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31.
Ta-Jen Li Chia-Yu Lin A. Balamurugan Chung-Wei Kung Jen-Yuan Wang Chih-Wei Hu Chun-Chieh Wang Po-Yen Chen R. Vittal Kuo-Chuan Ho 《Analytica chimica acta》2012
A modified glassy carbon electrode was prepared by depositing a composite of polymer and mediator on a glassy carbon electrode (GCE). The mediator, flavin adenine dinucleotide (FAD) and the polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) were electrochemically deposited as a composite on the GCE by applying cyclic voltammetry (CV). This modified electrode is hereafter designated as GCE/PEDOT/FAD. FAD was found to significantly enhance the growth of PEDOT. Electrochemical quartz crystal microbalance (EQCM) analysis was performed to study the mass changes in the electrode during the electrodeposition of PEDOT, with and without the addition of FAD. The optimal cycle number for preparing the modified electrode was determined to be 9, and the corresponding surface coverage of FAD (ΓFAD) was ca. 5.11 × 10−10 mol cm−2. The amperometric detection of iodate was performed in a 100 mM buffer solution (pH 1.5). The GCE/PEDOT/FAD showed a sensitivity of 0.78 μA μM−1 cm−2, a linear range of 4–140 μM, and a limit of detection of 0.16 μM for iodate. The interference effects of 250-fold Na+, Mg2+, Ca2+, Zn2+, Fe2+, Cl−, NO3−, I−, SO42− and SO32−, with reference to the concentration of iodate were negligible. The long-term stability of GCE/PEDOT/FAD was also investigated. The GCE/PEDOT/FAD electrode retained 82% of its initial amperometric response to iodate after 7 days. The GCE/PEDOT/FAD was also applied to determine iodate in a commercial salt. 相似文献
32.
《Analytical letters》2012,45(15):2705-2721
Abstract Recently affinity chromatography with a biospecific stationary phase was widely used in separation and purification processes of all kinds of enzymes. In this paper, a series of synthetic reactions of solid-liquid phase on a silica surface are described. By using a wide-pore (30μm). microspheric silica (8μm) as the matrix and γ-aminopropyltriethoxy-silane as the activating agent, the nicotinamide adenine dinucleotide (NAD) was bonded through its amino groups with carboxylic groups of linked phospholipid by a covalent bond on the aminated supports. This bonded stationary phase provided high thermal stability which could be used for separating nucleotides with good resolution. At the same time, the effects of pH, organic modifier and ionic strength on the retention properties of nucleotides were also investigated. 相似文献
33.
Nicotinamide adenine dinucleotide (oxidized form, free acid, NAD+) was utilized as an auxiliary for polar alignment of gallic acid (=3,4,5‐trihydroxybenzoic acid, GA) in the crystalline molecular complex NAD+?(GA)2?(H2O)5. In this adduct, NAD+ takes up a novel U‐shaped conformation accepting a GA molecule to give rise to a pincer‐type π‐complex. With the assistance of further GA molecules, these pincer assemblies build up infinite donor? acceptor π‐stacks in the crystal. An extended network of H‐bonds among the multitude of pertinent active functional groups and the water molecules supports the crystal structure. These findings may imply noteworthy material properties, in particular nonlinear optical effects, and might also serve to trigger inspiring biochemical connections to be made. The crystal structure of anhydrous GA is also reported, which is centrosymmetric and non‐polar. 相似文献
34.
Noboru Ikeya Konstantin L. Ivanov Kiminori Maeda Jonathan R. Woodward 《Molecular physics》2019,117(19):2604-2617
ABSTRACTIn this work, we propose to extend the scope of single-molecule spectroscopy to spin chemistry investigations of single radical pairs. A consistent theory of single-molecule spectroscopy on single radical pairs is proposed, which allows one to show that bunching phenomena are affected by singlet–triplet interconversion in radical pairs, which is, in turn, affected by local and external magnetic fields. A detailed study on the feasibility of such experiments with single flavin adenine dinucleotide, FAD, molecules is presented. We conclude that the observation of magnetic field effects on single FAD molecules is feasible but experimentally challenging for measurements on integrated fluorescence intensity and fluorescence event statistics. 相似文献
35.
Sabrina M. Pancera Luis H. M. da Silva Watson Loh Rosangela Itri Adalberto Pessoa Jr Denise F. S. Petri 《Colloids and surfaces. B, Biointerfaces》2002,26(4):291-300
The effect of poly(ethylene glycol), PEG, on the enzymatic activity of glucose-6-phosphate dehydrogenase (G-6-PDH) in the oxidation of glucose-6-phosphate (G-6-P), using NADP+ as co-enzyme was investigated. The enzymatic activity was determined by means of spectrophotometry in three different media: pure Tris–HCl buffer, solution of PEG400 (20 wt.%) and of PEG4000 (20 wt.%), both in buffer. Comparing the enzymatic activity values measured in pure buffer with those in the polymer solutions, an increase in the enzymatic activity of 20% was observed in the presence of PEG400 as well as in PEG4000. Calorimetric studies indicated the absence of preferential interactions between G-6-PDH and PEG400 or PEG4000. Nevertheless, the interaction enthalpy, ΔHint, between NADP+ and PEG400 and PEG4000 amounted to −9.3 and −26.7 kJ/mol, respectively. Small angle X-ray scattering (SAXS) measurements were performed in a higher concentration range. Data analysis performed from SAXS curves by means of the intra-particle distance distribution function p(r) and Guinier plots yielded for G-6-PDH in pure buffer and PEG400 solutions radius of gyration, Rg, of about 70 Å and in PEG4000 solutions, Rg of about 40 Å. The latter has the same dimension as that found in the dimeric crystallographic structure of G-6-PDH, evidencing that G-6-PDH preserves its dimeric configuration in PEG4000 solution. On the contrary, different aggregates of G-6-PDH are formed in the presence of either buffer or PEG400. These findings show that the presence of PEG in solution can exert an effect on the enzyme structure and activity. 相似文献
36.
Understanding redox reactions in reaction of nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP+) requires a clear grasp of the textbook content. The reactions in nicotinamide coenzymes with reduced and oxidized forms have been compared in various biochemistry textbooks. Incorrect interpretations usually emphasize the valence changes that at nitrogen in the pyridine ring of a nicotinamide from +5 to +3. Actually, the valence of nitrogen in pyridine ring is -3. We have gathered shreds of evidences and provide here possible suggestions and caution for readers and instructors. 相似文献
37.
Catherine M HalliwellEvelyne Simon Chee-Seng TohPhilip N Bartlett Anthony E.G Cass 《Analytica chimica acta》2002,453(2):191-200
The immobilisation of enzymes on an electrode surface, in such a manner that they retain both substrate specificity and high levels of catalytic activity, is of great importance in bioelectrochemistry. This includes areas such as the development of enzyme-catalysed fuel cell electrodes, biosensors and other biotechnological applications. We have investigated the catalytic activity of hexahistidine tagged variants of lactate dehydrogenase (EC 1.1.1.27) from the thermophile Bacillus stearothermophilus both in solution and when immobilised on poly(aniline)-poly(acrylate) (PANi-PAA) or poly(aniline)-poly(vinyl sulphonate) (PANi-PVS) composite films. Both the C- and N-terminally tagged enzymes are readily immobilised on the modified electrode and catalyse the conversion of lactate and NAD+ to pyruvate and NADH. The NADH that is generated can be readily oxidised at the PANi-modified electrode surface.In solution, the activity of the C-tagged enzyme (LDH-CHis) was some 30% less that of the wild-type under comparable conditions, whereas the N-tagged enzyme was found to possess essentially the same activity as the wild-type. However, when the enzymes were immobilised on PANi-PAA and PANi-PVS the C-tagged enzyme films showed a higher NADH-dependent current than the wild-type LDH whilst the N-tagged enzyme had the highest of the three. In addition, the C-tagged enzyme film appeared more stable than the wild-type LDH-PANi film. A novel immobilisation chemistry of the enzyme is proposed to account for these observations. 相似文献
38.
咖啡酸玻碳修饰电极对烟酰胺腺嘌呤二核苷酸的电催化氧化 总被引:1,自引:0,他引:1
研究了咖啡酸修饰电极的制备、性质及对NADH的电催化作用。修饰电极在0.1mol/L PBS缓冲溶液中(pH7.0)于0.0~ 050V(vs.Ag/AgCl)电位范围内呈现一对氧化还原峰,式量电位(E^0‘‘)为 0.250V(vs.Ag/AgCl)。E^0‘‘随pH增加而朝负方向移动,pH在5.0~8.0范围内,其线性回归方程为E^0‘‘=0.6233-0.05996pH,R=0.9969。表观电极反应速率常数(Kb)为12.3s^-1。电极反应的电子数为2且有2个质子参与。该修饰电极对NADH的氧化具有很好的电催化作用。NADH浓度在0.1—6.0mmol/L.范围内与峰电流呈现良好的线性关系。文中对电催化过程进行了探讨。 相似文献
39.
Protein–DNA interactions induce conformational changes in DNA such as B‐ to A‐form transitions at a local level. Such transitions are associated with a junction free energy cost at the boundary of two different conformations in a DNA molecule. In this study, we performed umbrella sampling simulations to find the free energy values of the B–A transition at the dinucleotide and trinucleotide level of DNA. Using a combination of dinucleotide and trinucleotide free energy costs obtained from simulations, we calculated the B/A junction free energy. Our study shows that the B/A junction free energy is 0.52 kcal mol?1 for the A‐philic GG step and 1.59 kcal mol?1 for the B‐philic AA step. This observation is in agreement with experimentally derived values. After excluding junction effects, we obtained an absolute free energy cost for the B‐ to A‐form conversion for all the dinucleotide steps. These absolute free energies may be used for predicting the propensity of structural transitions in DNA. 相似文献
40.
A new method for the determination of lactic acid based on the immobilization enzyme fluorescence capillary analysis (IE-FCA) was proposed. Lactic dehydrogenase (LDH) was immobilized on inner surface of a capillary with glutaraldehyde, and an immobilized enzyme lactate capillary bioreactor (IE-LCBR) was formed for the determination of lactic acid. After nicotinamide adenine dinucleotide (NAD+) is mixed with lactic acid solution, it was sucked into the IE-LCBR and was detected at λex 353 nm/λem 466 nm. Optimized conditions are as follows: the temperature is 38 °C; the reaction time is 15 min; the concentrations of Tris buffer (pH 8.8) and NAD+ are 0.1 mol L−1 and 4 mmol L−1, respectively; the concentration of LDH used for immobilization is 15 kU L−1. The concentration of lactic acid is directly proportional to the fluorescence intensity measured from 0.50 to 2.0 mmol L−1; and the analytical recovery of added lactic acid was 99–105%. The minimum detection limit of the method is 0.40 mmol L−1 and sensitivity of the IE-CBR is 4.6 F mmol−1 L−1 lactate. Its relative standard deviation (R.S.D.) is ≤2.0%. This IE-FCA method was employed for determination of lactate in milk drink. 相似文献