Molecular hydrogen sensor Because hydrogen presents a significant risk of fire and explosion, there is a need for more real-time accuracy in spatial measurements of the gas. Ross C. Thomas and Robert C. Hughes of Sandia National Laboratories describe a simple process to fabricate Pd/Ni resistors for detecting H2 using a shadow mask. This approach is then adapted to the manufac ture of wide-range hydrogen (WRH) microsensors, which combine the Pd/Ni resistor, a metal-oxide semiconductor capacitor, and a thin-film metal heater and temperature sensor for the rapid. detection of the partial pressure of H2 from 1 mTorr to 700 Torr The resistive device is manufactured by a two-mask lift-off process. The first step deposits the Pd/Ni alloy as a resistor with four bonding pads and a larger
Chemicals in the food chain Predicting how much of a pollutant will end up in the food chain is difficult because its bioavailability depends on many factors, including how much is associated with dissolved organic matter and how much is bound to particulate matter or in solid form. A method commonly used to predict the amount of a compound available for biopartitioning involves estimation techniques that rely on the water/1-octanol partition coefficient K Although K has become almost a standard for determining biological activity in the environmental field, models involving K do not always accurately predict bioaccumulation processes Differences in the thermodynamic properties of biopartitioning processes, arising from structural differences between octanol and the actual lipid of interest, have been linked to the failure of bioaccumulation models based on Kow. John G. Dorsey and Brran N.
Woodrow of Florida State University investigate water-micelle partitioning as an alternative to water/1-octanol partitioning for predicting biopartitioning. The method involves using micellar electrokinetic chromatography (MEKC) to determine the thermodynamic properties—including enthalpy, entropy, and free energy of transfer—of 67 solutes with varying functional groups. Water-micelle partition coefficients are also presented for the various solutes. The resulting values are compared with those in the literature for both water/1-octanol partitioning and biopartitioning The MEKC method shares several advantages with capillary electrophoresis, including fast analysis times, low sample consumption, and use of aqueous buffers and low volumes of organic solvents. The authors attempt to demonstrate that water-micelle partitioning is a better predictor of biopartitioning than is water/1-octanol partitioning. (Environ. .ci. Technol. o997, 31, 2812-20)
chip surface and then introducing the appropriate partner in the mobile phase. The authors report that the binding of recovSchematic diagram of wide-range hydrogen erin was strictly dependent on the pressensor produced by two-mask process; m Many proteins involved in signal transducrepresents four resistors and a metal-oxide ence of Ca2+ and the myristoyl group. At tion are N-terminally acylated by myristic 2+ semiconductor capacitor; and • marks a acid. In some cases, the modification is nec- saturated Ca concentrations, the dissothin-film heater and a temperature sensor. ciation constant for recoverin and phosessary for protein association with cellular (Adapted with permission. Copyright 1997 pholipid liposomes was —150 uM. Assomembranes. If additional cofactors are inThe Electrochemical Society.) volved in the membrane binding, the myris- ciation and dissociation were fast and biphasic with time constants of —0.1 s_1 toyl moiety becomes part of a molecular and 0.01 s"1, respectively. (Biochemistry switch known as the myristoyl switch. 1997, 36,12019-26) Recoverin is one example of a myrissquare for the metal-oxide capacitor. A 2+ second step places a large square for the toyl switch—an 7V-myrrstoylated Ca binding protein that is involved in thin-film metal heater and temperature feedback mechanisms underlying sensor resistor. Close positioning of the vertebrate photoreceptor light heater and temperature sensor provides adaptation. To further understand good thermal control of the sensor in the molecular mechanism of the case of a sudden change in sample recoverin Ca2+-myristol switch, temperature. Karl-Wilhelm Koch and Christian Prototype sensors were annealed in Lange of the Institut fur Biolo2% H2 in N2 for 2 h at various temperatures. A temperature of >350 ° C yielded gische Informationsverarbeitung (Germany) studied the dynamics devices with essentially no undershoot of the myristoyl membrane bindand less drift than other sensors built at ing by surface plasmon resonance Sandia. The authors also correlated (SPR) spectroscopy. changes in surface morphology with the response of the prototypes. All of these SPR allowed the determination observations should aid in fabricating of affinity constants and kinetic more reliable and reversible WRH miparameters. Binding was probed SPR sensorgrams showing the affinity of varying crosensors. (J. Electrochem. Soc. 1917, by immobilizing recoverin or concentrations of native recoverin for phospholipid 144, 3245-49) phospholipid vesicles on a sensor membranes.
Protein dynamics by SPR
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