The dynamics of the calcium-induced chain-chain association in the polyuronate systems

The calcium-induced formation of strong, hydrophilic gels is the important feature of polyuronates, connected with most of their practical applications. The insight into the molecular details of gelling process dynamics is hardly feasible for both experimental and theoretical methods. Here, the application of the transition path sampling method for studying this problem is reported; the focus was on the poly(α-L-guluronate) systems, treated as the representative for all polyuronate-containing systems. The results allowed for identifying several distinct local minima of the free energy lying on the transition paths and visited by the system during the process of chain-chain association. These minima usually correspond to the intermediate structures in which the water molecules bridge calcium ion and carboxyl groups. This work emphasizes the importance of water and provides more complete understanding of the calcium binding by the polyuronate chains.