Concentration Dependence of Elastic and Viscoelastic Properties of
Aqueous Solutions of Ficoll and Bovine Serum Albumin by Brillouin Light
Scattering Spectroscopy
The cellular environment is crowded with macromolecules of different shapes
and sizes. The effect of this macromolecular crowding has been studied in a
variety of synthetic crowding environments: two popular examples are the
compact colloid-like Ficoll macromolecule, and the globular protein bovine
serum albumin (BSA). Recent studies have indicated a significant component of
bound or surface-associated water in these crowders reduces the available free
volume. In this work, Brillouin light scattering experiments were performed on
aqueous solutions of Ficoll 70 and Ficoll 400 with concentrations ranging from
1 wt% to 35 wt% and BSA with concentrations of 1 wt% to 27 wt%. From the
dependence of spectral peak parameters on polymer concentration, we determined
fundamental solution properties: hypersound velocity, adiabatic bulk modulus
and compressibility, apparent viscosity, and hypersound attenuation. Existing
theory that ignores intermolecular interactions can only capture the observed
linear trends in the frequency shift up to a threshold concentration, beyond
which a quadratic term accounting for intermolecular interactions is necessary.
This likely indicates a transition from the dilute to semi-dilute regime. In
the Ficoll solutions (but not BSA) we see evidence for a central mode, with a
characteristic relaxation time of 20 ps, that we attribute to exchange of the
bound water.Comment: 10 pages, 4 figures, 4 table