Quantitative analysis of aggregation in dilute solutions of effectively rigid biomacromolecules via the combination of oscillatory flow birefringence and viscoelasticity measurements: example study of aggregation of bovine fibrinogen in aqueous glycerol,

Oscillatory flow birefringence (OFB) properties have been measured for dilute solutions of bovine fibrinogen in 65–68% aqueous glycerol with the Miller–Schrag Thin Fluid Layer (TFL) apparatus employing either titanium or stainless steel surfaces in contact with the solutions. The shearing frequency range was 1 to 2500 Hz, the concentrations ranged from 4 to 8 mg/ml, and measurement temperatures were 9.9, 10.0, and 15.8 °C. The data showed evidence of significant amounts of aggregation that apparently is caused by the presence of glycerol; contributions from the various aggregates were readily detected since the staggered half-overlap aggregation in this system results in substantial differences in the rotational relaxation times of the various effectively rigid aggregates. The combination of oscillatory flow birefringence and viscoelasticity (VE) data provided sensitive and precise characterization of aggregation in these example systems; all aggregates exhibited the expected positive optical anisotropy. The length of unaggregated fibrinogen in solution was found to be that obtained via electron microscopy. Addition of guanidine hydrochloride to hopefully reduce aggregation did so but also resulted in formation of a very large (2800 to 3500 Å), apparently nearly monodisperse, negatively birefringent aggregate, suggesting that this new species might be formed by lateral aggregation.