Ultrafast spectroscopy of model biological membranes
Ghosh, A.
Citation
Ghosh, A. (2009, September 2). Ultrafast spectroscopy of model biological membranes.
Retrieved from https://hdl.handle.net/1887/13945
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License: Licence agreement concerning inclusion of doctoral thesis in the Institutional Repository of the University of Leiden
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Stellingen
x Ultrafast dynamics studies of interfacial water molecules at the air-water interface show that surface water behaves very similarly to bulk water in terms of its vibrational dynamics. (This thesis, Chapter 3)
x Ultrafast dynamics studies of lipid membrane-water interfaces show that membrane-bound water molecules are different from the ones in bulk water or those at the air-water interface.
(This thesis, Chapter 4).
x Stacks of (partially) hydrated lipid bilayers do not necessarily present good model systems for biological membranes. Specifically, the dynamics of water molecules incorporated in hydrated lipid bilayer stacks are very different from those at the interface of bulk water and lipids. (Volkov et al., Phys. Rev. Lett. 99, 78302, 2007; this thesis, Chapter 4 and 5).
x The generic understanding of the complexity of biological membrane function has largely overlooked the role of membrane-bound water, owing to the technical challenges in probing a water layer as thin as ~5 Å – leading to a convenient, yet insufficient assumption that the interfacial water is simply an effective dielectric continuum around the membrane system.
x The two peaks in the SFG spectrum of surface water at 3200 and 3450 cm-1 were initially proposed to be the result of “ice-like” and “liquid-like” water species existing at the surface.
SFG experiments on isotopically diluted water however proves that the two-peak feature in the spectrum can be best explained if the dip in the spectrum is the result of a Fermi resonance between the bend overtone and the stretch fundamental modes of the water molecule and not due to different species of water at the surface. (Sovago et al, Phys. Rev. Lett. 100, 173901, 2008).
x SFG spectroscopy although a powerful tool in the surface science community, must be used in conjunction with other traditional surface techniques, in order to understand the true nature of surfaces and interfaces.
x Although SFG spectroscopy is highly surface-sensitive (sensitive to ~1 monolayer of matter), the efficacy of the technique largely depends on the kind of surfaces it is being used to probe:
if the material symmetry is maintained to a large extent into the bulk from the surface, SFG will be sensitive only where the symmetry breaks, i.e. a few monolayers beneath the actual surface.
x SFG spectral intensities of interfacial water at charged lipid monolayers are much larger than those at zwitterionic or neutral lipid monolayers, primarily due to the second-order P(2) of the interfacial water being enhanced by a bulk (3) response originating from the DC-field provided by the sheet of charged head-groups. (This thesis, Chapter 4).
x By extending the time-resolved SFG setup, mentioned in this thesis, to a twodimensional SFG setup, one can address the molecular vibrational couplings and their evolution in real-time, in a very surface-specific manner. (Bredenbeck et al, J. Am. Chem. Soc. 130(7), 2152, 2008).
x The concept of “Stellingen” is archaic and environmentally unfriendly since it takes up an extra piece of paper which people usually don’t read or it gets lost somewhere down the line.
