Complexation typical timescales

Intact-rock techniques involve more realistic surface areas and liquid solid ratios, but the experimental equipment is generally more complex and timescales are longer. It is recognized that machining of the samples to the required size and shape may result in some alteration to the rock surface. This effect could be important in the case of strongly sorbing radionuclides where the depth of penetration will be very small over typical laboratory timescales (e.g. 1-2 years). 

TR methods were originally developed in om laboratories to study excited-state structures and dynamics of transition metal complexes such as Ru + (bpy)s and metaUoproteins. TR measurements rely on a pump-probe approach in which two separate laser pulses are used, one to excite the system and the other to probe the transient Raman spectrum. The time resolution of the experiment is determined by the width of the laser pulses (typically 7 ns for a Q-switched laser or as short as 1 ps for a mode-locked laser). The pulses are variably delayed with respect to one another to achieve time resolution, either by optically dela)dng the probe pulse with respect to the pump pulse or by electronically delaying two independently tunable lasers. Thus, two different approaches are required depending on the time scale of interest. The fastest timescale (from 10 to 10 s) requires optical delay to achieve sufficiently short separation between the pump and probe pulses. In such a scheme, the probe pulse is sent through a fixed path, but the pump pulse is sent through a variable path that can be scanned. Since hght travels about 1 ft per ns, a difference in pathlength of a few feet is sufficient. The second approach typically uses two Q-switched Nd YAG lasers that are electronically delayed with respect to one another, to access... 

Interestingly, the diffusional behavior of membrane proteins measured experimentally by FRAP, FCS, or single particle tracking in cells is more complex than predicted by this model. This technique is described best for the case of cell surface proteins, as assessed by FRAP. Such measurements indicate that diffusion is typically much slower than one would expect based on membrane viscosity. In cell membranes, typical values of D for transmembrane proteins are approximately 0.05 pm /s or less, which is much slower than observed in artificial membranes composed of purified lipids. In addition, a significant fraction of proteins is often immobile over the timescale of diffusion experiments (4, 5). Furthermore, diffusional mobilities vary among proteins, and sometimes they differ for the same protein expressed in different cell lines (4, 5). Deviations from pure diffusion are more readily apparent when the trajectories... 

Geminate recombinations and spur reactions have been widely studied in water, both experimentally and theoretically [13-16], and also in a few alcohols [17,18]. Typically, recombinations occur on a timescale of tens to hundreds of picoseconds. In general, the primary cation undergoes a fast proton transfer reaction with a solvent molecule to produce the stable solvated proton and the free radical. Consequently, the recombination processes are complex and depend on the solvent. The central problem in the theory of geminate ion recombination is to describe the relative motion and reaction between the two particles with opposite charges initially separated by a distance rg. In water, the primary products of solvent radiolysis are the hydrated electron e ", the hydroxyl radical OH and the hydronium cation H3O+ ... 

EIS is the experimental technique based on the measurement, under equilibrium or steady-state conditions, of the complex impedance of the cell at different frequencies of an imposed sinusoidal potential of small amplitude. As a result, a record of the variation of impedance with frequency (impedance spectrum) is obtained. Typically, EIS experiments are conducted from millihertz to kilohertz, so that available information covers a wide range of timescales (Retter and Lohse, 2005). 

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