Possibility of long-distance heat transport in weightlessness using supercritical fluids.

Heat transport over large distances is classically performed with gravity or capillarity driven heat pipes. We investigate here whether the "piston effect," a thermalization process that is very efficient in weightlessness in compressible fluids, could also be used to perform long-distance heat transfer. Experiments are performed in a modeling heat pipe (16.5 mm long, 3 mm inner diameter closed cylinder), with nearly adiabatic polymethylmethacrylate walls and two copper base plates. The cell is filled with H2 near its gas-liquid critical point (critical temperature: 33 K). Weightlessness is achieved by submitting the fluid to a magnetic force that compensates gravity. Initially the fluid is isothermal. Then heat is sent to one of the bases with an electrical resistance. The instantaneous amount of heat transported by the fluid is measured at the other end. The data are analyzed and compared with a two-dimensional numerical simulation that allows an extrapolation to be made to other fluids (e.g., CO2, with critical temperature of 300 K). The major result is concerned with the existence of a very fast response at early times that is only limited by the thermal properties of the cell materials. The yield in terms of ratio, injected or transported heat power, does not exceed 10-30% and is limited by the heat capacity of the pipe. These results are valid in a large temperature domain around the critical temperature.

Microbial remediation of NTO in aqueous industrial wastes.

The bioremediation of aqueous wastes containing 5-nitro-1,2,4-triazol-3-one (NTO) was investigated. The microorganism used is a Bacillus licheniformis strain, isolated from the contaminated solutions by enrichment techniques. The biodegradation was carried out in the waste (15 g l-1 NTO) and proceeded through the nitroreduction of NTO, followed by the ring cleavage of the formed primary amine 5-amino-1,2,4-triazol-3-one (ATO). Both steps were optimized and according to the optimal conditions, the nitroreduction of NTO is total in 24 h, while the degradation of ATO requires 2 weeks of incubation. The end products of the biodegradation were carbon dioxide (40%), urea and a polar compound, assumed to be hydroxyurea. A mechanism of ATO ring cleavage was postulated in the light of experimental data, and led us to propose an overall degradation sequence for NTO.

Photocatalytic degradation of 5-nitro-1,2,4-triazol-3-one NTO in aqueous suspension of TiO2. Comparison with Fenton oxidation.

5-nitro-1,2,4-triazol-3-one (NTO) is a powerful insensitive explosive, present in industrial waste waters. A remediation method based on photochemical decomposition and Fenton oxidation of NTO has been evaluated by monitoring the mineralization of 14C-labelled NTO. The TiO2-catalyzed photodegradation (lambda > 290 nm, TiO2 0.4 g/l, NTO 150 mg/l)) leads to the complete mineralization of NTO in 3 hours. This degradation involves a simultaneous denitrification and ring scission of NTO leading to nitrites, nitrates and carbon dioxide. No significant photo-degradation of NTO was detected in the absence of the catalyst. Long term irradiation over one week, leads to a complete degradation of concentrated NTO (5 g/l), suggesting that this method could be useful to clean-up NTO wastes. Fenton oxidation offers an efficient cost-effective method for NTO remediation. This reaction is faster that the TiO2 catalyzed photolysis and find application on the mineralization of high concentrations of NTO (15 g/l). Fenton oxidation provokes ring cleavage and subsequent elimination of the two carbon atoms of NTO as CO2. During this reaction, the nitro group is completely transformed into nitrates.

Metabolism of 14C-labelled 5-nitro-1,2,4-triazol-3-one by rat liver microsomes--evidence for the participation of cytochrome P-450.

In the present study, we synthesized 14C-labelled 5-nitro-1,2,4-triazol-3-one (NTO) and investigated its hepatic metabolism by dexamethasone-induced murine hepatic microsomes. Under the nitrogen atmosphere, 5-amino-1,2,4-triazol-3-one was the only detected metabolite of NTO. The microsomal nitroreductase activity was dependent on NADPH, totally inhibited by carbon monoxide and partially inhibited by oxygen. In aerobic conditions, beside a low amount of amine, the major metabolite formed is the 5-hydroxy-triazolone, urazole. This compound resulted from the oxidative denitrification of NTO, which produced equivalent amount of nitrite. This reaction, like the nitroreductase activity, was dependent on NADPH and totally inhibited by carbon monoxide. Both nitroreduction and oxidative denitrification were inhibited by imidazole-related inhibitors: miconazole and methimazole, and to a less extent by N-octylamine. The microsomal denitrification was induced by the treatment of rats with dexamethasone and phenobarbital. The microsomal reductase activity is present in untreated rat microsomes, and recovered with various inducers. The results of this study indicate the role played by cytochrome P-450 in the metabolism of NTO, supported by its transformation with reconstituted cytochrome P-450 systems.

Bromocriptine is a strong inhibitor of brain nitric oxide synthase: possible consequences for the origin of its therapeutic effects.

The ergot alkaloid bromocriptine (BKT) was found to act as a strong inhibitor of purified neuronal nitric oxide synthase (NOS) (IC50 = 10 +/- 2 microM) whereas it was poorly active towards inducible macrophage NOS (IC50 > 100 microM). BKT affects the activation of NOS by calmodulin, as it not only inhibits L-arginine oxidation to NO and L-citrulline but also NADPH oxidation and calmodulin-dependent cytochrome c reduction catalyzed by neuronal NOS. These results suggest that BKT could exert some of its therapeutic effects by interfering with the NOS-dependent formation of nitric oxide and/or superoxide ion in various tissues.

Dechlorination of Atrazine by a Rhizobium sp. Isolate.

A Rhizobium sp. strain, named PATR, was isolated from an agricultural soil and found to actively degrade the herbicide atrazine. Incubation of PATR in a basal liquid medium containing 30 mg of atrazine liter(sup-1) resulted in the rapid consumption of the herbicide and the accumulation of hydroxyatrazine as the only metabolite detected after 8 days of culture. Experiments performed with ring-labeled [(sup14)C]atrazine indicated no mineralization. The enzyme responsible for the hydroxylation of atrazine was partially purified and found to consist of four 50-kDa subunits. Its synthesis in PATR was constitutive. This new atrazine hydrolase demonstrated 92% sequence identity through a 24-amino-acid fragment with atrazine chlorohydrolase AtzA produced by Pseudomonas sp. strain ADP.

Strong inhibition of neuronal nitric oxide synthase by the calmodulin antagonist and anti-estrogen drug tamoxifen.

The anti-estrogen drug tamoxifen (TMX) was found to act as a strong inhibitor of purified neuronal nitric oxide synthase (nNOS) (IC50 = 2 +/- 0.5 microM), whereas it was inactive toward inducible macrophage NOS (IC50 > 100 microM). TMX affected the activation of NOS by calmodulin, as it not only inhibited L-arginine oxidation to nitric oxide and L-citrulline but also NADPH oxidation and calmodulin-dependent cytochrome c reduction catalyzed by nNOS. These results suggest that TMX could exert some of its biological effects by interfering with constitutive NOS-dependent formation of nitric oxide and/or superoxide ion in various tissues.

Horseradish peroxidase and glycosylated BSA induce nitric oxide production in murine macrophages.

The in vitro activation of murine macrophages by horseradish peroxidase (HRP) induced nitric oxide production in a dose-dependent manner, and increased the induction of NO-synthase by LPS. Nitrite production after HRP stimulation was inhibited by NG-monomethyl-L-arginine (NMMA), a specific inhibitor of NO-synthase. Equivalent amounts of nitrite were obtained with native and heat-inactivated HRP. High concentrations of mannose inhibited nitric oxide production, while the HRP inhibitor 3-aminotyrosine did not. Glycosylated serum albumin derivatives also induced murine macrophage NOS, probably by an interaction between carbohydrates and their specific cell membrane receptors. The inability of HRP apoprotein to stimulate NO production, and the specific inhibition of HRP-mediated activation of macrophages by hemin suggests that the heme moiety of this enzyme is involved in NO-synthase induction.