Flow-quench methods

Barman, Thomas F., and Travers, Franck, The Rapid-Flow-Quench Method in the Study of Fast Reactions in Biochemistry Extension to Subzero VOL. PAGE... 

Fast Reactions in Biochemistry, the Rapid-Flow-Quench Method in the Study of... 

Barman, T. E. Travers, F. (1985). The rapid-flow-quench method in the study of fast reactions in biochemistry extension to subzero conditions. Methods in Biochemical Analysis, 31,1-59. 

Barman, T. E., Hillaire, D. Travers, F. (1983) Evidence for two step binding of ATP to myosin subfragment 1 by the flow-quench method. Biochemical Journal, 209,617-26. 

Refers to that initial period of nonhnear product formation, commencing with the initiation of the reaction and ending when the system is at steady state. Typically, the pre-steady-state phase lasts from milliseconds to a few seconds after mixing reactants. The time course of pre-steady-state rate processes often can be evaluated using stopped-flow, temperature-jump, and mix-quench methods. 

Various NMR spectroscopic techniques have been applied to investigate the conversion of methanol on acidic zeolites in the low-temperature (r<523K) formation of DME and the high-temperature (T>523 K) formation of alkenes and gasoline. Techniques successfully applied were the stop-and-go method under batch reaction conditions 258,259), the pulse-quench method 113), and various flow techniques 46,49,74.207,260 263). This section is a summary of the recent progress in investigations of the mechanism of the MTO process by NMR techniques. 

Perhaps the most difficult aspect of learning transient-state kinetic methods is that it is not possible to lay down a prescribed set of experiments to be performed in a given sequence to solve any mechanism. Rather, the sequence of experiments will be dictated by the details of the enzyme pathway, the relative rates of sequential steps, and the availability of signals for measurement of rates of reaction. The latter constraint applies mainly to stopped-flow methods, and less so for chemical-quench-flow methods provided that radiolabeled substrates can be synthesized. Therefore, 1 will describe the kinetic methods used to establish an enzyme reaction mechanism with emphasis on the direct measurement of the chemical reactions by rapid quenching methods. Stopped-flow methods are useful in instances in which optical signals provide an easy means to measure the rates of individual steps of the reaction. 

A simple and fast flow injection fluorescence quenching method for the determination of low levels of iron(III) in water has been developed. For this purpose, a preconcentration minicolumn consisting of cation-exchange resin was coupled to the FIA system. The use of mini-column in the system provided an improvement in sensitivity and the developed FIA method was successfully applied to the on-line determination of low levels of iron in real samples without the pre-concentration process. Fluorimetric determination was based on the measurement of the quenching effect of iron on salicylic acid fluorescence. An emission peak of salicylic acid in aqueous solution occurs at 409 nm with excitation at 299 nm. The effect of interferences from various metals and anions commonly present in water was also studied. The method was successfully applied to the determination of low levels of iron in real samples (river, sea, and spring waters). 

Thermal diffusivity has usually been measured using a quenching method, i.e.. the. solid sample at a uniform temperature is immersed in a temperature-controlled bath at a different temperature. The rate of change of temperature at the center is then monitored with an embedded thermocouple. The sample dimensions are usually chosen so that lateral heat flow can be ignored and regular sample geometries, i.e., "infinite flat slabs, "infinite" cylinders, or spheres, are used. 

A highly sensitive fluorescence quenching method for the determination of silicate based on the formation of an ion associate between molybdosilicate and Rhodamin B (RB) in nitric acid medium was developed. A flow-injection system coupled with a fluorescence detector was used for the measmement of fluorescence intensity at 560 and 580 ran as excitation and emission wavelengths, respectively. The calibration graph for Si showed a linear range of 0.1-5 ng/cm with correlation coefficient of 0.9999, and the detection limit of 0.06 ng/cm. The proposed method was successfully applied to the determination of silicate in ultrapurified water with satisfactory results. 

Write a brief report on a recent research article in which at least one of the following techniques was used to study the kinetics of a biochemical reaction stopped-flow techniques, flash photolysis, chemical quench-flow methods, or freeze-quench methods. Your report should be similar in content and extent to one of the Case studies found throughout this book. 

The steady-state and rapid equilibrium kinetics do not give detailed information on the existence of multiple intermediates or on their lifetimes. Such information is provided by fast (or transient) kinetics. The methods can be divided in two categories rapid-mixing techniques (stopped-flow, rapid-scanning stopped-flow, quenched flow) which operate in a millisecond time scale and relaxation techniques (temperature jump, pressure jump) which monitor a transient reaction in a microsecond time scale. Most of the transient kinetic methods rely on spectrophotomet-rically observable substrate changes during the course of enzyme catalysis. 

Many reactions between fluorophores and their environment will reduce DOM fluorescence and are termed quenching reactions. Huorescence is related primarily to various chemical components constituting DOM, which is reflects DOM sources and molecular size and mass. Colloidal organic matter (COM), fractionated by a variety of ultrafiltration and flow fractionation methods, shows distinct patterns in fluorescence, but these patterns are not consistent among freshwater and seawater sources. In freshwater environments protein fluorescence is often found in the highest molecular size fractions, whereas in seawater environments, fluorescence is often found in lower molecular size fractions. 

Another method iavolves an electric-arc vaporizer which is >2000° C before burning (25,32). One of the features of the process is a rapid quench of the hot gas flow to yield very fine oxide particles (<0.15 nm). This product is quite reactive and imparts accelerated cure rates to mbber. Internally fired rotary kilns are used extensively ia Canada and Europe and, to a limited extent, ia the United States (24). The burning occurs ia the kiln and the heat is sufficient to melt and vaporize the ziac. Because of the lower temperatures, the particles are coarser than those produced ia the other processes. In a fourth process, ziac metal which is purified ia a vertical refining column is burned. In essence, the purification is a distillation and impure ziac can be used to make extremely pure oxide. Also, a wide range of particle sizes is possible (33). 

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