arXiv subjects

Sharon Berkowicz

Publications and source records attributed to Sharon Berkowicz.

7 recordsLinked to original sources

arXiv2026

Liquid-liquid phase separation precedes crystallization in supercooled water-glycerol solutions

Understanding the structural evolution of supercooled water-glycerol solutions is important for cryopreservation, yet distinguishing liquid-state transformations from ice crystallization remains challenging. Here, we investigate a deeply supercooled water-glycerol solution by X-ray photon correlation spectroscopy (XPCS) in ultra-small-angle X-ray scattering (USAXS) geometry, combined with wide-angle X-ray scattering (WAXS). This combination simultaneously captures the structural and dynamical evolution of the supercooled liquid upon quenching to cryogenic temperatures (172 K). We observe discontinuous changes in the liquid structure on molecular length scales and formation of microscale domains. The dynamics slow down during this stage and exhibit hyper-diffusive, ballistic-like relaxation. This transformation precedes ice crystallization, which we identify from the emergence of ice Bragg peaks in WAXS, allowing the two processes to be temporally separated. Phase-field (Cahn-Hilliard) simulations qualitatively reproduce the experimental observations and show that a spinodal-decomposition scenario is consistent with the measured scattering evolution. These findings are consistent with a liquid-liquid phase separation scenario preceding ice crystallization and provide a route to disentangle the two processes in supercooled aqueous systems.

cond-mat.soft↗

arXiv2025

Nanoscale Protein Diffusion in Supercooled Cryoprotectant Solutions

Vitrification during cryopreservation requires a quantitative understanding of protein transport in deeply supercooled cryoprotectant solutions, yet direct measurements at molecular length scales remain scarce. Here, we combine X-ray Photon Correlation Spectroscopy (XPCS) and small-angle X-ray scattering (SAXS) to investigate ferritin diffusion in glycerol-water mixtures from ambient conditions down to 210 K. The measured diffusion coefficients reveal that ferritin retains a higher mobility upon cooling than expected from hydrodynamic scaling based on measurements of larger silica reference tracers, with the difference emerging below approximately 230 K. A minimal fluctuating-friction model reproduces the observed relative enhancement in diffusion, illustrating how local variations in the effective friction can give rise to such behavior. These measurements provide direct experimental benchmarks for future theoretical and simulation studies aimed at understanding molecular transport in deeply supercooled liquids approaching the glass transition.

cond-mat.soft↗

arXiv2024

Supercritical density fluctuations and structural heterogeneity in supercooled water-glycerol microdroplets

Recent experiments and theoretical studies strongly indicate that water exhibits a liquid-liquid phase transition (LLPT) in the supercooled domain. An open question is how the LLPT of water can affect the properties of aqueous solutions. Here, we study the structural and thermodynamic properties of supercooled glycerol-water microdroplets at dilute conditions ($\chi_g=3.2~\%$ glycerol mole fraction). The combination of rapid evaporative cooling with ultrafast X-ray scattering allows us to outrun crystallization and gain access to the deeply supercooled regime down to $T=229.3$ K. We find that the density fluctuations of the glycerol-water solution or, equivalently, its isothermal compressibility, $\kappa_T$, increases upon cooling. This is confirmed by molecular dynamics simulations, which indicate that the presence of glycerol shifts the temperature of maximum $\kappa_T$ from $T=230$ K in pure water down to $T=223$ K in the solution. Our findings elucidate the interplay between the complex behavior of water, including its LLPT, and the properties of aqueous solutions at low temperatures, which can have practical consequences in cryogenic biological applications and cryopreservation techniques.

cond-mat.soft↗

arXiv2024

Coherent X-rays reveal anomalous molecular diffusion and cage effects in crowded protein solutions

Understanding protein motion within the cell is crucial for predicting reaction rates and macromolecular transport in the cytoplasm. A key question is how crowded environments affect protein dynamics through hydrodynamic and direct interactions at molecular length scales. Using megahertz X-ray Photon Correlation Spectroscopy (MHz-XPCS) at the European X-ray Free Electron Laser (EuXFEL), we investigate ferritin diffusion at microsecond time scales. Our results reveal anomalous diffusion, indicated by the non-exponential decay of the intensity autocorrelation function $g_2(q,t)$ at high concentrations. This behavior is consistent with the presence of cage-trapping in between the short- and long-time protein diffusion regimes. Modeling with the $\delta\gamma$-theory of hydrodynamically interacting colloidal spheres successfully reproduces the experimental data by including a scaling factor linked to the protein direct interactions. These findings offer new insights into the complex molecular motion in crowded protein solutions, with potential applications for optimizing ferritin-based drug delivery, where protein diffusion is the rate-limiting step.

cond-mat.soft↗

arXiv2023

Nanocrystallites Modulate Intermolecular Interactions in Cryoprotected Protein Solutions

Studying protein interactions at low temperatures has important implications for optimizing cryostorage processes of biological tissue, food, and protein-based drugs. One of the major challenges is related to the formation of ice nanocrystals which can occur even in the presence of cryoprotectants and can lead to protein denaturation. Here, using a combination of small- and wide-angle X-ray scattering (SAXS and WAXS), we investigate the structural evolution of concentrated Lysozyme solutions in a cryoprotected glycerol-water mixture upon cooling from room temperature (T=300 K) down to cryogenic temperatures (T=195 K). Upon cooling, we observe a transition near the melting temperature of the solution (T~245 K), which manifests both in the temperature dependence of the scattering intensity peak position reflecting protein-protein length scales (SAXS) and the interatomic distances within the solvent (WAXS). Upon thermal cycling, a hysteresis is observed in the scattering intensity, which is attributed to the formation of nanocrystallites in the order of 10 nm. The experimental data is well described by the two-Yukawa model, which indicates temperature-dependent changes in the short-range attraction of the protein-protein interaction potential. Our results demonstrate that the nanocrystal growth yields effectively stronger protein-protein attraction and influences the protein pair distribution function beyond the first coordination shell.

cond-mat.soft↗

arXiv2023

Coherent X-ray Scattering Reveals Nanoscale Fluctuations in Hydrated Proteins

Hydrated proteins undergo a transition in the deeply supercooled regime, which is attributed to rapid changes in hydration water and protein structural dynamics. Here, we investigate the nanoscale stress relaxation in hydrated lysozyme proteins stimulated and probed by X-ray Photon Correlation Spectroscopy (XPCS). This approach allows us to access the nanoscale dynamic response in the deeply supercooled regime (T = 180 K) which is typically not accessible through equilibrium methods. The relaxation time constants exhibit Arrhenius temperature dependence upon cooling with a minimum in the Kohlrausch-Williams-Watts exponent at T = 227 K. The observed minimum is attributed to an increase in dynamical heterogeneity, which coincides with enhanced fluctuations observed in the two-time correlation functions and a maximum in the dynamic susceptibility quantified by the normalised variance $\chi_T$. Our study provides new insights into X-ray stimulated stress relaxation and the underlying mechanisms behind spatio-temporal fluctuations in biological granular materials.

cond-mat.soft↗

arXiv2022

Resolving molecular diffusion and aggregation of antibody proteins with megahertz X-ray free-electron laser pulses

X-ray free-electron lasers (XFELs) with megahertz repetition rate can provide novel insights into structural dynamics of biological macromolecule solutions. However, very high dose rates can lead to beam-induced dynamics and structural changes due to radiation damage. Here, we probe the dynamics of dense antibody protein (Ig-PEG) solutions using megahertz X-ray photon correlation spectroscopy (MHz-XPCS) at the European XFEL. By varying the total dose and dose rate, we identify a regime for measuring the motion of proteins in their first coordination shell, quantify XFEL-induced effects such as driven motion, and map out the extent of agglomeration dynamics. The results indicate that for average dose rates below $1.06\,\mathrm{kGy}\mathrm{\mu s}^{-1}$ in a time window up to $10\,\mathrm{\mu s}$, it is possible to capture the protein dynamics before the onset of beam induced aggregation. We refer to this approach as correlation before aggregation and demonstrate that MHz-XPCS bridges an important spatio-temporal gap in measurement techniques for biological samples.

physics.bio-ph↗