首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 281 毫秒
1.
We report on the redox behaviour of the microperoxidase‐11 (MP‐11) which has been electrostatically immobilized in a matrix of chitosan‐embedded gold nanoparticles on the surface of a glassy carbon electrode. MP‐11 contains a covalently bound heme c as the redox active group that exchanges electrons with the electrode via the gold nanoparticles. Electroactive surface concentration of MP‐11 at high scan rate is between 350±50 pmol cm?2, which reflects a multilayer process. The formal potential (E°′) of MP‐11 in the gold nanoparticles‐chitosan film was estimated to be ?(267.7±2.9) mV at pH 7.0. The heterogeneous electron transfer rate constant (ks) starts at 1.21 s?1 and levels off at 6.45 s?1 in the scan rate range from 0.1 to 2.0 V s?1. Oxidation and reduction of MP‐11 by hydrogen peroxide and superoxide, respectively have been coupled to the direct electron transfer of MP‐11.  相似文献   

2.
Magneto‐controlled OR, AND and INHIB logic gates were designed using cobalt ferrite magnetic nanoparticles (CoFe2O4, saturated magnetization ca. 70 emu g?1, 17±2 nm diameter) functionalized with microperoxidase‐11. Tunable magnetic field generated by three external permanent magnets (NdFeB) upon moving them below the electrochemical cell resulted in translocation of the biofunctionalized magnetic nanoparticles between conductive and nonconductive domains of a solid plate. This resulted in electrochemically readable output signals with the Boolean logic controlled by the magnetic input signals. The current corresponding to the reversible redox process of the heme measured at ?0.4 V (vs. SCE) was considered as “1” output signal, while a small background current obtained from the conducting interface in the absence of the magnetic nanoparticles was considered as “0” output signal. Addition of H2O2 to the solution resulted in the generation of a cathodic catalytic current when the microperoxidase‐11‐functionalized magnetic nanoparticles are associated with the conductive domain of the support. This resulted in the amplification of “1” output signal and the increased difference between “1” and “0” signals generated by the cell, thus reducing the possibility of errors in the Boolean logic operations.  相似文献   

3.
Although the reaction products are unstable at the reaction temperatures, at a heating rate of 2 deg·min?1 ammonium peroxo vanadate, (NH4)4V2O11, decomposes to (NH4)[VO (O2)2 (NH3)] (above 93°C); this in turn decomposes to (NH4) [VO3 (NH3)] (above 106°C) and then to ammonium metavanadate (above 145°C). On further heating vanadium pentoxide is formed above 320°C. The first decomposition reaction occurs in a single step and the Avrami-Erofeev equation withn=2 fits the decomposition data best. An activation energy of 148.8 kJ·mol?1 and a ln(A) value of 42.2 are calculated for this reaction by the isothermal analysis method. An average value of 144 kJ·mol?1 is calculated for the first decomposition reaction using the dynamic heating data and the transformation-degree dependence of temperature at different heating rates.  相似文献   

4.
The investigation on fabrication of Fe3O4-chitosan-pectinase nanobiocatalyst was performed by covalently binding the pectinase onto carboxyl group activated chitosan-coated magnetic nanoparticles (CMNPs). The morphological and size distribution analysis of the different magnetic nanoparticles (MNPs) was done using transmission electron microscopy (TEM), and the average diameter was 11.07?±?3.04, 11.55?±?3.16, and 11.59?±?3.16 nm for MNPs, CMNPs, and fabricated nanobiocatalyst, respectively, suggesting that there was no significant change in the size of MNPs after coating and binding. The characteristic peaks occurred at 2θ of 30.39, 35.43, 43.37, 57.22, and 62.9, and their corresponding indices 220, 311, 400, 520, and 441 for different MNPs from the X-ray diffraction (XRD) studies confirmed the presence of Fe3O4 with the spinel structure, and there was no phase change even after coating and binding. The various required characteristic absorption peaks (575, 585, 1,563, 1,614, 1,651, and 1,653 cm?1) from Fourier transform infrared (FT-IR) spectroscopy confirmed the surface modifications and binding of pectinase onto the MNPs. At the weight ratio of about 19.8?×?10?3 mg bound pectinase/mg activated CMNPs, the activity of fabricated nanobiocatalyst was found to be maximum. In order to monitor their improved activity, the pH, temperature, reusability, storage ability, and kinetic studies were established.  相似文献   

5.
The substitution equilibria AuCl 2 ? + iNH 4 + = Au(NH3)iCl2 ? i + iCl? + iH+, β i * . were studied pH-metrically at 25°C and I = 1 mol/L (NaCl) in aqueous solution. It was found that logβ 1 * = ?5.10±0.15 and logβ 2 * = ?10.25±0.10. For equilibrium AuNH3Clsolid = AuNH3Cl, log K s = ?3.1±0.3. Taking into account the protonation constants of ammonia (log K H = 9.40), the obtained results show that for equilibria AuCl 2 ? + iNH3 = Au(NH3)iCl2 ? i + iCl?, logβ1 = 4.3±0.2, and logβ2 = 8.55±0.15. The standard potentials E 0 1/0 of AuNH3Cl0 and Au(NH3) 2 + species are equal to 0.90±0.02 and 0.64±0.01 V, respectively.  相似文献   

6.
By combining results from a variety of mass spectrometric techniques (metastable ion, collisional activation, collision-induced dissociative ionization, neutralization-reionization spectrometry, 2H, 13C and 18O isotopic labelling and appearance energy measurements) and high-level ab initio molecular orbital calculations, the potential energy surface of the [CH5NO]+ ˙ system has been explored. The calculations show that at least nine stable isomers exist. These include the conventional species [CH3ONH2]+ ˙ and [HO? CH2? NH2]+ ˙, the distonic ions [O? CH2? NH3]+ ˙, [O? NH2? CH3]+ ˙, [CH2? O(H)? NH2]+ ˙, [HO? NH2? CH2]+ ˙, and the ion-dipole complex CH2?NH2+ …? OH˙. Surprisingly the distonic ion [CH2? O? NH3]+ ˙ was found not to be a stable species but to dissociate spontaneously to CH2?O + NH3+ ˙. The most stable isomer is the hydrogen-bridged radical cation [H? C?O …? H …? NH3]+ ˙ which is best viewed as an immonium cation interacting with the formyl dipole. The related species [CH2?O …? H …? NH2]+ ˙, in which an ammonium radical cation interacts with the formaldehyde dipole is also a very stable ion. It is generated by loss of CO from ionized methyl carbamate, H2N? C(?O)? OCH3 and the proposed mechanism involves a 1,4-H shift followed by intramolecular ‘dictation’ and CO extrusion. The [CH2?O …? H …? NH2]+ ˙ product ions fragment exothermically, but via a barrier, to NH4+ ˙ HCO…? and to H3N? C(H)?O+ ˙ H˙. Metastable ions [CH3ONH2]+…? dissociate, via a large barrier, to CH2?O + NH3+ + and to [CH2NH2]+ + OH˙ but not to CH2?O+ ˙ + NH3. The former reaction proceeds via a 1,3-H shift after which dissociation takes place immediately. Loss of OH˙ proceeds formally via a 1,2-CH3 shift to produce excited [O? NH2? CH3]+ ˙, which rearranges to excited [HO? NH2? CH2]+ ˙ via a 1,3-H shift after which dissociation follows.  相似文献   

7.
The decay of NH2 radicals, from 193 nm photolysis of NH3, was monitored by 597.7 nm laser-induced fluorescence. Room-temperature rate constants of (1.21 ± 0.14) × 10?10, (1.81 ± 0.12) × 10?11, and (2.11 ± 0.18) × 10?11 cm3 molecule?1 s?1 were obtained for the reactions of NH2 with N, NO and NO2, respectively. The production of NH in the reaction of NH2 with N was observed by laser-induced fluorescence at 336.1 nm.  相似文献   

8.
A newly isolated bacterial strain, Bacillus sp. MX47, was actively producing extracellular xylanase only in xylan-containing medium. The xylanase was purified from the culture broth by two chromatographic steps. The xylanase had an apparent molecular weight of 26.4?kDa with an NH2-terminal sequence (Gln-Gly-Gly-Asn-Phe) distinct from that of reported proteins, implying it is a novel enzyme. The optimum pH and temperature for xylanase activity were 8.0 and 40?°C, respectively. The enzyme activity was severely inhibited by many divalent metal ions and EDTA at 5?mM. The xylanase was highly specific to beechwood and oat spelt xylan, however, not active on carboxymethyl cellulose (CMC), avicel, pectin, and starch. Analysis of the xylan hydrolysis products by Bacillus sp. MX47 xylanase indicated that it is an endo-??-1,4-xylanase. It hydrolyzed xylan to xylobiose as the end product. The K m and V max values toward beechwood xylan were 3.24?mg?ml?1 and 58.21???mol?min?1?mg?1 protein, respectively.  相似文献   

9.
Carbonic anhydrases (CAs) have been given much attention as biocatalysts for CO2 sequestration process because of their ability to convert CO2 to bicarbonate. Here, we expressed codon-optimized sequence of ??-type CA cloned from Dunaliella species (Dsp-aCAopt) and characterized its catalyzing properties to apply for CO2 to calcite formation. The expressed amount of Dsp-aCAopt in Escherichia coli is about 50?mg/L via induction of 1.0?mM isopropyl-??-d-thiogalactopyranoside at 20?°C (for the case of intact Dsp-aCA, negligible). Dsp-aCAopt enzyme shows 47?°C of half-denaturation temperature and show wide pH stability (optimum pH 7.6/10.0). Apparent values of K m and V max for p-nitrophenylacetate substrate are 0.91?mM and 3.303?×?10?5???M?min?1. The effects of metal ions and anions were investigated to find out which factors enhance or inhibit Dsp-aCAopt activity. Finally, we demonstrated that Dsp-aCAopt enzyme can catalyze well the conversion of CO2 to CaCO3, as the calcite form, in the Ca2+ solution [8.9?mg/100???g (172?U/mg enzyme) with 10?mM of Ca2+]. The obtained expression and characterization results of Dsp-aCAopt would be usefully employed for the development of efficient CA-based system for CO2-converting/capturing processes.  相似文献   

10.
Stable complexes are required during the ion chromatographic (IC) separation of Fe‐polycarboxylic acid complexes. Electrospray ionization mass spectrometry (ESI‐MS) was used to identify 1:1 stoichiometric complexes of Fe[HEDTA], Fe[EDTA]1? and Fe[DTPA]2?, and the spectra showed that these Fe complexes were stable in solution. Furthermore, inductively coupled plasma mass spectrometry (ICP‐MS) using an octopole reaction system (ORS) reduced polyatomic ion 40Ar16O+ interference in the detection of 56Fe via the addition of either H2 or He to the ORS, with He at a flow rate 3.5 mL min?1 being the optimum collision gas. Finally, IC/ICP‐MS was used for the separation and detection of Fe complexes with an eluent containing 30 mM (NH4)2HPO4 at pH 8.0, but only Fe[HEDTA], Fe[EDTA]1? and Fe[DTPA]2? were observed within 10 min with reasonable resolution. Detection limits in the range of 10–13 µg L?1 were achieved using He as the collision gas. The proposed method was used for the determination of Fe species in soil solutions. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

11.
The NCI(F?) and NCI(NH2?) mass spectra of a series of aliphatic acetates and of methyl and ethyl trimethylacetate have been obtained. The formation of fluoroenolate ions CH2COF? and of carboxamide anions RCONH? (R ? CH3))CH3C). respectively, is observed besides formation of [M ? H]? ions and carboxylate ions RCOO? (R ? CH3, (CH3)3C). The relative intensities of the different anions depend on the structure of the ester molecules and on the primary reactant anions. Usually, the NCI(NH2?) spectra of the acetates are dominated by [M ? H]? ions ([M? D]? ions in the case of trideuteroacetates) fragmenting unimolecularly by elimination of an alcohol. The carboxylate ions are important fragments, too, but carboxamide ions are only observed with large intensities in the NCI(NH2? spectra of the trimethylacetates. The NCI(F?) spectra show much larger intensities of carboxylate ions and fluoroenolate ions. The mechanisms of the fragmentation reactions are discussed. The results indicate that most or even all of the fragment ions in the NCI(F? mass spectra of aliphatic esters are formed by addition-elimination reactions via a tetrahedral intermediate, while competition between direct proton abstraction and addition-elimination reactions occurs in the NCI(NH2?) mass spectra because of the higher basicity of NH2? resulting in an early transition state for direct proton abstraction.  相似文献   

12.
In this study, the catalytic activity and stability of flowerlike hybrid horseradish peroxidase (HRP) nanobiocatalyst (HRP-Cu 2+ ) obtained from Cu 2+ ions and HRP enzyme in the polymerization reaction of guaiacol were analyzed. We demonstrated that HRP-Cu 2+ and hydrogen peroxide (H 2 O 2 ) initiator showed significantly increased catalytic activity and stability on the polymerization of guaiacol compared to that of free HRP enzyme. Poly(guaiacol) was observed with quite high yields (88%) and molecular weights (38,000 g/mol) under pH 7.4 phosphate-buffered saline (PBS) conditions at 60 °C with 5 weight% of HRP-Cu 2+ loading. HRP-Cu 2+ also shows very high thermal stability and works even at 70 °C reaction temperature; free HRP enzyme denatures at that temperature. Furthermore, HRP-Cu 2+ provided considerable repeated use and showed some degree of catalytic activity, even after the fourth recycle, in the polymerization of guaiacol.  相似文献   

13.
Lattice Vibration Spectra. LXXI Hydrogen Bonding and Synergetic Effect in Solid Amides: a Case Study for NaAl(NH2)4 IR and Raman spectra (4000 - 200 cm?1, 90 K and 300 K) of NaAl(NH2)4 and of deuterated samples are recorded and discussed with respect to the bonding of NH2? ions in condensed phases compared to that of H2O molecules and OH?-ions. The bands observed are assigned to the internal vibrations and librations of the NH2? ions and skeleton vibrations of the distorted tetrahedral Al(NH2)4? units (breathing vibration v1, 572 cm?1). Owing to the high charge density of the Al3+ ions the NH-stretching modes are shifted to higher wavenumbers by as many as 200 cm?1 compared to those of free amide ions. Furthermore the H-bond donor strenght of the NH2? ions is so much enlarged (synergetic effect) that weak, unusally long (d( …? N) > 360 pm) NH2 …? NH2 hydrogen bonds are formed. These H-bonds share layers of vertex connected Al(NH2)4 and Na(NH2)4 tetrahedra within the structure.  相似文献   

14.
Four polyaniline hybrid materials doped with iron-substituted silicotungstate isomers α,?β i - K5?n H n [SiW11Fe(H2O)O39]?·?xH2O (βi?=?β1, β2, β3) were prepared. The materials were characterized by elemental analysis, IR spectra, UV-Vis spectra, scanning electron microscopy (SEM), TG-DTA and X-ray diffraction (XRD). The conductivity and fluorescence were determined and thermal stability was studied. The UV-Vis, IR and XRD results confirm the existence of Keggin anions. Thermal analysis indicates that SiW11Fe/PANI has better thermal stability. The images of scanning electron microscopy (SEM) show that the materials are microporous. The materials exhibit excellent proton conductivity of 8.5?×?10?2?S?cm?1 at room temperature (20°C). The spectral data indicate that polyaniline doped with α, βi-SiW11Fe have similar fluorescence, λem?=?418–470?nm, and emit blue light.  相似文献   

15.
The present research discusses the structure stabilizing and protecting effects of Ni2+ against suicide-peroxide inactivation of horseradish peroxidase (HRP). Suicide inactivation of HRP by hydrogen peroxide (3 mM) was monitored by measuring change in the absorbance of the colored product (tetraguaiacol) of the catalytic reaction cycle at 470 nm. Progress curves of the catalytic reaction cycle were obtained at 27 °C, phosphate buffer (5 mM), pH 7.0. The corresponding kinetic parameters (e.g., initial enzyme activity (αo) and the apparent rate constant (ki) of suicide inactivation of HRP by peroxide) were evaluated using a kinetic equation derived in this study. Comparative activatory and inhibitory effects of Ni2+ on the kinetics of suicide-peroxide inactivation of HRP are discussed.  相似文献   

16.
A series of five complexes that incorporate the guanidinium ion and various deprotonated forms of Kemp’s triacid (H3KTA) have been synthesized and characterized by single‐crystal X‐ray analysis. The complex [C(NH2)3+] ? [H2KTA?] ( 1 ) exhibits a sinusoidal layer structure with a centrosymmetric pseudo‐rosette motif composed of two ion pairs. The fully deprotonated Kemp’s triacid moiety in 3 [C(NH2)3+] ? [KTA3?] ( 2 ) forms a record number of eighteen acceptor hydrogen bonds, thus leading to a closely knit three‐dimensional network. The KTA3? anion adopts an uncommon twist conformation in [(CH3)4N+] ? 2 [C(NH2)3+] ? [KTA3?] ? 2 H2O ( 3 ). The crystal structure of [(nC3H7)4N+] ? 2 [C(NH2)3+] ? [KTA3?] ( 4 ) features a tetrahedral aggregate of four guanidinium ions stabilized by an outer shell that comprises six equatorial carboxylate groups that belong to separate [KTA3?] anions. In 3 [(C2H5)4N+] ? 20 [C(NH2)3+] ? 11 [HKTA2?] ? [H2KTA?] ? 17 H2O ( 5 ), an even larger centrosymmetric inner core composed of eight guanidinium ions and six bridging water molecules is enclosed by a crust composed of eighteen axial carboxyl/carboxylate groups from six HKTA2? anions.  相似文献   

17.
Intramolecular Antiferromagnetism in [Cr2(μ-NH2)3(NH3)6]I3 The magnetism of [Cr2(μ-NH2)3(NH3)6]I3 which consists of binuclear cations with NH2?-bridged face-sharing octahedral coordination polyhedra and a metal-metal separation of 264.9 pm can be explained by antiferromagnetically exchange-coupled CrIII-3d3 pairs. The magnetochemical analysis in the temperature range 5 K – 295 K on the basis of the isotropic Heisenberg model (spin Hamiltonian ? = ?2 J?1 · ?2) leads to the parameter value J = ?98(3) cm?1. Compared to the exchange coupling in corresponding binuclear chromium compounds with OH? bridges and identical metal-metal separation the strength of the coupling is significantly enhanced (JNH2/JOH ≈? 1.6).  相似文献   

18.
The role of C? C bond‐forming reactions such as aldol condensation in the degradation of organic matter in natural environments is receiving a renewed interest because naturally occurring ions, ammonium ions, NH+4, and carbonate ions, CO32?, have recently been reported to catalyze these reactions. While the catalysis of aldol condensation by OH? has been widely studied, the catalytic properties of carbonate ions, CO32?, have been little studied, especially under environmental conditions. This work presents a study of the catalysis of the aldol condensation of acetaldehyde in aqueous solutions of sodium carbonate (0.1–50 mM) at T = 295 ± 2 K. By monitoring the absorbance of the main product, crotonaldehyde, instead of that of acetaldehyde, interferences from other reaction products and from side reactions, in particular a known Cannizzaro reaction, were avoided. The rate constant was found to be first order in acetaldehyde in the presence of both CO32? and OH?, suggesting that previous studies reporting a second order for this base‐catalyzed reaction were flawed. Comparisons between the rate constants in carbonate solutions and in sodium hydroxide solutions ([NaOH] = 0.3–50 mM) showed that, among the three bases present in carbonate solutions, CO32?, HCO3?, and OH?, OH? was the main catalyst for pH ≤ 11. CO32? became the main catalyst at higher pH, whereas the catalytic contribution of HCO3? was negligible over the range of conditions studied (pH 10.3–11.3). Carbonate‐catalyzed condensation reactions could contribute significantly to the degradation of organic matter in hyperalkaline natural environments (pH ≥ 11) and be at the origin of the macromolecular matter found in these environments. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 676–686, 2010  相似文献   

19.
Molten LiCl and related eutectic electrolytes are known to permit direct electrochemical reduction of N2 to N3? with high efficiency. It had been proposed that this could be coupled with H2 oxidation in an electrolytic cell to produce NH3 at ambient pressure. Here, this proposal is tested in a LiCl–KCl–Li3N cell and is found not to be the case, as the previous assumption of the direct electrochemical oxidation of N3? to NH3 is grossly over‐simplified. We find that Li3N added to the molten electrolyte promotes the spontaneous and simultaneous chemical disproportionation of H2 (H oxidation state 0) into H? (H oxidation state ?1) and H+ in the form of NH2?/NH2?/NH3 (H oxidation state +1) in the absence of applied current, resulting in non‐Faradaic release of NH3. It is further observed that NH2? and NH2? possess their own redox chemistry. However, these spontaneous reactions allow us to propose an alternative, truly catalytic cycle. By adding LiH, rather than Li3N, N2 can be reduced to N3? while stoichiometric amounts of H? are oxidised to H2. The H2 can then react spontaneously with N3? to form NH3, regenerating H? and closing the catalytic cycle. Initial tests show a peak NH3 synthesis rate of 2.4×10?8 mol cm?2 s?1 at a maximum current efficiency of 4.2 %. Isotopic labelling with 15N2 confirms the resulting NH3 is from catalytic N2 reduction.  相似文献   

20.
We report on a novel non-enzymatic sensor for hydrogen peroxide (HP) that is based on a biocomposite made up from chitosan (CS), hemoglobin (Hb), and silver nanoparticles (AgNPs). The AgNPs were prepared in the presence of CS and glucose in an ultrasonic bath, and CS is found to act as a stabilizing agent. They were then combined with Hb and CS to construct a carbon paste biosensor. The resulting electrode gave a well-defined redox couple for Hb, with a formal potential of about ?0.17?V (vs. SCE) at pH?6.86 and exhibited a remarkable electrocatalytic activity for the reduction of HP. The sensor was used to detect HP by flow injection analysis, and a linear response is obtained in the 0.08 to 250?μM concentration range. The detection limit is 0.05?μM (at S/N?=?3). These characteristics, along with its long-term stability make the sensor highly promising for the amperometric determination of HP.
Figure
(A) FIA it graphs of the different concentrations of H2O2 at CS/Hb/AgNP/CPE in the PBS (pH?6.86). Applied potential: ?0.4?V. (1) 0.8?×?10?6?mol?L?1, (2) 2.4?×?10?6?mol?L?1, (3) 4?×?10?6?mol?L?1 (B) Plot of catalytic peak currents vs. the concentration of H2O2.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号