Selective catalytic oxidation of DMF over Cu-Ce/H-MOR by modulating the surface active sites.

Selective catalytic oxidation of the hazardous DMF exhaust gas presents a significant challenge in balancing oxidation activity and products selectivity (CO, NOx, N2, etc.). It is found that Cu/H-MOR demonstrates superior performance for DMF oxidation compared to CuO on other supports (γ-Al2O3, HY, ZSM-5) in terms of product selectivity and stability. The geometric and electronic structures of CuO active sites in Cu/H-MOR have been regulated by CeO2 promoter, leading to an increase in the ratio of active CuO (highly dispersed CuO and Cu+ specie). As a result, the oxidation activity and stability of the Cu/H-MOR catalyst were enhanced for DMF selective catalytic oxidation. However, excessive CuO or CeO2 content led to decreased N2 selectivity due to over-high oxidation activity. It is also revealed that Ce3+ species, active CuO species, and surface acid sites play a critical role in internal selective catalytic reduction reaction during DMF oxidation. The 10Cu-Ce/H-MOR (1/4) catalyst exhibited both high oxidation activity and internal selective catalytic reduction activity due to its abundance of active CuO specie as well as Ce3+ species and surface acid sites. Consequently, the 10Cu-Ce/H-MOR (1/4) catalyst demonstrated the widest temperature window for DMF oxidation with high N2 selectivity. These findings emphasize the importance of surface active sites modification for DMF selective catalytic oxidation.

Additive anticancer effects of chrysin and low dose cisplatin in human malignant glioma cell (U87) proliferation and evaluation of the mechanistic pathway.

PURPOSE: To evaluate the anticancer effect of chrysin and its additive combination with low-dose cisplatin in human glioma (U87) cancer cells and to study its underlying mechanism. METHODS: Inverted phase and fluorescence microscopic studies were done to demonstrate the effect of chrysin and its combination with cisplatin on cellular morphology and apoptosis. Annexin V-FITC assay was used to quantify the extent of apoptosis in chrysin and chrysin+cisplatin treated cells. Flow cytometry using propidium iodide (PI) as a staining agent was used to study the effect of chrysin and its combination with cisplatin on cell cycle phase distribution. RESULTS: The results showed chrysin brought about a potent and dose-dependent antiproliferative effect in human glioma cancer cells. However, the combination of chrysin with low dose cisplatin led to a much higher growth inhibitory effects indicating an additive effect between the two compounds. The combined effect of chrysin and cisplatin also gave rise to a greater apoptosis induction as well as cell cycle arrest in comparison to the treatment by chrysin or cisplatin alone. Fluorescence microscopy as well as inverted phase contrast microscopy also revealed that the combination of chrysin plus cisplatin resulted in greater apoptosis induction as well as cell morphology alterations. Combination treatment of chrysin and cisplatin resulted in greater percentage of cells in early as well as in late apoptotic stages. The combination effect was also seen in mitochondrial membrane potential loss. CONCLUSION: Chrysin additively potentiates the antiproliferative, cell cycle arrest and apoptotic activity of cisplatin in human glioma cancer (U87) cells.

Exploration of two-enzyme coupled catalysis system using scanning electrochemical microscopy.

In biological metabolism, a given metabolic process usually occurs via a group of enzymes working together in sequential pathways. To explore the metabolism mechanism requires the understanding of the multienzyme coupled catalysis systems. In this paper, an approach has been proposed to study the kinetics of a two-enzyme coupled reaction using SECM combining numerical simulations. Acetylcholine esterase and choline oxidase are immobilized on cysteamine self-assembled monolayers on tip and substrate gold electrodes of SECM via electrostatic interactions, respectively. The reaction kinetics of this two-enzyme coupled system upon various separation distance precisely regulated by SECM are measured. An overall apparent Michaelis-Menten constant of this enzyme cascade is thus measured as 2.97 mM at an optimal tip-substrate gap distance of 18 µm. Then, a kinetic model of this enzyme cascade is established for evaluating the kinetic parameters of individual enzyme by using the finite element method. The simulated results demonstrate the choline oxidase catalytic reaction is the rate determining step of this enzyme cascade. The Michaelis-Menten constant of acetylcholine esterase is evaluated as 1.8 mM. This study offers a promising approach to exploring mechanism of other two-enzyme coupled reactions in biological system and would promote the development of biosensors and enzyme-based logic systems.

Simple approach for efficient encapsulation of enzyme in silica matrix with retained bioactivity.

We developed an alcohol-free sol-gel approach to encapsulate biomolecules such as horseradish peroxidase (HRP) in an electrochemically induced three-dimensional porous silica matrix by a one-step process. In this sol-gel process, the electrochemically generated hydroxyl ions at the electrode surface by applying cathodic current promote the hydrolysis of ammonium fluorosilicate to produce silica, and simultaneously the generated hydrogen bubbles play an important role in forming porous silica matrix. If HRP is mixed with ammonium fluorosilicate solution, it can be encapsulated in the forming silica matrix. Since there is no ethanol involved in the entire procedure, bioactivities of the encapsulated HRP can be effectively retained. As revealed by scanning electron microscopy (SEM) characterization, the resultant silica matrix has interconnected and network-like porous structures. Macroporous holes induced by hydrogen bubbles scattering on the relatively flat areas of porous structure can be observed. Such structure free from cracks provides effective mass transport and long-term stability. Scanning electrochemical microscope (SECM) characterization shows that the immobilized HRP molecules uniformly distribute in the silica matrix. The present HRP electrochemical biosensor exhibits a quick response (within 5 s) to H(2)O(2) in the concentration range from 0.02 to 0.20 mM (correlation coefficient of 0.9934) with a detection limit of 3 microM. The apparent Michaelis-Menten constant is 0.88 mM. The present alcohol-free sol-gel approach is effective for biomolecule encapsulation and is promising for the construction of biosensors, bioelectronics, and biofuel cells.

Electric-field distribution at the end of a charged capillary - a coupling imaging study.

The electric-field distribution at the end of a charged capillary system is detected using a scanning electrochemical microscopy (SECM) coupling imaging mode. A theoretical model based on the resistance of solution at the capillary end describes the three-dimensional distribution of the electric field. The effect of the detection electrode position and separation high voltage on solution potential is observed and analyzed. Results demonstrate that the electric field at the end-channel shows an isopotential contour changing from a disk shape into a hemispherical shape when leaving the capillary opening. The solution potential decreases along the central axis of the capillary to the detection reservoir. In the same scanning plane, the solution potential decreases along the radial direction. Increase of the separation high voltage results in the increase of the absolute solution potential but does not change the relative spatial electric-field distribution.

Highly selective amperometric glucose microdevice derived from diffusion layer gap electrode.

Although most of enzyme catalytic reactions are specific, the amperometric detection of the enzymatic reaction products is largely nonselective. How to improve the detection selectivity of the enzyme-based electrochemical biosensors has to be considered in the sensor fabrication procedures. Herein, a highly selective amperometric glucose biosensor based on the concept of diffusion layer gap electrode pair which we previously proposed was designed. In this biosensor, a gold tube coated with a conductive layer of glucose oxidase/Nafion/graphite was used to create an interference-free region in its diffusion layer by electrochemically oxidizing the interfering electroactive species at proper potentials. A Pt probe electrode was located in this diffusion layer of the tube electrode to selectively detect hydrogen peroxide generated from the enzyme catalytic oxidation of glucose in the presence of oxygen in the solution. In practical performance of the microdevice, parameters influencing the interference-removing efficiency, including the tip-tube opening distance, the tube electrode potential and the electrolyzing time had been investigated systematically. Results showed that glucose detection free from interferents could be achieved at the electrolyzing time of 30s, the tip-tube opening distance of 3mm and the tube electrode potential of 0.4V. The electrochemical response showed linear dependence on the concentration of glucose in the range of 1 x 10(-5) to 4 x 10(-3) M (the correlation coefficient: 0.9936, without interferents; 0.9995, with interferents). In addition, the effectiveness of this device was confirmed by numerical simulation using a model system of a solution containing interferents. The simulated results showed good agreement with the experimental data.

One-step immobilization of glucose oxidase in a silica matrix on a Pt electrode by an electrochemically induced sol-gel process.

We demonstrate here that the electrochemical generation of hydroxyl ions and hydrogen bubbles can be used to induce the synthesis of enzyme- or protein-encapsulated 3D porous silica structure on the surface of noble metal electrodes. In the present work, the one-step synthesis of a glucose oxidase (GOD)-encapsulated silica matrix on a platinum electrode is presented. In this process, glucose oxidase was mixed with ethanol and TEOS to form a doped precursory sol solution. The electrochemically generated hydrogen bubbles at negative potentials assisted the formation of the porous structure of a GOD-encapsulated silica gel, and then the one-step immobilization of enzyme into the silica matrix was achieved. Scanning electron microscopy (SEM) and scanning electrochemical microscopy (SECM) characterizations showed that the GOD-encapsulated silica matrix adhered to the electrode surface effectively and had an interconnected porous structure. Because the pores started at the electrode surface, their sizes increased gradually along the distance away from the electrode and reached maximum at the solution side, and effective mass transport to the electrode surface could be achieved. The entrapped enzyme in the silica matrix retained its activity. The present glucose biosensor had a short response time of 2 s and showed a linear response to glucose from 0 to 10 mM with a correlation coefficient of 0.9932. The detection limit was estimated to be 0.01 mM at a signal-to-noise ratio of 3. The apparent Michaelis-Menten constant (K m app) and the maximum current density were determined to be 20.3 mM and 112.4 microA cm-2, respectively. The present method offers a facile way to fabricate biosensors and bioelectronic devices in situ.