Experimental Evidence for a Cluster Glass Transition in Concentrated Lysozyme Solutions

Abstract

Lysozyme is known to form equilibrium clusters at pH ≈ 7.8 and at low ionic strength as a result of a mixed potential. While this cluster formation and the related dynamic and static structure factors have been extensively investigated, its consequences on the macroscopic dynamic behavior expressed by the zero shear viscosity η0 remain controversial. Here we present results from a systematic investigation of η0 using two complementary passive microrheology techniques, dynamic light scattering based tracer microrheology, and multiple particle tracking using confocal microscopy. The combination of these techniques with a simple but effective evaporation approach allows for reaching concentrations close to and above the arrest transition in a controlled and gentle way. We find a strong increase of η0 with increasing volume fraction ϕ with an apparent divergence at ϕ ≈ 0.35, and unambiguously demonstrate that this is due to the existence of an arrest transition where a cluster glass forms. These findings demonstrate the power of tracer microrheology to investigate complex fluids, where weak temporary bonds and limited sample volumes make measurements with classical rheology challenging.

Effect of aggregation on adsorption phenomena

“…Based on our results, one can expect very nontrivial dynamics of formation of ordered patterns, as has been already observed in Ref. [14,28] for the SALR systems in bulk.…”

Potential and limits of a colloid approach to protein solutions

“…25,[40][41][42] Particularly interesting in this context is the fact that such clusters were found to undergo an arrest transition from a cluster fluid to a cluster glass that occurs at a significantly lower volume fraction when compared to the hard sphere glass at f g E 0.58. 41,60,61 Phase behavior and the occurrence of dynamical arrest upon an increase in concentration is indeed of prime importance in protein solutions in a wide range of areas, and the contents of Fig. 1 will thus reappear again below.…”

“…25 These charged clusters increase in size with increasing protein concentration and form a cluster glass. 60,61 Due to the relatively open structure and the long-range repulsion between the clusters, the corresponding arrest transition occurs already at volume fractions as low as f g E 0.28. 60 Increasing the temperature reduces the cluster growth slightly, and thus also shifts the arrest transition to somewhat larger volume fractions.…”

Mesoscopic theory for systems with competing interactions near a confining wall

“…We Fourier-transformV I (k , k ⊥ ) given by (20) back to the real space in the direction perpendicular to the surface z = 0, introduce the operatorV I (k , i ∂ ∂z ) bŷ…”

“…In the consistent approximation, we truncate the expansion ofV I (k , k ⊥ ) (see (20)) at the lowest-order term, and obtainV…”