Water Related Systems

The main goals of this section can be grouped together into the following categories:
   • Synthesis, properties and stability of ice clathrates
   • High pressure effects on aqueous solutions: salts, supramolecular aggregates and proteins
   • Microbiology under extreme conditions of pressure and temperature

a. Water Related Systems: Synthesis, properties and stability of ice clathrates

Clathrates can be thought of as combination of a gas and normal water ice that forms a single solid substance at low temperatures and high pressures. The water molecules in clathrates form an ice-like structure that traps small molecules in nearly spherical cavities.

Our interest in clathrates is motivated by 1) an increasing recognition of its abundance in Earth’s subsurface and on icy bodies of the solar system (like Europa), 2) its possible economic importance as a source of fuel, and 3) its potential role in climate changes. For these reasons we shall study specifically CO2, methane and H2 clathrates.

b.  Water Related Systems: High pressure effects on aqueous solutions: salts, supramolecular aggregates and proteins

The study of the effect of pressure on non-covalent interactions in solution is a relatively unexplored area that can lead to unexpected discoveries. The effect of pressure on the formation of host-guest complexes is an interesting playground with applications ranging from basic chemistry to pharmaceutical and medical applications. Alongside this type of interactions, another phenomenon that worths mentioning is the aggregation, i.e. micelle formation, under pressure. Again, this is a fundamental issue since it paves the way to the field that we refer to as high pressure supramolecular chemistry, a discipline in continuous interaction with others as Materials and Life Sciences.

Computer simulation of proteins, based on atomistic models and molecular dynamics calculations, has been commonly used to study pressure-induced denaturalization processes. This type of simulations presents however rather high spatial and temporal resolutions. If an aqueous solvent is considered, the time scale is of the order of nanoseconds, while the denaturalization transit of a protein ranges from milliseconds to seconds at atmospheric pressure or even longer in a compressed state. Thus, these studies provide limited information about the pressure response of native structure. Models of better resolution allow us the study of the complete equilibrium process between native and denatured forms. These simplified models include mean-field potentials, where both the attraction between hydrophobic residues (short distances) and the desolvation barriers (intermediate distances) depend on pressure. In MALTA we shall consider simulation techniques with improved mean-field potentials obtained from precise quantum mechanical calculations. Monte Carlo simulations allowing an efficient sampling of the accessible conformational space will likely provide reasonable thermodynamic results for the protein stability and the modification of their energy-pressure range. These calculations can be extended to systems with several chains (small proteins) to analyze the effect of pressure on the protein aggregation process at high concentrations.

c.  Water Related Systems: Microbiology under extreme conditions of pressure and temperature

Through the study of the behaviour of microbiological systems under extreme conditions of pressure and temperature, the MALTA initiative will cover in this section a varied list of high-pressure-related topics ranging from the origing of life to food pocessing.