Laboratory for Membrane and Protein Dynamics
We do experimental biophysics. We synthesize membrane/protein systems composed of different types of lipids, membrane active proteins, such as cholesterol and ethanol, and proteins and peptides in our biophysical preparation facility. We operate the BLADE, a powerful in-house x-ray instrument dedicated to membrane research. Molecular structure and dynamics of lipids and proteins are then studied using x-ray and neutron scattering. Neutron scattering is done in-house, using the McMaster Nuclear Reactor, and at neutron facilities all over the world.




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Humidity Chambers for Neutron and X-ray Scattering

When working with biological or biophysical samples, the important thermodynamic parameters are temperature but also hydration. Lipid membranes for instance as model systems for more complex biological membranes cannot be understood without taking into account the structure and dynamics of their aqueous environment. The structure and dynamical properties of the bound water layers next to the bilayer as well as the 'free' (bulk) water further away from the water/lipid interface are of importance in understanding the thermal, elastic and transport properties of membranes. Furthermore, the interaction between two bilayers is mediated by the hydration water. A recent Molecular Dynamics (MD) simulation pointed out the importance of hydration water dynamics for the understanding of the dynamical transition of proteins. The sample is usually hydrated from (heavy/light) water vapor to a beam path through bulk water. The basic design of humidity cells is rather simple and consists of a water container and the sample in a temperature controlled enclosed space. In reality things are much more complex and the development of humidity cells is a highly complex task and needs careful control of temperatures to, e.g., avoid temperature gradients and temperatures below the dew point what would lead to an immediate loss of hydration.


Highlights of the new design are:

1)     The temperatures of the sample, the water containers and the surrounding cell can be adjusted independently from each other.

2)     Tempering is fast by Peltier elements.

3)     The chamber is very versatile, i.e., different covers can be fabricated and used for different sample geometries and adapted to different neutron instruments as three-axis, reflectometers, time-of-flight instruments. For x-ray instruments, a Beryllium/Kapton window has been built in.

4)     The chamber is ‘intelligent’, i.e., the electronics controls all temperatures and the hydration. The communication to the instrument computer by RS232 or IEC bus or wireless LAN just includes set and is values for sample temperature and hydration.

5)     By regulating the different temperatures it is possible to adjust different levels of hydration. Usually the hydration is set by different saturated salt solutions, i.e., K2SO4 for about 97 %RH, with the disadvantage that the chamber has to be opened, the salt solution replaced and the sample hydrated again, what usually took a few hours.

6)     D2O and H2O can be exchanged easily to measure at different scattering contrasts without opening the cell.