Polyoxometalates entrapped in sol–gel matrices for reducing electron exchange column applications

Electron exchange columns were developed by utilizing the redox properties of polyoxometalates (POMs) entrapped in silica matrices via the sol–gel route. The properties of the columns strongly depend on the composition of the precursors used to prepare the matrices. The columns exhibit good reversibility and are the first ‘reducing’ electron exchange columns ever prepared. They are also the first columns where both the matrix and the entrapped redox agent are inorganic compounds. This increases their stability. However, the redox properties of the entrapped POMs in the matrices are affected by the composition of the matrices.     

二氧化硫脲性质的分光光度法研究

二氧化硫脲性质的分光光度法研究＊曾秀琼夏式均（杭州大学化学系杭州３１００２８）关键词二氧化硫脲分光光度法二氧化硫脲（ＴＤ）是一种白色粉末，由于它的还原能力强，性质稳定，易于贮藏和运输等特点，在国内外已广泛作为高效还原剂用于纺织、印染、造纸等工业领域［...     

Evaluation of the surface charge properties of porous graphitic carbon stationary phases treated with redox agents

The effect of treatment of porous graphitic carbon (PGC) stationary phases with hydrogen peroxide and with sodium sulfite on the retention behavior of analyte compounds has been investigated using benzene, aromatic sulfonate ions, and benzyltrialkylammonium ions as model compounds. It is shown that the retention times of the cationic analytes are increased by treating the PGC column with the reducing agent, while decreased by treating it with the oxidizing agent. On the other hand, the retention times of the anionic analytes are decreased by treating the column with the reducing agent, while increased by treating it with the oxidizing agent. The effect of the redox treatment on the retention of benzene is negligibly small. The investigation of the ion-exchange property of the PGC packings have shown that PGC has anion-exchange property and the anion-exchange capacity is decreased by treating PGC with the reducing agent, whereas it is increased by treatment with the oxidizing agent. This means that the modification of the retention selectivity of the PGC stationary phases with redox treatment can be interpreted in terms of the change of the surface charge. The mechanism of chemical modification of the PGC stationary phase with redox treatment is discussed on the basis of the experimental results obtained on the ion-exchange capacity and the redox activity.     

UV-induced reduction of Ag<Superscript>+</Superscript> by diazene sulphonates: new method of metallisation of surfaces

The metallisation of surfaces would be technologically very simple if it were possible to use the properties of the substances that decompose upon UV irradiation and produce species with a strong redox potential. In this work, diazene sulphonates are presented as possible reducing agents for Ag⁺ in aqueous solutions and in thin solid layers. The photo-formation of Ag^m+_n clusters in the presence of diazene sulphonates in solutions was investigated via UV-VIS spectroscopy. Significant differences were observed in the electrical properties of surfaces after photo reduction; these occurred without any additional reducing agent.     

Electron exchange columns through entrapment of a nickel cyclam in a sol-gel matrix

An electron exchange column (analogous to ion exchange columns) was developed using the unique redox properties of the nickel-tetraazamacrocyclic complexes (nickel cyclam [Ni(II)L(1)](2+)) and nickel-trans-III-meso-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, ([Ni(II)L(2)](2+)), and the physical and chemical stability of the ceramic materials using the sol-gel process to entrap the complexes. The entrapment by the biphasic sol-gel method is based on non-covalent bonds between the matrix and the complex; therefore the main problem was leaching. Parameters controlling the leaching were investigated. Redox cycles with the reducing agent ascorbic acid, and persulfate as the oxidizing agent were performed.     

Preparation and properties of redox responsive modified hyaluronic acid hydrogels for drug release

A series of oxidized hyaluronic acid (oxi‐HA)/3,3′‐dithiobis (propionohydrazide) (DTP) redox responsive hydrogels by Schiff base reaction under physiological conditions were designed and prepared. The influence of the concentration of oxi‐HA and DTP on rheological properties, equilibrium swelling ratio, and degradation rate were investigated. All oxi‐HA/DTP hydrogels exhibited good rheological properties, high equilibrium swelling ratio, low degradation rate, and sustainable drug release properties, and the comprehensive performance of oxi‐HA5/DTP6 hydrogel was better than that of others. The redox responsiveness was evaluated by means of degradation and in vitro bovine serum albumin release behavior investigation with the stimulus of different concentration of dithiothreitol as reducing agent. The intelligent hydrogels could be potentially applied in the fields of drug delivery system, tissue engineering, or cell scaffold materials. Copyright © 2017 John Wiley & Sons, Ltd.     

Redox initiated cationic polymerization of oxetanes

3,3‐Disubstituted oxetane monomers were found to undergo rapid, exothermic redox initiated cationic ring‐opening polymerization in the presence of a diaryliodonium or triarylsulfonium salt oxidizing agent and a hydrosilane reducing agent. The redox reaction requires a noble metal complex as a catalyst and several potential catalysts were evaluated. The palladium complex, Cl₂(COD)Pd^II, was observed to provide good shelf life stability while, at the same time, affording high reactivity in the presence of a variety of hydrosilane reducing agents. A range of structurally diverse oxetane monomers undergo polymerization under redox cationic conditions. When a small amount of an alkylated epoxide was added as a “kick‐start” accelerator to these same oxetanes, the redox initiated cationic polymerizations were extraordinarily rapid owing to the marked reduction in the induction period. A mechanistic interpretation of these results is offered. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1854–1861     

Formation of gold nanoparticles using amine reducing agents

We report on the use of amines as reducing agents in the formation of gold nanoparticles. We can predict whether the amines will function as reducing agents in this reaction based on their redox properties. The kinetics of AuNP formation can be understood in terms of Marcus electron transfer theory, where the slower reactions proceed in the inverted region owing to the difference between the Au reduction potential and the amine oxidation potential. For a certain number of the amine reducing agents, following reduction of HAuCl4, a subsequent reaction of the amine radical cation with other reducing agent molecules in solution can form poly(amine)s. These findings point collectively to the utility of amines as reducing agents in AuNP formation and provide information on the conditions under which these reactions will proceed.     

Aqueous polymerization of ethyl acrylate initiated by ceric ion-reducing agent system in sulphuric acid medium

Kinetic study of aqueous polymerization of ethyl acrylate (EA) is carried out at 30 °C in dilute sulphuric acid medium by employing ammonium ceric sulphate–methyl ethyl ketone (MEK) as redox initiator system. The ceric ion consumption is found to be first order with respect to ceric ion and half order with respect to reducing agent concentrations. No complex formation between ceric ion and reducing agent is observed. The orders with respect to ceric ion, reducing agent and monomer concentrations are evaluated for the aqueous polymerization of EA by Ce(IV)–MEK redox initiator system, and are found to be 0.5, 0.5 and 1.4, respectively . The overall activation energy, E _overall, for aqueous polymerization of EA in the temperature region of 27–40°C is found to be 20.27 kJ/mol. A kinetic scheme for the aqueous polymerization of EA initiated by Ce(IV)–MEK redox initiator system is presented.This revised version was published online in June 2005 with corrections to figure legends as well as small corrections within text.     

One‐electron redox properties of DNA nucleobases and common tautomers

The redox properties of DNA play an influential role in several important processes such as DNA mutation and the interaction of DNA with drugs. Structural changes in DNA nucleobases from its canonical form to its tautomeric forms can alter these properties and may lead to DNA mutation due to altered base‐pairing properties. Experimental results for the standard value of DNA redox properties vary due to choice of methodology and solvent. Theoretical determination of these properties is helpful in pinpointing standard values but still vary depending on methodology and chosen experimental benchmark. However, it is of importance to identify the overall trend of electron mobility within DNA while providing reliable standard values for redox reactions. In this work, we present the results of theoretical calculations for redox properties. Using the thermodynamic cycle, we can approximate reliable values. We report the electron affinities, ionization potentials, and redox potential for the canonical DNA nucleobases and their rare tautomers. For each of these properties, we evaluate its overall trend to gain a greater understanding of the role that electron attachment and electron mobility have within the DNA strand. All calculations are computed at the M06‐2X/6–31++G(d,p) level of theory. © 2014 Wiley Periodicals, Inc.     

Redox Intitiated Cationic Polymerization

Two novel redox initiator systems have been developed for carrying out the cationic polymerizations of vinyl and heterocyclic monomers. The initiators are based on various onium salts as the oxidant together with an alkylborane or an organosilane as the reducing agent. Using both redox cationic initiator systems, the polymerizations of a wide variety of monomers can be carried out at or below room temperature in the presence or absence of unreactive solvents. Also described in this communication is the novel use of a two-component redox system in which the reducing agent, a silane, is delivered to the monomer sample in the vapor state. Optical pyrometry (infrared thermography) was employed as a convenient method with which to monitor the polymerizations in real-time. A study of the effects of variations in the structures of the onium salt, the silane and the type of noble metal catalyst were carried out. The use of these initiator systems for carrying out commercially attractive crosslinking polymerizations for coatings, composites and electronic encapsulations is discussed.     

Redox‐Sensitive Stomatocyte Nanomotors: Destruction and Drug Release in the Presence of Glutathione

The development of artificial nanomotor systems that are stimuli‐responsive is still posing many challenges. Herein, we demonstrate the self‐assembly of a redox‐responsive stomatocyte nanomotor system, which can be used for triggered drug release under biological reducing conditions. The redox sensitivity was introduced by incorporating a disulfide bridge between the hydrophilic poly(ethylene glycol) block and the hydrophobic polystyrene block. When incubated with the endogenous reducing agent glutathione at a concentration comparable to that within cells, the external PEG shells of these stimuli‐responsive nanomotors are cleaved. The specific bowl‐shaped stomatocytes aggregate after the treatment with glutathione, leading to the loss of motion and triggered drug release. These novel redox‐responsive nanomotors can not only be used for remote transport but also for drug delivery, which is promising for future biomedical applications.     

Redox behavior of pyridinium salts and their polymers having radical stabilizing groups

The redox behavior of pyridinium salts having various substituents capable of stabilizing pyridinyl radicals at the 4-position was investigated by cyclic voltammetry in water with a platinum electrode, and their redox potentials were more positive in the order of 4-substituents of acetyl > cyano > carbomethoxy > carbamide groups. Sodium dithionite was found to be suitable for a chemical reducing agent of the pyridinium salts. Two types of homopolymers with pendant 4-carbamido-pyridinium groups were prepared and their redox potentials were more positive than the corresponding model compounds. The positive shift might be caused by charge repulsion between the neighboring pyridinium cations on the polymer main chain in the oxidized state.     

Self‐Sufficient Formaldehyde‐to‐Methanol Conversion by Organometallic Formaldehyde Dismutase Mimic

The catalytic networks of methylotrophic organisms, featuring redox enzymes for the activation of one‐carbon moieties, can serve as great inspiration in the development of novel homogeneously catalyzed pathways for the interconversion of C₁ molecules at ambient conditions. An imidazolium‐tagged arene–ruthenium complex was identified as an effective functional mimic of the bacterial formaldehyde dismutase, which provides a new and highly selective route for the conversion of formaldehyde to methanol in absence of any external reducing agents. Moreover, secondary amines are reductively methylated by the organometallic dismutase mimic in a redox self‐sufficient manner with formaldehyde acting both as carbon source and reducing agent.     

Extraordinary Modulation of Disulfide Redox‐Responsiveness by Cooperativity of Twin‐Disulfide Bonds

Disulfide bonds have frequently been incorporated into synthetic materials to promote sensitivity of the systems towards different redox environments. Although many strategies have been developed to rationally tune the stability of disulfide linkers, methods to tune their responsiveness towards different redox environments remain elusive. In this work we have developed and explored a disulfide linker bearing two independent disulfide bonds, referred to as a twin‐disulfide linker. We have demonstrated that the twin‐disulfide linker displays an ultrahigh stability at lower concentrations of reducing agent or in weakly reducing environments without a significant compromise in the sensitivity of its response to highly reducing environments such as cytoplasm, a feature that is in remarkable contrast to the traditional single disulfide bonds. Such an extraordinary responsiveness arises from the cooperativity of the twin‐disulfide bonds, which should be of particular interest for applications such as controlled drug delivery and sensing, because relatively large differences in disulfide stability in different redox environments is desired in these applications.     

Pt-FeOx催化剂微结构对催化CO氧化性能的影响

借助较为成熟的纳米技术手段,采用PVP为保护剂、乙二醇为还原剂制备具有不同Pt/Fe比例的双金属纳米粒子,最终通过氧化处理获得具有不同微结构环境的纳米Pt-FeO_x催化剂,并以此为模型考察它们对CO氧化性能的影响。结果表明FeO_x物种的数量一方面影响Pt物种的价态,同时也影响Fe物种自身的氧化还原性质,这些性质直接和间接地影响着CO和氧分子的活化,Pt周围适量FeO_x物种的存在对构建高活性CO氧化催化剂有利。     

Recent advances on the chemistry of transition metal complexes of 2-(arylazo)pyridines and its arylamino derivatives

Recent advancement on the redox properties of a selection of transition metal complexes of the azoaromatic ligands: bidentate L(1) [2-(arylazo)pyridine] and tridentate HL(2) [2-(aminoarylphenylazo)pyridine] are described and compared. Due to the presence of a low lying azo-centered π*-orbital, these azoaromatic ligands may exist in multiple valent states. The coordination chemistry of the L(1) ligands was thoroughly studied during the 1980s. These complexes undergo facile reduction in solution at low accessible potentials. One electron reduced azo-complexes, though known for a long time to occur in solution, have only recently been isolated in a crystalline state. New synthetic protocols for the synthesis of metal-bound azo-radical complexes have been developed. Low-valent metal complexes such as metal carbonyls have been found to be excellent starting materials for this purpose. In a few selected cases, syntheses of these complexes were also achieved from very high valent metal oxides using triphenylphosphine as both a reducing and oxo-abstracting agent. Issues related to the ambiguities of the electronic structures in the azo-metal complexes have been discussed considering bond parameters, redox and spectral properties. Unusual redox events such as RIET (Redox-Induced Electron Transfer) phenomena in a few systems have been elaborated and compared with the known example. Novel examples of N=N bond cleavage reactions via four-electron reduction and subsequent C-N bond formation in metal-bound coordinated ligands have been noted.     

杯芳烃衍生物对K＋和电子的耦合液膜传输

在文献的基础上设计了一套电子/阳离子同向耦合传输的新体系,以多硫1,2-二硫醇烯镍的配合物为电子载体,杯芳烃的酯类衍生物为阳离子载体,采用连二亚硫酸钠和铁氰化钾作为还原剂和氧化剂,成功地实现了电子/钾离子同向耦合传输.研究了电子载体和离子载体对耦合传输的影响,并对电子耦合传输的传输机理做了初步的研究.     

MPEGMAA/G-570/DEM/AMPS新型酯类聚羧酸系减水剂的制备

以甲基丙烯酸聚乙二醇单甲醚酯600（MPEGMAA600）、 γ-甲基丙烯酰氧基丙基三甲氧基硅烷（G-570）、马来酸二乙酯（DEM）和2-丙烯酰胺-2-甲基丙磺酸（AMPS）为原料,过硫酸钾 硫酸亚铁为引发剂,合成了G-570/MPEGMAA/DEM/AMPS酯类聚羧酸系减水剂,其结构和组成经傅立叶变换红外光谱（FT-IR）和凝胶色谱（GPC）表征。通过正交实验确定最佳合成工艺为:MPEGMAA与DEM、 AMPS和G-570的摩尔比为1.0:1.0:2.0:0.4,过硫酸钾-硫酸亚铁总质量占聚合单体总质量的0.4%,于45 ℃聚合反应8 h,单体转化率为91.71%,水泥初始净浆流动度为225 mm。通过X-射线衍射（XRD）和热重（TG-DTG）分析对加入该减水剂的硬化水泥石微观结构进行了分析。结果表明：该减水剂链段中含有酯基、氨基、磺酸基、醚键、硅氧键等基团,平均相对分子质量分布集中,峰值大都集中在1.2~1.7万。同时,该减水剂可以延缓24 h内水泥水化。