The accuracy of liquid-liquid phase transition temperatures determined from semiautomated light scattering measurements

Off-Critical Wetting Layer Divergence at the Liquid / Vapor Interface of Binary Liquid Mixtures

Surface wetting phenomena impact chemistry, physics, biology, and engineering. The wetting behaviors of partially-miscible binary liquid systems are especially complex. Here we report evidence of universal behavior in the divergence of wetting layer growth at liquid-vapor interfaces of the cyclohexane + aniline, hexane + o-toluidine, and methanol + carbon disulfide systems. Layer growth on the micron scale was followed using visible light scattering from stirred samples. Layer thicknesses diverged with decreasing temperature when coexistence was approached from the one-phase region, but only for solutions richer in the higher density / higher surface tension component. The onset of divergence was <1 K above the bulk coexistence temperature; nearer the critical composition, the onset temperature was the critical temperature itself. All three systems showed identical divergent wetting properties after variable normalization. In contrast, no divergent wetting layer formation was seen in the benzene + 1,2-propanediol or water + phenol systems. The mathematical sign of the Hamaker constant correlates with the contrasting behaviors. Collectively, these results have implications for theoretical descriptions of adsorption layer growth and crossover behavior, for measurements of complete wetting temperatures, and for practical applications.

Liquid-Liquid Phase Separation by Intrinsically Disordered Protein Regions of Viruses: Roles in Viral Life Cycle and Control of Virus-Host Interactions

Intrinsically disordered proteins (IDPs) are unable to adopt a unique 3D structure under physiological conditions and thus exist as highly dynamic conformational ensembles. IDPs are ubiquitous and widely spread in the protein realm. In the last decade, compelling experimental evidence has been gathered, pointing to the ability of IDPs and intrinsically disordered regions (IDRs) to undergo liquid-liquid phase separation (LLPS), a phenomenon driving the formation of membrane-less organelles (MLOs). These biological condensates play a critical role in the spatio-temporal organization of the cell, where they exert a multitude of key biological functions, ranging from transcriptional regulation and silencing to control of signal transduction networks. After introducing IDPs and LLPS, we herein survey available data on LLPS by IDPs/IDRs of viral origin and discuss their functional implications. We distinguish LLPS associated with viral replication and trafficking of viral components, from the LLPS-mediated interference of viruses with host cell functions. We discuss emerging evidence on the ability of plant virus proteins to interfere with the regulation of MLOs of the host and propose that bacteriophages can interfere with bacterial LLPS, as well. We conclude by discussing how LLPS could be targeted to treat phase separation-associated diseases, including viral infections.

The effects of cosolutes and crowding on the kinetics of protein condensate formation based on liquid-liquid phase separation: a pressure-jump relaxation study

Biomolecular assembly processes based on liquid-liquid phase separation (LLPS) are ubiquitous in the biological cell. To fully understand the role of LLPS in biological self-assembly, it is necessary to characterize also their kinetics of formation and dissolution. Here, we introduce the pressure-jump relaxation technique in concert with UV/Vis and FTIR spectroscopy as well as light microscopy to characterize the evolution of LLPS formation and dissolution in a time-dependent manner. As a model system undergoing LLPS we used the globular eye-lens protein γD-crystallin. As cosolutes and macromolecular crowding are known to affect the stability and dynamics of biomolecular condensates in cellulo, we extended our kinetic study by addressing also the impact of urea, the deep-sea osmolyte trimethylamine-N-oxide (TMAO) and a crowding agent on the transformation kinetics of the LLPS system. As a prerequisite for the kinetic studies, the phase diagram of γD-crystallin at the different solution conditions also had to be determined. The formation of the droplet phase was found to be a very rapid process and can be switched on and off on the 1-4 s timescale. Theoretical treatment using the Johnson-Mehl-Avrami-Kolmogorov model indicates that the LLPS proceeds via a diffusion-limited nucleation and growth mechanism at subcritical protein concentrations, a scenario which is also expected to prevail within biologically relevant crowded systems. Compared to the marked effect the cosolutes take on the stability of the LLPS region, their effect at biologically relevant concentrations on the phase transformation kinetics is very small, which might be a particular advantage in the cellular context, as a fast switching capability of the transition should not be compromised by the presence of cellular cosolutes.

Determination of liquid-liquid critical point composition using 90^{∘} laser light scattering

Despite over a century of characterization efforts, liquid-liquid critical point compositions are difficult to identify with good accuracy. Reported values vary up to 10% for even well-studied systems. Here, a technique is presented for high-precision determination of the critical composition of a partially miscible binary liquid system. Ninety-degree laser light-scattering intensities from single-phase samples are analyzed using an equation derived from nonclassical power laws and the pseudospinodal approximation. Results are reported for four liquid-liquid systems (aniline + hexane, isobutyric acid + water, methanol + cyclohexane, and methanol + carbon disulfide). Compared to other methods, the 90^{∘} light-scattering approach has a strong dependence on composition near the critical point, is less affected by temperature fluctuations, and is insensitive to the presence of trace impurities in the samples. Critical compositions found with 90^{∘} light scattering are precise to the parts-per-thousand level and show long-term reproducibility.

A study of the conformational changes of β-lactoglobulin in the vicinity of critical point of binary mixed solvents

Most of the protein is entangled in the upper IB rich phase.

Transmission Measurements as Tool to Study Phase Transitions of Liquid Mixtures

We present a quantitative method to determine the phase transition temperatures between one-phase and two-phase regions of multi-component liquid mixtures via temperature-dependent transmission measurements with an UV/Vis spectrometer. The method is based on the fact that multi-phase samples are turbid, while one-phase samples are transparent. We describe the method in detail and discuss the choice of the experimental parameters (wavelength, sample layer thickness), a suitable temperature program as well as the data analysis. We prove the validity of our method by measuring the phase diagrams of two model systems, namely a liquid and a gelled microemulsion. The results are in good agreement with those obtained with the conventional visual method used for phase studies.