Electrochemistry of Prussian Blue in silica sol-gel electrolytes doped with polyamidoamine dendrimers

The inclusion of a generation-4 polyamidoamine (G4-PAMAM) dendrimer in a silica sol-gel yielded a solid electrolyte that was used to encapsulate Prussian Blue (PB), iron(III) hexacyanoferrate(II), and cobalt hexacyanoferrate. The PB was synthesized in the doped silica by sequential immersion of a monolith in 0.1 M K₄Fe(CN)₆, water, and 0.1 M FeCl₃. Inclusion of G4-PAMAM resulted in a nanoporous anion-exchange material with a capacity of 10.1 mmol g^–1, which is about four times greater than the capacity of silica alone. Relative to its G0 counterpart, the G4-PAMAM doped silica increased the rate of formation of PB by a factor of ca. 20. The solid state voltammetry of PB in the doped silica had the usual features for this compound. At 0.1 V vs. a Ag quasi-reference electrode, a reversible reduction was seen; the relationship between current and scan rate was that for a surface-confined redox couple. The quasi-reversible oxidation of PB was observed at 0.85 V. Inclusion of G4-PAMAM increased the lifetime of silica as a solid electrolyte from a few days to at least three months. Raman microprobe mapping analysis demonstrated that PB was homogeneously distributed across the entire width (ca. 1 mm) of the G4-doped monolith with 20-h immersions. Electronic Publication     

Amperometric Study of Au‐Colloid Function on Xanthine Biosensor Based on Xanthine Oxidase Immobilized in Polypyrrole Layer

Four kinds of xanthine oxidase (XOD) based amperometric biosensors were fabricated and their analytical performances were compared. Polypyrrole (PPY)/XOD biosensor was constructed by electrochemical oxidation of pyrrole in the solution containing xanthine oxidase and pyrrole in this paper. Colloidal Au was then immobilized on the biosensor. On the other hand, electron mediator, Prussian Blue (PB), was deposited on the electrode before the immobilization of PPY/XOD to enhance electron‐transfer rate and current response. The results showed that PPY/XOD, PPY/XOD/Au‐colloid, PB/PPY/XOD and PB/PPY/XOD/Au‐colloid biosensors exhibit good response to xanthine in 1×10^?6 M and 2×10^?5 M and Michaelis‐Menten constants (K_m) of these biosensors were 242.2, 113.4, 144.5, 43.2 μmol?L^?1, respectively. The dependence of current responses with applied voltages was discussed, and different mechanisms of these biosensors were discussed. It has been found that colloidal Au can enhance the current response at the same concentration of xanthine solution and decrease the energy‐barrier of electron‐transfer reaction on the electrode.     

Effect of removing silica in rice husk for the preparation of activated carbon for supercapacitor applications

The significant influence of silica inside rice husk in the preparation and electrochemical performances of activated carbon are investigated. The removing of silica results in high mesoporous ratio and good rate capability.     

Study of CsCl incorporation in silica via sol-gel synthesis catalyzed by biogenic compounds

Incorporation of CsCl in silica via sol-gel route catalyzed by biogenic compounds with three different concentrations of CsCl has been carried out by using organic compounds extracted from Nitzschia spp., a freshwater diatom alga. The visual integrity, nitrogen adsorption and electron microscopies were used to characterize the silica gels obtained from the biocatalysts employing sol-gel process with tetraethylorthosilicate (TEOS) as precursor. The usual sequence for the sol-gel process was used: sol preparation, gelation, aging, drying and heat treatment. Differential thermal analysis (DTA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to characterize the incorporation of CsCl in the biomimetic silica. Chemical analysis of the biocatalysts was used to explain the exothermic behavior of the samples during DTA and DSC. The incorporation of CsCl in the silica matrix with a process using biogenic catalysts proved to be more effective compared to another process using inorganic catalysts.     

新型葡萄糖氧化酶电极用于临床血糖的测定

在稳定的普鲁士蓝修饰电极上先涂一酶层 ,然后将二氧化硅溶胶 -凝胶薄膜敷着其上用于固定酶 ,制成了葡萄糖氧化酶电极。采用恒电位安培检测 ,葡萄糖浓度在0.05～4.75mmol/L范围内与响应电流成线性关系 ,检出限为0.02mmol/L ,灵敏度高达1.182μA·mmol -1·L ,响应时间为12s ;该酶电极不受抗坏血酸、尿酸等电活性物质的干扰 ,稳定性较好。该电极用于临床血糖的测定 ,回收率为96 %～110 % ,测定结果与酶偶联比色法结果一致 ,可用于临床糖尿病人血糖的检测。     

Characterization of physical structure of silica nanoparticles encapsulated in polymeric structure of polyamide films

Polyamide nanocomposite films were prepared from nanometer sized silica particles and trimesoyl chloride–m-phenylene diamine based polyamides. The type of silica nanoparticles used is commercial LUDOX^® HS-40 and the particle size characterized by the radius of gyration (R_g) is about 66 Å. The immediately prepared films were easily broken into particles to form colloidal-like dilute suspension of the silica–polyamide composite particles in D₂O–H₂O solutions for SANS measurements, that in this dilute system SANS data the complication of scattering data from the interacting particles is minimized. At about 60% D₂O of the sample solution, the silica is contrasted out, therefore the SANS profiles are predominantly from the organic polyamide scattering. The SANS profile of the sample solutions measured at 90% D₂O clearly indicates scattering from both silica and polymer. The scattering heterogeneities for two-phase system were evident from the validity of the Debye–Bueche expression in case of the nanocomposite with high silica loading. At limited silica loading of the nanocomposite, interaction between the silica and polymer chains forming core–shell morphology was observed. The transport properties of the membranes made from the nanocomposite films were measured on a batch type test kit with an aqueous solution of 500 ppm dioxane concentration at pressures ranging from 50 to 200 psig, and correlated to their composite structure.     

A Switch in the Hydrophobic/Hydrophilic Gas-Adsorption Character of Prussian Blue Analogues: An Affinity Control for Smart Gas Sorption

Porous coordination polymers are molecule-based materials presenting a high degree of tunability, which offer many advantages for targeted applications over conventional inorganic materials. This work demonstrates that the hydrophilic/hydrophobic character of Prussian blue analogues having a lipophilic feature may be tuned to optimize the gas adsorption properties. The role of the coordinatively unsaturated metal sites is emphasized through a combination of theoretical and experimental study of water, ethanol, and n-hexane adsorption.     

Changes in density and surface tension of water in silica pores

 The density and surface tension of water in small pores of silicas have been investigated. These physical properties of water in the pores were calculated from a comparison of pore volumes and pore radii which were estimated from adsorption and desorption isotherms of nitrogen and water. Below a pore radius of about 5 nm both the density and the surface tension of water in the pores were smaller than those of the bulk liquid and decreased with a decrease in pore size. The density of water in the pores decreased with an increase in the concentration of surface hydroxyl groups. Similarly the surface tension of water in the pores is influenced by the surface hydroxyl groups. Anomalous changes in the density and surface tension of the water in the pores are attributed to the interaction of water molecules with surface hydroxyl groups and hydrogen-bond formation among water molecules. Received: 20 April 1999 Accepted in revised form: 17 November 1999     

Drying dissipative patterns of colloidal crystals of silica spheres in organic solvents

Drying dissipative structural patterns formed in the course of drying colloidal crystals of silica spheres (110 nm in diameter) in water, methyl alcohol, ethyl alcohol, 1-propyl alcohol, diethyl ether, and in the mixtures of ethyl alcohol with the other solvents above have been studied on a cover glass. The macroscopic broad rings were formed in the outside edges of the dried film for all the solvents examined. Furthermore, much distinct broad rings appeared in the inner area when the solvents were ethyl alcohol, methyl alcohol, and their mixtures. Profiles of the thickness of the dried films were sensitive to the organic solvents and explained well with changes in the surface tensions, boiling points, and viscosities of the solvents. The macroscopic and microscopic spoke-like crack patterns formed. The drying area (or the drying time) increased (or decreased) as the surface tension of the solvent decreased. However, the absolute values of these drying parameters are determined also by the boiling points of the solvents. Importance of the fundamental properties of the solvents is supported in addition to the characteristics of colloidal particles in the drying dissipative pattern formation.     

Drying dissipative patterns of the colloidal crystals of silica spheres in an dc-electric field

Drying dissipative structural patterns of the colloidal crystals of silica spheres were studied under an dc-electric field. Platinum plate electrodes of anode and cathode were set on a cover glass. The broad hills accumulated with the spheres were observed at the outer edges of the dried film without and also with the electric fields. The column-like structures were formed by the electric flux, and movement of the spheres took place toward anode. The dried film kept colloidal crystal structure, where the nearest-neighbored spheres contact each other more compactly in the areas closer to the anode. Drying times needed for the complete dryness of the suspensions decreased as the strength of the electric field increased. Addition of sodium chloride to the suspensions retarded the movement of spheres toward the anode substantially.     

分光光度法同时测定硅石中的铁和铝

在邻二氮菲(Phen)、铬天青S(CAS)和十四烷基二甲基苄基氯化铵(TDMBA)的共同存在下,于pH 5～6的酸性介质中,铁、铝分别生成Fe-Phen和Al-CAS-TDMBA络合物,用同一份试液,在波长510 nm测定铁,在625 nm测定铝,两种络合物互不干扰。用该法可同时测定硅石中的铁和铝。     

An Electrochemical Study of Prussian Blue Microcrystalines Mixed in PEO_400 Polymer Electrolyte by Solid-state Voltammetry

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Spectral characterization of chlorophyll fluorescence in extract of barley leaves embedded in silica xerogel matrix

We have used the sol-gel method to prepare SiO₂ based matrix containing barley leaves extracts and studied the spectral characteristics of chlorophyll fluorescence of the glass under structural evolution promoted by heat treatment. One primary effect on the fluorescence for barley leaves embedded in glass is that PSII chlorophyll fluorescence transients are not present. We obtain a higher PSII thermostability for leaves embedded in xerogel matrix than in the green barley leaves. We observed for high temperatures that fluorescing aggregates are formed. The behavior of the PSII fluorescence under heat treatment will be used in subsequent works to study the microstructural evolution during the silica-gel-glass conversion and their optical properties.     

Nucleation and growth processes in the colloidal crystallization of silica spheres in the presence of sodium chloride as studied by reflection spectroscopy

Time-resolved reflection spectroscopic measurements are made for the kinetic analyses of the nucleation and growth processes of soft-type colloidal crystals of silica spheres (110 nm in diameter) in the presence of sodium chloride. Fast-scanning reflection spectra are taken using a continuous circulating-type stopped-flow cell system. The cell system is composed of a peristaltic pump and a quartz flow cell, which are connected with a PharMed tube in a closed circuit. The volume fraction of the spheres is 0.028. Induction periods range from 0.2 to 1.3 s and increase as salt concentration increases. Nucleation rates are 1 × 10⁴ to 7 × 10⁴ spheres/mm³s and decrease as salt concentration increases. The crystallization process has been observed from the sharpening and the increase in intensity of the reflection peaks. The crystal growth rate in the absence of salt is 23 μm/s, and decreases as salt concentration increases. The importance of electrostatic intersphere repulsion through the electrical double layers and the cooperative and synchronous fluctuation of colloidal spheres in the crystallization processes is supported. Received: 15 July 1998 Accepted in revised form: 18 September 1998     

KInSe~2的中温固相合成及结构表征

采用反应性熔盐法,以n(K~2Se~3):n(In):n(Se)=1:1:5的摩尔比,在500℃下反应5d,生成淡黄色柱状晶体KInSe~2。该晶体属于单斜晶系,空间群为C2/c,晶胞参数,a=1.414(2)nm,b=1.1410(2)nm,c=1.5586(3)nm,β=100.60(3)°,Z=16,R=0.0656。KInSe~2晶体具有层状结构,每层由具有二维网状结构的[InSe~2]^-负离子和K^+组成,层与层之间按ABAB方式堆积。     

Dispersion of silica nano-particles in sol-gel hybrid resins for fabrication of multi-scale hybrid nanocomposite

Multi-scale hybrid nanocomposites containing both ∼15 nm silica colloids and ∼2 nm oligosiloxanes in a methacryl polymer matrix were newly designed and fabricated. Colloidal silica sols were dispersed in methacryl oligosiloxanes nano-hybrid resins synthesized by sol-gel reaction of methacryloxypropylmethoxysilane and diphenylsilanediol. On the basis of TEM and SANS analyses, it was confirmed that the silica colloids were compatibly dispersed and different sizes of colloidal silica and oligosiloxanes co-exist in the solutions. Multi-scale hybrid nanocomposites fabricated by UV and thermal curing with incorporation of silica colloids in the nano-hybrid materials show enhanced mechanical and thermal characteristics.     

Sulfur and selenium: the role of oxidation state in protein structure and function

Sulfur and selenium occur in proteins as constituents of the amino acids cysteine, methionine, selenocysteine, and selenomethionine. Recent research underscores that these amino acids are truly exceptional. Their redox activity under physiological conditions allows an amazing variety of posttranslational protein modifications, metal free redox pathways, and unusual chalcogen redox states that increasingly attract the attention of biological chemists. Unlike any other amino acid, the "redox chameleon" cysteine can participate in several distinct redox pathways, including exchange and radical reactions, as well as atom-, electron-, and hydride-transfer reactions. It occurs in various oxidation states in the human body, each of which exhibits distinctive chemical properties (e.g. redox activity, metal binding) and biological activity. The position of selenium in the periodic table between the metals and the nonmetals makes selenoproteins ideal catalysts for many biological redox transformations. It is therefore apparent that the chalcogen amino acids cysteine, methionine, selenocysteine, and selenomethionine exhibit a unique biological chemistry that is the source of exciting research opportunities.