32 research outputs found
Calorimetric study of water's two glass transitions in the presence of LiCl
A DSC study of dilute glassy LiCl aqueous solutions in the water-dominated regime provides direct evidence of a glass-to-liquid transition in expanded high density amorphous (eHDA)-type solutions. Similarly, low density amorphous ice (LDA) exhibits a glass transition prior to crystallization to ice Ic. Both glass transition temperatures are independent of the salt concentration, whereas the magnitude of the heat capacity increase differs. By contrast to pure water, the glass transition endpoint for LDA can be accessed in LiCl aqueous solutions above 0.01 mole fraction. Furthermore, we also reveal the endpoint for HDA's glass transition, solving the question on the width of both glass transitions. This suggests that both equilibrated HDL and LDL can be accessed in dilute LiCl solutions, supporting the liquid-liquid transition scenario to understand water's anomalies.Fil: Ruiz, Guadalupe N.. Universidad de Innsbruck; Austria. Universidad PolitĂ©cnica de Catalunya; EspañaFil: Amann Winkel, Katrin. AlbaNova University Center; Suecia. Universidad de Innsbruck; AustriaFil: Bove, Livia E.. UniversitĂ© Pierre et Marie Curie; FranciaFil: Corti, Horacio Roberto. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. ComisiĂłn Nacional de EnergĂa AtĂłmica; Argentina. Universidad de Buenos Aires; ArgentinaFil: Loerting, Thomas. Universidad de Innsbruck; Austri
Response to Comment on âMaxima in the thermodynamic response and correlation functions of deeply supercooled waterâ
Caupin et al. have raised several issues regarding our recent paper on maxima in thermodynamic response and correlation functions in deeply supercooled water. We show that these issues can be addressed without affecting the conclusion of the paper.113Ysciescopu
Melting Domain Size and Recrystallization Dynamics of Ice Revealed by Time-Resolved X-ray Scattering
The phase transition between water and ice is ubiquitous and one of the most
important phenomena in nature. Here, we performed time-resolved x-ray
scattering experiments capturing the melting and recrystallization dynamics of
ice. The ultrafast heating of ice I is induced by an IR laser pulse and probed
with an intense x-ray pulse, which provided us with direct structural
information on different length scales. From the wide-angle x-ray scattering
(WAXS) patterns, the molten fraction, as well as the corresponding temperature
at each delay, were determined. The small-angle x-ray scattering (SAXS)
patterns, together with the information extracted from the WAXS analysis,
provided the time-dependent change of the size and the number of the liquid
domains. The results show partial melting (~13 %) and superheating of ice
occurring at around 20 ns. After 100 ns, the average size of the liquid domains
grows from about 2.5 nm to 4.5 nm by the coalescence of approximately six
adjacent domains. Subsequently, we capture the recrystallization of the liquid
domains, which occurs on microsecond timescales due to the cooling by heat
dissipation and results to a decrease of the average liquid domain size
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
. Our study provides new insights into X-ray stimulated stress
relaxation and the underlying mechanisms behind spatio-temporal fluctuations in
biological granular materials
Electron Beam-Induced Transformation in High-Density Amorphous Ices
Amorphous ice is commonly used as a noncrystalline matrix for protecting sensitive biological samples in cryogenic electron microscopy (cryo-EM). The amorphization process of water is complex, and at least two amorphous states of different densities are known to exist, high- and low-density amorphous ices (HDA and LDA). These forms are considered to be the counterparts of two distinct liquid states, namely, high- and low-density liquid water. Herein, we investigate the HDA to LDA transition using electron diffraction and cryo-EM. The observed phase transition is induced by the impact of electrons, and we discuss two different mechanisms, namely, local heating and beam-induced motion of water molecules. The temperature increase is estimated by comparison with X-ray scattering experiments on identically prepared samples. Our results suggest that HDA, under the conditions used in our cryo-EM measurements, is locally heated above its glass-transition temperature
Verrucomicrobia in situ abundance and water chemistry in a humic lake during the year 2000
Members of the highly diverse bacterial phylum Verrucomicrobia are globally distributed in various terrestrial and aquatic habitats. They are key players in soils, but little is known about their role in aquatic systems. Thus, we applied newly designed 16S rRNA-targeted probe set for the identification of Verrucomicrobia and of clades within this phylum to a study concerning the seasonal abundance of Verrucomicrobia in waters of the humic lake GroĂe Fuchskuhle (Germany) by catalyzed reporter deposition fluorescence in situ hybridization. The Lake GroĂe Fuchskuhle is located in the large Mecklenburg-Brandenburg lake district near Berlin (53°10'N, 13°02'E). The lake was artificially divided into four basins (northwest, northeast, southwest, and southeast). We chose the two most contrasting basins, the acidotrophic humic southwestern (SW) basin with a high influx of allochthonous dissolved organic carbon (DOC) and the more mesotrophic northeastern (NE) basin, to study abundance and seasonality of Verrucomicrobia. Lake water was collected from depths of 0.5 m (oxic) and 4.5 m (seasonally anoxic) approximately trimonthly in 2000 (March, June, September and December). The lake hosted diverse Verrucomicrobia clades in all seasons. Either Spartobacteria (up to 19%) or Opitutus spp. (up to 7%) dominated the communities, whereas Prosthecobacter spp. were omnipresent in low numbers (<1%). Verrucomicrobial abundance and community composition varied between the seasons, and between more and less humic basins, but were rather stable in oxic and seasonally anoxic waters
Temperature dependent anomalous fluctuations in water: shift of â1âkbar between experiment and classical force field simulations
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 issues is related to the formation of ice nanocrystals, which can occur even in the presence of cryoprotectants and can lead to protein denaturation. The presence of ice nanocrystals in protein solutions poses several challenges since, contrary to microscopic ice crystals, they can be difficult to resolve and can complicate the interpretation of experimental data. 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 glycerolâwater mixture 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 â 245 K), which manifests both in the temperature dependence of the scattering intensity peak position reflecting proteinâprotein 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 are well described by the two-Yukawa model, which indicates temperature-dependent changes in the short-range attraction of the proteinâprotein interaction potential. Our results demonstrate that the nanocrystal growth yields effectively stronger proteinâprotein attraction and influences the protein pair distribution function beyond the first coordination shell