Fundamentals and applications of lipid systems

Although many of the fundamental forces affecting the behaviour of lipid
systems are well understood, the delicate interplay between them often
results in surprising behaviour of multi-component systems. A large
contribution to these anomalous results is the testing environment for model
systems; whilst much literature in the past has focused on model systems in
water, the effect of biologically relevant conditions has recently been found
to have non-negligible effects on their behaviour: after all, biology does not
happen in water.
The delicate stability of lipid systems is further of interest regarding their
current and potential future applications. Most notably, the bicontinuous
cubic phase has been used as a template for the crystallisation of
membrane proteins, to an increasing degree of success. In particular, there
is current interest in so-called sponge phase of lipid systems. As a
disordered, fluid, and yet still bicontinuous phase of lipid systems, the
sponge phase has attracted recent interest in its ability to interconvert with
the more ordered cubic phases, including the potential to form oriented films
under shear. Among all possible lipid systems and phases, the sponge is
perhaps the least well explored and understood. Currently, the
overwhelming majority of sponges are formed of the lipid monoolein, the
solvent butanediol, and water. However, by varying the proportion of these
components, and the addition of further ones to the membrane, it is
proposed that the physical properties of the sponge system may be adapted
sufficiently for useful technological applications.
Although the lipid in meso crystallisation of proteins uses the cubic phase of
lipid systems, recent work has also shown that the sponge phase holds
promise as an intermediate stage for the successful growth of protein
crystals, among other applications.
In conjunction with recent developments in synchrotron technology, as well
as the advent of XFEL beamlines, an further understanding of the
fundamental physical properties of the sponge phase will further aid the
development of both its, and closely related, applications.