Electronics temperature-jump

The His35, with coordinated His46 in close proximity, has frequently been suggested as a site for electron transfer reactivity of azurin. Two processes have been detected in a temperature-jump study on the equihbration of azurin with cytochrome C551, its physiological partner [57]. The fast process is assigned to electron transfer, and the slower process to a conversion between inactive and active forms of reduced azurin. It has been concluded that the active form is protonated. A second H-bonded form of His35 is believed to result from the protonation [2]. 

Method. When rapid techniques are involved the following abbreviations apply F, flow TJ, temperature jump PJ, pressure jump E, electrochemical NMR, nuclear magnetic resonance ESR, electron spin resonance SA, sound absorption EF, electric field. Classical methods for investigating kinetics are not specified unless low temperatures (LT) have been used. 

The concept of a mobility edge has proved useful in the description of the nondegenerate gas of electrons in the conduction band of non-crystalline semiconductors. Here recent theoretical work (see Dersch and Thomas 1985, Dersch et al. 1987, Mott 1988, Overhof and Thomas 1989) has emphasized that, since even at zero temperature an electron can jump downwards with the emission of a phonon, the localized states always have a finite lifetime x and so are broadened with width AE fi/x. This allows non-activated hopping from one such state to another, the states are delocalized by phonons. In this book we discuss only degenerate electron gases here neither the Fermi energy at T=0 nor the mobility edge is broadened by interaction with phonons or by electron-electron interaction this will be shown in Chapter 2. 

Refs. [i] Bard AJ, FaulknerLR (2001) Electrochemical methods, 2nd edn. Wiley, New York, pp 487-516 [ii] Amatore C, Maisonhaute E (2005) Anal Chem 77-.303A [iii] FeldbergSW, Newton MD, Smalley JF (2003) The indirect laser-induced temperature jump method for characterizing fast interfacial electron transfer concept, application, and results. In Bard AJ, Rubinstein I (eds) Electroanalytical chemistry, vol. 22. Marcel Dekker, New York, pp 101-180... 

Bemasconi and co-workers have studied the kinetics of disproportion-ation-comproportionation in azaviolene systems by temperature jump, stopped-flow, and pH jump techniques, examining the electron transfer process in the light of Marcus theory.316-318... 

Siegel, D. P., Green, W., and Talmon, J. (1994), The mechanism of lamellar-to-inverted hexagonal phase transitions A study using temperature-jump cryo-electron microscopy, Biophys. /., 66,402-414. 

Tegoni, M., Silvestrini, M. C., Guigliarelli, B., ASSO, M., Brunori, M., and Bertrand, P., 1998, Temperature-jump and potentiometric studies on recombinant wild type and Y143F and Y254F mutants of Saccharomyces cerevisiae flavocytochrome b2 role of the driving force in intramolecular electron transfer kinetics. Biochemistry 37 12761nl2771. 

Temperature jump [25] with Joule heating was used in an early study of rapid outer-sphere electron-transfer reactions [22] between polypyridine metal complexes and haxachloro- and hexabromometalates, Eq. 25,... 

In recent years, temperature-jump methods have been used widely in studies of enzymatic and biological electron transfer. These methods seem to be ideally suited for the task owing to the existence of finely balanced, easily perturbed equilibria in biological systems. Kinetic determinations are facilitated by the large molar absorptivities of most metalloenzymes, so that even small concentration changes provide measurable signals. 

An adaptation of the temperature-jump method, named indirect laser-induced temperature jump [29], was used in studies of distance dependence of electron transfer at electrodes. A pulsed Nd YAG laser was used to cause a sudden (<5 ns) change in temperature (<5 K) at an electrode/electrolyte interface. The increase in temperature causes a change in the open-circuit potential. The relaxation step is a function of the dissipation of thermal energy and the rate of electron transfer between the electrode and its redox partners. 

Laser flash photolysis studies using the deazariboflavin system [80, 81] have shown that pyruvate binding also exerts a strong influence on intramolecular ET. In the one-electron reduced enzyme, ET from the FMN semiquinone to the oxidized heme can be observed only in the presence of pyruvate for this reaction, k j = 500 s. When the enzyme is completely reduced by stoichiometric addition of lactate prior to laser photolysis with dRf alone, pyruvate binding inhibits ET from fully reduced flavin to oxidized heme. This reaction has an observed /cet = 2000 s in the absence of pyruvate [81]. Similar values for these two rate constants have been obtained by temperature-jump measurements [82]. 

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