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1.
NO3?-dependent O2 in synchronous Scenedesmus obtusiusculus Chod. in the absence of CO2 is stoichiometric with NH4+ excretion, indicating a close coupling of NO3? reduction to non-cyclic electron flow. Also in the presence of CO2, NO3? stimulates O2 evolution as manifested by an increase in the O2/CO2 ratio from 0.96 to 1.11. This quotient was increased to 1.36 by addition of NO2?, without competitive interaction with CO2 fixation, indicating that the capacity for non-cyclic electron transport at saturating light is non-limiting for simultaneous reduction of NO3? and CO2 at high rates. During incubation with NO3?+ CO2, no NH4+ is released to the outer medium, whereas during incubation with NO2?+ CO2, excess NH4+ is formed and excreted. NO3? uptake is stimulated by CO2, and this stimulation is also significant when the cellular energy metabolism is restricted by moderate concentrations of carbonyl cyanide-p-trifluoromethoxyphenylhydrazone, whereas NO3? uptake in the absence of CO2 is severely inhibited by the uncoupler. Also under energy-restricted conditions NO3? uptake is not competitive with CO2 fixation. Antimycin A is inhibitory for NO3? uptake in the absence of CO2, and there is no enhancement of NO3? uptake by CO2 in the presence of antimycin A. It is assumed that the energy demand for NO3? uptake is met by energy fixed as triosephosphates in the Calvin cycle. Antimycin A possibly affects the transfer of reduced triose phosphates from the chloroplast to the cytoplasm. Active carbon metabolism also seems to exert a control effect on NO3? assimilation, inducing complete incorporation of all NO3? taken up into amino acids. This control effect is not functional when NO2? is the nitrogen source. Active carbon metabolism thus seems to be essential both for provision of energy for NO3? uptake and for regulation of the process.  相似文献   

2.
Developing an effective method for the detection of nitrite (NO2) ions in the natural environment especially in environmental waters and soils is very necessary, since they will cause serious damage to human health once excess NO2 ions enters the human body. Therefore, a new colorimetric fluorescent probe NB-NO2 for determining NO2 ions was designed, which possesses good water-solubility and satisfactory selectivity over other common ions for NO2 ions. The addition of NO2 ions changed the color of solution from blue to colorless seen by the naked-eye. Furthermore, through test and calculation, the detection limit of the probe NB-NO2 is 129 nM. Based on the earlier excellent characteristics, the probe NB-NO2 was successfully used for monitoring NO2 ions in environmental waters and soils.  相似文献   

3.
The acute toxicity of nitrite (NO?2) to salmonids is strongly ameliorated by chloride (Cl?) ions rendering it almost harmless in most fresh waters apart from those with low Cl? content. In Cl? poor fresh water external NO?2 is concentrated in the blood plasma until it is at approximately the same molar concentration as haemoglobin (about 8 mmol) and at this point most of the haemoglobin has been oxidized to methaemoglobin this being a contributory cause of death. Two theories are advanced to account for NO?2 concentration in the blood. The first supposes that gills are impermeable to NO?2 but allow its conjugate acid nitrous acid (HNO2) to diffuse into the blood where it dissociates according to the blood pH value. Thus NO?2 will accumulate in the blood plasma if it has a higher pH value than the water. The second supposes that the Cl? uptake mechanism in the freshwater gill has an affinity for NO?2 and accounts for the fact that NO?2 entry to the blood is suppressed when external Cl? is present in significant amounts. The results also suggest that NO?2 and Cl? behave similarly as diffusing ions. Thus NO?2 diffusion into the blood of seawater fish and from the blood of NO?2 loaded freshwater fish occurs at approximately the same rate as the corresponding Cl? fluxes. Nitrite loss from seawater fish is thought to be mainly by diffusion although there is some evidence for the active Cl? extrusion mechanism having a weak affinity for nitrite.  相似文献   

4.
(1) The kinetics of isotope exchange catalysed by the membrane-bound hydrogenase of Paracoccus denitrificans have been studied by measuring H2H, H2 or 2H2 produced when the enzyme catalyses the exchange between 2H2 and H2O or H2 and 2H2O. (2) In the 2H2-H2O system the measured rate of H2 production was always higher than that of H2H. The H2H2H ratio remained constant (about 1.70) in the protein concentration range 0.08–1.32 mg. The very rapid formation of H2 with respect to H2H is consistent with the hypothesis of a heterolytic cleavage of 2H2 into a deuteron and an enzyme hydride that can exchange with the solvent. (3) In the H2-2H2O system, the exchange rate was much lower than in the 2H2-H2O system, indicating a marked isotopic effect of 2H2O. (4) The H-2H exchange activity, determined from the initial velocity of H2H formation, is optimal at pH 4.5. A second maximum of activity is observed at pH 8.3. The pH value of 4.5 is also the pH optimum for H2 production while at pH 8.3–8.5 there is a maximum of H2 oxidation activity. (5) In ordinary H2O the Km for hydrogen uptake estimated either from H2 consumption or from benzyl viologen reduction was 0.06–0.07 μM for both H2 and 2H2 indicating a strong affinity of the enzyme for hydrogen at pH 8.3–8.5. Shifting from H2O to 2H2O does not affect the Km of the enzyme for H2 but lowers the Vmax value about 10-fold. The Km for benzyl viologen and methyl viologen was 0.08 and 2 mM, respectively.  相似文献   

5.
In many Gram-positive bacteria PerR is a major peroxide sensor whose repressor activity is dependent on a bound metal cofactor. The prototype for PerR sensors, the Bacillus subtilis PerRBS protein, represses target genes when bound to either Mn2+ or Fe2+ as corepressor, but only the Fe2+-bound form responds to H2O2. The orthologous protein in the human pathogen Staphylococcus aureus, PerRSA, plays important roles in H2O2 resistance and virulence. However, PerRSA is reported to only respond to Mn2+ as corepressor, which suggests that it might rely on a distinct, iron-independent mechanism for H2O2 sensing. Here we demonstrate that PerRSA uses either Fe2+ or Mn2+ as corepressor, and that, like PerRBS, the Fe2+-bound form of PerRSA senses physiological levels of H2O2 by iron-mediated histidine oxidation. Moreover, we show that PerRSA is poised to sense very low levels of endogenous H2O2, which normally cannot be sensed by B. subtilis PerRBS. This hypersensitivity of PerRSA accounts for the apparent lack of Fe2+-dependent repressor activity and consequent Mn2+-specific repressor activity under aerobic conditions. We also provide evidence that the activity of PerRSA is directly correlated with virulence, whereas it is inversely correlated with H2O2 resistance, suggesting that PerRSA may be an attractive target for the control of S. aureus pathogenesis.  相似文献   

6.
The effects of divalent ions on fully charged poly(S-carboxymethyl-l-cysteine) have been examined using circular dichroism for eight species: CuCl2, CdCl2, ZnCl2, NiCl2, CoCl2, BaCl2, CaCl2, and MgCl2. Five of them are effective inducers of β-form in the order: Cu2+Cd2+Zn2+Ni2+Co2+, in media with no salt added. However, the other three ions (Ba2+, Ca2+ and Mg2+), are not effective. Precipitation occurs when metal chlorides reach the vicinity of the equivalent point except for Ca2+ and Mg2+. Precipitation of the random coil form is slow, while that of the β-form is rapid. Addition of NcCl reduces the solubility of the β-form considerably. The pH value varies linearly with the logarithm of metal chloride concentration CM for Ba2+, Ca2+ and Mg2+ ions, while nonlinear dependence of pH on log CM is found for Cu2+, Ni2+ and Co2+ ions.  相似文献   

7.
Complexes of the types cis- and trans-Pt(amine)2I2 containing cyclic amines were synthesized and studied mainly by IR and multinuclear NMR spectroscopies. The compounds were converted to cis- and trans-Pt(amine)2(NO3)2, which were also investigated. The hydrolysis and the aquation reactions of the latter compounds were then studied in D2O in different conditions of pH. In acidic medium, the aqueous product is [Pt(amine)2(D2O)2]2+ and for a few amines, [Pt(amine)2(D2O)(NO3)]+ was detected. In basic pH, the main product is Pt(amine)2(OD)2 and Pt(amine)2(OD)(NO3) was detected for several compounds. In neutral pH, the cis isomers form between two and four species in fresh solutions. The most shielded species in 195Pt NMR is the monoaqua-monohydroxo complex cis-[Pt(amine)2(D2O)(OD)]+ and the less shielded compound is the dihydroxo-bridged dimer [Pt(amine)2(μ-OD)2Pt(amine)2]2+, which were observed for all the compounds. For a few amines, the monohydroxo-bridged dimer [Pt(D2O)(amine)2(μ-OD)Pt(OD)(amine)2]2+ was detected and for cyclohexylamine, a fourth signal was assigned to a cyclic hydroxo-bridged trimer [(Pt(amine)2(μ-OD))3]3+. 195Pt NMR spectroscopy has shown that the concentration of the monomer decreases with time, while the concentration of the dimers increases. Only one product was observed for the trans isomers in neutral pH. The signal was assigned to the monoaqua-monohydroxo species trans-[Pt(amine)2(D2O)(OD)]+. The 13C and 1H NMR spectra of most of the complexes were measured. All the coupling constants 2,3J(195Pt-1H) and 2,3J(195Pt-13C) are larger in the cis compounds than in the trans isomers.  相似文献   

8.
1. (1) VO3 combines with high affinity to the Ca2+-ATPase and fully inhibits Ca2+-ATPase and Ca2+-phosphatase activities. Inhibition is associated with a parallel decrease in the steady-state level of the Ca2+-dependent phosphoenzyme.
2. (2) VO3 blocks hydrolysis of ATP at the catalytic site. The sites for VO3 also exhibit negative interactions in affinity with the regulatory sites for ATP of the Ca2+-ATPase.
3. (3) The sites for VO3 show positive interactions in affinity with sites for Mg2+ and K+. This accounts for the dependence on Mg2+ and K+ of the inhibition by VO3. Although, with less effectiveness, Na+ substitutes for K+ whereas Li+ does not. The apparent affinities for Mg2+ and K+ for inhibition by VO3 seem to be less than those for activation of the Ca2+-ATPase.
4. (4) Inhibition by VO3 is independent of Ca2+ at concentrations up to 50 μM. Higher concentrations of Ca2+ lead to a progressive release of the inhibitory effect of VO3.
Keywords: Ca2+-ATPase; Vanadate inhibition; K+; Li+; (Red cell membrane)  相似文献   

9.
VS2 is one of the attractive layered cathodes for alkali metal‐ion batteries. However, the understanding of the detailed reaction processes and energy storage mechanism is still inadequate. Herein, the Li+/Na+/K+ insertion/extraction mechanisms of VS2 cathode are elucidated on the basis of experimental analyses and theoretical simulations. It is found that the insertion/extraction behavior of Li+ is partially irreversible, while the insertion/extraction behavior of Na+/K+ is completely reversible. The detailed intermediates and final products (Li0.33VS2, LiVS2, Na0.5VS2, NaVS2, K0.6VS2, KzVS2, z > 0.6) during the discharging/charging processes are identified, indicating that VS2 undergoes different phase transitions and solid–solution reactions in different battery systems, which have a great influence on the battery performance. Moreover, the diffusion of Na+ in VS2 cathode is demonstrated to be much slower than that of Li+ and K+. Such mechanistic research provides a reference for in‐depth understanding of energy storage in layered transition metal sulfides/selenides.  相似文献   

10.
Abstract

Geometry optimizations and energy calculations have been carried out via molecular orbital methods at the density functional B3LYP/LANL2DZ level on the molecules PO3 ?, OPO3 3-, HOPO3 2-, CH3OPO3 2-, H(CH3OPO3 ?, O(PO3)2 4-, HO(PO3)2 3-, CH2 (PO3)2 4-, (CH3OPO2)O(PO3)3-, O(PO3)3 5-, HO(PO3)3 4-, (PO3)3 3-, (CH3OPO2)O(PO3)2 3-, [Mg{O(PO3)2}]2-, [Ca{O(PO3)2}]2-, [Ca{CH2 (PO3)2}]2-, [Ca{CH3OPO2)O(PO3)}]?, [Ca(PO3)3]?, [Ca{O(PO3)3}]3-, and [Ca{CH3OPO2)O(PO3)2}]2- with the aim to find reliable and easily accessible computational methods to simulate some phosphate-containing molecules of importance for the living cells and to study the energetics for protonation and metal-complex formation reactions. The analysis is part of a general investigation on phosphate-containing molecules as potential dissolving agents for calcium pyrophosphate dihydrate (CPPD) crystals which deposit in certain articular diseases. The basis set was expanded to 6–31G** for the P atoms for all the molecules investigated and to 6–31G* for the O atoms for OPO3 3-. Calculations at the semi- empirical MNDO/d level were also carried out for comparison purposes on the free ligand molecules and on [Mg{O(PO3)2}]2-. The density functional analysis reproduced well the geometry found at the solid state via X-ray diffraction. The analyses of the geometrical parameters and the total electronic energy of the molecules shows that O(PO3)2 4- and other di- and tri-phosphates are versatile ligands for divalent metal ions like Ca2+. The computed P-O-P bond angle for free O(PO3)3 4- is 180° and the conformation of the two PO3 ? groupings is staggered along the P…P vector. The linear arrangement for P-O-P is assisted by P-Oπ interactions. The bending of the P-O-P angle when accompanied by a slight P-O(b) elongation requires a very small amount of energy; 4.65 kcal/mol to pass from 180 to 140°, as calculated at the DFT level. The computed Ca-O and Mg-O bond distances for [M{O(PO3)2}]2- are 2.378 and 2.079Å, when the metal ions link two oxygen atoms from each PO3 group. The computed Ca-O bond lengths for [Ca{CH3OPO2)O(PO3)}]? are 2.482 (PαO2) and 2.358Å (PβO2), showing a significant lengthening for Ca-OPα, when compared to the pyrophosphate derivative. The Ca-O bond lengths for [Ca{O(PO3)3}]3- and [Ca{CH3OPO2)O(PO3)2}]2- are 2.251Å and 2.525 (PαO2), 2.407 and 2.338 (PβO2), and 2.251 and 2.228Å (PγO2), showing a shortening for the Ca-OPγ bond upon methylation. The (Pβ)O-Pγ bond length increases significantly (0.09 Å) upon Ca(II) coordination to (CH3OPO2)O(PO3)2 4- via all the three PO3 groups. This latter result suggests that metal complexes of linear organic-triphosphates have a larger tendency to release the PγO3 group when compared to the free ligand molecules. The electronic contribution to the energy of the complex formation reaction for [Ca{CH2 (PO3)2}]2- is only slightly higher (some 1.8 kcal) than that for [Ca{O(PO3)2}]2-; but is much higher (some 63 kcal) than that relevant to the formation of [Ca{CH3OPO2)O(PO3)2}]2-. Therefore the linear methyltriphosphates (and reasonably nucleoside triphosphates) are predicted to form metal complexes which are less stable than diphosphonate or inorganic diphosphate ligands, at least in the case the organic moiety does not have any appreciable coordination ability toward the metal. The energy of complex formation for [Ca{O(PO3)3}]3- is much higher than that for [Ca{O(PO3)2}]2- and [Ca(PO3)3}]? (some 116 and 345 kcal, respectively). This is in part a rationale for the high dissolving ability (DA) toward CPPD crystals, shown by solutions of pentasodium tripolyphosphate. DA values of 65.4±3.0 μg Ca/mL were detected, via atomic absorption spectroscopy, in solutions of Na5{O(PO3)3} 0.06 M after digestion (1.00 h, 37°C, pH 7.4) in the presence of CPPD crystals. Efficient non-toxic dissolving agents for CPPD crystals are needed to cure chondrocal-cinosis desease. The semi-empirical computations gave correct overall optimized structures and conformations for, at least, the free not-substituted ligands and the relevant Mg(II)-com- plexes. The optimized structure for [Mg{O(PO3)2}]2- has computed P-O(t) and P-O(d) bond distances of 1.503 and 1.598Å, in perfect agreement with the results from DFT calculations.  相似文献   

11.
Abstract

An efficient alternative which makes use of the reliable 3J1′2′. value to derive the endocyclic torsion angle constraints is proposed in this study. Based on the information embedded in the two plots, (i) the vicinal proton-proton J-couplings, 3J1′2′., 3J1′2″., 3J2′3′., 3J2”3′ and 3J3′4′ against the pseudorotation phase angle, and (ii) 3J1′2″, 3J2′3′., 3J2″3′ and 3J3′4′ against 3J1′2′; using the calculated J-couplings obtained for a range of sugar geometries of deoxyribose ring in nucleosides and nucleotides encountered along the pseudorotation itinerary [J. van Wijk, B.D. Huckriede, J.H. Ippel and C. Altona, Methods Enzymol. 211, 286–306 (1992)], it is suggested that the vicinal 3J1′2′ possesses structural information other than the vicinal torsion angle φ1′2′. This study is divided into two parts. In Part I, a correlation diagram between the endocyclic torsion angles vi (i=0,1,2,3,4) and the restrained vicinal torsion angle φ1′2′ is obtained through the use of the J-coupling restrained molecular mechanics (JrMM) protocol. The established φ1′2′.-vi correlation shows vi can be deduced from the reliable 3J1′2′. value and it forms the basis for developing an alternative protocol to derive endocyclic torsion angle constraints. In Part II of this series, extensive testing demonstrating the validity of the JrMM protocol to derive Vi for defining the sugar geometry of solution DNA molecules is presented.  相似文献   

12.
Here we report the synthesis and characterization of a membrane-impermeant fluorogenic probe, hydropropidine (HPr+), the reduction product of propidium iodide, for detecting extracellular superoxide (O2•−). HPr+ is a positively charged water-soluble analog of hydroethidine (HE), a fluorogenic probe commonly used for monitoring intracellular O2•−. We hypothesized that the presence of a highly localized positive charge on the nitrogen atom would impede cellular uptake of HPr+ and allow for exclusive detection of extracellular O2•−. Our results indicate that O2•− reacts with HPr+ (k=1.2×104 M−1 s−1) to form exclusively 2-hydroxypropidium (2-OH-Pr2+) in cell-free and cell-based systems. This reaction is analogous to the reaction between HE and O2•− (Zhao et al., Free Radic. Biol. Med. 34:1359–1368; 2003). During the course of this investigation, we also reassessed the rate constants for the reactions of O2•− with HE and its mitochondria targeted analog (Mito-HE or MitoSOX Red) and addressed the discrepancies between the present values and those reported previously by us. Our results indicate that the rate constant between O2•− and HPr+ is slightly higher than that of HE and O2•− and is closer to that of Mito-HE and O2•−. Similar to HE, HPr+ undergoes oxidation in the presence of various oxidants (peroxynitrite-derived radicals, Fenton's reagent, and ferricytochrome c) forming the corresponding propidium dication (Pr2+) and the dimeric products (e.g., Pr2+-Pr2+). In contrast to HE, there was very little intracellular uptake of HPr+. We conclude that HPr+ is a useful probe for detecting O2•− and other one-electron oxidizing species in an extracellular milieu.  相似文献   

13.
To test the possibility of inorganic carbon limitation of the marine unicellular alga Emiliania huxleyi (Lohmann) Hay and Mohler, its carbon acquisition was measured as a function of the different chemical species of inorganic carbon present in the medium. Because these different species are interdependent and covary in any experiment in which the speciation is changed, a set of experiments was performed to produce a multidimensional carbon uptake scheme for photosynthesis and calcification. This scheme shows that CO2 that is used for photosynthesis comes from two sources. The CO2 in seawater supports a modest rate of photosynthesis. The HCO is the major substrate for photosynthesis by intracellular production of CO2 (HCO+ H+→ CO2+ H2O → CH2O + O2). This use of HCO is possible because of the simultaneous calcification using a second HCO, which provides the required proton (HCO+ Ca2+→ CaCO3+ H+). The HCO is the only substrate for calcification. By distinguishing the two sources of CO2 used in photosynthesis, it was shown that E. huxleyi has a K½ for external CO2 of “only” 1.9 ± 0.5 μM (and a Vmax of 2.4 ± 0.1 pmol·cell−1·d−1). Thus, in seawater that is in equilibrium with the atmosphere ([CO2]= 14 μM, [HCO]= 1920 μM, at fCO2= 360 μatm, pH = 8, T = 15° C), photosynthesis is 90% saturated with external CO2. Under the same conditions, the rate of photosynthesis is doubled by the calcification route of CO2 supply (from 2.1 to 4.5 pmol·cell−1·d−1). However, photosynthesis is not fully saturated, as calcification has a K½ for HCO of 3256 ± 1402 μM and a Vmax of 6.4 ± 1.8 pmol·cell−1·d−1. The H+ that is produced during calcification is used with an efficiency of 0.97 ± 0.08, leading to the conclusion that it is used intracellularly. A maximum efficiency of 0.88 can be expected, as NO uptake generates a H+ sink (OH source) for the cell. The success of E. huxleyi as a coccolithophorid may be related to the efficient coupling between H+ generation in calcification and CO2 fixation in photosynthesis.  相似文献   

14.
A testable mechanism of CO2 accumulation in photolithotrophs, originally suggested by Pronina & Semenenko, is quantitatively analysed. The mechanism involves (as does the most widely accepted hypothesis) the delivery of HCO3? to the compartment containing Rubisco. It differs in proposing subsequent HCO3? entry (by passive uniport) to the thylakoid lumen, followed by carbonic anhydrase activity in the lumen; uncatalysed conversion of HCO3? to CO2, even at the low pH of the lumen, is at least 300 times too slow to account for the rate of inorganic C acquisition. Carbonic anhydrase converts the HCO3? to CO2 at the lower pH maintained in the illuminated thylakoid lumen by the light-driven H+ pump, generating CO2 at 10 times or more the thylakoid HCO3? concentration. Efflux of this CO2 can suppress Rubisco oxygenase activity and stimulate carboxylase activity in the stroma. This mechanism differs from the widely accepted hypotheses in the required location of carbonic anhydrase, i.e. in the thylakoid lumen rather than the stroma or pyrenoid, and in the need for HCO3? influx to thylakoids. The capacity for anion (assayed as Cl?) entry by passive uniport reported for thylakoid membranes is adequate for the proposed mechanism; if the Cl? channel does not transport HCO3?, HCO3? entry could be by combination of the Cl? channel with a Cl? HCO3? antiporter. This mechanism is particularly appropriate for organisms which lack overt accumulation of total inorganic C in cells, but which nevertheless have the gas exchange characteristics of an organism with a CO2-concentrating mechanism.  相似文献   

15.
A mononuclear macrocyclic complex NiIIL3a (L3a = dianion of 2,3-dioxo-5,6:13,14-dibenzo-9,10-cyclohexyl-7,12-bis(methoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene), which shows high DNA cleavage activity in the presence of H2O2, was reported in our previous work. Considering that many systems for natural enzyme-mediated DNA cleavage contain two or more metal active sites, two new trinuclear complexes [Cu(NiL3a)2(dca)2]·2CH3OH (abbreviated as Cu(NiL3a)2) and [Ag(NiL3a)2(NO3)]·2CH3OH·0.5H2O (abbreviated as Ag(NiL3a)2) were synthesized in this work, where dca is the dicyanamide. The complexes were structurally characterized by single crystal X-ray analysis. The central Cu(II) or Ag(I) atom is linked to two [NiL3a] ligands by oxamido bridges forming a trinuclear structure. In Cu(NiL3a)2, the central Cu(II) ion is in an octahedral coordination geometry. Whereas in Ag(NiL3a)2, the central Ag(I) ion is in a rarely reported trigonal-prismatic coordination geometry. The DNA cleavage behavior of the complexes in the presence of H2O2 was studied in detail. Comparing with the NiL3a, the trinuclear complex Ag(NiL3a)2 nearly has no ability to cleave DNA, whereas Cu(NiL3a)2 is a much better DNA cleavage agent. Cu(NiL3a)2 can efficiently convert supercoiled DNA to nicked DNA with a rate constant of 0.074 ± 0.002 min−1 when 40 μM Cu(NiL3a)2 and 0.6 mM H2O2 are used. The cleavage mechanism between the complex Cu(NiL3a)2 and plasmid DNA is likely to involve singlet oxygen as reactive oxygen species. Circular dichroism (CD) and fluorescence spectroscopy indicate that both Cu(NiL3a)2 and NiL3a bind to DNA by a groove binding mode, and the binding between Cu(NiL3a)2 and DNA is much stronger than that between NiL3a and DNA. The present results may provide some information for the design of efficient multinuclear artificial nucleases.  相似文献   

16.
Singlet oxygen (1O2) has been shown to play an important role in salivary defense system, but its generation process and level from human saliva remain uncertain due to the lack of a reliable detection method. We have previously reported 4,4′(5′)-bis[2-(9-anthryloxy)ethylthio]tetrathiafulvalene (BAET) as a novel chemiluminescence probe for 1O2. In this work, the probe is successfully used to characterize H2O2-dependent generation of 1O2 from saliva in real time. However, the yield of 1O2 is found to be very low, for example, being about 0.13 nmol from 200 μL saliva in the presence of 1 mM of hydrogen peroxide over a 5-s reaction period. The result is also compared with that obtained with another 1O2 probe 2-methyl-6-phenyl-3,7-dihydroimidazo[1,2-a]pyrazin-3-one (CLA), demonstrating that, besides 1O2, the other reactive oxygen species such as hydroxyl radical may also be involved in the reaction of saliva with H2O2. Furthermore, the present study shows that the selectivity of BAET for 1O2 is much higher than that of CLA and thus BAET is highly suited for the detection of 1O2 in the presence of other reactive oxygen species in biological systems.  相似文献   

17.
Electrocatalytic nitrite (NO2) reduction reaction (NO2RR) for ammonia (NH3) synthesis is a promising alternative for NO2 resource utilization. Herein, a dual-site copper-cobalt oxide catalyst is reported for the efficient electrocatalytic reduction of NO2 to NH3, exhibiting NH3 Faradaic efficiency that remained above 95% (0.1 m NaNO2) over a wide potential window (−0.1 to −0.6 V vs reversible hydrogen electrode, vs RHE). More importantly, the high NH3 Faradaic efficiency maintains an over 85% (−0.1 to −0.3 V vs RHE) at a low concentration of NaNO2 (0.01 m ). Theoretical calculations demonstrate that CuO serves the *NO2 to *NO and is subsequently converted to NH3 on Co3O4. Coupled anodic ethylene glycol (EG) oxidation reaction endows low cell voltage (ΔU = 480 mV, 10 mA cm−2) and energy consumption saving (>23%) in a two-electrode system. This work provides a reference for a co-upcycling electrolyzer for NO2 and EG.  相似文献   

18.
19.
 The acidity constants of methyl phosphoric acid, CH3OPO(OH)2, and orthophosphoric acid, HOPO(OH)2, and the stability constants of the 1 : 1 complexes formed between Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, or Cd2+ and methyl phosphate, CH3OPO3 2–, or hydrogen phosphate, HOPO3 2–, were determined by potentiometric pH titration in aqueous solution (25  °C;I = 0.1 M, NaNO3). On the basis of previously established log K versus pK a straight-line plots for the complexes of simple phosphate monoesters and phosphonate derivatives, R-PO3 2–, where R is a noncoordinating residue, it is shown that the stability of the M(CH3OPO3) complexes is solely determined (as one might expect) by the basicity of the –PO3 2– residue. It is emphasized that the mentioned reference lines may also be used to reveal increased complex stabilities, for example, for certain complexes formed with 8-quinolyl phosphate the occurrence of 7-membered chelates can be proven in this way; the same procedure is also applicable to complexes of nucleotides, etc. The M(HOPO3) complexes are slightly more stable (on average by 0.08 log unit) than it is expected from the basicity of HPO4 2–; this observation is attributed to a more effective solvation, including hydrogen bonding, than is possible with CH3OPO3 2– species. Received: 9 November 1995 / Accepted: 5 February 1996  相似文献   

20.
Phosphatase activity of a kidney (Na + K)-ATPase preparation was optimally active with Mg2+ plus K+. Mn2+ was less effective and Ca2+ could not substitute for Mg2+. However, adding Ca2+ with Mg2+ or substituting Mn2+ for Mg2+ activated it appreciably in the absence of added K+, and all three divalent cations decreased apparent affinity for K+. Inhibition by Na+ decreased with higher Mg2+ concentrations, when Ca2+ was added, and when Mn2+ was substituted for Mg2+. Dimethyl sulfoxide, which favorsE 2 conformations of the enzyme, increased apparent affinity for K+, whereas oligomycin, which favorsE 1 conformations, decreased it. These observations are interpretable in terms of activation through two classes of cation sites. (i) At divalent cation sites, Mg2+ and Mn2+, favoring (under these conditions)E 2 conformations, are effective, whereas Ca2+, favoringE 1, is not, and monovalent cations complete. (ii) At monovalent cation sites divalent cations compete with K+, and although Ca2+ and Mn2+ are fairly effective, Mg2+ is a poor substitute for K+, while Na+ at these sites favorsE 1 conformations. K+ increases theK m for substrate, but both Ca2+ and Mn2+ decrease it, perhaps by competing with K+. On the other hand, phosphatase activity in the presence of Na+ plus K+ is stimulated by dimethyl sulfoxide, by higher concentrations of Mg2+ and Mn2+, but not by adding Ca2+; this is consistent with stimulation occurring through facilitation of an E1 to E2 transition, perhaps an E1-P to E2-P step like that in the (Na + K)-ATPase reaction sequence. However, oligomycin stimulates phosphatase activity with Mg2+ plus Na+ alone or Mg2+ plus Na+ plus low K+: this effect of oligomycin may reflect acceleration, in the absence of adequate K+, of an alternative E2-P to E1 pathway bypassing the monovalent cation-activated steps in the hydrolytic sequence.  相似文献   

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