Macromolecular cooperative effects

Table 1 - Overview of cooperative effects on macromolecular chain...

In biological systems, a macromolecular chain effectively selects a complementary one to form an intermacromolecular complex. In this way, very specific functionalities become effective. Synthetic polymers can also form intermacromolecular complexes, but the ability of a synthetic polymer to select only one objective polymer as in biological systems has not yet been realized, except for several specific systems of pairs of polymers which include one of the complementary base pairs of nucleic add individually, e.g. po y(A)-poly(U) and poly(I)-poly(C) (see Sect. 3.3). The intermacromolecular complex formation of synthetic polymers is controlled by many factors such as interaction forces, solvent, ionic strength, temperature, pH, etc. Moreover, the cooperative and concerted interactions of each active site play an important role in complex formation. These phenomena suggest that the selective intermacromolecular complexation can be realized under suitable conditions. 

This is caused by the cooperative effect arising from the change in the macromolecular form during complex formation. The cooperative interactions in the system macroligand-MX in solution also produce a change in the charge of the chain. 

Attaining the nondraining limit is usually accomplished by using high-molecular-weight polymers. The cooperative effect of the large number of subchains entrains all the solvent within the coil. Measurements of the macromolecular friction coefficient for a random coil are then interpreted in... 

Indeed, the existence of purely conformational optical activity is not a unique macromolecular requisite, being well known in low molecular weight atro-pisomerism. However, in polymers it assumes a very specific characteristic connected with the occurrence of cooperative effects which allow transmittance of molecular asymmetry along the chain to very long distances [3]. 

Even in macromolecular systems, the secondary binding forces mentioned up to here act in the same manner as in the case of low molecular weight compounds, if one considers secondary bonds individually. However, for all practical purposes, they act at the same time in an extremely complicated manner, concertedly and never separately. Moreover, each active site of the molecule interacts cooperatively with other sites because of the neighboring effect (for details see Sect. 4). Therefore, in intra- and intermacromolecular interaction systems, it is quite difficult to investigate separately the effective secondary binding forces, and it should be noted that the total interaction force might not be the sum of the individual binding forces. 

Figure 21 illustrates the dependence of the reduced viscosity on PEG chain length in the alternating copolymer MAn/MAA-PEG systems. The curve resembles that for the PMAA-PEG system For PEG with molecular weights lower than 3000, the high values of the reduced viscosity with an anomalous concentration dependence, due to the polyelectrolyte effect, are observed. Then, in a very narrow interval of the PEG molecular weight, a sharp decrease of the reduced viscosity down to very low and constant values occurs. The sigmoid character of the curve indicates the cooperative character of interaction of the macromolecular components. 

Cl is a Ca -dependent macromolecular complex having a sedimentation rate of 16 S (Ziccardi and Cooper, 1977). It can be dissociated into three subcomponents, Clq, Cls, and Clr, by chelation of Ca with EDTA (Lepow et al., 1963). Recently Clt was proposed as the fourth subcomponent of Cl (Assimeh and Painter, 1975), but now there is evidence which directly rules out any effect of Clt on the Cl macromolecule. Apparently Clt copurifies with Cl when affinity chromatography on a Sepharose bed is used (Gigli et al., 1976 Ziccardi and Cooper, 1977 Pepys et al., 1977). 

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