Ionic liquids were initially proposed as replacements for conventional organic solvents; however, their chemistry has developed remarkably and offers unexpected opportunities in numerous fields, ranging from electrochemistry to biology. As a consequence of ionic liquids advancing towards potential and actual applications, a comprehensive determination of their environmental, health and safety impact is now required. This critical review aims to present an overview of the current understanding of the toxicity and environmental impact of the principal ionic liquid groups, and highlights some emerging concerns. Each cation type is considered separately, examining the significance of the biological data, and identifying the most critical questions, some yet unresolved. The need for more, and more detailed, studies is highlighted (176 references).

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A variety of sugars are known to enhance the stability of biomaterials. Trehalose, a nonreducing disaccharide composed of two alpha, alpha(1 --> 1)-linked D-glucopyranose units, appears to be one of the most effective protectants. Both in vivo and in vitro, trehalose protects biostructures such as proteins and membranes from damage due to dehydration, heat, or cold. However, despite the significant amount of experimental data on this disaccharide, no clear picture of the molecular mechanism responsible for its stabilizing properties has emerged yet. Three major hypotheses (water-trehalose hydrogen-bond replacement, coating by a trapped water layer, and mechanical inhibition of the conformational fluctuations) have been proposed to explain the stabilizing effect of trehalose on proteins. To investigate the nature of protein-trehalose-water interactions in solution at the molecular level, two molecular dynamics simulations of the protein lysozyme in solution at room temperature have been carried out, one in the presence (about 0.5 M) and one in the absence of trehalose. The results show that the trehalose molecules cluster and move toward the protein, but neither completely expel water from the protein surface nor form hydrogen bonds with the protein. Furthermore, the coating by trehalose does not significantly reduce the conformational fluctuations of the protein compared to the trehalose-free system. Based on these observations, a model is proposed for the interaction of trehalose molecules with a protein in moderately concentrated solutions, at room temperature and on the nanosecond timescale.

The disaccharide trehalose is well known for its bioprotective properties. Produced in large amounts during stress periods in the life of organisms able to survive potentially damaging conditions, trehalose plays its protective role by stabilizing biostructures such as proteins and lipid membranes. In this study, molecular dynamics simulations are used to investigate the interaction of trehalose with a phospholipid bilayer at atomistic resolution. Simulations of the bilayer in the absence and in the presence of trehalose at two different concentrations (1 or 2 molal) are carried out at 325 K and 475 K. The results show that trehalose is able to minimize the disruptive effect of the elevated temperature and stabilize the bilayer structure. At both temperature, trehalose is found to interact directly with the bilayer through hydrogen bonds. However, the water molecules at the bilayer surface are not completely replaced. At high temperature, the protective effect of trehalose is correlated with a significant increase in the number of trehalose-bilayer hydrogen bonds, predominantly through an increase in the number of trehalose molecules bridging three or more lipid molecules.

Explicit-solvent molecular dynamics simulations (50 ns, 300 K) of the eight reducing glucose disaccharides (kojibiose, sophorose, nigerose, laminarabiose, maltose, cellobiose, isomaltose, and gentiobiose) have been carried out using the GROMOS 45A4 force field (including a recently reoptimized carbohydrate parameter set), to investigate and compare their conformational preferences, intramolecular hydrogen-bonding patterns, torsional dynamics, and configurational entropies. The calculated average values of the glycosidic torsional angles agree well with available experimental data, providing validation for the force field and simulation methodology employed in this study. These simulations show in particular that: 1) (1-->6)-linked disaccharides are characterized by an increased flexibility, the absence of any persistent intramolecular hydrogen bond and a significantly higher configurational entropy (compared to the other disaccharides); 2) cellobiose presents a highly persistent interresidue hydrogen bond and a significantly lower configurational entropy (compared to the other disaccharides); 3) persistent hydrogen bonds are observed for all disaccharides (except (1-->6)-linked) and typically involve a hydrogen donor in the reducing residue and an acceptor in the nonreducing one; 4) the probability distributions associated with the glycosidic dihedral angles and psi are essentially unimodal for all disaccharides, and full rotation around these angles occurs at most once or twice for (never for psi) on the 50-ns timescale; and 5) the timescales associated with torsional transitions (except around and psi) range from approximately 30 ps (rotation of hydroxyl groups) to the nanosecond range (rotation of the lactol and hydroxymethyl groups, and around the omega-glycosidic dihedral angle in (1-->6)-linked disaccharides).

Molecular dynamics simulations are used to investigate the interaction of the sugars trehalose, maltose, and glucose with a phospholipid bilayer at atomic resolution. Simulations of the bilayer in the absence or in the presence of sugar (2 molal concentration for the disaccharides, 4 molal for the monosaccharide) are carried out at 325 and 475 K. At 325 K, the three sugars are found to interact directly with the lipid headgroups through hydrogen bonds, replacing water at about one-fifth to one-quarter of the hydrogen-bonding sites provided by the membrane. Because of its small size and of the reduced topological constraints imposed on the hydroxyl group locations and orientations, glucose interacts more tightly (at identical effective hydroxyl group concentration) with the lipid headgroups when compared to the disaccharides. At high temperature, the three sugars are able to prevent the thermal disruption of the bilayer. This protective effect is correlated with a significant increase in the number of sugar-headgroups hydrogen bonds. For the disaccharides, this change is predominantly due to an increase in the number of sugar molecules bridging three or more lipid molecules. For glucose, it is primarily due to an increase in the number of sugar molecules bound to one or bridging two lipid molecules.

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