Mobility nanosecond

In liquid Ne, evidence has been found for a high-mobility species, which may be a delocalized electron, that converts to a low-mobility species in several tens of nanoseconds (Sakai et al, 1992). Field dependence of the low-mobility species is supralinear, but the lifetime of the high-mobility species increases with the field strength and decreases with temperature from -2 to -100 ns. 

The dynamics of a supramolecular system are defined by the association and dissociation rate constants of the various components of the system. The time-scale for the dynamic events is influenced by the size (length-scale) and by the complexity of the system. The fastest time for an event to occur in solution is limited by the diffusion of the various components to form encounter complexes. This diffusion limit provides an estimate for the shortest time scale required for kinetic measurements. The diffusion of a small molecule in water over a distance of 1 nm, which is the length-scale for the size of small host systems such as CDs or calixarenes, is 3 ns at room temperature. In general terms, one can define that mobility within host systems can occur on time scales shorter than nanoseconds, while the association/dissociation processes are expected to occur in nanoseconds or on longer time scales. The complexity of a system also influences its dynamics, since various kinetic events can occur over different time scales. An increase in complexity can be related to an increase in the number of building blocks within the system, or complexity can be related to the presence of more than one binding site. 

Analysis of rotational mobility of fluorophores by observation of fluorescence depolarization with nanosecond time resolution(28) or by variation of the lifetime (by the action of quenchers ).(9,29 30)... 

Recent results show large variations in intramolecular rotations of tryptophan residues in proteins on the nanosecond time scale, ranging from complete absence of mobility to motions of considerable angular amplitudes. Among native proteins with internal tryptophan residues, wide angular amplitude rotations were observed only in studies of azurin,(28 29) where the correlation time of the rapid component was x = 0.51 ns.(28) The existence of... 

J. R. Lakowicz and G. Weber, Nanosecond segmental mobilities of tryptophan residues in proteins observed by lifetime-resolved fluorescence anisotropies, Biophys. J. 32, 591-601 (1980). 

A. P. Demchenko, On the nanosecond mobility in proteins. Edge excitation fluorescence red... 

It is important to consider the magnitude of the recombination rate in studies of this type. For methane, is 1.7 x 10 sec at 93 K [81]. Thus if a concentration of ions of 0.1 pM was formed in the pulse, the electrons would disappear with a first half-life of 50 psec. For 2,2,4-trimethylpentane, k,. is 3.6 x 10 sec and for a similar concentration of electrons, the recombination lifetime would be a few nanoseconds. Where the electron mobility is lower, the recombination rate is slower. For methylcyclohexane,... 

Figure 16 shows the absorption spectrum obtained by additive-free polyethylene [67], At ambient temperature the absorption observed on nanosecond time-scale increased continuously from 500 to 200 nm without showing any maximum. The absorption in UV is similar to that obtained by y-irradiation. Considering the results obtained by liquid alkanes, the absorption seems to be comprised of several different free radicals. At 95 K additional absorption due to the trapped electron was observed at wavelengths longer than 600 nm the band was observable even at ambient temperature in the picosecond time-domain [96]. The electron decays presumably by the hole-electron recombination. The decay of the trapped electron was independent of the presence of carbon tetrachloride, suggesting that the additives reacted with a mobile electron but not with the trapped electron. On adding naphthalene, the radiation-induced spectrum showed the bands due to the first excited triplet state and the radical... 

The dynamic state of sperm-whale myoglobin monitored by spin, fluorescence, and Mossbauer labels (Likhtenshtein, 1988, 1993) as a function of temperature was compared with the results ofkinetic studies on the photodissociation and reassociation of CO-deoxymyoglobin (Frauenfelder et al, 1991). The three independent labelling methods showed sharp increases in nanosecond mobility in the vicinity of the label in a temperature region of approximately 200-220 K. These temperatures were close to the temperatures of the dramatic increases in the relative quantum yield of the photodissociation, as well as to the fraction of non-dissociated molecules for 10"2 s... 

Backbone fluctuations with correlation times in the nanosecond regime are revealed in variations of the R1 residue scaled mobility, Ms, along the sequence (see Section III,A,1 for definition). Figure 15A (see color insert) shows a plot of Ms versus sequence for C1-C3, H8, and adjacent sequences in the TM helices. Figure 15B shows the cytoplasmic surface of rhodopsin color-coded according to Ms values. In this figure, C3 was modeled from the SDSL data, as in Fig. 9. 

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