Ions play key roles in virtually all the chemical processes in nature. They are abundant in cells and proteins where they provide the background electrolytes for living systems, they play structural roles or promote conformational changes in proteins or they serve as oxidation-reduction centers for the manipulation of electrons in cytochromes and oxido-reductases. Ions are important in atmospheric chemistry and interstellar processes; there is an increasing evidence that halide anions on the surface of aerosol particles act as scavengers of reactive gases such as ozone or hydroxyl radical in the trophosphere. They are also, of course, the principal constituents of many materials of technological interest including catalysts and electronic ceramics. Hence, understanding of ions in different environments ranging from aqueous solutions to ion channels, and DNA (RNA) to metalloenzymes, is vital.
The response of the ion to changes in its environment is recognised as of crucial importance in many of nature's designs. For instance, anions in crystals are different from their free counterparts: they are smaller, less polarisable and more strongly bound. In solids, the importance of these many-body effects is well recognised, but in bio-systems, these effects have received less attention.
The popular way to gain insight into the behaviour of ions in biological systems is the use of the so-called atomistic simulations. Usually, the interactions between atoms are described by empirical potential functions, which are used to integrate the classical equations of motion. This process yields a trajectory of the system in time, from which structural and dynamical quantities can be calculated using the principles of statistical mechanics. Central to such simulations is the modelling of the non-bonded interactions between the ions and the rest of the system. Unfortunately, this is most empirical and remains problematic. More accurate quantum models are restricted to handling the ion and its closest ligands, typically ignoring the rest of the protein or including it in an empirical fashion. Therefore, there is much to be gained by applying quantum techniques in the study of common biological cations and anions where induced polarisation effects cannot be neglected.
Many biological systems, especially membrane transport proteins, and ion channels in particular, have key roles for inorganic ions. Some of my research work is focus on these proteins, the ions channels. I am also involved in the application of first-principles methods and classical molecular dynamics for the study of the mechanisms that govern the behaviour of the calcium dependent phospholipases, a kind of enzymes which perform their chemistry at the aqueous membrane interface.