Jean-Pierre Busnel

Study of junction zones in gelatin gels through selective enzymatic digestion

Abstract A full topological description of gelatin gels requires knowledge of the number, size and functionality of the helical segments, which act as effective junction zones. Selective enzymatic attack on renatured gelatin has allowed us to isolate the helical segments by size exclusion chromatography. For sharp fractions, the size of the helical segments is almost independent of initial molecular weight and is about 100–200 amino acid residues for each strand. This size does not depend very much on concentration, but increases slowly with renaturation time and with temperature. We believe that helical segments are always formed by the same process: in accordance with previous kinetic studies, the starting point would be a bimolecular nucleation. For such nucleation, two strands are necessarily antiparallel, and this can explain the limited length of the helices.

Study of the steric partition coefficient in size-exclusion chromatography by Monte Carlo simulation

Abstract Monte Carlo generation of polymer chains allows evaluation of the steric partition coefficient, K, for any pore shape and any chain flexibility. This in turn enables the chromatographic radius of macromolecules, Rc, to be defined as the radius of a sphere with the same K value and allows the ratio Rc/Rη to be studied. Rn is defined as the radius of the sphere with the same product [η]M, where M is the molar mass and [η] the intrinsic viscosity. Rc is shown to depend on the pore geometry. For a given pore geometry, Rc/Rη is not strictly independent of the flexibility and the relative thickness of the macromolecule. Experimentally, for flexible polymers, the so-called universal calibration is often found to work well. However, simulations show that the universal calibration is not strictly valid and deviations are expected in particular when the global flexibility of standard and sample are different.