Coil to extended coil transition in polygalacturonic acid: Conductometric titration and Monte Carlo simulations

The conformational transition from coil to extended coil for polygalacturon ic acid has been studied by conductometric titrations and Monte Carlo simul ations. The results of conductometric titrations at different polymer conce ntrations have been analyzed using the model proposed by Manning,(1) which describes the conductivity of polyelectrolitic solutions. This experimental approach provides the transport factor and the average distance between ch arged groups at different degrees of ionization (alpha). The mean distances between charged groups have been compared with the values obtained by Mont e Carlo simulations. In these simulations the polymer chain is modeled as a self-avoiding random walk in a cubic lattice. The monomers interact throug h the unscreened Coulombic potential. The ratio between the end-to-end dist ance and the number of ionized beads provides the average distance between charged monomers. The experimental and theoretical values are in good agree ment for the whole range of ionization degrees accessed by conductometric t itrations. These results suggest that the electrostatic interactions seem t o be the major contribution for the coil to extended coil conformational ch ange. The small deviations for alpha less than or equal to 0.5 suggests tha t the stiffness of the chain, associated with local interactions, becomes i ncreasingly significant as the fraction of charged groups is decreased.