Publication costs assisted by the National Institutes of Health Experiments provide strong evidence that surface adsorption is not involved in the frequency dispersion of small-signal electrode polarization capacitance, and that the dissipative processes which are involved are located entirely in the electrolyte phase. The data show that this polarization is neither solventnor ionspecific, and that its dependence on electrolyte properties is through a single parameter, g, the bulk electrolyte conductivity. The polarization capacitance varies as ga, where a is the same fractional power involved in the well-known frequency dependence relation. This information leads to a theory of lateral charge spreading in the diffuse double layer which associates the frequency dependence with microscopic surface roughness, and the fractional power a with branching in the pathways of charge spreading. Branched ladder networks with distributed properties are shown to have input properties with fractional power frequency dependence, and to form a class whose topological arrangement may bear a relation to the topology of electrical processes in polarization. The theory requires no detail surface model, uses no distribution functions, and prevails in the absence of faradaic processes. The analysis may have application to other fractional power dispersion phenomena, such as polarization of biological membranes.
Guidance can help learners overcome the difficulties of getting started in a novel domain, but it is often ineffective in promoting learning and transfer. This article examines two aspects of guidance--communicating solution strategies for a problem domain and providing working memory support--in learning a novel problem-solving skill. Subjects in two experiments learned to troubleshoot simulated information networks. The learning environment varied in type of guidance provided--none, variable template, fixed template, and procedural instruction--and in availability of memory aiding. Variable-template guidance was effective when memory aiding was provided, and procedural instructions produced effective learning with or without memory aiding. However, fixed-template guidance was not effective, and there was no consistent effect of memory aiding in unguided, discovery learning conditions. The results have theoretical implications for the locus of guided-learning effects and suggest practical guidelines for the design of guided-learning environments.
When a dissolved macromolecule is in chemical equilibrium with a free ionic species, the charge configuration, and hence the dipole vector, of the macromolecule is fluctuating. Expressions for the static dielectric constant and the relaxation spectrum of such a mixture are here derived in terms of the components of the mean moment and the root mean square fluctuation moment, the molecular relaxation time constants, and the chemical rate constants of the ionic binding reaction. Contrary to a previous treatment of this problem by Kirkwood and Shumaker (1), it is shown that fluctuations introduce no independent components into the relaxation spectrum.
The technique of real time dielectric relaxation measurement coupled with a conventional stopped-flow device has made it possible to measure the rates of association and dissociation of the complex of human serum albumin with its most prevalent ligands, the long-chain fatty acids. This association was previously shown to proceed in two steps: a fast, probably diffusion-controlled, nonspecific association, followed by a slower (;3 sec') rearrangement of Long-chain fatty acids (FA), which in higher animals are the source of about half the normal energy requirements of the organism, are transported in the serum by means of reversible association of high affinity (107-108 M-1) with serum albumin. Aside from its physiological importance, this binding reaction shares a number of unique properties with a limited class of other strongly hydrophobic ligands. For these reasons the present investigation was aimed at developing an understanding of the mechanism of this association. There is reason to believe that it will be possible, and useful, ultimately to compare the characterization of the fatty acid complexation with that of other organic ligands of serum albumin to attempt to define more precisely the classes of ligand and the categories of binding site.Serum albumin, a globular protein of molecular weight 67,000, performs multiple functions, of which the most extensively studied is the transport function. Some 200 distinct organic species, including metabolites, hormones, drugs, and waste products, are bound with affinities ranging from 104 to 108 M-'. Albumin serves as solubilizer, reservoir, controlled release mechanism, and detoxifier. Thirty to 70 mol of FA can be bound to each mol of human serum albumin (HSA), but the physiological range is normally between 1 and 5 mol/mol. The first 2 or 3 mol are bound very tightly (Keq 107-108 M-l) (1).The equilibrium properties of the HSA-FA association and the widespread and complex interactions of this association with the binding affinities of many other compounds have been extensively studied (1-12).In spite of the long history of this problem, the mechanism of such binding is not well understood. METHODS AND MATERIALSIn this study, the kinetics of the association of oleic acid with HSA were measured by a method (24) that couples repeatable rapid dielectric measurements with stopped-flow mixing. A diagram of the measurement system is shown in Fig. 1. This method monitors the progress of association by taking advantage of the strong dependence of dielectric increment of serum albumin on the mole ratio of bound FA (25). Moreover, by taking advantage of the sizeable quantitative difference between this dependence in HSA and in BSA, it has been possible to measure the kinetics of dissociation, by measuring FA exchange between HSA and BSA (26).Abbreviations: HSA, human serum albumin; BSA, bovine serum albumin; FA, fatty acid.
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