Temperature jump method Joule heating

The p-jump method has several advantages over the t-jump technique. Pressure-jump measurements can be repeated at faster intervals than those with t-jump. With the latter, the solution temperature must return to its ini-lial value before another measurement can be conducted. This may take 5 min. With p-jump relaxation, one can repeat experiments every 0.5 min. One can also measure longer relaxation times with p-jump than with t-jump relax-mion. As noted earlier, one of the components of a t-jump experiment is It heat source such as Joule heating. Such high electric fields and currents can destroy solutions that contain biochemical compounds. Such problems lIo not exist with the p-jump relaxation method. 

Activation parameters are more and more frequently being reported as important features of temperature jump relaxation method kinetic studies. This is true in spite of the fact that the restricted temperature range accessible to a Joule heating temperature jump apparatus and the usual 10% uncertainties in measured relaxation times are not favorable characteristics for achieving precise values of AH and AS. ... 

A Joule heating temperature jump (T-jump) relaxation method study (8) of the kinetics of complexation of monovalent cations in methanol by dibenzo-30-crown-10 particularly intrigued us. Chock had found the rate of complexation of several monovalent cations (Na, K+,NHi +,etc.) to be almost diffusion controlled and essentially too fast for precise determination by T-jump equipment then available to him. He also noted an even faster relaxation process that was completely inaccessible. This latter relaxation process Chock ascribed to a conformational change of the dibenzo-30-crown-10 between two ligand conformers one of which is more suitable for complexing the cation. Such an inference is entirely consistent with known, rapid conformational equilibria in solutions of valinomycin (2), for example. 

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