Effect of gelatin molecular charge heterogeneity on formation of intermolecular complexes and coacervation transition

We investigate the molecular charge heterogeneity of gelatin molecules at three different pHs: isoelectric pH = 5 (pI), and at pHs = p1 +/- 1 by measuring the zeta potential distributions. Its effect on the formation of soluble intermolecular complexes induced by the presence of a nonsolvent, ethanol, was explored. The charge distributions were found to be symmetric at pH = 5, where the onset of binding, and formation of soluble complexes were observed to be facilitated by the presence of a small net charge (close to zero) with the molecules exhibiting polyampholyte (PA) behavior. These distributions turned asymmetric at pH 6, yet complex formation and coacervation occurred. On the other hand, for pH 4 samples, these distributions were found to be strongly asymmetric with the molecules possessing very high net positive charge, such a system did not yield coacervation. The PA to polyelectrolyte transition and its repercussion on coacervation has been discussed in the light of the experimental results obtained from electrophoresis, turbidimetry, atomic force microscopy, and nanoindentation studies. (c) 2007 Wiley Periodicals, Inc