T-jump technique

The electrophilic reactions of NP with SH- and several SR- have been studied and reviewed (28). The nature of the reversible addition reactions [Eq. (5)] are reasonably well understood for the thiolates. A kinetic study including some bioinorganically relevant nucleophiles (cysteine, glutathione) was performed by using stopped-flow and T-jump techniques (77). The rate constants for the forward and reverse processes in Eq. (5) were in the range 103-104 M-1 s-1 and 101 K)3 s-1 at 25 °C, respectively. 

The stopped-flow and T-jump techniques were used by Mao and co-workers (34j) to investigate the kinetics of complex formation of [Cu(tren)(OH2)]2+ by HC03. In large excess of HC03 and pH = 6-9, the formation of the mononuclear bicarbonato/carbonato complex was too fast to be studied kinetically. The kinetically observed reaction was the reversible formation of the binuclear complex, [(Cu(tren))2(02C0)]2+ and this occurred as shown below ... 

In another recent study, Mao et al. (34k) have used the Cu11 complexes of 2,2 -bypridine and 1,10-phenanthroline to identify the different carbonate coordination modes which may be kinetically significant. Stopped-flow and T-jump techniques were used. The... 

Temperature-jump 31) measurements (with a time resolution in the microsecond range) only yielded a lower limiting value for the rate of the monactin-Na+ system. The relaxational amplitudes of these measurements could be evaluated in order to obtain the stability constant (Kgtab) and heat of reaction (/IH) 18). The time constant for the reaction of monactin with Na+ was obtained by the sound absorption technique 32). The rate constant of recombination was found to be ( form) 2—3 X 10 M i sec i. The complex formation of trinactin with Na+ (at high ionic strength) was just detectable with the T-jump technique since the time constant for this system was sufficiently larger than the time constant of heating 33). 

Another compound studied was antamanide. It is a cyclic decapeptide isolated from amanita phalloides. Its structure was determined by Th. Wisland and his coworkers 34). This compormd was also found to have carrier properties, however with a pronounced Na+ specificity. The relaxation time of the complex formation process between antamanide and Na+ is in the millisecond range 35). It could therefore be investigated by means of the T-jump technique. 

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. 

Accordingly, four types of T-jump techniques have been developed i) U. V. flash T-jump (heating by electronic excita-... 

We have first developed this apparatus to study very fast prototropic transformations in purine and pyrimidine aqueous solutions. For example Uracil with a pH above 9.5 exists in solution as a mixture of tautomeric anions. The interconversion of these two species is always very fast (100 ns < t < 3 ys) and must be studied with the laser T-jump technique. The study of the variation of the relaxation time with the pH and the concentration has allowed us to show that the N(1)H/N(3)H tautomeric interconversion of uracil monoanions proceeds via a dissociative mechanism as it does for cytosine and isocytosine >. ... 

This chapter reviewed the kinetics of phase transitions in systems based on surfactants and hpids. The use of the p-jump and T-jump techniques with a detection of the relaxation by means of TR-SAXS has permitted much progress in the field. The characteristic times for many phase transitions have been determined and found to be relatively short, in most instances in the time range of a few seconds or less. Intermediate phases have been identified. However, work remains to be done in two main directions. First, the effect of the amphtude of the perturbation on the characteristic time of the transition should be investigated more in detail. Indeed, several of the reviewed studies revealed a very large increase of the time characterizing the transition when the amplitude of the p-jump or T-jump was reduced. This may be partly due to the fact that most studies used very large perturbations and that the condition necessaiy in relaxation studies of very small perturbations was not met. This may affect both the... 

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