Temperature jump system

Markwalder B, Gozel P and van den Berg H 1992 Temperature-jump measurements on the kinetics of association and dissociation in weakly bound systems N2O4 + M = NO2 + NO2 + M J. Chem. Phys. 

In this manuscript we will first describe the characteristics of the temperature jumps and the resulting molecular desorption which can be produced by a laser pulse. We then describe how we have implemented FTMS as a detection method in these experiments and present our results on several adsorbate systems. 

The most common methodology for measuring fast kinetics in real time is to perturb a system at equilibrium for a time duration that is much shorter than the relaxation kinetics that follow perturbation. This perturbation can be achieved by changing the concentration of chemicals through fast mixing (stopped-flow), changing the temperature of the solution (temperature jump), simultaneously changing the... 

In summary, the necessary condition for temperature jump experiments is that the equilibrium for the chemical system of interest changes with a change in temperature. The advantages of temperature jump experiments are that the perturbation is achieved by a change in a property of the solvent, a fast time resolution can be achieved, as short as picoseconds when using lasers, and a time domain over more than 6 orders of magnitude can be probed with the same technique. The disadvantage of the technique... 

A number of stopped-flow systems are commercially available. Three of the most used are manufactured by Atago Bussan (formerly Union Giken), Japan Dionex (formerly Durrum), USA and Hi-Tech Scientific, UK. These also manufacture rapid scan spectrophotometers, multimixer, temperature-jump and flash photolysis equipment. 

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. 

Biochemical processes such as protein unfolding/refold-ing and supramolecular assembly/disassembly take place on a time scale of seconds to minutes after readjusting the temperature of a system. Most commercially available glass-jacketed cuvettes are not suitable for temperature jumps on this time scale, as a result of the slow kinetics of heat transfer across substances with characteristically high dielectric constants, and their use can convolute the time scale of the temperature change onto the time scale... 

Jnmps of a proton along the hydrogen bond represent another type of dynamics observed in hydrogen-bonded complexes. Mechanistically, this process is simplest for intramolecular hydrogen bonds. The fast enol-enolic equilibrium shown in Scheme 2.2 illustrates an intramolecular proton-jumping system [27]. Here, substituent X dictates the equilibrium constant as well as the rate of proton transfer. It should be noted that such proton jumps can be stopped on the H NMR time scale only at very low temperatures. 

For very rapid reactions such as the ionization of H2O, it is difficult to determine the rate constants using conventional methods. One often-used method is the relaxation method. The system is initially at equilibrium under a given set of conditions. The conditions are then suddenly changed so that the system is no longer at equilibrium. The system then relaxes to a new equilibrium state. The speed of relaxation is measured, usually by spectrophotometry, and the rate constants can be obtained. One technique to change the conditions is to increase temperature suddenly by the rapid discharge from a capacitor. This technique is called temperature-jump technique. 

Observing relaxation. Kinetic measurements over periods of tens of microseconds or less can be made by rapidly inducing a small displacement from the equilibrium position of a reaction (or series of reactions) and observing the rate of return (relaxation) of the system to equilibrium. Best known is the temperature jump method devised by Eigen and associates. Over a period of about 10-6 s a potential difference of -100 kV is applied across the experimental solution. A rapid electrical discharge from a bank of condensers passes... 

Clearly, this method cannot be applied to systems in which there are irreversible chemical processes. It is most suitable for situations involving simple ligand binding (such as NAD+ with a dehydrogenase), inhibitor binding, or conformational changes in the protein. There have been some attempts to combine the temperature-jump with the stopped-flow method. 

There have been very few studies on the kinetics of micellization in block copolymer solutions. Micellization in aqueous surfactant systems close to equilibrium occurs on a time-scale far below one second. Experimental results obtained by fast reaction techniques, such as temperature jumps or pressure jumps or steady-state methods such as ultrasonic absorption, NMR and ESR, show that at least... 

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