Macromolecular association thermodynamics

The probabilistic model of macromolecular association introduced in the previous section, for the case of large a and n B, may be recast into the formal language in terms of statistical thermodynamics. Recall from Chapter 1 that the chemical potential of a species has two terms, a structural energy (enthalpy) term and a concentration/entropy term ... 

The stresses induced in collapsing the network out of its reference configuration are compensated by short-range, cohesive attractions between the individual macromolecular network strands. The presence of a liquid, a solvent for the macromolecules that constitute the network, is thus a necessity in order to maintain porosity. Only in the presence of a solvent will it be thermodynamically preferable for the network strands to be surrounded by the solvent rather than to self-associate into a precipitate. So strong, indeed, is the tendency to be mixed, that, in contact with excess solvent, a permanent gel (i.e., a covalently cross-linked network) will swell well beyond the unstressed reference configuration. 

The appeal of fluorescence spectroscopy in the study of biomolecular systems lies in the characteristic time scale of the emission process, the sensitivity of the technique, and its ability to accommodate rapid and facile changes in the solvent milieu under conditions corresponding to thermodynamic equilibrium. The time scale of the emission process invites exploitation in two related manners. First, information on hydrodynamic aspects of the system is available from steady-state or time-resolved measurements. Second, detailed information on local dynamic processes within the biomolecular matrix may be derived. Information on hydrodynamic aspects of a macromolecular system may be used to study binding processes, that is, the association of small ligands with macromolecules or macromolecule-macromolecule interactions. In this chapter we focus on the latter applications of polarization or anisotropy data. We shall also try to clarify aspects of this area that our experience has shown to be occasionally misunderstood by initiates. 

A solution of a macromolecular or association colloid is a single phase from the thermodynamical point of view. 

Both stmcture and macromolecular d5mamics render the significant influence on its stability, i.e., chemical nature of the solvent (plasticizer), its basicity, specific and non-specific solvation, degree of PVC in a solution (solubility), segmental mobility of macromolecules, thermodynamic properties of the solvent (plasticizer), formation of associates, aggregates, etc. 

On the basis of changing values of characteristic viscosity [rj] (which are associated with the rotation and elastic - viscous deformation of macromolecular balls in a stream of solvent) and Hagging s constant one may determine the thermodynamic affinity of solvent to studied polymers or their mixes [2,3]. [rj] is a measure of additional losses of energy during spreading of the solution). Hagging s constant depends on a degree of interaction of polymeric molecules with solvent and is determined by the formula... 

Whenever block copolymers are dissolved in a selective solvent that is a thermodynamical good solvent for one block and a precipitant for the other, the copolymer chains may associate reversibly to form micellar aggregates in deep analogy with the situation observed for classical low-MW surfactants, hi this respect, a CMC can be defined and experimentally measured for block copolymer micelles, as discussed in Sect. 2.1. Compared to low-MW surfactants, the values of the CMC are much lower in the case of block copolymer macrosurfactants. This motivates, e.g., the use of block copolymer micelles as nanocontainers for drug dehvery. In contrast to low-MW surfactants, these block copolymer nano containers do not dissociate into unimers whenever they are diluted in the blood stream and can therefore transport the drugs to a specifically targeted area provided that they are functionalized by suitable mo cities for site-recognition [3]. Nevertheless, macromolecular chains can encounter some dissolution problems whenever they are placed in a se-... 

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