Aqueous solutions macroscopic properties

The extrapolation of physical attributes of substances to the submicroscopic level of representation was evident when students explained the changes in the displacement reaction between zinc powder and aqueous copper(II) sulphate. The decrease in intensity of the blue colour of the solution was attributed by 31% of students to the removal of blue individual Cu + ions from aqueous solution. The suggestion that individual Cu + ions (the submicroscopic level) are blue may be indicative of the extrapolation of the blue colour of the aqueous copper(II) sulphate (the macroscopic level) to the colour of individual Cu + ions (the submicroscopic level). Thirty-one percent of students also suggested that reddish-brown, insoluble individual atoms of copper were produced in this chemical reaction, again suggesting extrapolation of the bulk properties of copper, i.e., being reddish-brown and insolnble in water (the macroscopic level), to individual copper atoms having these properties (the snbmicroscopic level). 

Statistical mechanics provides a bridge between the properties of atoms and molecules (microscopic view) and the thermodynmamic properties of bulk matter (macroscopic view). For example, the thermodynamic properties of ideal gases can be calculated from the atomic masses and vibrational frequencies, bond distances, and the like, of molecules. This is, in general, not possible for biochemical species in aqueous solution because these systems are very complicated from a molecular point of view. Nevertheless, statistical mechanmics does consider thermodynamic systems from a very broad point of view, that is, from the point of view of partition functions. A partition function contains all the thermodynamic information on a system. There is a different partition function... 

Table 1 Magnitudes of molecular parameters and macroscopic properties of the aqueous solutions of the two de novo-designed self-assembling 3-tape forming peptides P -l and P -2 (Aggeli et al., 2001b)... 

Water is one of the most familiar material in our life and is indispensable to all living things. In contrast to its apparently simple molecular structure, water shows many anomalous properties from both macroscopic and microscopic points of view. However, the basic physical property of water, for example the dynamical structure of water, has not yet been fully clioified. To un rstand the dynamical aspect of water structure and its significant role in life, it is essential to clarify not only the dynamics of water molecules themselves but also the dynamics of water in the aqueous solutions. 

Another method suggested by the authors for predicting the solubility of gases and large molecules such as the proteins, drugs and other biomolecules in a mixed solvent is based on the Kirkwood-Buff theory of solutions [18]. This theory connects the macroscopic properties of solutions, such as the isothermal compressibility, the derivatives of the chemical potentials with respect to the concentration and the partial molar volumes to their microscopic characteristics in the form of spatial integrals involving the radial distribution function. This theory allowed one to extract some microscopic characteristics of mixtures from measurable thermodynamic quantities. The present authors employed the Kirkwood-Buff theory of solution to obtain expressions for the derivatives of the activity coefficients in ternary [19] and multicomponent [20] mixtures with respect to the mole fractions. These expressions for the derivatives of the activity coefficients were used to predict the solubilities of various solutes in aqueous mixed solvents, namely ... 

In this chapter the synthesis performed in aqueous solutions is considered, first, on a thermodynamic, macroscopic scale and later on a microscopic level using atomic properties of the elements to explain or to predict the processes occurring. 

There are basically two main developments in the molecular theory of solutions in the sense of route —IV one based on the inversion of the Kirkwood-Buff (KB) theory the second is the introduction of a new measure to study solvation properties. Both of these use measurable macroscopic, or global quantities to probe into the microscopic, or the local properties of the system. The types of properties probed by these tools are local densities, local composition, local change of order, or structure (of water and aqueous solutions) and many more. These form the core of properties discussed in this book. Both use exact and rigorous tools of statistical mechanics to define and to calculate local properties that are not directly accessible to measurements, from measurable macroscopic quantities. 

Domain associations in hydrophobically modified copolymers and associations of macroions in aqueous solution can lead to remarkable solution properties in properly tailored systems. An example of each type and selected observations of experimental findings were presented herein. The challenge now for the scientific community is to thoroughly understand the balance of structural forces responsible for macroscopic behavior so that systems may be properly tailored for specific commercial application. 

THE SOLVATION FORCE. The electrostatic and van der Waals disj>ersion forces retain the common attribute of depending on the nature of liquid water in the aqueous solution phase only through the macroscopic dielectric constant. In the case of the electrostatic force as exemplified in Eq. 6.16, the only dependence on the properties of liquid water comes through the parameter k, which, as shown in connection with Eq. 5.11, is a function of the bulk (zcro>frequency) dielectric constant, D. Similarly, for... 

As is well known, statistical thermodynamics is a theory that links the molecular properties and the macroscopic properties of matter. Specifically, for water, it provides the relationship between some specific features of the pair potential, and some of the outstanding properties of water and aqueous solutions. 

The experimental difficulties encountered using the homogeneous phase method have shown that these measuring conditions are valid only if the homogeneity of the radioactive aqueous solution and the liquid scintillator selected is maintained, not only at the macroscopic level, but especially at the molecular level. Further, these difficulties have shown that the calibrations carried out with small sized molecules (tri-tiated water, -or C- thymidine, for example) are not necessarily valid in the case of large sized molecules (DNA, for example), because of the physico-chemical properties of macromolecules. Finally, these difficulties have shown that the measurement artefacts encountered are not revealed by the standard methods of analysis and correction. 

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