Complex Coacervate Core Micelles Containing Poly(vinyl alcohol) Inhibit Ice Recrystallization.

Complex coacervate core micelles (C3Ms) form upon complexation of oppositely charged copolymers. These co-assembled structures are widely investigated as promising building blocks for encapsulation, nanoparticle synthesis, multimodal imaging, and coating technology. Here, the impact on ice growth is investigated of C3Ms containing poly(vinyl alcohol), PVA, which is well known for its high ice recrystallization inhibition (IRI) activity. The PVA-based C3Ms are prepared upon co-assembly of poly(4-vinyl-N-methyl-pyridinium iodide) and poly(vinyl alcohol)-block-poly(acrylic acid). Their formation conditions, size, and performance as ice recrystallization inhibitors are studied. It is found that the C3Ms exhibit IRI activity at PVA monomer concentrations as low as 1 × 10-3 m. The IRI efficacy of PVA-C3Ms is similar to that of linear PVA and PVA graft polymers, underlining the influence of vinyl alcohol monomer concentration rather than polymer architecture.

Monitoring Protein Capsid Assembly with a Conjugated Polymer Strain Sensor.

Semiconducting polymers owe their optoelectronic properties to the delocalized electronic structure along their conjugated backbone. Their spectral features are therefore uniquely sensitive to the conformation of the polymer, where mechanical stretching of the chain leads to distinct vibronic shifts. Here we demonstrate how the optomechanical response of conjugated polyelectrolytes can be used to detect their encapsulation in a protein capsid. Coating of the sensor polymers by recombinant coat proteins induces their stretching due to steric hindrance between the proteins. The resulting mechanical planarizations lead to pronounced shifts in the vibronic spectra, from which the process of capsid formation can be directly quantified. These results show how the coupling between vibronic states and mechanical stresses inherent to conjugated polymers can be used to noninvasively measure strains at the nanoscale.

Equivalent pathways in melting and gelation of well-defined biopolymer networks.

We use multiple particle tracking microrheology to study the melting and gelation behavior of well-defined collagen-inspired designer biopolymers expressed by the transgenic yeast P. Pastoris. The system consists of a hydrophilic random coil-like middle block and collagen-like end block. Upon cooling, the end blocks assemble into well-defined transient nodes with exclusively 3-fold functionality. We apply the method of time-cure superposition of the mean-square displacement of tracer beads embedded in the biopolymer matrix to study the kinetics and thermodynamics of approaching the gel point from both the liquid and the solid side. The melting point, gel point, and critical relaxation exponents are determined from the shift factors of the mean-square displacement and we discuss the use of dynamic scaling exponents to correctly determine the critical transition. Critical relaxation exponents obtained for different concentrations in both systems are compared with the currently existing dynamic models in literature. In our study, we find that, while the time scales of gelation and melting are different by orders of magnitude, and show inverse dependence on concentration, that the pathways followed are completely equivalent.