Understanding the Role of Hyponitrite in Nitric Oxide Reduction

Herein, we review the preparation and coordination chemistry of cis and trans isomers of hyponitrite, [N2O2](2-). Hyponitrite is known to bind to metals via a variety of bonding modes. In fact, at least eight different bonding modes have been observed, which is remarkable for such a simple ligand. More importantly, it is apparent that the cis isomer of hyponitrite is more reactive than the trans isomer because the barrier of N2O elimination from cis-hyponitrite is lower than that of trans-hyponitrite. This observation may have important mechanistic implications for both heterogeneous NOx reduction catalysts and NO reductase. However, our understanding of the hyponitrite ligand has been limited by the lack of a general route to this fragment, and most instances of its formation have been serendipitous

Learning user queries in multimodal dissimilarity spaces

Different strategies to learn user semantic queries from dissimilarity representations of video audio-visual content are presented. When dealing with large corpora of videos documents, using a feature representation requires the online computation of distances between all documents and a query. Hence, a dissimilarity representation may be preferred because its offline computation speeds up the retrieval process. We show how distances related to visual and audio video features can directly be used to learn complex concepts from a set of positive and negative examples provided by the user. Based on the idea of dissimilarity spaces, we derive three algorithms to fuse modalities and therefore to enhance the precision of retrieval results. The evaluation of our technique is performed on artificial data and on the complete annotated TRECVID corpus

Nodulating symbiotic bacteria and soil quality

Chapitre 9 : Plant microbe interactions and soil quality Partie : 9-2International audienc

Heme oxidation in a chimeric protein of the α-selective Neisseriae meningitidis heme oxygenase with the distal helix of the δ-selective Pseudomonas aeruginosa

Heme oxygenases from the bacterial pathogens Neisseriae meningitidis (nm-HO) and Pseudomonas aeruginosa (pa-HO) share significant sequence identity (37%). In nm-HO, biliverdin IXα is the sole product of the reaction, whereas pa-HO yields predominantly biliverdin IXδ. We have previously shown by NMR that the in-plane conformation of the heme in pa-HO is significantly different from that of nm-HO as a result of distinct interactions of the heme propionates with the protein scaffold [Caignan, G. A., Deshmukh, R., Wilks, A., Zeng, Y., Huang, H. W., Moenne-Loccoz, P., Bunce, R. A., Eastman, M. A., and Rivera, M. (2002) J. Am. Chem. Soc. 124, 14879-14892]. In the report presented here, we have extended these studies to investigate the role of the distal helix by preparing a chimera of nm-HO (nm-HOch), in which distal helix residues 107-142 of nm-HO have been replaced with the corresponding residues of the δ-regioselective pa-HO (112-147). Electronic absorption spectra, resonance Raman and FTIR spectroscopic studies confirm that the orientation and hydrogen bonding properties of the proximal His ligand are not significantly altered in the chimera relative those of the wild-type proteins. The catalytic turnover of the nm-HOch-heme complex yields almost exclusively α-biliverdin and a small but reproducible amount of δ-biliverdin. NMR spectroscopic studies reveal that the altered regioselectivity in the chimeric protein likely stems from a dynamic equilibrium between two alternate in-plane conformations of the heme (in-plane heme disorder). Replacement of K16 with Ala and Met31 with Lys in the chimeric protein in an effort to tune key polypeptide-heme propionate contacts largely stabilizes the in-plane conformer conducive to δ-meso hydroxylation. © 2005 American Chemical Society