The name is absent

single DNA Strand-Iipid membrane interactions. They have suggested that a membrane
composed of mobile surface groups will differ appreciably in its interaction with DNA,
when compared with a membrane having immobile surface charges. Experimental
evidence for lipid mobility resulting from Inacromolecule-Iipid interactions has been in
the form of lipid phase separation observations. These have been reported for various
systems; e.g., the binding of polylysine [72], cardiotoxin II [73], cytochrome c [74] and
model peptides [75] onto monovalently charged membranes, as well as membranes
containing multivalent lipids [76, 77]. This evidence has typically been at the micron-
scale, observed using fluorescence optical microscopy.

The following work represents the first experimental demonstration of mobile lipid
charge regulation at the nanoscale using AFM. We will show that short-range deviation
of the AFM data from the model given in Chapter 2 is due to mobile lipid charge
regulation under the influence of the AFM tip (Figure 3.1).

ω ≡≡≡≡≡≡
≡≡≡≡≡≡

AFM lip

- Anionic lipid molecules move

φ)                                        away from under the tip

≡≡≡≡≡≡
≡≡≡≡≡≡

Figure 3.1: Schematic of AFM tip-induced mobile charge regulation. Neutral lipids are
shown in yellow and the anionic lipids are shown in white, (a) In an unperturbed lipid
bilayer, the neutral and the anionic lipids are distributed homogenously, (b) The close
proximity of the negatively charged AFM tip induces the negative lipid molecules to
move away and results in a patch of mostly neutral lipids forming underneath the AFM
tip.

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