Macromolecules aggregation

Here mass transport is of minor importance compared to the changes in relaxation times induced by phase changes such as crystallization of water or lipid, phase separation, gelation and/or macromolecule aggregation and denatur-ation. Since relaxation times are sensitive to temperature, relaxation time maps might also be used to follow temperature changes and heat transport. 

In diluted polymer solutions the reaching of dynamical equilibrium between the macromolecules aggregation and degradation processes (which are realized by the way of formation of new bonds between monomers or decay of former ones) is possible, when macromolecules are, as a rule, in the fractal state. Moreover, the processes of synthesis and degradation can be realized simultaneously. In Ref. [13], the analytical expression was obtained for the mass spectra of macromolecular fractals in diluted polymer solutions. 

The dynamical equilibrium of the macromolecules aggregation and degradation processes can be expressed mathematically by the equation for a monomers number in macromolecular ftactal evolution (the fractal mass is directly proportional to monomers number) [13] ... 

Stoll, S. and Buffle, J. (1995). Computer simulations of coUoids and macromolecules. Aggregate formation. Chimia, 49, 300-307. 

Equation 16 is valid when the molar signal of each species is independent of concentration (i.e. in the absence of ligand and macromolecule aggregation). 

A series of O-acetyl derivatives of pectic acid has been prepared to study the intramolecular binding of Ca + ions to pectic acids. The electrostatic free enthalpy of dissociation of these polyacids and the rate of exchange of the counter-ion from Ca + to K+ were determined by potentiometric titration measurements. The binding of Ca + ions was characterized by the production of single ion affinity coefficients determined in solutions of the calcium salts of 0-acetyl pectic acids and by the circular dichroism measurements of calcium and potassium salts of the pectate derivatives. The intramolecular binding of Ca + ions to isolated pectate macromolecules is purely of electrostatic character in contrast to the intermolecular chelate binding of Ca + ions which takes place when the pectate macromolecules aggregate. 

The formation of ECC is not only an extension of a portion of the macromolecule but also a mutual orientational ordering of these portions belonging to different molecules (intermolecular crystallization), as a result of which the structure of ECC is similar to that of a nematic liquid crystal. After the melt is supercooled below the melting temperature, the processes of mutual orientation related to the displacement of molecules virtually cannot occur because the viscosity of the system drastically increases and the chain mobility decreases. Hence, the state of one-dimensional orientational order should be already attained in the melt. During crystallization this ordering ensures the aggregation of extended portions to crystals of the ECC type fixed by intermolecular interactons on cooling. 

Wanka, G Hoffman, H Ulbricht, W, Phase Diagrams and Aggregation Behavior of Poly (oxyethylene)-Poly(oxypropylene)-Poly(exyethylene) Triblock copolymers in Aqueous Solutions, Macromolecules 27, 4145, 1994. 

The values of Huggins constant were close and indicated that there was an increased tendency towards aggregation for the dissolved macromolecules. 

Shuto, K., Oishi, Y, Kajiyama, T. and Han, C. C. (1993) Aggregation structure of a two-dimensional ultrathin polystyrene film prepared by the water casting method. Macromolecules, 26, 6589-6594. 

Le Bon, C., Nicolai, T., and Durand, D., Kinetics of Aggregation and gelation of globular proteins after heat-induced denaturation, Macromolecules, 32,6120, 1999. 

Disperse systems can also be classified on the basis of their aggregation behavior as molecular or micellar (association) systems. Molecular dispersions are composed of single macromolecules distributed uniformly within the medium, e.g., protein and polymer solutions. In micellar systems, the units of the dispersed phase consist of several molecules, which arrange themselves to form aggregates, such as surfactant micelles in aqueous solutions. 

To answer Staudinger s critics, Carothers knew he had to resolve three issues. First, he would have to build one of Staudinger s macromolecules. Next, he would have to confirm that they were indeed long-chained molecules, not merely aggregates of smaller molecules, as others claimed. Finally, he would have to prove that the forces holding the chains together were ordinary valence bonds, rather than a mysterious weak force. 

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