Ice nucleation in aqueous solutions of short- and long-chain poly(vinyl alcohol) studied with a droplet microfluidics setup.

Poly(vinyl alcohol) (PVA) has ice binding and ice nucleating properties. Here, we explore the dependence of the molecular size of PVA on its ice nucleation activity. For this purpose, we studied ice nucleation in aqueous solutions of PVA samples with molar masses ranging from 370 to 145 000 g mol-1, with a particular focus on oligomer samples with low molar mass.

Machine-Learning-Based Prediction of the Glass Transition Temperature of Organic Compounds Using Experimental Data.

Knowledge of the glass transition temperature of molecular compounds that occur in atmospheric aerosol particles is important for estimating their viscosity, as it directly influences the kinetics of chemical reactions and particle phase state. While there is a great diversity of organic compounds present in aerosol particles, for only a minor fraction of them experimental glass transition temperatures are known. Therefore, we have developed a machine learning model designed to predict the glass transition temperature of organic molecular compounds based on molecule-derived input variables.

Water-organizing motif continuity is critical for potent ice nucleation protein activity.

Bacterial ice nucleation proteins (INPs) can cause frost damage to plants by nucleating ice formation at high sub-zero temperatures. Modeling of Pseudomonas borealis INP by AlphaFold suggests that the central domain of 65 tandem sixteen-residue repeats forms a beta-solenoid with arrays of outward-pointing threonines and tyrosines, which may organize water molecules into an ice-like pattern. Here we report that mutating some of these residues in a central segment of P.

Specific Ion-Protein Interactions Influence Bacterial Ice Nucleation.

Ice nucleation-active bacteria are the most efficient ice nucleators known, enabling the crystallization of water at temperatures close to 0 °C, thereby overcoming the kinetically hindered phase transition process at these conditions. Using highly specialized ice-nucleating proteins (INPs), they can cause frost damage to plants and influence the formation of clouds and precipitation in the atmosphere. In nature, the bacteria are usually found in aqueous environments containing ions.

Ice Nucleation Properties of Ice-binding Proteins from Snow Fleas.

Ice-binding proteins (IBPs) are found in many organisms, such as fish and hexapods, plants, and bacteria that need to cope with low temperatures. Ice nucleation and thermal hysteresis are two attributes of IBPs. While ice nucleation is promoted by large proteins, known as ice nucleating proteins, the smaller IBPs, referred to as antifreeze proteins (AFPs), inhibit the growth of ice crystals by up to several degrees below the melting point, resulting in a thermal hysteresis (TH) gap between melting and ice growth.

Contrasting Behavior of Antifreeze Proteins: Ice Growth Inhibitors and Ice Nucleation Promoters.

Several types of natural molecules interact specifically with ice crystals. Small antifreeze proteins (AFPs) adsorb to particular facets of ice crystals, thus inhibiting their growth, whereas larger ice-nucleating proteins (INPs) can trigger the formation of new ice crystals at temperatures much higher than the homogeneous ice nucleation temperature of pure water. It has been proposed that both types of proteins interact similarly with ice and that, in principle, they may be able to exhibit both functions.

Second inflection point of water surface tension in the deeply supercooled regime revealed by entropy anomaly and surface structure using molecular dynamics simulations.

The surface tension of supercooled water is of fundamental importance in physical chemistry and materials and atmospheric sciences. Controversy, however, exists over its temperature dependence in the supercooled regime, especially on the existence of the "second inflection point (SIP)". Here, we use molecular dynamics simulations of the SPC/E water model to study the surface tension of water (σw) as a function of temperature down to 198.

A physically constrained classical description of the homogeneous nucleation of ice in water.

Liquid water can persist in a supercooled state to below 238 K in the Earth's atmosphere, a temperature range where homogeneous nucleation becomes increasingly probable. However, the rate of homogeneous ice nucleation in supercooled water is poorly constrained, in part, because supercooled water eludes experimental scrutiny in the region of the homogeneous nucleation regime where it can exist only fleetingly. Here we present a new parameterization of the rate of homogeneous ice nucleation based on classical nucleation theory.

Global distribution of particle phase state in atmospheric secondary organic aerosols.

Secondary organic aerosols (SOA) are a large source of uncertainty in our current understanding of climate change and air pollution. The phase state of SOA is important for quantifying their effects on climate and air quality, but its global distribution is poorly characterized. We developed a method to estimate glass transition temperatures based on the molar mass and molecular O:C ratio of SOA components, and we used the global chemistry climate model EMAC with the organic aerosol module ORACLE to predict the phase state of atmospheric SOA.

Boreal pollen contain ice-nucleating as well as ice-binding 'antifreeze' polysaccharides.

Ice nucleation and growth is an important and widespread environmental process. Accordingly, nature has developed means to either promote or inhibit ice crystal formation, for example ice-nucleating proteins in bacteria or ice-binding antifreeze proteins in polar fish. Recently, it was found that birch pollen release ice-nucleating macromolecules when suspended in water.

Sensitivity of liquid clouds to homogenous freezing parameterizations.

Unlabelled: Water droplets in some clouds can supercool to temperatures where homogeneous ice nucleation becomes the dominant freezing mechanism. In many cloud resolving and mesoscale models, it is assumed that homogeneous ice nucleation in water droplets only occurs below some threshold temperature typically set at -40°C. However, laboratory measurements show that there is a finite rate of nucleation at warmer temperatures.

Size dependence of phase transitions in aerosol nanoparticles.

Phase transitions of nanoparticles are of fundamental importance in atmospheric sciences, but current understanding is insufficient to explain observations at the nano-scale. In particular, discrepancies exist between observations and model predictions of deliquescence and efflorescence transitions and the hygroscopic growth of salt nanoparticles. Here we show that these discrepancies can be resolved by consideration of particle size effects with consistent thermodynamic data.

Glass formation processes in mixed inorganic/organic aerosol particles.

Recent experiments suggest that organic aerosol particles may transform into a glassy state at room temperature under dry conditions. Information on glass forming processes in mixed inorganic/organic aerosol particles is sparse, however, because inorganic crystal nucleation is usually very likely in such mixtures. Here we investigate the glass transition temperatures Tg of various organics (trehalose, sucrose, citric acid, sorbitol, and glycerol as well as 3-MBTCA) in binary mixtures with either NaNO3 or NH4HSO4 at different mass fractions.

Glass-forming properties of 3-methylbutane-1,2,3-tricarboxylic acid and its mixtures with water and pinonic acid.

3-Methylbutane-1,2,3-tricarboxylic acid (3-MBTCA) is an atmospheric oxidation product of α-pinene and has been identified as the most relevant tracer compound for atmospheric terpene secondary organic aerosol (SOA) particles. Little is known, however, of its physicochemical properties such as water solubility and phase state (e.g.

Formation of highly porous aerosol particles by atmospheric freeze-drying in ice clouds.

The cycling of atmospheric aerosols through clouds can change their chemical and physical properties and thus modify how aerosols affect cloud microphysics and, subsequently, precipitation and climate. Current knowledge about aerosol processing by clouds is rather limited to chemical reactions within water droplets in warm low-altitude clouds. However, in cold high-altitude cirrus clouds and anvils of high convective clouds in the tropics and midlatitudes, humidified aerosols freeze to form ice, which upon exposure to subsaturation conditions with respect to ice can sublimate, leaving behind residual modified aerosols.

The homogeneous ice nucleation rate of water droplets produced in a microfluidic device and the role of temperature uncertainty.

Ice nucleation was investigated experimentally in water droplets with diameters between 53 and 96 micrometres. The droplets were produced in a microfluidic device in which a flow of methyl-cyclohexane and water was combined at the T-junction of micro-channels yielding inverse (water-in-oil) emulsions consisting of water droplets with small standard deviations. In cryo-microscopic experiments we confirmed that upon cooling of such emulsion samples ice nucleation in individual droplets occurred independently of each other as required for the investigation of a stochastic process.

Antifreeze glycopeptide diastereomers.

Antifreeze glycopeptides (AFGPs) are a special class of biological antifreeze agents, which possess the property to inhibit ice growth in the body fluids of arctic and antarctic fish and, thus, enable life under these harsh conditions. AFGPs are composed of 4-55 tripeptide units -Ala-Ala-Thr- glycosylated at the threonine side chains. Despite the structural homology among all the fish species, divergence regarding the composition of the amino acids occurs in peptides from natural sources.

Influence of sequential modifications and carbohydrate variations in synthetic AFGP analogues on conformation and antifreeze activity.

Certain Arctic and Antarctic ectotherm species have developed strategies for survival under low temperature conditions that, among others, consist of antifreeze glycopeptides (AFGP). AFGP form a class of biological antifreeze agents that exhibit the ability to inhibit ice growth in vitro and in vivo and, hence, enable life at temperatures below the freezing point. AFGP usually consist of a varying number of (Ala-Ala-Thr)(n) units (n=4-55) with the disaccharide β-D-galactosyl-(1→3)-α-N-acetyl-D-galactosamine glycosidically attached to every threonine side chain hydroxyl group.

Glass transition and phase state of organic compounds: dependency on molecular properties and implications for secondary organic aerosols in the atmosphere.

Recently, it has been proposed that organic aerosol particles in the atmosphere can exist in an amorphous semi-solid or solid (i.e. glassy) state.

From nanoscale liquid spheres to anisotropic crystalline particles of tin: decomposition of decamethylstannocene in organic solvents.

Routes are presented for synthesizing nano- and mesostructured β-tin particles in the form of monocrystalline spheres, cubes, and bars, as well as polycrystalline rods and needles, by the decomposition of decamethylstannocene in organic solvents under various conditions. The formation of the observed shapes is based on the presence of liquidlike and of partly crystalline droplets. These particle stages allow structure-determining processes such as entire coalescence, oriented superficial coalescence or superficial induced crystallization.

Gas uptake and chemical aging of semisolid organic aerosol particles.

Organic substances can adopt an amorphous solid or semisolid state, influencing the rate of heterogeneous reactions and multiphase processes in atmospheric aerosols. Here we demonstrate how molecular diffusion in the condensed phase affects the gas uptake and chemical transformation of semisolid organic particles. Flow tube experiments show that the ozone uptake and oxidative aging of amorphous protein is kinetically limited by bulk diffusion.

Synthesis and characterization of natural and modified antifreeze glycopeptides: glycosylated foldamers.

In Arctic and Antarctic marine regions, where the temperature declines below the colligative freezing point of physiological fluids, efficient biological antifreeze agents are crucial for the survival of polar fish. One group of such agents is classified as antifreeze glycoproteins (AFGP) that usually consist of a varying number (n = 4-55) of [AAT]( n )-repeating units. The threonine side chain of each unit is glycosidically linked to β-D: -galactosyl-(1 → 3)-α-N-acetyl-D: -galactosamine.

Ultra-slow water diffusion in aqueous sucrose glasses.

We present measurements of water uptake and release by single micrometre-sized aqueous sucrose particles. The experiments were performed in an electrodynamic balance where the particles can be stored contact-free in a temperature and humidity controlled chamber for several days. Aqueous sucrose particles react to a change in ambient humidity by absorbing/desorbing water from the gas phase.