Potential-dependent redistribution

Slow Dyes. Slow dyes generally operate by a potential-dependent partitioning between the extracellular medium and either the membrane or the cytoplasm. This redistribution of dye molecules is effected via the interaction of the voltage with the ionic charge on the dye. Unlike fast potentiometric indicators, slow redistribution dyes must be charged. Three chromophore types have yielded useful slow dyes cyanines, oxonols, and rhodamines. Each of these chromophores has special features that suit different kinds of experimental requirements. A set of important slow dyes is depicted in Chart III. 

When charges preferentially adsorb onto an interface adjacent to an aqueous solution they are balanced by counterions creating an electric double layer. For an aqueous NaCl solution I/kq = 30.4 nm at 10 M, 0.96 nm at 0. IM, and in pure water of pH 7, 1/kd is about one micron (e.g., Israelachvili 1992). With this in mind, the interfacial dynamics at an ice/solution interface can become quite complicated, and our studies of premelting dynamics might require consideration of a continuous variation in the interaction potential depending on the redistribution of ions. Preferential ion incorporation is best demonstrated in this context of solid/liquid solute distribution introducing ionic coefficients . A simple example for a monovalent electrolyte solution is... 

Nonpolarizable interfaces correspond to interfaces on which a reversible reaction takes place. An Ag wire in a solution containing Ag+ions is a classic example of a nonpolarizable interface. As the metal is immersed in solution, the following phenomena occur3 (1) solvent molecules at the metal surface are reoriented and polarized (2) the electron cloud of the metal surface is redistributed (retreats or spills over) (3) Ag+ ions cross the phase boundary (the net direction depends on the solution composition). At equilibrium, an electric potential drop occurs so that the following electrochemical equilibrium is established ... 

An arbitrary potential dilference nsnally exists between two pieces of metal that are insulated relative to each other its value depends on excess charges accidentally accumulated on the metal snrfaces. When the two pieces are brought in contact, the charges will undergo a redistribution and the potential difference will become well defined. When identical metals are involved, the potential difference wiff vanish completely, bnt when different metals are involved, a certain potential difference will be set np across the junction (interface) which depends on the conductors. This potential difference, between arbitrary points within the first and... 

Once in the blood stream, cocaine levels quickly rise in the brain, faster than plasma levels, which then redistribute to other tissues. Cocaine is rapidly metabolized in the blood and liver, with a half-life of 30 to 90 minutes. The major metabolites have a half-life of approximately 8 hours. Although cocaine itself is detected in urine for only 12 hours, the metabolite benzoylecgonine can be detected in urine for at least 48 hours and sometimes up to 2 weeks. Concurrent use of cocaine and ethanol produces an ethyl ester of benzoylecgonine called cocaethylene. Cocaethylene is an active metabolite, blocking dopamine reuptake, and potentiating the effect of cocaine. Thus, concurrent use of cocaine and ethanol can further increase the additional effects of the drugs and the risk of dependency. 

The argument is so general that its particularization for the metal/electrolyte interface was only for convenience. One could have carried out the discussion with equal validity for the gas/electrolyte or the glass (container)/electrolyte boundary of the electrolyte. Of course, one would have had to note the difference between the particles that constitute gases and glass and those that compose a metal. In all these systems, the conclusion would be reached that forces are direction dependent at the phase boundary and therefore new and compromise arrangements are assumed by the particles (of the two phases) in the phase boundary. If the particles are charged or are dipoles, not only is there a redistribution of particles but also an electrification of the interface and the development of a potential difference across it... 

In patients with obstruction of the internal carotid artery, numerous collateral pathways that redistribute blood to the deprived site can maintain adequate cerebral blood flow. The CW is considered an important primary collateral pathway with its potential believed to be dependent on the presence and size of the component vessels, which vary among normal individuals (Alpers and Berry 1963 Baumgartner et al. 1997 Krabbe-Hartkamp et al. 1998 Macchi et al. 1996 Patrux et al. 1994 Schomer et al. 1994). Using special 2D... 

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