Differential interactions of cyclodextrins with hydrophobic derivatives of sepharose CL-4B

The partition coefficients K_av between the solution phase and octyl- and phenyl-sepharose CL-4B were determined for three cyclodextrins (CDs), -CD, -CD and -CD in various aqueous solutions, as a measure of their interactions with the two hydrophobic ligands. K_av of the CDs increased in the order of -CD<-CD<-CD for octyl-sepharose CL-4B and -CD<-CD<-CD for phenyl-sepharose CL-4B. In all cases, K_av increased by increasing NaCl concentration in the aqueous solution phase and also by lowering temperature, but in the presence of NaBr and NaSCN, both chaotropic salts, K_av decreased markedly. The spontaneity of the transfer of the CDs from the aqueous solution phases to the gel phases was due to the enthalpy decrease. It was shown that discrete separation of the three CDs can be achieved by the hydrophobic chromatography on a short column (1×25cm) of octyl-sepharose CL-4B by adjusting the NaCl concentration and temperature.     

Adsorptive immobilization of intestinal brush border membrane on triton X-100-substituted sepharose 4B

Triton X-100-substituted Sepharose 4B (Sepharose-TX) was used for adsorptive immobilization of intestinal brush border membrane using lactose-phlorizin hydrolase as a representative membrane enzyme. Limited heating of membrane preparations was found to enhance binding. This enhancement is concluded to be owing to a greater availability of the hydrophobic sites, as also confirmed by the 1-anilino-8-naphthalene sulfonate fluorescence studies, for interaction with Triton X-100 moieties on the support. The immobilized preparations obtained by this procedure were found useful in hydrolysis of lactose, involving lactose-phlorizin hydrolase, in continuous operations. It is suggested that the approach may be of general utility for immobilization of biologic membranes by interaction of their extramembrane structures using supports with appropriate hydrophobic groups.     

Interaction of spermine,spermidine, and putrescine with heparin bound to sepharose beads

The binding of the polyamines spermine and spermidine, and of their precursor, putrescine, to heparin-sepharose have been investigated to provide the basic data for further application of this resin in the study of polyamine biological function.

1. Spermine binds heparin-sepharose in a cooperative phase, the empirical index of cooperativity is two, and the apparent binding constant is 1.41 × 10⁶ M^-1.
2. Spermidine binds heparin-sepharose in a cooperative and strong noncooperative phase. In the cooperative phase, the index of cooperativity is two and the apparent binding constant is 1.56 × 10⁶ M^-. In the strong noncooperative phase, the apparent binding constant is 2 × 10⁵ M^-1.
3. Putrescine binds heparin-sepharose in a strong noncooperative and a weak noncooperative phase. In the strong noncooperative phase the apparent binding constant is 2.6 × 10⁵ M^-1. In the weak noncooperative phase, the apparent binding constant is 3.2 × 10³ M^-1.

     

Microfabricated glucose biosensor with glucose oxidase entrapped in sol-gel matrix

A microfabricated glucose biosensor based on an amperometeric hydrogen peroxide electrode has been developed. A sol-gel layer with 5 A pore size and 2 mum thickness was used as the glucose oxidase entrapping matrix. The sol-gel matrix formed over the silicon-based sensor has good mechanical and chemical stability, and the ability to entrap a large amount of enzyme. The miniaturized electrode sensing system is composed of platinum as both working and counter electrodes and silver as a reference electrode. Nafion(R) coating was applied as the interference limiting layer. A series of technologies, such as standard photolithography, electron beam evaporation and image reverse lift-off were utilized for mass production allowing 143 electrodes to be produced at the same time. The effect of oxidable interferences was <10% of the background value of the sensor response. Calibration tests of a series of individual sensors manufactured from the same silicon wafer and dip coated in the same conditions, showed a highly reproducible response characteristics (linear range up to 500 mg dl(-1) and mean sensitivity of 0.54+/-0.14 nA mg(-1) dl(-1) (n=10)).     

Synthesis of alkyl-substituted 2-halo-4-aminomethyl-2-buten-4-olides

The reaction of esters of alkyl-substituted (E)-5-amino-4-hydroxy-2,3,epoxyvaleric acids with some hydrohalic acids gave the corresponding 2-halo-4-amino-methyl-2-buten-4-olides, the hydrochlorides of which have diuretic activity.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1471–1474, November, 1985.     

Oxygen-independent glucose microsensor based on glucose oxidase

A glucose oxidase-based needle-type microsensor is described that is independent of the local oxygen concentration. The sensor consists of an enzyme-coated platinum microelectrode that is inserted in a glass capillary with a tip of 5–25 μm, and connected to the environment via an agar membrane. Oxygen is supplied to the enzyme coating from the shaft of the capillary. Depending on the electrode configuration, the sensor has a response time of 1–10 s, and the measuring range extends from 0.01 to 0.4 mmol l^?1 or from 0.4 to 10 mmol l^?1. The signal is not affected by stirring.     

Amperometric determination of glucose with a ferrocene-mediated glucose oxidase/polyacrylamide gel electrode

Enzyme electrodes were constructed by immobilization of glucose oxidase and ferrocene into cross-linked polyacrylamide gels. Electrogenerated ferrocinium ion acts as a direct electron mediator between glucose oxidase and a reticulated vitreous carbon (RVC)/graphite support bed. The electrode is easily constructed, gives a current response proportional to glucose concentrations up to 30 mM, and has good chemical stability in water and air.     

含有BaMoO4纳米粒子的反胶束溶液与罗丹明B的相互作用

在三种带有不同电荷的表面活性剂构建的反胶束体系中(AOT/异辛烷、Oπ-10,环已烷、CTAB／正已醇)合成了BaMoO4的纳米粒子,采用透射电镜(TEM)观察其粒子呈球形,粒径在17-46 nm范围内,分布均匀;使用染料罗丹明B作为探针,采用紫外-可见光谱(UV-vis)和荧光光谱研究反胶束水池中罗丹明B与BaMoO4纳米粒子的相互作用;由于反胶束水池的空间和极性的限定,染料的光谱特征与其在纯水中发生很大变化,不同的反胶束体系中,由于染料分子所处的微观环境不同,导致其光谱特征也有较大区别。     

Biosensors for determination of glucose with glucose oxidase immobilized on an eggshell membrane

A glucose biosensor using an enzyme-immobilized eggshell membrane and oxygen electrode for glucose determination has been fabricated. Glucose oxidase was covalently immobilized on an eggshell membrane with glutaraldehyde as a cross-linking agent. The glucose biosensor was fabricated by positioning the enzyme-immobilized eggshell membrane on the surface of a dissolved oxygen sensor. The detection scheme was based on the depletion of dissolved oxygen content upon exposure to glucose solution and the decrease in the oxygen level was monitored and related to the glucose concentration. The effect of glutaraldehyde concentration, pH, phosphate buffer concentration and temperature on the response of the glucose biosensor has been studied in detail. Common matrix interferents such as ethanol, d-fructose, citric acid, sodium benzoate, sucrose and l-ascorbic acid did not give significant interference. The resulting sensor exhibited a fast response (100 s), high sensitivity (8.3409 mg L⁻¹ oxygen depletion/mmol L⁻¹ glucose) and good storage stability (85.2% of its initial sensitivity after 4 months). The linear response is 1.0×10⁻⁵ to 1.3×10⁻³ mol L⁻¹ glucose. The glucose content in real samples such as commercial glucose injection preparations and wines was determined, and the results were comparable to the values obtained from a commercial glucose assay kit based on a spectrophotometric method.     

Laccase/glucose oxidase electrode for determination of glucose

The electrode involves a layer of co-immobilized glucose oxidase and laccase in a gelatin membrane placed over a modified oxygen electrode. Hexacyanoferrate(III) is added to the samples to oxidize reductive interferents such as ascorbic acid, and the hexacyanoferrate(II) formed is re-oxidized by a laccase-catalyzed reaction. Ascorbic acid is completely eliminated up to a concentration of 20 mM in the sample.     

Wiring of glucose oxidase with graphene nanoribbons: an electrochemical third generation glucose biosensor

A reagentless third generation electrochemical glucose biosensor was fabricated based on wiring the template enzyme glucose oxidase (GOx) with graphene nanoribbons (GN) in order to create direct electron transfer between the co-factor (flavin adenine dinucleotide, FAD) and the electrode. The strategy involved: (i) isolation of the apo-enzyme by separating it from its co-enzyme; (ii) preparation of graphene nanoribbons (GN) by oxidative unzipping of multi-walled carbon nanotubes; (iii) adsorptive immobilization of GNs on the surface of a screen printed carbon electrode (SPCE); (iv) covalent attachment of FAD to the nanoribbons; (v) recombination of the apo-enzyme with the covalently bound FAD to the holoenzyme; and (vi) stabilization of the bio-layer with a thin membrane of Nafion. The biosensor (referred to as GN/FAD/apo-GOx/Nafion/SPCE) is operated at a potential of +0.475 V vs Ag/AgCl/{3 M KCl} in flow-injection mode with an oxygen-free phosphate buffer (pH 7.5) acting as a carrier. The signals are linearly proportional to the concentration of glucose in the range from 50 to 2000 mg?L^?1 with a detection limit of 20 mg?L^?1. The repeatability (10 measurements, at 1000 mg?L^?1 glucose) is ±1.4% and the reproducibility (5 sensors, 1000 mg?L^?1 glucose) is ±1.8%. The biosensor was applied to the determination of glucose in human serum.

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Graphical abstract Wiring of the apo-enzyme of glucose oxidase (apo-GOx) with graphene nanoribbons (GN) bound to FAD at a screen-printed carbon electrode (SPCE). Cyclic voltammetric and amperometric responses to various glucose concentrations.

     

Study on glucose oxidase fermentation coupled with membrane dialysis

The repression of glucose oxidase (GOD) biosynthesis by catabolites during fermentation can be alleviated through membrane dialysis fermentation (MDF). The results show that the volumetric enzyme productivity of MDF was two times higher than that of the control (fermentation without dialysis), and its total enzyme activity was increased by 30–50%. The operation conditions of MDF, such as pore size of the membrane, initiating time for membrane dialysis, and volume of dialysate used, were optimized. The content of amino acids and organic acids in the fermentation broth and the dialysate in the reservoir were assessed by amino acid analyzer and ionic chromatography, respectively. The relationship among the contents of pyruvic acid, gluconic acid, and enzyme activity during fermentation was analyzed quantitatively. Furthermore, the effect of membrane dialysis technology applied to the low-yield strain was found to be more effective than that applied to the high-yield strain.     

Analytical use of immobilized glucose oxidase

With the aim of immobilizing glucose oxidase (GO) for routine determination of glucose, a covalent bond immobilization method on titanium (IV) chloride activated silica supports was used (1). Several parameters were studied in order to optimize the residual activity upon immobilization and during operation. The immobilized enzyme can be reutilized at 25°C for several h a day alternating with storage (4°C) for at least 3,300 h.     

Comparison of amperometric measuring principles for determinations of glucose with electrodes based on glucose oxidase

The three measuring principles for glucose determination (H₂O₂ formation, O₂ consumption, or enzymatically reduced acceptor) were studied with an apparatus that was the same for all measurements, with virtually identical electrode design. The methods were compared with regard to measurement range, sensitivity, time behaviour, operational lifetime, precision and accuracy. Essential differences were found with respect to measurement range as well as to time. Measurements under anaerobic conditions have advantages over those done aerobically.     

Integration of a highly ordered gold nanowires array with glucose oxidase for ultra-sensitive glucose detection

A highly sensitive amperometric nanobiosensor has been developed by integration of glucose oxidase (GO_x) with a gold nanowires array (AuNWA) by cross-linking with a mixture of glutaraldehyde (GLA) and bovine serum albumin (BSA). An initial investigation of the morphology of the synthesized AuNWA by field emission scanning electron microscopy (FESEM) and field emission transmission electron microscopy (FETEM) revealed that the nanowires array was highly ordered with rough surface, and the electrochemical features of the AuNWA with/without modification were also investigated. The integrated AuNWA–BSA–GLA–GO_x nanobiosensor with Nafion membrane gave a very high sensitivity of 298.2 μA cm⁻² mM⁻¹ for amperometric detection of glucose, while also achieving a low detection limit of 0.1 μM, and a wide linear range of 5–6000 μM. Furthermore, the nanobiosensor exhibited excellent anti-interference ability towards uric acid (UA) and ascorbic acid (AA) with the aid of Nafion membrane, and the results obtained for the analysis of human blood serum indicated that the device is capable of glucose detection in real samples.