SELF-ASSEMBLY OF BIOPOLYMERIC STRUCTURES BELOW THE THRESHOLD OF RANDOM CROSS-LINK PERCOLATION

Self-assembly of extended structures via cross-linking of individual b iomolecules often occurs in solutions at concentrations well below the estimated threshold for random cross-link percolation. This requires solute-solute correlations. Here we study bovine serum albumin. Its un folding causes the appearance of an instability region of the set, not observed for native bovine serum albumin. As a consequence, spinodal demixing of the sol is observed. The thermodynamic phase transition co rresponding to this demixing is the determinative symmetry-breaking st ep allowing the subsequent occurrence of (correlated) cross-linking an d its progress up to the topological phase transition of gelation. The occurrence of this sequence is of marked interest to theories of spon taneous symmetry-breaking leading to morphogenesis, as well as to perc olation theories. The present results extend the validity of conclusio ns drawn from our previous studies of other systems, by showing in one single case, system features that we have hitherto observed separatel y in different systems. Time-resolved experimental observations of the present type also bring kinetic and diffusional processes and solute- solvent interactions into the picture of cross-link percolation.