Polarization electronic transitions, proteins

The current form contains an electronic tunneling factor, t ), and a nuclear activation factor. Nuclear activation in aU the vibrational, protein conformational, and external solvent polarization modes, along with driving force effects, thus precedes the electronic transition, which occurs at the crossing between the potential surfaces of reactants and products (Figure 2.1). 

As a further com dicating factor, tryptophan dis days complex spectral properties due to the presence of two nearly isoenergetic excited states. and The electronic transitions display distinct absorption, emission, and anisotropy spectra and are differently sensitive to solvent polarity. The complexity of indole photc hysics has stimulated detailed studies of protein fluorescence but has also inhibited interpretation of the data. 

Energy calculations show that the membrane potential can supply sufficient energy for this transition. The membrane seems to be this structure at which energy transfer takes place through a low energy barrier, and where the uncontroUed diffusion of electrons is prevented by nonadiabatic behavior in the electron transfer process. " The polar electronic structure of lipids and proteins holding vibrating ions is crucial here. 

These spectra, taken at variable temperatures and a small polarizing applied magnetic field, show a temperature-dependent transition for spinach ferredoxin. As the temperature is lowered, the effects of an internal magnetic field on the Mossbauer spectra become more distinct until they result at around 30 °K, in a spectrum which is characteristic of the low temperature data of the plant-type ferredoxins (Fig. 11). We attribute this transition in the spectra to spin-lattice relaxation effects. This conclusion is preferred over a spin-spin mechanism as the transition was identical for both the lyophilized and 10 mM aqueous solution samples. Thus, the variable temperature data for reduced spinach ferredoxin indicate that the electron-spin relaxation time is around 10-7 seconds at 50 °K. The temperature at which this transition in the Mossbauer spectra is half-complete is estimated to be the following spinach ferredoxin, 50 K parsley ferredoxin, 60 °K adrenodoxin, putidaredoxin, Clostridium. and Axotobacter iron-sulfur proteins, 100 °K. 

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