Discovery of nitric oxide in marine ecological system and the chemical characteristics of nitric oxide

Nitric oxide was discovered in both the lab and the alga culture pond of Daya Bay (1―300 m3) before the growth of alga reached the maximum. The results included: (1) NO was detected before the growth of alga reached the maximum in the case of red tide alga and food alga, and the concentration of NO decreased rapidly after the growth maximum; (2) the curve between NO con-centration and time indicated that the concentration of NO in the daytime was more than that at night, and the maximal concentration of NO appeared in the midday (1―3 pm); (3) the growth of alga reached the maximum in the alga culture pond of Daya Bay in about 8―10 d, and NO was discovered in 5―7 d; (4) the measured NO concentration was 10-9 mol/L, 10-9―10-8 mol/L, and 10-8 mol/L for Haeterosigma akashiwo, mixed alga in Daya Bay and Chaetoceros Curvisetus individually; (5) the relation of illumination with NO production was discussed.     

A novel oxygen-dependent deoximation by nitric oxide

A variety of aldoximes and ketoximes were oxidized to corresponding aldehydes and ketones by nitric oxide in the presence of oxygen.A presumed mechanism was suggested.     

The reaction of oximes with 4-phenyl-1,2,4-triazoline-3,5-dione to produce nitric oxide – Model compounds for nitric oxide synthase

Certain oximes form nitric oxide upon reaction with 4-phenyl-1,2,4-triazole-3,5-dione (PTAD). The oximes appear to undergo an Alder-ene reaction with the PTAD enophile to form a nitroso intermediate capable of dimerization and/or nitric oxide formation. Upon exposure to oxygen, the nitroso compounds eventually form ketones. This reaction may serve as a model for the study of nitric oxide synthase (NOS), the enzyme responsible for physiological production of nitric oxide. NOS is known to produce an oxime intermediate which reacts with oxygen to produce nitric oxide and citrulline.     

Oxidative aromatization of 3,5-disubstituted 2-isoxazolines by nitric oxide

3,5-Disubstituted 2-isoxazolines were oxidized to corresponding isoxazoles by nitric oxide in dichloromethane. The reaction more likely occurred via a one-electron transfer process.     

The features of nitric acid ‘mercerization’ of cellulose

Transformation of native cellulose species into cellulose-II polymorph through the additive Knecht compound formed under the action of 68.5% nitric acid has been studied. Probable causes of peculiar temperature effects in the course of phase transformations taking place in cellulose of various origin, crystallite dispersity, or morphologic structure are discussed. The processes of hydrolytic destruction and esterification of starting materials during their mercerization by this non-traditional agent at 20 °C and 0 °C are quantitatively characterized. In the case of mercerization of wood microcrystalline cellulose at 20 °C a decrystallizing effect due to side reactions of partial nitration is noted.     

Cerium oxide nanoparticles scavenge nitric oxide radical (˙NO)

In this study we have obtained evidence that cerium oxide nanoparticles (CeO(2) NPs) are able to scavenge nitric oxide radical. Surprisingly, this activity is present in CeO(2) NPs with a lower level of cerium in the 3+ state (CeO(2) NPs with low 3+/4+ ratio and therefore a reduced number of oxygen vacancies), in contrast to the superoxide scavenging properties which are correlated with an increased level of cerium in the 3+ state (CeO(2) NPs with high 3+/4+ ratio and therefore an increased number of oxygen vacancies).     

Interaction characteristics with bovine serum albumin and retarded nitric oxide release of ZCVI₄-2, a new nitric oxide-releasing derivative of oleanolic acid

ZCVI?-2 is a newly developed furoxan-based nitric oxide-releasing derivative of oleanolic acid. It exhibited strong cytotoxicity against human hepatocellular carcinoma (HCC) in vitro and significantly inhibited the growth of HCC tumors in vivo. However, its low aqueous solubility and toxicity due to the fast release of nitric oxide (NO) in blood challenged its formulation. In the present investigation, the interaction characteristics of ZCVI?-2 with bovine serum albumin (BSA) were studied by fluorescence spectrometry, synchronous fluorescence spectra and Fourier transform-infrared (FT-IR). It was found that ZCVI?-2 concentration, temperature and pH had significant effect on the interactions. ZCVI?-2 was able to bind BSA with high affinity, low temperature and neutral pH favor the binding. The interaction exhibited to be a spontaneous and exothermic process. ZCVI?-2 was buried in the hydrophobic pocket in subdomain IIB of BSA and the exact binding site was around 3.83 nm in average from Trp212. The NO releasing characteristics of nanocomplexes were compared with ZCVI?-2 solution by Griess Reagent Method. It was found that the release of NO from ZCVI?-2/BSA nanocomplexes was retarded significantly, thus making ZCVI?-2 into a BSA-bound nanocomplexes had the great potential to lower the toxicity due to the absence of organic solvents and surfactants and meanwhile the sustained release of NO.     

γ-ray radiolysis of dihydroxyurea in nitric acid and its radiolytic products

Journal of Radioanalytical and Nuclear Chemistry - Dihydroxyurea (DHU) is a new salt-free reducing agent applied for the separation of Pu and Np from U in spent fuel reprocessing. This paper...     

Speciation of 30 % tri-n-butyl phosphate solvent during extraction of nitric acid

Several solutions of 30 % TBP/n-dodecane were equilibrated with different concentrations of aqueous nitric acid solutions at 298.15 K at a phase ratio of unity. The resultant equilibrated aqueous and organic solutions were analyzed for acidity. A three-solvate model with molecular HNO₃ based mechanism was assumed for nitric acid extraction by TBP. With nonlinear chemometric methods, the coefficients were evaluated. With the set of optimized coefficients, derived on the basis of experiments reported in this work, the estimated solvate species and free-TBP species in the TBP containing organic phase were found to be in good agreement with the reported concentrations in the literature.     

Effect of tri-n-butyl phosphate on physical properties of dodecane–nitric acid system

Extraction power of solvent depends upon the physical properties of the system. Tri-n-butyl phosphate (TBP) in dodecane is a versatile solvent used in the nuclear fuel reprocessing like PUREX process. The study of physical properties like density, viscosity, interfacial tension and solubility for TBP–nitric acid–dodecane system will be helpful in carrying out different extraction studies during PUREX process. Thus, physical properties like density, viscosity, interfacial tension and solubility have been measured for TBP–nitric acid–dodecane system using pycnometer, viscometer, pendant drop method and high performance liquid chromatography respectively. It has been observed that density and viscosity increases but interfacial tension and solubility decreases with the concentration of TBP in dodecane–nitric acid system. Physical properties of 30 % TBP–nitric acid–dodecane system have also been studied in detail. All these studies will also be useful in stripping out dissolved TBP from the nuclear waste.     

The role of oxidizing radicals in neptunium speciation in γ-irradiated nitric acid

The irradiation of aqueous nitric acid solutions generates transient, reactive species that are known to oxidize neptunium. However, nitrous acid is also a long-lived product of nitric acid irradiation, which reduces neptunium. When we irradiated nitric acid solutions of neptunium and measured its speciation by UV/Vis spectroscopy, we found that at short irradiation times, oxidation of Np(V) to Np(VI) occurred due to reactions with radicals such as ^?OH, ^?NO₃ and ^?NO₂. However, at higher absorbed doses and after a sufficient amount of nitrous acid was produced, reduction of Np(VI) to Np(V) began to occur, eventually reaching an equilibrium distribution of these species depending on nitric acid concentration. Neptunium(IV) was not produced.     

Nitrogen doping into titanium dioxide by the sol–gel method using nitric acid

N-doped TiO₂ has been prepared by use of sol–gel systems containing titanium alkoxide, with nitric acid as the nitrogen source. The time needed for gelation of the systems was drastically reduced by ultrasonic irradiation. The peaks assigned to the nitrate and nitrous ions were observed by FT-IR measurement during the sol–gel reaction. The N-doping was confirmed by the observation of N–O peaks in the XPS spectrum of the sample heated at 400 °C. The nitrate ion acted as an oxidizer of the ethanol solvent and titanium species. The TiO₂ became doped with nitrogen oxide species as a result of reduction of nitrate ion incorporated into the dried gel samples. These results indicated that the added nitric acid was reduced during the sol–gel transition and heating process, and the resulting NO species were situated in the titania networks. The UV and visible photocatalytic activity of the samples was confirmed by the degradation of trichloroethylene.     

Is nitric oxide (NO) an antioxidant or a prooxidant for lipid peroxidation?

Antioxidant and prooxidant effects of nitric oxide (NO) on lipid peroxidation in aqueous and non-aqueous media were examined. In an aqueous solution, NO did not induce peroxidation of unoxidized methyl linoleate (ML) and suppressed the radical initiator-induced oxidation of ML. NO suppressed the Fe(II) ion-induced oxidation of mouse liver microsomes. NO reduced the O2 consumption during the radical initiator-induced oxidation of linoleic acid in an aqueous medium. NO conversion into NO2- in an aqueous medium was not affected by unoxidized ML and was slightly reduced by peroxidizing ML. On the other hand, as well as pure NO2, NO induced peroxidation of unoxidized ML in n-hexane in a dose-dependent fashion. NO did not suppress the radical initiator-induced oxidation of ML in n-hexane. Nitrogen oxide species (NO2 or N2O3) formed by autoxidation was dramatically lost in n-hexane in the presence of unoxidized ML. The results indicated that NO terminated lipid peroxidation in an aqueous medium, whereas NO induced lipid peroxidatiton in a non-aqueous medium. Hence, NO showed both antioxidant and prooxidant effects on lipid peroxidation depending on the solvents.     

A novel copper(Ⅱ) complex-based fluorescence probe for nitric oxide detecting and imaging

A novel copper(II) complex CuQNE with a naphthalimide-containing ligand was synthesized as a fluorescent sensor of nitric oxide (NO). It featured eightfold fluorescent enhancement toward NO from a dark-background with the detection limit of NO about 1 nM in aqueous solution. The fluorescence response of the CuQNE was specific for NO, the presence of other reactive oxygen species (ROS) and reactive nitrogen species (RNS) did not interfere with the detection of NO in aqueous solution. LC–MS and IR spectra of the reaction mixture both demonstrated that the fluorescence enhancement was possibly attributed to an NO-induced nitrosation of the amino group. Confocal fluorescence images of MCF-7 cells suggested that CuQNE could be applied for monitoring intracellular NO.     

Adsorption and corrosion inhibition behavior of polyethylene glycol on α-brass alloy in nitric acid solution

The corrosion performance of α-brass in 1 M HNO₃ and in the presence of polyethylene glycol (PEG) has been investigated using AC impedance spectra (EIS), potentiodynamic polarization (PP), electrochemical frequency modulation (EFM), and mass reduction (MR) techniques. The outcome data of EIS showed a rise in the resistance charge transfer (R_ct) and a decrease in the capacitance double layer (C_dl). Protection efficiency (IE) of PEG has been obtained by varying the dose of the PEG and temperature. PEG adsorbed on α-brass in acidic solution follows isotherm Langmuir. The polarization curves displayed that PEG acts as a mixed-kind inhibitor. The parameters obtained from thermodynamic activation of corrosion α-brass in 1 M HNO₃ were obtained and debated. The results obtained from all tests were in excellent agreement.     

Lanthanide–actinide separation by bis-2-ethylhexylphosphoric acid from citric acid–nitric acid medium

Phosphate rock (Pho-ore) is the starting raw material used in manufacturing of most phosphate products. This material contains phosphorous, natural uranium, thorium potassium radionuclide and other trace elements. Single super phosphate powder (SSPho-P), single super phosphate granules (SSPho-G), and triple super phosphate (TSPho) are the common phosphate products produced along with phosphogypsym (CaSO₄) as a waste product. Since these materials are industrially manufactured by the reaction of the phosphate ore with phosphoric and sulphuric acids, these products and the waste product are extremely acidic. Pho-ore, SSPho-P, SSPho-G, TSPho and CaSO₄ samples were used in our study. Chemical analyses showed that these phosphate samples contain phosphorous, iron, aluminum ions and traces of uranium ions. Accumulation of the fertilizers on soils usually transfers some of these ions from the fertilizer materials to the soil/water interfaces. The migration of uranium U(VI), P, Al and Fe in subsurface soils was found to be strongly influenced by the sorption/desorption reaction at the solid/water interfaces. Thus, dissolution of these ions in soil/water phases is very important. Speciation of U(VI), P, Al and Fe in soil/water phases were calculated using a geochemical code (MINTEQA2). This study was conducted to determine sorption properties and the surface electrical properties of these ions at the soil samples.     

L-arginine binding to human inducible nitric oxide synthase: an antisymmetric funnel route toward isoform-specific inhibitors?

Nitric oxide (NO) is an important signaling molecule produced by a family of enzymes called nitric oxide synthases (NOS). Because NO is involved in various pathological conditions, the development of potent and isoform-selective NOS inhibitors is an important challenge. In the present study, the dimer of oxygenase domain of human iNOS (iNOSoxy) complexed to its natural substrate L-arginine (L-Arg) and both heme and tetrahydro-L-biopterin (BH4) cofactors was studied through multiple molecular dynamics simulations. Starting from the X-ray structure available for that complex (PDB: 1NSI ), a 16 ns equilibration trajectory was first obtained. Twelve dynamics of slow extraction of L-Arg out from the iNOSoxy active site were then performed. The steered molecular dynamics (SMD) approach was used starting from three different points of the reference trajectory for a total simulation time of 35 ns. A probable unbinding/binding pathway of L-Arg was characterized. It was suggested that a driving force directed the substrate toward the heme pocket. Key intermediate steps/residues along the access route to the active site were identified along this "funnel shape" pathway and compared to existing data. A quasi-normal mode analysis performed on the SMD data suggested that large collective motions of the protein may be involved in L-Arg binding and that opening the route to the active site in one monomer promoted an inverse, closing motion in the second monomer. Finally, our findings might help to rationalize the design of human iNOS isoform competitive inhibitors.     

Oxygen-carrying plasma hemoprotein “albumin-heme”: nitric oxide binding and physiological responses after administration in vivo

Recombinant human serum albumin complexed with tetraphenylporphinatoiron(II) derivative, “albumin-heme (rHSA-FeP)”, is a synthetic oxygen (O₂)-carrying plasma hemoprotein, which becomes a new class of red blood cell substitute. The UV-vis. absorption and ESR spectroscopy revealed that rHSA-FeP formed six-coordinate nitrosyl complex after exposure of nitric oxide (NO) gas. Although the NO-binding affinity of rHSA-FeP (P_1/2^NO: 1.7 × 10⁻⁶ Torr, pH 7.3, 25°C) is 9-fold higher compared to that of hemoglobin (Hb), the administration of this artificial hemoprotein solution into anesthetized rat does not induce an acute increase in blood pressure (hypertension), which is often observed in Hb-based O₂-carriers due to the depletion of NO (endothelial derived relaxing factor).     

Separation of Am(III) from nitric acid medium by phosphonium ionic liquid–hydroxyacetamide mixture

A strongly hydrophobic phosphonium ionic liquid, trihexyltet radecylphosphonium bis(trifluoromethanesulfonyl)imide ([P₆₆₆₁₄][NTf₂]) was employed as the diluent for the extraction behavior of Am(III) using N,N-dihexyl-2-hydroxyacetamide(DHHy) as extractant. The extractibility of americium(III) in [P₆₆₆₁₄][NTf₂] phase was measured as a function of various parameters such as aqueous phase acidity (0.1–8 M), extractant concentration (0.01–0.15 M), equilibration time (5–120 min) and temperature (298–333 K). The extraction performance observed in DHHy/[P₆₆₆₁₄][NTf₂] was compared with those observed in N,N-dihexyloctamide (DHOA) in [P₆₆₆₁₄][NTf₂] and DHHy in other diluents such as [C₄mim][NTf₂] and n-dodecane. The effect of temperature on D _Am(III) in ionic liquid system and recovery of Am(III) from the loaded phase were ascertained in detail.