Actions Of HNO Research Articles

Nitroxyl, the novel redox sibling of NO, suppresses cerebrovascular NADPH oxidase

Background: Nitroxyl (HNO), the reduced and protonated congener of nitric oxide (NO), is emerging as a novel entity with distinct pharmacology and therapeutic advantages over NO• [1]. Importantly, HNO has vasoprotective actions with the potential to serve as an antioxidant. Here we explored the ability of HNO to modulate cerebrovascular NADPH oxidase activity, a major source of superoxide (.O2-) in the vasculature. Materials and methods: Intracranial (pooled middle cerebral and basilar) and extracranial (carotid) cerebral arteries from male C57BL/6J mice were treated with angiotensin II (10 nM) acutely (30 min) and chronically (24 h), respectively, in the absence and presence of the HNO donor, Angeli's salt (AS). NADPH (100 μM)-stimulated .O2- production was then measured using lucigenin (5 μM)-enhanced chemiluminescence. Results: AS (1 μM) did not scavenge .O2- generated in a cell free xanthine (100 μM)/xanthine oxidase (0.05 U/ml) activity assay (control: 447.9 ± 90.8; AS 507.1 ± 113.3 counts, n = 4). In contrast, acute and chronic treatment with AS (0.01–1 μM) caused a concentration-dependent decrease in NADPH oxidase-derived .O2- production by intracranial and extracranial cerebral arteries, respectively (carotid 0.59 ± 0.05; AS 0.1 μM 0.33 ± 0.08; AS 1 μM 0.16 ± 0.03 103 counts/s/mg, P < 0.05, n = 8). The effects of AS were reversed by the HNO scavenger, L-cysteine (3 mM) but unchanged in the presence of the NO• scavenger carboxy-PTIO (200 μM) and sGC inhibitor, ODQ (10 μM). Conclusion: HNO suppresses vascular NADPH-oxidase activity both acutely and chronically, possibly via a cGMP-independent mechanism. Such antioxidant actions of HNO may confer therapeutic advantages in the treatment of cerebrovascular disorders.

Denitration of cellulose nitrate under the action of aqueous nitric acid

The heterophase transformation of cellulose nitrate (CN) under the action of HNO 3 is characterized by a stronger dependence of the reaction rate on the acid concentration compared with the case of the reaction with H 2SO 4. For the same values of the acidity function H 0 the rate of denitration in HNO 3 may be higher by several orders. In relatively concentrated HNO 3 (65%) the reaction is greatly inhibited and is even stopped owing to competition of the reverse reaction of nitration. When reduced to medium acidity the denitration rate is the same in HNO 3 as in H 2SO 4. In 80% HNO 3 at temperatures above 80°C the rate becomes lower than that which is characteristic for acidic hydrolysis, as the reaction begins to be limited by diffusion of the acid in CN fibres. On the basis of the information obtained on the kinetics of denitration of pyroxylin No. 1 the effective rate constants have been determined for the acidic hydrolysis of cellulose tri-, di- and mononitrates, and for the nitration of cellulose and its mono- and dinitrate.

The characterisation of carbon-fibre-paper-supported platinum and platinum-ruthenium catalysts using temperature-programmed reduction and cyclic voltammetry

Temperature-programmed reduction (TPR) and cyclic voltammetry have been used to investigate Pt and PtRu dispersed catalysts unsupported and supported on conducting carbon at various stages of the catalyst preparation. Differences in the TPR profiles and the corresponding uptake of H 2 by unsupported and supported Pt(NH 3) 2(NO 2) 2 dried from HNO 3 solution at 120 °C are attributed to an interaction via ligand exchange between the nitrato-substituted Pt complex and nucleophilic surface groups formed on the carbon support by the action of HNO 3. A similar interaction was observed for carbon-supported Ru salts prepared from RuNO(NO 3) x . Support interactions present after the drying stage led to an enhanced catalyst dispersion and to the elimination of the original interaction after activation in air at 300 °C. Bimetallic PtRu catalysts display reducibilities in TPR intermediate between those observed for the pure components in both unsupported and supported forms. The influence of the carbon support is absent after activation in air. At 300 °C, activation produces a high bimetallic dispersion (90 m 2 g −1) whereas activation at 400 °C leads to more perfect alloy formation and consequently to an increased intrinsic activity as an electrocatalyst for methanol oxidation at the expense of a reduced dispersion (54 m 2 g −1). Cathodic processes at 0.1–0.4 V (vs RHE) during the initial linear potential sweep, corresponding to oxide reduction, are observed for air-activated Pt and PtRu catalysts. Electrochemical reduction of oxide species in this way is analogous to the characteristic processes observed in TPR except that initial cathodic reduction extends ca.4 atomic layers into the oxide particles. Our conclusions concerning air-activated Pt catalysts, largely composed of PtO 2, are in essential agreement with similar studies of oxide layers formed electrochemically on smooth Pt electrodes.