Conformational transitions hydrophobic polyelectrolytes

CONCLUSIONS This Study shows that fluorescence probing techniques are useful and powerful tools for investigation of conformational transitions of polyelectrolytes as induced by cationic surfactants, pH or other means. Studies on the interaction of cationic probes with polyelectrolytes provide useful information on the intermediates that lie between A states and B states. It is concluded that the conformational transition induced by pH is a progressive process over several pH units. Studies on the interaction of cationic surfactants with PMA at pH 8 show that the aggregates formed are large loose structures, while the interior of the aggregate has a hydrophobicity that is similar to that of a micelle. 

External polymers can also be employed to control leakage of entrapped solutes. Adsorption of the hydrophobic polyelectrolyte poly(2-ethylacrylic acid) on phosphatidylcholine membranes causes the disruption of vesicle membranes (Figure 4.32) with small changes in pH (7.4—>6.5). The surface polyelectrolyte undergoes a well-defined conformational transition from an... 

Photophysical studies on a conformational transition of PMA induced by cationic surfactants have been reported (7). The stretched PMA chain at pH 8 collapses on addition of cationic surfactants that is, the hydrophobic interactions between the cationic surfactants that are bonded to the PMA chain lead to refolding of the polymer chain, and thus provide a hydrophobic site for fluorescence probes at pH 8. The cationic polyelectrolyte poly(4-vinylpyridine) quatemized with n-dodecyl bromide (8 i0) or hexadecyl bromide (11) are also examples of hydrophobically modified polyelectrolytes. 

On the other hand, copolymers of maleic acid with various vinyl monomers had been investigated in studying the influence of local charge density on polyelectrolyte properties, and some alternating copolymers of maleic acid with n-alkyl vinyl ethers were found to undergo the conformational transitions from the compact form to the extended coil upon ionization of primary carboxyl groups in maleic acid. " The hydrophobic interaction seems to be responsible for stabilization of the compact form. Viscometric, potentiometric and calorimetric measurements have been used to study the transition mechanisms. 

Further studies on H- and C-NMR seem to be important to analyze the compact conformation and conformational transition of the hydrophobic polyelectrolyte. 

A similar behaviour is also found here for hydrophilic-hydrophobic copolymers obtained by partial hydrolysis of a polyacrylamide (COP,) [13]. By adjusting the percentage of hydrolysis, the hydrophobic character of chains can be varied and a behaviour from a normal polyelectrolyte to an abnormal one can thus be observed. As illustrated in Figure 3, the compact conformation stable at low a is dependent on the relative proportion of statistically distributed hydrophobic and hydrophilic sequences [18]. The transition region is shifted to higher values of a as the hydrophobic character of the chain increases. 

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