A dual-electrode approach for highly selective detection of glucose based on diffusion layer theory: experiments and simulation

A dual-electrode configuration for the highly selective detection of glucose in the diffusion layer of the substrate electrode is presented. In this approach, a glassy carbon electrode (GCE, substrate) modified with a conductive layer of glucose oxidase/Nafion/graphite (GNG) was used to create an interference-free region in its diffusion layer by electrochemical depletion of interfering electroactive species. A Pt microelectrode (tip, 5 microm in radius) was located in the diffusion layer of the GNG-modified GCE (GNG-G) with the help of scanning electrochemical microscopy. Consequently, the tip of the electrode could sense glucose selectively by detecting the amount of hydrogen peroxide (H2O2) formed from the oxidization of glucose on the glucose oxidase layer. The influences of parameters, including tip-substrate distance, substrate potential, and electrolyzing time, on the interference-removing efficiency of this dual-electrode approach have been investigated systematically. When the electrolyzing time was 30 s, the tip-substrate distance was 1.8 a (9.0 microm) (where a is the radius of the tip electrode), the potentials of the tip and substrate electrodes were 0.7 V and 0.4 V, respectively, and a mixture of ascorbic acid (0.3 mM), uric acid (0.3 mM), and 4-acetaminophen (0.3 mM) had no influence on the glucose detection. In addition, the current-time responses of the tip electrode at different tip-substrate distances in a solution containing interfering species were numerically simulated. The results from the simulation are in good agreement with the experimental data. This research provides a concept of detection in the diffusion layer of a substrate electrode, as an interference-free region, for developing novel microelectrochemical devices.     

Thermodynamics and dynamics of metallic glass formers: their correlation for the investigation on potential energy landscape

Great progress has been made in basic features of the potential energy landscape (PEL) theoretically. The present work, however, attempts to cast new light on it from experimental aspects. By a survey of experimental data related to thermodynamics or dynamics of metallic glass-forming liquids, it is found that the increased rate of excitation of vibrational entropy at glass transition tends to increase the rate of generation of configurational part. Although for the type of metallic materials a generally positive relationship exists between the density of the energy minima at glass transition and the liquid fragility strength, just as expected, our main attention is paid to the phenomenon of the scattering of the slopes. Analysis shows that the phenomenon results from the different average height of energy barriers between minima near glass transition. Investigation on the PdNiP metallic system indicates that the mismatch entropy is a dominant factor in the barrier height: a large value of it results in low energy barriers. Our previous work on the AlNiCe system gives the support to this finding.     

Steric hindrance-controlled Pd(0)-catalyzed coupling-cyclization of 2,3-allenamides and organic iodides. An efficient synthesis of iminolactones and gamma-hydroxy-gamma-lactams

Under the catalysis of 1 mol % Pd(PPh3)4, the reaction of 4,4-disubstituted 2,3-allenamides and organic iodides in toluene afforded iminolactones stereospecifically in >90% yields using K2CO3 (2 equiv)-5 mol % TBAB as the base. A similar reaction with 4-monosubstituted 2,3-allenamides afforded gamma-hydroxy-gamma-lactams in relatively lower yields. The N/O-attack selectivity may be determined by the steric effect at the 4-position of 2,3-allenamides.     

Detection of muonated free radicals through the effects of avoided level crossing. Theory and analysis of spectra

A treatment is developed for the analysis of μSR spectra of muonium-substituted free radicals detected under conditions of avoided level crossing in high longitudinal magnetic fields. Approximate analytical results are compared with those of numerical calculations, and an experimental example is presented.     

Quantum Information Entropies on Hyperbolic Single Potential Wells

In this work, we study the quantum information entropies for two different types of hyperbolic single potential wells. We first study the behaviors of the moving particle subject to two different hyperbolic potential wells through focusing on their wave functions. The shapes of these hyperbolic potentials are similar, but we notice that their momentum entropy densities change along with the width of each potential and the magnitude of position entropy density decreases when the momentum entropy magnitude increases. On the other hand, we illustrate the behaviors of their position and momentum entropy densities. Finally, we show the variation of position and momentum entropies Sx and Sp with the change of the potential well depth u and verify that their sum still satisfies the BBM inequality relation.     

Theoretical studies on organic transition-metal complexes—I. Parameterization and calibration of an extended CNDO/2 method for the calculation of stability constants

An extended CNDO/2 method has been developed for the calculation of stability constants of organic transition-metal complexes. An atom parameterization scheme is described for Mn to Zn using Slater exponents which is found to give a reasonable correlation with the ionization potential of the respective metal. The corresponding bonding parameters have been evaluated by initially deriving the best correlation between the calculated and experimental stability constants of a series of substituted copper bis(salicylaldehydes) and then relating these values to the other transition metals using the bond dissociation energies of simple diatomics as the essential criteria.     

Designable assembly of atomically precise Al4O4 cubane supported mesoporous heterometallic architectures

Heterometallic cluster-based framework materials are of interest in terms of both their porous structures and multi-metallic reactivity. However, such materials have not yet been extensively investigated because of difficulties in their synthesis and structural characterization. Herein, we reported the designable synthesis of atomically precise heterometallic cluster-based framework compounds and their application as catalysts in aldol reactions. By using the synergistic coordination protocol, we successfully isolated a broad range of compounds with the general formula, [Al₄M₄O₄(L)₁₂(DABCO)₂] (L = carboxylates; DABCO = 1,4-diazabicyclo[2.2.2]-octane; M²⁺ = Co²⁺, Mn²⁺, Zn²⁺, Fe²⁺, Cd²⁺). The basic heterometallic building blocks contain unprecedented main-group γ-alumina moieties and surrounding unsaturated transition metal centers. Interestingly, the porosity and interpenetration of these frameworks can be rationally regulated through the unprecedented strategy of increment of the metal radius in addition to general introduction of sterically bulky groups on the ligand. Furthermore, these porous materials are effective catalysts for aldol reactions. This work provides a catalytic molecular model platform with accurate molecular bonding between the supporters and catalytically active metal ions.

Mesoporous heterometallic architectures are designed by the incorporation of the Al₄O₄ cubane and interpenetration regulation.     

Structural defects in poly(vinyl chloride)—V. Thermal and photodegradation of copolymers of vinyl chloride with various acetylene derivatives

Vinyl chloride has been copolymerized with various acetylene derivatives in bulk at 50. It has been shown by ozonolysis that these copolymers contain a significantly increased amount of internal double bonds. A comparison of the thermal and photodegradation behaviours of the copolymers has been made. The built-in double bonds show an effect on the reactivity of the adjacent allylic chlorine depending on the electron-withdrawing or repelling nature of the substituent. Among the comonomers investigated, copolymers containing 3-chloropropine have the least reactive defect sites, because of the electron-withdrawing chloromethyl substituent. On the contrary, the electron-repelling n-butyl group, built-in by using hexine-1 as comonomer, results in enhanced reactivity of the allylic chlorines.     

Structural defects in poly(vinyl chloride)—IV. Thermal degradation of vinyl chloride/acetylene copolymers

Vinyl chloride/acetylene copolymers have been prepared under subsaturation conditions. Copolymerization rates and molecular weights of the copolymers decrease with increasing concentration of acetylene in the monomer feed, indicating that acetylene is a retarder in vinyl chloride polymerization. The concentration of internal double bonds in the copolymers determined by ozonolysis increases with increasing amount of acetylene in the feed. Thermal degradation has been performed at 110 with solid samples and at 170° in solution under inert atmosphere. The extent of HCl loss as a function of time shows a rapid initial phase followed by a slower steady rate The initial dehydrochlorination rates are higher for copolymer samples containing higher concentrations of internal double bonds. Quantitative analysis of the u.v. and visible spectra of degraded copolymers shows that the sum of the concentration of polyenes with 4–12 conjugated double bonds increases rapidly in the first phase of degradation, but then decreases slowly, due to secondary reactions of polyene sequences.