Ma. Yousef et al., Confirmation of free solvent model assumptions in predicting the osmotic pressure of concentrated globular proteins, J COLL I SC, 243(2), 2001, pp. 321-325
Previously the osmotic pressure of the concentrated globular proteins immun
o-gamma -globulin, bovine serum albumin, hen egg lysozyme, and ovalbumin in
moderate-ionic-strength solutions was successfully modeled using a free so
lvent model (Yousef et al., J. Colloid Interface Sci. 197,108,1998; 207, 27
3,1998; AIChE J., 2001). This model considered the average solute-solvent a
nd microion-solute interactions, represented the hydrated macromolecule and
the cooperative interacting water and salts as a single species, and used
a mole fraction concentration variable. Although the model assumed no fitte
d parameters, the hydration number was regressed on due to its sensitivity
and compared with the 1 g H2O/g BSA estimate determined from (H2O)-O-17 mag
netic resonance studies of other globular proteins. The resulting average h
ydration numbers were in agreement with the reported estimates. These resul
ts suggest that solvent-solute interactions are dominant factors when analy
zing nonidealities associated with the osmotic pressure data of concentrate
d protein solutions in moderate-ionic-strength solutions. However, the cond
ition for the applicability of the free solvent model is that long-range in
teractions between hydrated macromolecules are screened to reduce solute-so
lute interaction. This condition requires a moderately high salt concentrat
ion. The objective of this study is to confirm this requirement for a succe
ssful model representation of the osmotic pressure of these protein solutio
ns at high concentrations. To accomplish this, studies of concentrated solu
tions of ovalbumin at low ionic strength 0.01 M at pH 7.0 were carried out
and modeled using the free solvent approach. The results showed that no rea
sonable free solvent model solution could be obtained. These results streng
then the argument that the free solvent model has a physically realizable r
epresentation for concentrated protein solutions in moderate salt concentra
tions. (C) 2001 Academic Press.