Interplay of vitrification and ice formation in a cryoprotectant aqueous solution at low temperature.

The proneness of water to crystallize is a major obstacle to understanding its putative exotic behavior in the supercooled state. It also represents a strong practical limitation to cryopreservation of biological systems. Adding some concentration of glycerol, which has a cryoprotective effect preventing, to some degree, water crystallization, has been proposed as a possible way out, provided the concentration is small enough for water to retain some of its bulk character and/or for limiting the damage caused by glycerol on living organisms. Contrary to previous expectations, we show that, in the "marginal" glycerol molar concentration ≈ 18%, at which vitrification is possible with no crystallization on rapid cooling, water crystallizes upon isothermal annealing even below the calorimetric glass transition of the solution. Through a time-resolved polarized neutron scattering investigation, we extract key parameters, size and shape of the ice crystallites, fraction of water that crystallizes, and crystallization time, which are important for cryoprotection, as a function of the annealing temperature. We also characterize the nature of the out-of-equilibrium liquid phases that are present at low temperature, providing more arguments against the presence of an isocompositional liquid­liquid transition. Finally, we propose a rule of thumb to estimate the lower temperature limit below which water crystallization does not occur in aqueous solutions.

Direct Synthesis of Mesoporous Organosilica and Proof-of-Concept Applications in Lysozyme Adsorption and Supported Catalysis.

Mesoporous materials represent a useful alternative for exploiting the effects of confinement on molecular trapping and catalysis. Their efficiency often depends on the interactions between the surface and the targeted molecules. One way to enhance these interactions is to adjust the hydrophobic/hydrophilic balance of the surface. In the case of mesoporous silica, the incorporation of organic groups is an efficient solution to adapt the material for specific applications. In this work, we have used the co-condensation method to control the hydrophobicity of mesoporous organosilica. The obtained materials are methyl- or phenyl-containing silica with a pore size between 3 and 5 nm. The surface chemistry control has shown the enhanced performance of the materials in two proof-of-concept (PoC) applications: lysozyme adsorption and supported catalysis. The lysozyme adsorption is observed to be over 3 times more efficient with the phenyl-functionalized material than MCM-41, due to π-π interactions. For the catalysis, copper(II) was immobilized on the organosilica surface. In this case, the presence of methyl groups significantly enhanced the product yield for the catalyzed synthesis of a triazole derivative; this was attributed to the enhanced hydrophobic surface-reactant interactions. It was also found that the materials have a higher water adsorption capacity and an improved resistance to hydrolysis. The modulation of water properties in confinement with hydrophobic surfaces, consistently with the water as tuneable solvent (WaTuSo) concept, is a crucial aspect in the efficiency of mesoporous materials for dedicated applications.