Synthesis, redox and electrochemical properties of new anthraquinone-attached micelle- and vesicle-forming cationic amphiphiles

Three new cationic amphiphiles bearing anthraquinone moieties at the polar headgroup region were synthesized, The single-chain amphiphile, N,N-dimethyl-N-octadecyl-N-(9,10-dihydro dioxoanthracen-2-ylmethyl)ammonium bromide 1, in the presence of cetyltrimethylammonium bromide upon dispersion in water gave co-micellar aggregates containing covalently attached anthraquinone residues at the polar aqueous interfaces. The other two double-chain amphiphiles, N,N-dioctadecyl-N-methyl-N-(9,10-dihydro-9,10-dioxoanthracen-2-ylmethyl)ammonium bromide 2 and N,N-dimethyl-N-(1,2-bispalmitoyloxypropanyl)-N-(9,10-dihydro-9,10-dioxanthracen-2-ylmethyl)ammonium bromide 3, however, on dispersion in aqueous media produced vesicular aggregates. The critical temperatures for the gel to liquid-crystalline-like phase transition processes for the vesicular systems were determined by following temperature-dependent changes in the ratios of keto-enol tautomeric forms of benzoylacetanilide doped within respective. vesicular assemblies. The redox chemistry of the these supramolecular assemblies was also studied by following the time-dependent changes in the ITV-VIS absorption spectroscopy in the presence of exogenous reducing or oxidizing agents, Electrochemical studies using glassy carbon electrodes reveal that redox-active amphiphiles adsorb on to the glassy carbon surfaces to form electroactive deposits when dipped into aqueous suspensions of either of these aggregates irrespective of the micellar or vesicular nature of the dispersions.

Electrical-energy storage in hybrid ultracapacitors

There are several ways of storing electrical energy in chemical and physical forms and retrieving it on demand, and ultracapacitors are one among them. This article presents the taxonomy of ultracapacitor and describes various types of rechargeable-battery electrodes that can be used to realize the hybrid ultracapacitors in conjunction with a high-surface-area-graphitic-carbon electrode. While the electrical energy is stored in a battery electrode in chemical form, it is stored in physical form as charge in the electrical double-layer formed between the electrolyte and the high-surface-area-carbon electrodes. This article discusses various types of hybrid ultracapacitors along with the possible applications.

Multi-component Olivine for Lithium-Ion Hybrid Capacitor

A lithium-ion hybrid capacitor comprising of a battery type multi-component olivine (LiMn1/3Co1/3Ni1/3PO4) cathode and a capacitive type carbon negative electrode is reported. Olivine phosphate synthesized with chelating agent's polyvinylpyrrolidone (PVP) or triethanolamine (TEA) showed uniform carbon coating through in-situ process exhibiting a surface area 5.1 m(2)/g with porosity 0.02 cm(3)/g. The surface area for commercial carbon electrode was observed to be 1450 m(2)/g with high porosity 0.76 cm(3)/g. Galvanostatic charge/discharge cycling tests were conducted in the coin cells, olivine vs. Li, offering a cell voltage of 4.75 V vs. Li with a maximum specific capacitance of 125 F/g. In the case of olivine vs. carbon in a lithium-ion hybrid device delivered a high discharge capacitance of 86 F/g at a specific current of 0.12 A/g with a cycling retention of 53 F/g (38% loss) after 250 cycles. The obtained performance of PVP synthesized olivine material is manifested to uniform carbon coating and the trapped organic products that provide pathways for facile electrochemical reactions than their TEA counterparts.

Electrically conducting palladium selenide (Pd4Se, Pd17Se15, Pd7Se4) phases: synthesis and activity towards hydrogen evolution reaction

Electrically conducting, continuous films of different phases of palladium selenides are synthesized by the thermolysis of single source molecular precursors. The films are found to be adherent on flat substrates such as glass, indium tin oxide and glassy carbon and are stable under electrochemical conditions. They are electrocatalytically active and in particular, for hydrogen evolution reaction. Catalytic activities with low Tafel slopes of 50-60 mV per decade are observed.

新型纳米材料及离子载体化学修饰电极的制备及其在痕量重金属检测中的应用

随着工农业生产的迅速发展，重金属污染问题越来越严重。由于重金属能 够在土壤、水体等环境中不断积累，并且通过食物链而进入人体内蓄积，因此对 人类健康构成潜在的危害。当人体内重金属含量过量时，会导致各种疾病的发生。 所以对痕量重金属污染物进行监测和分析，在食品安全、临床诊断和环境监测等 方面具有重要的现实意义。因此，研究快速、准确、灵敏、方便的检测重金属的 新方法十分必要。 近年来，化学修饰电极由于能够赋予电极新的、特定的功能，在提高电化 学选择性和灵敏度方面有着独特的优越性，因而成为电分析化学领域研究的热 点，并且被广泛应用于重金属元素的测定。但是，由于电极材料的限制，灵敏度 虽然有所改进，却始终很难达到一个新的高度。要提高化学修饰电极对重金属检 测的灵敏度，必须加入一些辅助的方法。 最近，纳米材料在很多分析方法中得到广泛应用，这些材料表现出很多它 们在常规尺度时所没有的独特的性质，如量子尺寸效应、表面效应、小尺寸效应、 量子隧道效应以及介电限域效应等。因此，作为一种新型的电极材料在电化学检 测和分析方面受到人们的日益关注。由于纳米材料本身具有大的比表面积和高的 表面自由能，这种纳米材料修饰电极的灵敏度得到大幅度提高。 离子载体是一类具有一个特定空腔的大环分子，能够从溶液中实现对某一 特定离子的萃取使之进入到有机相中。离子载体是电位型传感器敏感膜中的核心 成分，尽管它具有很高的选择性，但是除了电位分析外，在其它方面的用途却很 少被关注，可能是由于其本身的非导电性能所致。本论文采用纳米材料所特有的 对重金属离子强大的吸附性能和离子载体优良的选择性，制备了纳米材料及离子 载体修饰玻碳电极并用来对实际水样中痕量的重金属进行检测。主要内容包括以 下几个方面： 1.制备新型碳纳米管/铋膜复合修饰电极，研究了重金属钴在电极上的电化 学性能。结果表明，这种新型复合修饰电极的灵敏度得到显著提高，能实现最低 检测限为8´10-11 M的钴的吸附富集溶出。 2.利用羟基磷灰石的强吸附能力和碳纳米管的优异电化学性能，制备了新型 新型纳米材料及离子载体化学修饰电极的制备及其在痕量重金属污染物检测中的应用 II 的碳纳米管-纳米羟基磷灰石的双纳米复合材料，并将其用于金属镉的富集溶出。 结果表明，双纳米复合材料具有比单一材料更优异的性能，更有助于金属镉的富 集溶出。采用碳纳米管-纳米羟基磷灰石的双纳米复合材料修饰电极，能实现最 低检测限为4´10-9 M的镉的富集溶出，灵敏度得到明显提高。 3. 将导电性好、抗氧干扰能力强的铋膜与对重金属具有良好选择性的离子 载体相结合，制备了基于铋膜/离子载体的新型修饰电极，研究了金属铅在其表 面的富集溶出。结果表明，这种新型修饰电极的灵敏度和选择性都大为提高，具 有更高的溶出峰电流和更好的抗干扰能力，可以实现最低检测限为4.4´10-11 M 的铅的富集溶出。 4. 利用羟基磷灰石的强吸附能力和其三维多孔结构、离子载体对重金属离 子优异的选择性以及Nafion 膜良好的离子交换作用和化学稳定性，制备了基于 纳米材料和离子载体的新型化学修饰电极。这种方法不仅有助于提高对金属铅的 选择性和灵敏度，而且大大提高了富集效率。采用该新型化学修饰电极，能够实 现最低检测限为1´10-9 M的铅的富集溶出。

Large scale, templateless, surfactantless route to rapid synthesis of uniform poly(o-phenylenediamine) nanobelts

We reported the interesting finding that large scale uniform poly(o-phenylenediamine) nanobelts with several hundred micrometers in length, several hundred nanometers in width, and several ten nanometers in height can be rapidly yielded from an o-phenylenediamine-HAuCl4 aqueous solution without the additional introduction of other templates or surfactants at room temperature.

Nanocomposite multilayer film of preyssler-type polyoxometalates with fine tunable electrocatalytic activities

Through layer-by-layer (LBL) assembly technique, iron oxide (Fe3O4) nanoparticles coated by poly (diallyldimethylammonium chloride) (PDDA) and Preyssler-type polyoxometalates (NH4)(14)NaP5W30O110.31H(2)O (P5W30) were alternately deposited on quartz and ITO substrates, and 4-aminobenzoic acid modified glassy carbon electrodes. Thus-prepared multilayer films were characterized by UV-visible spectroscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry. It was proved that the multilayer films are uniform and stable. And the electrocatalytic activities of the multilayer films can be fine-tuned by adjusting the assembly conditions in the LBL assembly process, such as the pH of the assembly solution. The multilayer films fabricated from P5W30 solutions dissolved in 0.1 M H2SO4 exhibit high electrocatalytic response and sensitivity toward the reduction of two substrates of important analytical interests, HNO2 and IO3- whereas the films assembled with P5W30 solutions dissolved in 1.0 M H2SO4 show remarkable electrocatalytic activity for the hydrogen evolution reaction (HER). Furthermore, the electrocatalytic properties of the HER of the latter film can be obtained from the former film upon exposure to 1.0 M H2SO4 for several hours.

Electrodepositing redox polymer on sandwich complex for the improvement of sensitivity in sandwich enzyme-linked immunoassay

Improvement of the sensitivity of electrochemical sandwich enzyme immunoassay has been achieved by electrodepositing redox polymer on screen-printed carbon electrode surface, on which the sandwich complex was formed.

Effect of DNA flanking sequence on charge transport in short DNA duplexes

Several factors can influence charge transport (CT)-mediated DNA, such as sequence, distance, base stacking, base pair mismatch, conformation, tether length, etc. However, the DNA context effect or how flanking sequences influence redox active drugs in the DNA CT reaction and later in DNA enzymatic repair and synthesis is still not well understood. The set of seven DNA molecules in this study have been characterized well for the study of flanking sequence effects. These DNA duplexes are formed from self-complementary strands and contain the common central four-base sequence 5'-A-G-C-T-3', flanked on both sides by either (AT)(n) or (AA)(n) (n = 2, 3, or 4) or AA(AT)(2). UV-vis, fluorescence, UV melting, circular dichroism, and cyclic voltammetry experiments were used to study the flanking sequence effect on CT-mediated DNA by using daunomycin or adriamycin cross-linked with these seven DNA molecules. Our results showed that charge transport was related to the flanking sequence, DNA melting free energy, and ionic strength. For (AA)(n) or (AT)(n) species of the same length, (AA)(n) series were more stable and more efficient CT was observed through the (AA)(n) series. The same trend was observed for (AA)(n) and (AT)(n) series at different ionic strengths, further supporting the idea that flanking sequence can result in different base stacking and modulate charge transport through these seven DNA molecules.

Study of the ion channel behavior of didodecyldimethylammonium bromide formed bilayer lipid membrane stimulated by PF6-

Bilayer lipid membranes ( BLM) formed from didode-cyldimethylammonium bromide were made on the freshly exposed surface of a glassy carbon (GC) and were demonstrated by the ac impedance spectroscopy. The ion channels of membrane properties induced by PF6- were studied by the cyclic voltammetric methods. Experimental results indicated that the ion channel of BLM was open in the presence of the PF6- due to the interaction of PF6- with the BLM, while it was switched off in the absence of PF6-. Because the ion channel behavior was affected by the concentration of PF6-, a sensor for PF6- can be developed.

Fabrication of layer-by-layer deposited multilayer films containing DNA and its interaction with methyl green

Multilayer films were fabricated by layer-by-layer electrostatic deposition techniques between poly(diallyIdimethylammonium chloride) (PDDA) and calf thymus DNA (CT DNA) on glassy carbon and quartz substrates. Electrochemical impedance spectroscopy (EIS), Fourier transform infrared (FTIR) spectroscopy and UV-vis spectroscopy demonstrated the uniform assembly of PDDA/DNA multilayer films, and X-ray photoelectron spectroscopy confirmed the elemental composition of the films. Moreover, the interaction of DNA in PDDA/DNA films with methyl green was investigated by UV-vis spectroscopy and circular dichroism (CD). (C) 2001 Elsevier Science B.V. All rights reserved.

Sol-gel biosensor

yA review with 44 references is presented on the development of sol-gel-based biosensor. The main discussions are devoted to the process, advantages and properties of sol-gel immobilization method, sol-gel optical biosensor and amperometric biosensor, also the trend in this field is forecasted.

Preparation of highly dispersed gold microparticles and their electrocatalytic activity for the oxidation of formaldehyde

The electrochemical preparation of highly dispersed Au microparticles on the surfaces of glassy carbon (GC) electrodes and their electrocatalytic activities for the oxidation of formaldehyde were studied. It was found that the reduction of Au3+ to Au is controlled by diffusion and the formation mechanism of Au microparticles on the GC surfaces corresponds to an instantaneous nucleation and diffusion-controlled three dimensional growth process. The particle size is about 80-90 nm in diameter after the electrochemical ageing treatment. These highly dispersed Au microparticles have high surface areas and exhibit better electrocatalytic activity than that of bulk-form Au toward the electrochemical oxidation of formaldehyde in alkaline media.