nuclear spin, the rolls and the receiver coil is analyzed with the method of finite differences in time domain (FDTD). The results show that small gains in the received signal are possible, but only if the losses (resistive and dielectric) in the rolls are reduced by over one order of magnitude from their present value in state-of-the-art materials. This situation arises because of the energy dissipation in the rolls and the mode splitting caused by the coupling between the rolls and the resonant coil.

Guest-host colloid crystals: experimental study and simulations.

Disorder in colloid crystals was induced by doping them with a different number of large or small guest particles, which had a different deviation in size from the host colloids. The change in optical properties of the guest-host colloid crystals was assessed by using optical transmission spectroscopy while the variation in crystal structure was examined using scanning electron microscopy (SEM). The disruption in the crystalline lattices depended on the relative deviation in sizes of the guest and host particles and the concentration of the guest colloids. In parallel with experiments, the packing of spheres in guest-host crystals was modeled with a simulated annealing algorithm. A good correlation was found between the changes in crystal structure observed by SEM imaging and the simulated sphere packing. The experimental and simulated changes in the transmission spectra of guest-host colloid crystals were in good agreement.

In situ study of colloid crystallization in constrained geometry.

We visualized in real time electrodeposition-driven colloid crystal growth on patterned conductive surfaces. The electrode was patterned with dielectric ribs and conductive grooves; the groove width was commensurate or incommensurate with a two-dimensional colloid crystal lattice. Electrodeposition was carried out against gravity to decouple sedimentation and electrodeposition of colloid particles. Our experiments reveal the following: (i) Colloid crystal growth occurs under the action of electrohydrodynamic forces, in contrast with colloid assembly under the action of capillary forces. (ii) Confinement of the colloid arrays reduces the size of particle clusters. Small clusters easily undergo structural rearrangements to produce close-packed crystals when the groove width is commensurate or nearly commensurate with the 2D lattice. (iii) Incommensurability between the two-dimensional crystalline lattice and the groove width exceeding ca. 15% leads to the formation of non-close-packed structures and the distortion of colloid arrays.