Nafion-二茂铁-双酶修饰的葡萄糖传感器

用二茂铁作为过氧化物酶与玻碳电极的电子传递体,通过牛血清白蛋白-戊二醛交联剂把葡萄糖氧化酶和过氧化物酶固定在Nafion-二茂铁修饰玻碳电极上,制备成葡萄糖传感器。由于工作电位低,电活性物质如抗坏血酸、尿酸等对测定无干扰。该传感器的线性范围为5.0×10～(-4)～2.5×10～(-2)mol/L,响应时间小于30s.     

1,4-二氧六环介质中辣根过氧化物酶电极的性能研究

用交联法制备辣根过氧化物酶(HRP)电极, 在1,4-二氧六环介质中研究其电化学行为。实验表明, 固定化的HRP在有机相中仍保持活性并可与电极进行直接电子传递, 因而能在没有其它电子传递体存在的条件下催化H~2O~2的电化学还原反应。当亚铁氰化物与酶共修饰至电极上之后, 它起着电子传递体的作用, 使HRP电极的性能大为改善。根据不同条件下得到的动力学参数, 讨论了影响酶电极性能的因素。     

生物功能电极（Ⅴ）：—葡萄糖氧化酶在环糊精聚合物中的固…

将葡萄糖氧化酶固定在α－环糊精聚合物中，而电子传递体分子被包含在环糊精腔穴中，固定化酶膜的ＦＴＩＲ测定表明，ＧＯＤ与环糊精聚合物发生共价连接，制备了含电子传递体的不同ＧＯＤ酶电极并比较了它们的性能，含四硫代富瓦烯的酶电极具有良好的电流响应特性，可望成为第二代葡萄糖酶电极的新构型。     

生物功能电极(Ⅴ)─葡萄糖氧化酶在环糊精聚合物中的固定化

将葡萄糖氧化酶(GOD)固定在α-环糊精聚合物中,而电子传递体分子被包含在环糊精腔穴中。固定化酶膜的FTIR测定表明,GOD与环糊精聚合物发生共价连接。制备了含电子传递体的不同GOD酶电极并比较了它们的性能。含四硫代富瓦烯的酶电极具有良好的电流响应特性,可望成为第二代葡萄糖酶电极的新构型。     

辣根过氧化物酶的电化学固定化及其对H2O2的生物电催化…

利用电化学固定化方法制备了聚吡咯／辣根过氧化物酶（ＰＰ／ＨＲＰ）膜电极，并研究了其电化学行为，在除氧的磷酸盐缓冲液介质中，ＰＰ／ＨＲＰ电极加速Ｈ２Ｏ２的还原，归因子酶加成物的直接电子传递，探索ＨＲＰ与电子传递体Ｋ４Ｆｅ（ＣＮ）６在聚吡咯（ＰＰ）膜中的同时固定化条件及其膜电极的电化学行为，实验证实，Ｋ４Ｆｅ（ＣＮ）６在酶膜中的存在使得Ｈ２Ｏ２的还原电位强烈正移，在－０．０５Ｖ的工作电位下能对Ｈ２Ｏ２     

聚邻苯二胺膜电极中辣根过氧化物酶的电子传递

利用酸的电化学固定法制备含辣根过氧化物酶的聚邻苯二胺膜电极，研究其伏安行为及对Ｈ２Ｏ２还原的生物电催化作用，结果表明，在所述生物电催化反应中酶与聚合物基质 直接电子传递，但对新制的酶电极而言，电聚合时生成并包埋在酶膜中的寡聚体可作为电子传递体加速氧化态酶的再生，根据酶电极电流响应实验曲线的拟合，发现经态酶的再生速度随是极电位的变化表观上符合Ｔａｆｅｌ关系式，提出了酶反应学参数的测定方法。     

二茂铁及其衍生物在传感器上的应用进展

二茂铁是一类具有夹心结构的有机金属配合物,有良好的氧化 还原特性,可有效改善传感器电极上的电子传递效率。 本文评述了近年来二茂铁及其衍生物在酶生物传感器、免疫传感器和离子传感器上的研究状况,并对其今后的发展方向做出展望。     

二茂铁-Nafion修饰葡萄糖传感器的研究

1 引言 第二代电流式酶传感器采用非生理的氧化还原介体如二茂铁及其衍生物、铁氰化钾、四硫富瓦烯、醌及其衍生物、钉化合物及麦尔多蓝等代替氧,起着酶与电极之间的电子传递作用,克服了第一代电流式酶传感器背景电流大,响应特性差,易受环境中氧浓度的影响,干扰大等缺点。但目前第二代电流式酶电极还存在着介体流失,电极污染及一些电活性物质干扰等问题。商品化的Nafion甲醇溶液不易溶解酶且能使部分酶失活,本文把Nafion甲醇溶液制成Nafion水溶液,将葡萄糖氧化酶溶解在Nafion水溶液,然后把它修饰在修饰有二茂铁的玻碳电极的表面,最后再修饰一层Nafion膜,成功地制备了二茂铁-Nafion修饰葡萄糖传感器,Nafion膜不仅能把抗坏血酸、尿酸等电活性物质阻挡在电极外,防止其干扰,同时具有防污性能,而且能防止二茂铁的流失,提高电极的稳定性。该传感器具有抗干扰能力强,响应快等特点。     

N—（3—二茂铁乙酰胺基）丙基吡咯聚合物修饰的葡萄糖电极的研究

于铂电极上修饰一层Ｎ－（３－二茂铁乙酰胺基）丙基吡咯聚合物膜，应用循环伏安法对聚合物的电化学性能进行研究，发现了Ｎ－位取代吡咯聚合物的电活性大大降低，聚合物中 二茂铁基团氧化还原性能稳定，制成酶电极后，在＋０．２Ｖ以葡萄糖有一明显的催化峰，而对抗坏血酸，尿酸则几乎没有呼应，该葡萄糖电极性能稳定，连续工作十天，响应值基本不变。     

二茂铁修饰青椒籽碳糊电极测定抗坏血酸

以二茂铁作为电子传递介体,制成Ｆｅ修饰的青椒籽碳糊电极,研究了该电极的性能,用恒电位电流法测定了抗坏血酸的浓度并用于药物中抗坏血酸的含量分析,结果与药典法相符。     

The true Johari-Goldstein beta-relaxation of monosaccharides

Broadband isothermal dielectric relaxation measurements of anhydrous fructose, glucose, galactose, sorbose, and ribose were made at ambient pressure in their liquidus and glassy states. We found a new secondary relaxation in fructose and glucose that is slower than those seen before by others. This new secondary relaxation also appears in the dielectric spectra of galactose, sorbose, and ribose, and hence it is a general feature of the relaxation dynamics of the monosaccharides. Dielectric measurements at elevated pressure of fructose and ribose show that the new secondary relaxation shifts to lower frequencies with applied pressures, mimicking the behavior of the alpha-relaxation. In contrast, the faster secondary relaxation remains stationary on applying pressure. These results together with other inferences indicate that the slower secondary relaxation bears relations to the alpha-relaxation, and hence, it is the true Johari-Goldstein secondary relaxation of the monosaccharides.     

Local measures of intermolecular free energies in solution

Proton spin-lattice relaxation rate changes induced by freely diffusing oxygen in aqueous and mixed solvents are reported for representative amino acids and glucose. The local oxygen concentration at each spectrally resolved proton was deduced from the paramagnetic contribution to the relaxation rate. The measured relaxation increment is compared to that of the force-free diffusion relaxation model, and the differences are related to a free energy for the oxygen association with different portions of the solute molecules. The free energy differences are small, on the order of -800 to -2000 J/mol, but are uniformly negative for all proton positions measured on the amino acids in water and reflect the energetic benefit of weak association of hydrophobic cosolutes. For glucose, CH proton positions report negative free energies for oxygen association, the magnitude of which depends on the solvent; however, the hydroxyl positions report positive free energy differences relative to the force-free diffusion model, which is consistent with partial occupancy in the OH region by a solvent hydrogen bond.     

Molecular dynamics and entropy changes in the agar-water system

Molecular dynamics in the agar-water systems was studied using proton spin relaxation and rotary viscosimetry techniques. The decrease of spin-lattice relaxation during biological evolution in the agar medium for the tissue culture contributes to the problem of the entropy changes in the open systems.     

Use of water spin-spin relaxation rate to probe the solvation of cyclodextrins in aqueous solutions

1H spin-spin relaxation rate constant, R2, of water was measured by using the Carr-Purcell-Meiboom-Gill sequence in aqueous solutions of native cyclodextrins (alpha, beta, and gamma-CD) and chemically modified CDs in order to probe the structuring of the water surrounding these cyclic carbohydrate molecules. R2 values for water in solutions containing glucose and dextran were also measured for comparison. A two-site model for bonded and free water molecules was used to fit the results for the dependence of R2 on the solute concentrations. The order of relaxation rates for water in aqueous solution at a fixed specific hydroxyl group concentration is glucose>dextran congruent with CDs. No significant difference was observed for R2 of water in solutions containing native CDs, which indicates that the size and nature of the cavity has a small effect on the spin-spin relaxation times of water. The lower relaxation rate for water in CD solutions was attributed to the intramolecular hydrogen bonding formed between the secondary hydroxyl groups that line the rim of the CDs. For comparison, the relaxation rates for water in solutions of two chemically modified CDs were also studied.     

Single-molecule measurements of trapped and migrating circular DNA during electrophoresis in agarose gels

The effect of agarose gel concentration and field strength on the electrophoretic trapping of open (relaxed) circular DNA was investigated using microscopic measurements of individual molecules stained with a fluorescent dye. Three open circles with sizes of 52.5, 115, and 220 kbp were trapped by the electric field (6 V/cm) and found to be predominately fixed and stretched at a single point in the gel. The length of the stretched circles did not significantly change with agarose concentration of the gels (mass fractions of 0.0025, 0.01, and 0.02). The relaxation kinetics of the trapped circles was also measured in the gels. The relaxation of the large open circles was found to be a slow process, taking several seconds. The velocity and average length of the 52.5 kbp open circles and 48.5 kbp linear DNA were measured during electrophoresis in the agarose gels. The velocity increased when the agarose concentrations were lowered, but the average length of the open-circle DNA (during electrophoresis) did not significantly change with agarose gel concentrations. The circles move through the gels by cycles of stretching and relaxation during electrophoresis. Linear dichroism was also used to investigate the trapping and alignment of the 52.5 kbp open circles. The results in this study provide information that can be used to improve electrophoretic separations of circular DNA, an important form of genetic material and commonly used to clone DNA.     

Viscoelastic study of the conformational transition of poly(methacrylic acid) in dilute aqueous solution

The dynamic viscosity of dilute aqueous solution of poly(methacrylic acid) (PMA) was measured over the frequency range 2–500 kHz for various degrees of ionization. The relaxation spectrum calculated from the viscosity exhibits a conformational relaxation spectrum in the short-time region and a rotational one in the long-time region. The former is fitted by the Zimm theory over the entire range of ionization, including the transition from a compact structure to an open one. The conformational relaxation time begins to increase at the midpoint of the transition region, but the rotational relaxation time increases very markedly in the initial stage of the transition. The present and previously reported experimental findings are interpreted in terms of the assumption that the compact structure is stabilized by short-range methyl–methyl bonding as well as “long-range” methyl–methyl bonding (bonding between methyl groups spatially close but remotely connected along the chain contour). In the initial stage of the transition, the latter primarily break up, resulting in expansion of overall chain dimensions, and subsequently the former are destroyed, resulting in the change in local chain conformation.     

Hydrogen bond dynamics and water structure in glucose-water solutions by depolarized Rayleigh scattering and low-frequency Raman spectroscopy

The effect of glucose on the relaxation process of water at picosecond time scales has been investigated by depolarized Rayleigh scattering (DRS) experiments. The process is assigned to the fast hydrogen bonding dynamics of the water network. In DRS spectra this contribution can be safely separated from the slower relaxation process due to the sugar. The detected relaxation time is studied at different glucose concentrations and modeled considering bulk and hydrating water contributions. As a result, it is found that in diluted conditions the hydrogen bond lifetime of proximal water molecules becomes about three times slower than that of the bulk. The effect of the sugar on the hydrogen bond water structure is investigated by analyzing the low-frequency Raman (LFR) spectrum sensitive to intermolecular modes. The addition of glucose strongly reduces the intensity of the band at 170 cm(-1) assigned to a collective stretching mode of water molecules arranged in cooperative tetrahedral domains. These findings indicate that proximal water molecules partially lose the tetrahedral ordering typical of the bulk leading to the formation of high density environments around the sugar. Thus the glucose imposes a new local order among water molecules localized in its hydration shell in which the hydrogen bond breaking dynamics is sensitively retarded. This work provides new experimental evidences that support recent molecular dynamics simulation and thermodynamics results.     

Molecular motion and interactions in aqueous carbohydrate solutions. III. A combined nuclear magnetic and dielectric-relaxation strategy

A strategy is developed for the complementary use of dielectric and nuclear magnetic relaxation methods to elucidate the molecular dynamics in aqueous solutions of small hydrophilic molecules, and hence determine extents of hydration. The nuclear magnetic relaxation data, as well as characterizing the motional properties of various carbohydrate solutes, is used here to test alternative models for the resolution of the dielectric spectra into their component relaxation processes. This approach results in a much more confident analysis of solvent relaxation properties than has in the past been usual, to yield information relating to the extents of hydration of small sugars and the possible orientation-specific nature of this hydration. It is demonstrated that the dielectric relaxation of the sugar molecules themselves is unequivocally not due to the reorientation of the whole molecule and most likely is dominated by the rotation of hydrate side chain groups (hydroxyls and hydroxymethyl). In proton magnetic relaxation studies of glucose in D₂O it is observed that one particular proton (H-1 in the -form only) is extremely susceptible to inter-molecular proton-proton interactions while the remaining protons are very effectively shielded. This observation is shown to be fully consistent with the conformational and hydration properties of glucose.     

Constitutive modeling for characterizing the compressive behavior of PMMA open‐cell foams

A constitutive model for evaluating the compressive behavior of Poly(methyl‐methacrylate) (PMMA) open‐cell foams is herein proposed. Specifically, the study investigates the viscoelastic and viscoplastic behaviors of the PMMA open‐cell foams. The constitutive equation is expressed in terms of the following polymer and foam properties: elastic modulus, relative density, as well as the relaxation and densification constants. PMMA open‐cell foams are manufactured using a gas foaming/particulate leaching method and uniaxial compression tests are performed. The mechanical properties and compressive stress‐strain responses obtained from the experiments are compared with those predicted by the proposed constitutive model. The results suggest that the constitutive model is an apt one for assessing and evaluating the compressive behaviors of PMMA open‐cell foams. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 436–443, 2007     

DSC and TSDC Study of Unsaturated Polyester Resin. Influence of the promoter content

This work reports on the curing kinetics of unsaturated polymer resins (UPRs) cured with styrene, studied by differential scanning calorimetry and Fourier transform infrared spectroscopy. The data lead to determination of the experimental conditions with which to obtain a fully cured material and open the way for study of the relaxation phenomena by means of thermally stimulated depolarization current analysis (TSDC). In relaxation studies on fully cured resins, the TSDC spectra revealed important overlapping of the main relaxation peak with an extra upper peak. The importance of this extra peak a priori prevents further analysis of the main relaxation. To identify the origins of this peak (space charge or other), the purity of the resin was checked by X-ray fluorescence spectroscopy. The use of UPR specimens with different compositions (in terms of the resin/activator/initiator ratio) demonstrated that the bulk of the impurities Cl, K, Ca, Sr, Zr and Ba are due to the promoter. Decoupling of the mixed peaks (α-relaxation and extra) revealed that the a peak is independent of the proportion of the promoter in the resin and that the extra peak is principally due to the presence of these impurities. This revised version was published online in July 2006 with corrections to the Cover Date.