Low Hydration Levels Research Articles

Enhanced Chemical Stability of Tetramethylammonium Head Groups via Deep Eutectic Solvent: A Computational Study.

The chemical stability of tetramethylammonium (TMA) head groups, both with and without the presence of a choline chloride and ethylene glycol-based deep eutectic solvent (DES), was studied using Density Functional Theory (DFT) calculations and ab initio Molecular Dynamics (MD) simulations. DFT calculations of transition state energetics (ΔEreaction, ΔGreaction, ΔEactivation, and ΔGactivation) for key degradation mechanisms, ylide formation (YF) and nucleophilic substitution (SN2), suggested that the presence of DES enhances the stability of the TMA head groups compared to systems without DES. Ab initio MD simulations across hydration levels (HLs) 1 to 5 indicated that without DES, YF dominates at lower HLs, while SN2 does not occur. In contrast, both mechanisms are suppressed in the presence of DES. Temperature also plays a role: without DES, YF dominates at 298 K, while SN2 becomes prominent at 320 K and 350 K. With DES, both degradation mechanisms are inhibited. These findings suggest DES could improve the chemical stability of TMA head groups in anion exchange membranes.

Stratum corneum hydration levels are negatively correlated with HbA1c levels in the elderly Chinese.

Highlights Stratum corneum hydration levels are negatively correlated with HbA1c levels and positively correlated with skin surface pH. Individuals with type 2 diabetes display lower levels of stratum corneum hydration. Because low stratum corneum hydration levels can increase circulating levels of proinflammatory cytokines, which are linked to the pathogenesis of type 2 diabetes, improvement in stratum corneum hydration can be an alternative approach in the management of type 2 diabetes.

On the role of water in regulating the mechanics of collagen fibers

The mechanical properties of collagen fiber–based materials have garnered considerable attention owing to their application in various hydration environments. Herein, we conducted a comprehensive investigation on the mediatory role of water in the mechanical properties and structure of collagen fibers. Lower hydration levels are conducive to the mechanical strength, particularly the tensile and tear properties, and reduce the softness of collagen fibers as well as the D-period and the lateral spacing between collagen molecules. Atomic force microscopy measurements indicate that lower hydration levels also enhance the roughness, adhesion force and lateral forces between collagen fibers. Theoretical calculations further reveal that the hydration level regulates weaker components of water-mediated interactions, such as electrostatic and van der Waals forces, which dominate the resistance against mechanical shock. Our findings provide valuable insights into the role of water in regulating the mechanical behaviour of collagen fibers, thereby contributing to the development of novel high-performance collagen fiber materials.

Structural build-up of cement pastes - Underlying mechanisms considering the particle packing, colloidal interactions and hydration kinetics

This study aims to investigate the decisive mechanisms of structural build-up of cement pastes. The structural build-up can be divided into three stages, with distinct developments in particle packing, colloidal interactions, and CSH bridges at each stage. Our model framework demonstrates that the first stage of structural build-up is influenced by heightened colloidal interactions and enhanced particle packing. The second stage is propelled by the strengthening of CSH bridges, while the third stage involves reinforced CSH bridges and increased particle packing. It should be noted that the impact of particle packing may be limited at low hydration levels. Upon examination, the physical-based structural build-up rates (Athix,f, ACA$H and ACSH) are identified as the results of enhanced colloidal interactions, increased particle packing and augmented CSH bridges, respectively. These parameters are validated as consequences of the initial particle packing parameter and rate factors, which denote the increase rate of van der Waals forces, the hydration rate at the beginning of hydration, and in the subsequent second and third stages.

Characteristics of and foundation application among Chinese females with sensitive skin.

We conducted a study on women with sensitive skin of various skin tones to analyse their skin characteristics and preferences for foundation shades. Volunteers were categorized based on their individual typological angle, and their preferences were assessed using self-perception and software-based mass aesthetic assessment. The Baumann Questionnaire is a valuable tool for identifying patients with sensitive skin and gaining a comprehensive understanding of their skin sensitivity. The skin characteristics of two groups were compared using a more suitable classification method. Individuals diagnosed with sensitive skin typically have skin tones classified as Types I, II and III, with Type I being the most common in sensitive skin cases. The sensitive group exhibited higher levels of transepidermal water loss, lighter skin tone, lower yellowness, increased glossiness, higher haemoglobin content, more acne, fewer blackheads, and fewer pores. Among them, Type I skin is characterized by lower elasticity, increased oiliness, higher hydration levels and fewer visible pores. Type II skin is characterized by lower hydration levels, higher oiliness and increased redness. Type III exhibits more pores, decreased oiliness and enhanced elasticity. Foundations No. 2 and No. 3 are fairer than foundations No. 1 and No. 4. In the self-assessment, Type I and Type II subjects preferred No. 3, while Type III subjects preferred No. 1 and No. 4 because they matched their skin tone. The results of the software evaluation showed that popular aesthetics preferred Type I and Type II to use No. 2, and Type III to use No. 2 and No. 3, as they resulted in a fairer complexion. Sensitive skin of different skin tone types confronts different skin problems. The findings also highlight the public's inclination towards lighter foundation shades, despite the common practice of selecting shades that harmonize with one's inherent skin tone.

1,2,3-Triazolium vs 1,2,4-triazolium quaternized poly (2, 6-dimethyl-1, 4-phenylene oxide) (PPO) anion exchange membranes (AEMs): A molecular dynamics (MD) study

This work investigates AEMs prepared from Poly (2, 6-dimethyl-1, 4-Phenylene Oxide) (PPO) quaternized with 1,2,3-triazolium and 1,2,4-triazolium, using molecular dynamics (MD) simulations to compare and evaluate their hydroxide transport and their stability against hydroxide degradation at different hydration levels. Hydroxide diffusivity (DOH) at λ = 6 is 0.69 × 10−10 m2/s, and 0.23 × 10−10 m2/s, at λ = 9 is 0.97 × 10−10 m2/s, and 0.67 × 10−10 m2/s and at λ = 12 is 1.85 × 10−10 m2/s, and 1.69 × 10−10 m2/s for 1,2,3-triPPO and 1,2,4-triPPO, respectively. At lower hydration levels (λ = 6 and λ = 9), 1,2,4-triPPO is stable against hydroxide degradation. However, at higher hydration levels, 1,2,3-triPPO has fewer hydroxide ions around the cationic group due to the hydroxide ions being solvated by the water, making it harder for the hydroxide ions to approach the cationic group at higher hydration levels, which means 1,2,3-triPPO is stable against hydroxide degradation.

An organic proton cage that is ultra-resistant to hydroxide-promoted degradation

Alkaline polymer membrane electrochemical energy conversion devices offer the prospect of using non-platinum group catalysts. However, their cationic functionalities are currently not sufficiently stable for vapor-phase applications, such as fuel cells. Herein, we report 1,6-diazabicyclo[4.4.4]tetradecan-1,6-ium (in-DBD), a cationic proton cage, that is orders of magnitude more resistant to hydroxide-promoted degradation than state-of-the-art organic cations under ultra-dry conditions and elevated temperature, and the first organic cation-hydroxide to persist at critically low hydration levels ( < 10% RH at 80 °C). This high stability against hydroxide-promoted degradation is due to the unique combination of endohedral protection and intra-bridgehead hydrogen bonding that prevents the removal of the inter-cavity proton and lowers the susceptibility to Hofmann elimination. We anticipate this discovery will facilitate a step-change in the advancement of materials and electrochemical devices utilizing anion-exchange membranes based on in-DBD that will enable stable operation under extreme alkaline conditions.

Ion and Water Dynamics in the Transition from Dry to Wet Conditions in Salt-Doped PEG.

The influence of the water content on ion and water transport mechanisms in polymer membranes under low to moderate hydration conditions remains poorly understood. In this study, we combine ion and water diffusivity (PFG-NMR) measurements with atomistic molecular dynamics simulations to better understand transport processes in hydrated salt-doped poly(ethylene glycol). Above the water percolation threshold, the experimental and simulated diffusivities are in good agreement with the free volume transport models. At low hydration levels, unlike dry systems, ion diffusion cannot be described by polymer segmental dynamics alone. We rationalize such observations by the interplay between ion-water and ion-polymer solvation of cations and between ion-water and cation-anion interactions for anions. Further, we demonstrate that a two-state model combining ion-water solvation and free volume transport can describe water dynamics across the entire hydration range of interest. Our findings provide a more encompassing analysis of ion and water transport in hydrated polyelectrolytes, specifically in the low hydration regime.

Molecular weight impacts the alkaline stability of poly(terphenylene alkylene) anion exchange membranes

Improving the alkaline durability is crucial for developing anion exchange membranes used for electrochemical energy devices. In contrast to the exploitation of new cationic moieties or robust polymer backbone, the influence of polyelectrolyte molecular weight on the membrane's alkaline stability has received little attention. In this contribution, quaternized poly(terphenylene alkylene)s with Mw ranging from 30 to 118 kDa were synthesized to quantify the variations in alkaline stability and other physicochemical properties. Measurements of ex-situ alkaline soaking, either in high or low hydration levels, and in-situ cell operating demonstrate that Mw is positively correlated to the alkaline stability of the membrane. In addition, the water absorption and ion conductivity of AEM are negatively correlated to its Mws, and incline to reach a plateau as the Mw over 100 kDa. These results have important implications to elucidate the alkaline stability limitation and may open the way toward highly stable AEMs.

Generating Predictive Chemical Kinetic Models for Quaternary Ammonium Monomers Chemical Degradation in Anion Exchange Membrane

It is widely accepted that the high cost of Proton Exchange Membrane (PEM) fuel cells (FC) is a major inhibitor of the transition to extensive commercialization of hydrogen-fueled FCs. One known alternative to this technology is Anion Exchange Membrane (AEM), greatly reducing the need for precious metals, e.g., platinum, and allowing a wider choice of lower cost polymeric materials1. Although research in the field of AEM has greatly evolved recently, AEM-FCs still lack sufficient durability and cell longevity. The current major challenge revolves around the chemical and structural stability of polymers constructing the membrane, which undergo different degradation reactions under cell operating conditions. A widely investigated AEM monomer is Benzyl trimethylammonium (BTMA), a quaternary ammonium (QA) cation, in which the positively charged nitrogen atom enables the selective transfer of hydroxide ions through the membrane2. BTMA degradation occurs in several reaction paths, the main one involving a nucleophilic attack of the hydroxide at the benzylic carbon atom, resulting in complete displacement of the functional group (Fig. 1a). Recently, it has also been shown that low hydration levels of hydroxide, evidently more relevant to the FC’s environment, have an immense impact on the reduced stability of BTMA3,4. Despite the elaborate research done on BTMA degradation, as well as on other QA monomers, complete understanding of the chemical mechanisms affecting the stability of AEM-FCs is still lacking. Modeling these mechanisms can assist in facilitating practical implementation of this promising technology, discovering novel chemically-stable ionomers, while saving time and resources in trial-and-error efforts.The goal of this research is to develop an automated workflow for generating and refining predictive chemical kinetic models describing chemical degradation of AEM monomers, by combining several computational tools, and tailoring them to suit our specific needs. The first is the Reaction Mechanism Generator (RMG) software, which automatically generates chemical kinetic models by utilizing a basic comprehension of chemical reactions5. RMG derives its data from “libraries” of kinetic and thermodynamic parameters based on the literature, and from estimations schemes based on group or decision trees. Since RMG currently does not support ion chemistry, it is required to add this feature to the software, along with solvation corrections, while extending its estimation schemes. To achieve this, accurate kinetic and thermodynamic parameters of the species and reactions of interest are necessary.The present work focuses on describing BTMA degradation. Preliminary results for the temperature-dependent rate coefficient and thermodynamic properties were obtained using the Automated Rate Calculator (ARC) software6. This tool facilitates electronic structure calculations relevant for chemical kinetic modeling, by automatically spawning, tracking, and analyzing relevant computations. We computed the BTMA + OH– reaction rate coefficient at a low hydration level (λ=1) at the ωB97xD/Def2-TZVP level of theory, and compared it to the experimental results obtained at three different temperatures (Fig. 1b). The calculations were performed using the SMD solvation model with DMSO as the solvent, in accordance with the experimental conditions. Our preliminary results show some agreement with experimental measurements, and we expect this agreement to improve by calculating single-point energies using the more accurate coupled-cluster (CC) theory.The methods developed to generate a chemical kinetic model for BTMA, can then be applied for other potential QA monomers. Furthermore, an additional software called The Tandem Tool (T3), can be used to perform model refinement, through a process of iterations between RMG and ARC, creating the desired automated model generation workflow. This process is designed to obtain quantum mechanics-based calculated parameters for significant species and reactions in the model, chosen using sensitivity analysis. Altogether, this work can create a powerful tool, providing insights on known AEM ionomers, as well as the flexibility to investigate additional polymeric materials, with minimal experimental resources.

Strong H-bonding from Zeolite Bro̷nsted Acid Site to Water: Origin of the Broad IR Doublet.

Hydrogen bonding between water molecules and zeolite Bro̷nsted acid sites (BAS) has received much attention due to the significant influence of water on the adsorption and catalytic properties of these widely used porous materials. When a single water molecule is adsorbed at the BAS, the zeolite O-H stretch vibration decreases in frequency and splits into two extraordinarily broad bands peaked near 2500 and 2900 cm-1 in the infrared (IR) spectrum. This broad doublet feature is the predominant IR signature used to identify and interpret water-BAS H-bonding at low hydration levels, but the origin of the band splitting is not well understood. In this study, we used broadband two-dimensional infrared (2D IR) spectroscopy to investigate zeolite HZSM-5 prepared with a single water molecule per BAS. We find that the 2D IR spectrum is not explained by the most common interpretation of Fermi resonance coupling between the stretch and the bend of the BAS OH group, which predicts intense excited-state transitions that are absent from the experimental results. We present an alternative model of a double-well proton stretch potential, where the band splitting is caused by excited-state tunneling through the proton-transfer barrier. This one-dimensional model reproduces the basic experimental pattern of transition frequencies and amplitudes, suggesting that the doublet bands may originate from a highly anharmonic potential in which the excited state proton wave functions are delocalized over the H-bond between zeolite BAS and adsorbed H2O. Additional details about molecular orientation and coordination of the adsorbed water molecule are also resolved in the 2D IR spectroscopy.

Impact of deposited Pt particles on water channel connectivity and proton conductivity in proton exchange membranes: A molecular dynamics study

Deposition of platinum ions in the proton exchange membrane significantly affects the long-term stability and proton transport capacity of the membrane electrode assembly. In this study, the impacts of deposited Pt particles on the intrinsic properties of proton exchange membranes and its mechanisms are investigated using molecular dynamics simulation method. The effect of differently sized Pt particles on water channel connectivity and proton conductivity in proton exchange membranes under dry, normal, and saturated conditions was detailly discussed. The results reveal that Pt particles reduce water channel connectivity at low hydration level while increasing it at normal and high hydration levels. However, the enhancement mechanism is different. Moreover, proton conductivity was evaluated by examining the diffusion of hydronium ions and hydrogen bond dynamics. We found that the proton conduction performance of the membranes at low hydration levels is significantly reduced by Pt particles. We believe this study can promote the design of more robust and efficient proton exchange membranes.

Lysozyme-Sucrose Interactions in the Solid State: Glass Transition, Denaturation, and the Effect of Residual Water.

The freeze-drying of proteins, along with excipients, offers a solution for increasing the shelf-life of protein pharmaceuticals. Using differential scanning calorimetry, thermogravimetric analysis, sorption calorimetry, and synchrotron small-angle X-ray scattering (SAXS), we have characterized the properties at low (re)hydration levels of the protein lysozyme, which was freeze-dried together with the excipient sucrose. We observe that the residual moisture content in these samples increases with the addition of lysozyme. This results from an increase in equilibrium water content with lysozyme concentration at constant water activity. Furthermore, we also observed an increase in the glass transition temperature (Tg) of the mixtures with increasing lysozyme concentration. Analysis of the heat capacity step of the mixtures indicates that lysozyme does not participate in the glass transition of the sucrose matrix; as a result, the observed increase in the Tg of the mixtures is the consequence of the confinement of the amorphous sucrose domains in the interstitial space between the lysozyme molecules. Sorption calorimetry experiments demonstrate that the hydration behavior of this formulation is similar to that of the pure amorphous sucrose, while the presence of lysozyme only shifts the sucrose transitions. SAXS analysis of amorphous lysozyme-sucrose mixtures and unfolding of lysozyme in this environment show that prior to unfolding, the size and shape of lysozyme in a solid sucrose matrix are consistent with its native state in an aqueous solution. The results obtained from our study will provide a better understanding of the low hydration behavior of protein-excipient mixtures and support the improved formulation of biologics.

Protonation-State Dependence of Hydration and Interactions in the Two Proton-Conducting Channels of Cytochrome c Oxidase.

Cytochrome c Oxidase (CcO), a membrane protein of the respiratory chain, pumps protons against an electrochemical gradient by using the energy of oxygen reduction to water. The ("chemical") protons required for this reaction and those pumped are taken up via two distinct channels, named D-channel and K-channel, in a step-wise and highly regulated fashion. In the reductive phase of the catalytic cycle, both channels transport protons so that the pumped proton passes the D-channel before the "chemical" proton has crossed the K-channel. By performing molecular dynamics simulations of CcO in the O→E redox state (after the arrival of the first reducing electron) with various combinations of protonation states of the D- and K-channels, we analysed the effect of protonation on the two channels. In agreement with previous work, the amount of water observed in the D-channel was significantly higher when the terminal residue E286 was not (yet) protonated than when the proton arrived at this end of the D-channel and E286 was neutral. Since a sufficient number of water molecules in the channel is necessary for proton transport, this can be understood as E286 facilitating its own protonation. K-channel hydration shows an even higher dependence on the location of the excess proton in the K-channel. Also in agreement with previous work, the K-channel exhibits a very low hydration level that likely hinders proton transfer when the excess proton is located in the lower part of the K-channel, that is, on the N-side of S365. Once the proton has passed S365 (towards the reaction site, the bi-nuclear centre (BNC)), the amount of water in the K-channel provides hydrogen-bond connectivity that renders proton transfer up to Y288 at the BNC feasible. No significant direct effect of the protonation state of one channel on the hydration level, hydrogen-bond connectivity, or interactions between protein residues in the other channel could be observed, rendering proton conductivity in the two channels independent of each other. Regulation of the order of proton uptake and proton passage in the two channels such that the "chemical" proton leaves its channel last must, therefore, be achieved by other means of communication, such as the location of the reducing electron.

Elucidating the impact mechanism of temperature and water content on thermal conductivity of hydrated Nafion membranes by molecular dynamics simulation

The thermal conductivity of the proton exchange membrane significantly affects the operating performance of the fuel cell. In this work, the impact of water content and temperature on thermal conductivity of hydrated Nafion membranes was investigated via molecular dynamics simulations and the influencing mechanism was explained from the perspective of interchain and intrachain heat transfer. The study shows that the thermal conductivity is mainly positively affected by water content, which is a result of the triple effect of hydrogen bonding acting as interchain heat transfer bridge, the stronger microphase separation allowing water to behave more like bulk water, and the decrease in the degree of chain torsion resulting in less phonon scattering along the chain. Particularly, we emphasized two crucial paths in which hydrogen bonding improves interchain heat transport. Furthermore, the temperature has little and slightly negative effects on thermal conductivity at low and high hydration levels, respectively. That is because, in low hydration levels, the incomplete hydrogen bond network is hardly influenced, but the bridging effect is suppressed and intrachain heat transfer capacity is reduced in high hydration levels. We believe this study can broaden the design basis of high temperature polymer electrolyte membranes.

Moisturizing at a molecular level - The basis of Corneocare.

This review covers the last 20 years of research we and our collaborators have conducted on ethnic differences in facial skin moisturization placed in historical context with previous research. We have focussed particularly on the biochemical and cellular gradients of the stratum corneum (SC) with the aim of discovering new skin moisturization and SC maturation mechanisms, identifying new technologies and/or providing conceptual innovations for ingredients that will improve our understanding and treatment of dry skin. Specifically, we discuss gradients for corneodesmosomes and proteases, corneocyte phenotype-inducing enzymes, filaggrin and natural moisturizing factor (NMF), and barrier lipids. These gradients are interdependent and influence greatly corneocyte maturation. The interrelationship between corneodesmolysis and the covalent attachment of ω-hydroxy ceramides and ω-hydroxy fatty acids to the corneocyte protein envelope forming the corneocyte lipid envelope is especially relevant in our new understanding of mechanisms leading to dry skin. This process is initiated by a linoleoyl-ω-acyl ceramide transforming enzyme cascade including 12R lipoxygenase (12R-LOX), epidermal lipoxygenase-3 (eLOX3), epoxide hydrolase 3 (EPHX3), short-chain dehydrogenase/reductase family 9C member 7 (SDR9C7), ceramidase and transglutaminase 1. Our research has opened the opportunity of using novel treatment systems for dry skin based on lipids, humectants, niacinamide and inhibitors of the plasminogen system. It is clear that skin moisturization is a more complex mechanism than simple skin hydration.

Structural and thermodynamic effects of hydration in Na-zeolite A (LTA) from low-temperature heat capacity

Zeolite A (Linde Type A; LTA) is an industrially important porous mineral that has recently been shown to exhibit framework flexibility upon changes in hydration level. To investigate the flexibility transition from a thermodynamic perspective, we have performed heat capacity measurements on sodium zeolite A at seven incremental hydration levels ranging from zero to equilibrium with ambient air. Excess low-frequency vibrations beyond the predictions of the Debye model are found in all samples, and the frequency of these vibrations increases as a function of hydration level. This suggests that an increase in hydration causes a decrease in at least one type of framework flexibility for sodium zeolite A. In addition, a subtle excess heat capacity contribution from 150 to 280 K is observed only for low and intermediate hydration levels, which may arise from a transformation tied to framework flexibility previously observed in zeolite A via gas absorption calorimetry. Values of the standard thermodynamic functions Cp,m°, Δ0TSm°, Δ0THm°, andΦm° are also reported.

Designing sulfonated polyimide-based fuel cell polymer electrolyte membranes using machine learning approaches

Fuel cells are the efficient electrochemical energy conversion devices with wide-ranging applications. Polymer Electrolyte Membrane (PEM) is the primary component of a PEM fuel cell whose proton conductivity majorly determines the performance of the fuel cells. Due to the high cost and limited range of operating parameters, alternatives of perfluorinated ionomers based commercial PEMs are urgently required. Sulfonated polyimides (SPIs) based hydrocarbon PEMs, have exhibited better proton conductivity even at low hydration levels and high temperatures, making them possible candidates for replacing commercial PEMs. However, finding alternative SPI PEMs is a critical polymer discovery problem that requires enormous experimental efforts where Machine learning (ML) approaches can help to reduce such efforts. To this end, both supervised and unsupervised ML approaches are developed to predict the proton conductivity of SPIs. A hybrid dataset of 81 unique SPIs is generated that consists of collected chemical structure–properties data from reported literature and calculated quantitative structure–property and semi-empirical quantum chemical descriptors. Using simple and interpretable Decision Trees, rules that lead to a low or high class of proton conductivity labels with high accuracy are identified. The trained decision tree model can accurately predict the proton conductivity class labels with a prediction accuracy of 88% and a kappa statistic of 0.77. The random forest regression (RFR) model, on the other hand, identified additional set of features that can predict proton conductivity with reasonable error. Thus, high information-gain features have been identified and their correlation with the proton conductivity class labels have been explored. These findings are key to designing novel SPI PEMs while correlating proton transport at the ionomer level with factors such as the morphology of the microstructure and inter-chain interactions.

Innovative Insight into O2/N2 Permeation Behavior through an Ionomer Film in Cathode Catalyst Layers of Polymer Electrolyte Membrane Fuel Cells.

It is crucial to clarify the permeation behavior of O2 through the ionomer film for enhancing local O2 transport in cathodes of fuel cells. However, all existing studies mainly deal with pure O2 rather than air. Herein, the permeation behavior of the O2/N2 mixture through the ionomer film has been well explored in view of molecular bond length variations by molecular dynamics simulations. The bond lengths for O2 and N2 are shortened under a low hydration level when permeating through a dense layer with small free voids while no obvious change occurs at higher hydration. In the bulk ionomer region, O2 molecules residing in water domains are energetically unstable because the bond lengths deviate far from the equilibrium length; thus, O2 diffuses through the interfacial or hydrophobic regions. N2 molecules show similar properties with O2. This study provides a novel perspective on the permeation behavior of O2 and N2 through the ionomer film, which definitely benefits enhancing local O2 transport.

Low-temperature investigation of residual water bound in free-living Antarctic Prasiola crispa

AbstractAntarctic algae are extremophilic organisms capable of surviving harsh environmental conditions such as low temperatures and deep dehydration. Although these algae have various adaptations for life in extreme environments, the majority of the molecular mechanisms behind their resistance to dehydration and freezing are not yet fully understood. The aim of our research was to observe the behaviour of bound water freezing in the free-living Antarctic alga Prasiola crispa. One way to avoid frost damage involves deep dehydration of the algal thallus. For that reason, a detailed analysis of water freezing at different sample hydration levels was carried out. Nuclear magnetic resonance investigation revealed two types of water immobilization: cooperative bound water freezing for samples with sample hydration levels above Δm/m0 = 0.40 and non-cooperative bound water immobilization for lower thallus hydration levels. In the differential scanning calorimetry experiment, 2-h incubation at -20°C suggested the diffusion and final binding of supercooled water to the ice nuclei and a lower hydration level threshold, at which ice formation could be observed (Δm/m0 = 0.21). Our research provides a new perspective on water sorption and freezing in Antarctic algae, which may be important not only in biological systems, but also in such novel materials as metal-organic frameworks or covalent organic frameworks.