Molecular structure, phenomenological

With respect to the carrier mechanism, the phenomenology of the carrier transport of ions is discussed in terms of the criteria and kinetic scheme for the carrier mechanism the molecular structure of the Valinomycin-potassium ion complex is considered in terms of the polar core wherein the ion resides and comparison is made to the Enniatin B complexation of ions it is seen again that anion vs cation selectivity is the result of chemical structure and conformation lipid proximity and polar component of the polar core are discussed relative to monovalent vs multivalent cation selectivity and the dramatic monovalent cation selectivity of Valinomycin is demonstrated to be the result of the conformational energetics of forming polar cores of sizes suitable for different sized monovalent cations. 

In what follows, the phenomenology of carrier transport will be briefly reviewed along with the mechanism of the Valinomycin model of carrier transport. The development of the molecular structure of Valinomycin will be considered in some detail, since the key to the dramatic selectivity of Valinomycin is thought to reside in the energetics of the molecular structure. Confidence in an understanding of the molecular structure of the Valinomycin-cation complex becomes tantamount to confidence in the presented basis of ion selectivity. 

This idea is elegant for its simplicity and also for its usefulness. While often in phenomenological theories of materials, control of parameters with molecular structure would provide useful properties, but the parameters are not related in any obvious way to controllable molecular structural features. Meyer s idea, however, is just the opposite. Chemists have the ability to control enantiomeric purity and thus can easily create an LC phase lacking reflection symmetry. In the case of the SmC, the macroscopic polar symmetry of this fluid phase can lead to a macroscopic electric dipole, and such a dipole was indeed detected by Meyer and his collaborators in a SmC material, as reported in 1975.2... 

Since the molecular crazing criteria require a substantial amount of detailed information about the molecular structure of the solid polymer and no clear correlation to the macroscopic phenomena observed experimentally exists, phenomenological criteria analogous to those for shear yielding were proposed. The... 

In Section VII we have applied a phenomenological approach in point of the forms of the potential wells characteristic for water. Now we shall consider a principally another way of modelling of intermolecular interactions pertinent to vibration of the H-bonded molecules. Recently [10, 12, 12a], a preliminary studies of the molecular dynamics was undertaken based on some picture (although very crude) of the molecular structure of water. We shall here briefly represent these results, namely ... 

The lattice model of mass transfer gives self-consistent expressions for sorption isotherms and permeability coefficients for microheterogeneous membranes of variable thickness at an arbitrary degree of filling. The parameters of the lattice model can be related to the molecular structure of a matrix and to the parameters of the interaction between diffusant and matrix [191]. The lattice model can serve as a basis to construct phenomenological models, which are capable of describing the features of a molecular system diffusant-membrane matrix . 

By introducing -dependent susceptibilities one can, at a phenomenological level, imitate the molecular structure of solvent around the solute with any desired degree of accuracy. Invoking isotropic and uniform approximations such as Equations (1.138) or (1.140) constrains the ability of such an approach to a certain degree. In any case, this is an essential extension of structureless local models of solvent. 

There are general relationships of transport phenomena based on phenomenological theory, i.e., on the correlations between macroscopically measurable quantities. The molecular theories explain the mechanism of transport processes taking into account the molecular structure of the given medium, applying the kinetic-statistical theory of matter. The hydrodynamic theories are also applied especially to describe - convection. 

A phenomenological description of nature is necessarily incomplete. With every new step that is made in our understanding of the microscopic or molecular structure of matter there is an added compulsion to review our macroscopic knowledge and relate or reduce it in terms of molecular structure. The goal of this molecular approach is thus to understand the macroscopic properties of systems in terms of their molecular structures and ultimately to reduce the chemical constants to molecular constants. 

It is precisely such a program which has created a renewed interest in the phenomenological findings of kinetic studies in recent decades. The molecular interpretations of kinetic processes throw a new light on molecular structure, which adds to our understanding in this field. At the same time these interpretations must themselves conform to and be consistent... 

In this chapter, the glass transition phenomenon is treated in moderate detail, including phenomenological aspects, molecular theories, and the effect of molecular structure. In addition, relaxation occurring in the glassy state below the glass transition temperature (Tg) is discussed. 

The phenomenological theory, as its name implies, concerns itself only with the observed behavior of elastomers. It is not based on considerations of the molecular structure of the polymer. The central problem here is to find an expression for the elastic energy stored in the system, analogous to the free energy expression in the statistical theory [equation (6-72)]. Consider again the deformation of our unit cube in Figure 6-3. In order to arrive at the state of strain, a certain amount of work must be done which is stored in the body as strain energy ... 

Summarising, clear phenomenological similarities were observed between bulk and interfacial gelling behaviour with changes in the molecular structure of glycinin. Besides, foaming properties could be related to interfacial behaviour of glycinin in relation to aspects of the molecular structure. 

A theory which would tie together the phenomenology of the viscosity behavior of liquids with their molecular structure would be desirable not only as an intellectual accomplishment but also as a useful aid in predicting the behavior of liquids as lubricants over a wide range of conditions. However, this goal is far from being attained because of basic deficiencies in present-day theories of liquids and because of the complex constitution of the hydrocarbon mixtures present in lubricating oils. 

According to Gibbs [1], one can view an interface as a layer of finite thickness within which the composition and thermodynamic characteristics are different from those in the bulk of phases in contact. This approach allows one to describe the properties of interfaces phenomenologically in terms of excesses of the thermodynamic functions in the interfacial layer in comparison with the bulk of individual phases. With this approach one does not need to introduce any model considerations regarding the molecular structure of the interfacial layer or utilize particular values of layer thickness. 

The previous sections dealt with a generalized theory of heterogeneous electron-transfer kinetics based on macroscopic concepts, in which the rate of the reaction was expressed in terms of the phenomenological parameters, and a. While useful in helping to organize the results of experimental studies and in providing information about reaction mechanisms, such an approach cannot be employed to predict how the kinetics are affected by such factors as the nature and structure of the reacting species, the solvent, the electrode material, and adsorbed layers on the electrode. To obtain such information, one needs a microscopic theory that describes how molecular structure and environment affect the electron-transfer process. 

It is clear that the new information developed from spectroscopic and multidisciplinary studies provides a basis for initiating diffractometric studies with a different set of constraints than those used in the past. The refinements are likely to be more complex, but the expectation is that the structures thus derived will more closely approximate the molecular structure of cellulose. Such models may then provide more comprehensive rationalizations of the phenomenology of cellulose. 

Both types of model are phenomenological, based on experimental measurements, and the model elements do not generally correspond directly with fine structure at the molecular level. They should not, however, be inconsistent with structural observations, and possible similarities between the models and molecular structure will be discussed. 

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