Ozonation of CI Reactive Black 5 using rotating packed bed and stirred tank reactor

This study investigates the ozonation of CI Reactive Black 5 (RB5) by using the rotating packed bed (RPB) and completely stirred tank reactor (CSTR) as ozone contactors. The RPB, which provides high gravitational force by adjusting the rotational speed, was employed as a novel ozone contactor. The same ozone dosage was separately introduced into either the RPB or the CSTR for the investigation, while the experimental solution was continuously circulated within the apparatus consisting of the RPB and CSTR. The decolorization and mineralization efficiencies of RB5 in the course of ozonation are compared for these two methods. Moreover, the dissolved and off‐gas ozone concentrations were simultaneously monitored for the further analysis. As a result, the ozone mass transfer rate per unit volume of the RPB was significantly higher because of its higher mass transfer coefficient and gas–liquid concentration driving force. Furthermore, ozonation kinetics was found to be independent of the gravitational magnitude of an ozone gas–liquid contactor. Therefore, the results suggest employing RPBs as ozone‐contacting devices with the advantage of volume reduction. The experimental results, which can be used for further modeling of the ozonation process in the RPB, also show the requirement of correct design for the RPB. Consequently, the present study is useful for the understanding of practical application of RPBs. Copyright © 2004 Society of Chemical Industry     

The number and biodiversity of the parasites from small mammals in the evacuation area of the Chernobyl Nuclear Power Station

The study of the micromammalian parasite complexes in the Belorussian part of the evacuation zone of the Chernobyl nuclear station revealed 13 species of Coccidia and 30 species of ectoparasitic Arthropoda. Total increase of abundance and biodiversity of both parasites and their hosts was observed. The part of ectoparasites being epidemically hazardous was significantly increased. An analysis of a long-term dynamics of parasite abundance reveals their adaptation to new conditions in the Belorussia.     

A stereoselective cobalt-containing nitrile hydratase

Nitrile hydratase from Pseudomonas putida NRRL-18668 has been purified and characterized. The purified enzyme catalyzes the hydration of 2(S)-(4'-chlorophenyl)-3-methylbutyronitrile at least fifty times faster than that of 2(R)-(4'-chlorophenyl)-3-methylbutyronitrile. This enzyme is a member of the class of nitrile hydratase that contains cobalt. Visible absorption and CD spectra suggest the cobalt exists as a non-corrin low-spin Co3+ ion in a tetragonally-distorted octahedral ligand field. Chemical reduction of the native enzyme results in a species with the EPR signature of a low-spin Co2+ complex. Like the other cobalt-containing nitrile hydratases, this enzyme is relatively stable, maintaining its activity below 35 degrees C, and it shows a broad activity optimum between pH 7.2 and 7.8. The structural genes for this enzyme have been cloned and sequenced. The deduced amino acid sequences for the alpha and beta subunits show 48-63% and 35-41% homology, respectively, to other sequenced nitrile hydratases. In particular, the cysteine residues in the alpha subunit that have been suggested to coordinate the metal ion in the iron-containing nitrile hydratases [Brennan, B. A., Cummings, J. G., Chase, D. B., Turner, I. M., Jr., & Nelson, M. J. (1996) Biochemistry 35, 10068-10077] are conserved in this enzyme, suggesting that this nitrile hydratase, like the enzyme from Rhodococcus rhodochrous J1, is a member of a newly described class of metalloenzymes with Co3+-thiolate ligation [Brennan, B. A., Alms, G., Nelson, M. J., Durney, L. T., & Scarrow, R. C. (1996) J. Am. Chem. Soc. 118, 9194-9195].     

Kinetic evidence for low chemical processivity in ncd and Eg5

We have examined the formation of hydroxyphenols, nitrophenols, and the minor products 4-nitrosophenol, benzoquinone, 2,2'-biphenol, and 4,4'-biphenol from the reaction of peroxynitrite with phenol in the presence and absence of added carbonate. In the absence of added carbonate, the product yields of nitrophenols and hydroxyphenols have different pH profiles. The rates of nitration and hydroxylation also have different pH profiles and match the trends observed for the product yields. At a given pH, the sum of the rate constants for nitration and hydroxylation is nearly identical to the rate constant for the spontaneous decomposition of peroxynitrite. The reaction of peroxynitrite with phenol is zero-order in phenol, both in the presence and absence of added carbonate. In the presence of added carbonate, hydroxylation is inhibited, whereas the rate of formation and yield of nitrophenols increase. The combined maximum yield of o- and p-nitrophenols is 20 mol% (based on the initial concentration of peroxynitrite) and is about fourfold higher than the maximal yield obtained in the absence of added carbonate. The o/p ratio of nitrophenols is the same in the presence and absence of added carbonate. These results demonstrate that hydroxylation and nitration occur via two different intermediates. We suggest that the activated intermediate formed in the isomerization of peroxynitrous acid to nitrate, ONOOH*, is the hydroxylating species. We propose that intermediate 1, O=N-OO-CO2-, or secondary products derived from it, is (are) responsible for the nitration of phenol. The possible mechanisms responsible for nitration are discussed.     

Association of INAD with NORPA is essential for controlled activation and deactivation of Drosophila phototransduction in vivo

Visual transduction in Drosophila is a G protein-coupled phospholipase C-mediated process that leads to depolarization via activation of the transient receptor potential (TRP) calcium channel. Inactivation-no-afterpotential D (INAD) is an adaptor protein containing PDZ domains known to interact with TRP. Immunoprecipitation studies indicate that INAD also binds to eye-specific protein kinase C and the phospholipase C, no-receptor-potential A (NORPA). By overlay assay and site-directed mutagenesis we have defined the essential elements of the NORPA-INAD association and identified three critical residues in the C-terminal tail of NORPA that are required for the interaction. These residues, Phe-Cys-Ala, constitute a novel binding motif distinct from the sequences recognized by the PDZ domain in INAD. To evaluate the functional significance of the INAD-NORPA association in vivo, we generated transgenic flies expressing a modified NORPA, NORPAC1094S, that lacks the INAD interaction. The transgenic animals display a unique electroretinogram phenotype characterized by slow activation and prolonged deactivation. Double mutant analysis suggests a possible inaccessibility of eye-specific protein kinase C to NORPAC1094S, undermining the observed defective deactivation, and that delayed activation may similarly result from NORPAC1094S being unable to localize in close proximity to the TRP channel. We conclude that INAD acts as a scaffold protein that facilitates NORPA-TRP interactions required for gating of the TRP channel in photoreceptor cells.     

Inhibition of acid secretion in gastric parietal cells by the Ca2+/calmodulin-dependent protein kinase II inhibitor KN-93

A novel Ca2+/calmodulin-dependent protein kinase II (CaM Kinase II) inhibitor, KN-93 potently inhibits gastric acid secretion from parietal cells. As previously reported (1), treatment of parietal cells with a selective inhibitor of CaM kinase II, KN-62 resulted in the inhibition of cholinergic-stimulated rabbit parietal cell secretion, whereas it failed to inhibit the histamine and forskolin response. In contrast effects of carbachol, histamine and forskolin were significantly inhibited by KN-93 with an IC50 of 0.15, 0.3 and 1 microM, respectively; these effects occurred without any changes in intracellular cyclic AMP and Ca2+ levels. In the present study we investigated the mechanism by which KN-93 acts upon the acid-secreting machinery of gastric parietal cells. Neither redistribution of the proton pump activity nor the morphological transformation were affected by KN-93. The drug only weakly inhibited the H+, K(+)-ATPase activity but strongly dissipated the proton gradient formed in the gastric membrane vesicles and reduced the volume of luminal space. Thus KN-93 acts at pH gradient formation whereas KN-62 acts only at CaM Kinase II.