Micropolarization measurements

Berezin MY, Lee H, Akers W, Achilefu S (2007) Near infrared dyes as lifetime solvato-chromic probes for micropolarity measurements of biological systems. Biophysical J 93 2892-2899... 

To obtain the stoichiometric number experimentally, it is necessary to measure i by two independent methods from extrapolation of the linear Tafel region to q = 0 and from micropolarization measurements. Equation 51F can then be used to calculate v, since the value of n is determined independently. Unless one considers a very complex system, both n and v are integers, and it is easy to distinguish experimentally among a small number of possible values of v. 

Less frequently used at present is electron spin resonance spectroscopy, which is based on the use of spin probes as model componnds or covalent spin labeling of drugs. Microviscosity and micropolarity of the molecnlar environment of the probe can be derived from electron spin resonance spectra. Moreover, the spectra allow us to differentiate isotropic and anisotropic movements, which result from the incorporation of the probe into liposomal structures. Quantitative distribution of the spin probes between the internal lipid layer, the snrfactant, and the external water phase is to be determined noninvasively. On the basis of the chemical degradation of drugs released from the lipid compartment, agents with reductive features (e.g., ascorbic acid) allow us to measure the exchange rate of the drugs between lipophilic compartments and the water phase [27,28]. 

The polarity within a surfactant assembly will be quite different from that of the bulk solution. It is useful to know the micropolarity of these assem-bhes for such applications where different substrates are compartmentalized inside these surfactants. The micropolarity of the surfactant assembhes can be determined using any fluorescence probe whose emission characteristics change with solvent polarity. The emissions of the probe are measured in solvents of known polarities and the polarity of the surfactant assembhes is determined by comparison. 

Pyrene carboxaldehyde and a series of pyrene carboxylic acids were found useful as fluorescence probes in describing the constitution of inverted micelles of certain calcium alkarylsulfonates in hydrocarbon media. 1-Pyrene carboxaldehyde is a convenient probe for studying the particle sizes of micelles in the region of lOOA. A series of graded probes, pyrene carboxylic acids with varying alkyl chain length, have been used to determine internal fluidity and micro-polarity as a function of distance from the polar core of these Inverted micelles. Pyrene exclmer to monomer fluorescence intensity ratio and fluorescene lifetime provided the means of measurement of internal fluidity and micropolarity, respectively. 

The present study demonstrates the utility of the above probe in describing the constitution of aggregates of certain alkarylsulfonates in hydrocarbon media. It also demonstrates the use of the probe technique in measuring the micropolarity of these same aggregates as a function of distance from the polar core. The micro-viscosity of inverted or normal micelles in the past has been estimated only as an average value of either the polar or non-polar regions (6). 

The micropolarity around the dendrophane core is reduced with increasing dendrimer generation. In the third generation material the polarity is roughly equivalent to that of ethanol, as measured by the fluorescent polarity probe 6 (p-toluidino) naphthalene-2-sulfonate (closely related to ANS). 

A number of electrochemical techniques were applied for the electrochemical analysis of Li electrodes in a large variety of electrolyte solutions. These include chronopotentiometry [230-233], potentiodynamic measurements (cyclic voltammetry) [88,89], transient methods (micropolarization) [81], fast OCV measurements [90,91] and impedance spectroscopy (EIS) [92-100], It should be noted that electrochemical analysis of Li electrodes is very complicated for the following reasons ... 

The use of fast transient methods (micropolarization) that do not change the electrodes during measurements by very much... 

Information on micropolarity and microviscosity can be obtained by measuring the hyperfine splitting constant An and the rotational correlation time tc. The hyperfine splitting... 

Photophysical processes have been adapted to provide systems for the measurement of temperature, critical micellar concentrations, micropolarity and microviscosity of organized media, and sol-gel transition points. 

The advantage of this approach over kinematically extended continua is twofold first, the additional parameter is abstract and does not require special assumptions of the local kinematics as it is necessary in micropolar continua, for example. As a consequence, the corresponding boundary conditions can be formulated more flexibly. Second, the coupling between the macroscopic balance of momentum and the additional balance of equilibrated forces is obtained consti-tutively, via the free Helmholtz energy function and not via the free energy function in combination with measures of deformation assumed a priori. Therefore, such an approach allows for size effects in both ways - either smaller is stiffer" or smaller is weaker depending on the boundary conditions. 

There are a number of studies on pyrene labelled or doped polymer materials. Dendritic size and electrostatic forces in poly(amido) dendrimers with pyrene residues have been determined through the use of a variety of quenchers. As the dendritic size increases so the Stern-Volmer quenching constant decreases, owing to blocking of the pyrene chromophore by the growing dendritic network. The photophysical properties of poly(acrylic acids) tagged with pyrene has been measured in micellar media at various pHs." The ratio of monomer to excimer gave valuable information on the micropolarity sensed by the pyrene label, as well as the influence of external stimuli. The surfactant... 

As expected, water pool microviscosity decreased and micropolarity increases as Wq increases. With some probes, bulk water values are not obtained until Wq is much greater than 10 these may be cases where the probe reports on interfacial water as well as on the free bulk water in the pool. Indeed, the fluorescence polarization measurements of Zinsli [55] using l-amino-naphthalene-4-sulfonic acid (a water pool probe) and 2-(N-tetradecyl)amino-naphthalene-6-sulfonic acid (an interfacial probe) and the pKa measurements of Sunamoto and co-workers [56] on excited state pyranine have been interpreted in terms of a radially inhomogeneous microviscosity and micropolarity, with a viscous boundary layer of hydration water (type I) at the pool periphery and an inner core of water (type II) whose properties rapidly approach those of ordinary bulk water as Wq increases. 

Assuming that there exists a stress potential Z = 2( 1 ), we find that the constitutive equations for an isotropic (isothermal) micropolar elastic solid are given, up to quadratic terms in strain measures, in Cartesian tensor notation [9] ... 

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