TemperatureControlled Structure and Kinetics of Ripple Phases in One and TwoComponent Supported Lipi

1
Temperature-Controlled Structure and Kinetics of
Ripple Phases in One- and Two-Component Supported
Lipid Bilayers

• Thomas Kaasgaard, Chad Leidy, John H. Crowe  ,
  Ole G. Mouritsen  and Kent Jørgensen Biophys J
  85 350-360 Jul. 2003
• Xiuquan Sun
• Department of Chemistry Biochemistry
• University of Notre Dame

2
Outline

• AFM
• Lipid structure
• Result and Discussion
• Conclusion
• Acknowledgement

3
Scanning Probe Microscopy (SPM)

• A family of microscopy technique where a sharp
  probe is scanned across a surface and tip/sample
  interactions are monitored
• Scanning tunneling Microscopy (STM)
• Atomic Force Microscopy (AFM)
• Other forms of SPM
• Lateral force
• Force modulation
• Magnetic or electric force
• surface potential
• scanning thermal
• phase imaging

4
What is AFM?

• AFM, which can be operated in air or water,
  uses a fine tip to measure surface morphology and
  properties through an interaction between the tip
  and surface. Almost all materials can be measured
  without specific sample preparations.

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The Basic Principle of AFM

• 1. Laser
• 2. Mirror
• 3. Photodetector
• 4. Amplifier
• 5. Register
• 6. Sample
• 7. Probe
• 8. Cantilever

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Resolution

• The ability to distinguish two separate points on
  an image is the standard by which lateral
  resolution is usually defined.
• It is the radius of curvature of the tip that
  significantly influences the resolving ability of
  the AFM.

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AFM Provides

• Topographic images with a height resolution of
  0.1 nm and lateral resolution down to
  nanometers.
• Friction force images to distinguish different
  materials, phases, and chemical properties
• Adhesion forces on surfaces which can be a
  measure of surface energy (especially useful in
  revealing surface modifications).

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The Common AFM Modes

• Non-contact Mode
• Force- Feedback is from attractive
  Van der Waals forces
• Contact Mode
• Force- Feedback is from repulsive
  electronic forces
• Tapping Mode
• Probe oscillates between Non-Contact
  and Contact Regions

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Feedback Operation

• With feedback control
• ?constant force
• ?
  height mode
• Without feedback control
• ?constant height
• 
  ?deflection mode

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Chemical Structure of Phospholipids
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Phosphatidylcholine (PC)
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Lipid Organization
Amphiphilic structure Self-organization Inverted
micelle Inverted hexagonal cylinder Bilayer
vesicle Planar Bilayer Globular
micelle Hexagonal cylinder Micelle
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Temperature-Composition Phase Diagram of Hydrated
DMPC
Janiak, M. J., D. M. Small, and G. G. Shipley.
J. Biol. Chem. 1979 2546068-6078
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The Phase Transition of DPPC
Cited from Gregor Cevc, Derek Marsh
Phospholipid Bilayers 1987 Work done by Hinz and
Sturtevant 1972
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The Structure of Ripple Phase
W.-J. Sun, S. Tristram-Nagle, R. M. Suter, and
J. F. Nagle PNAS 1996 93 7008-7012.
c
J. Katsaras, S. Tristram-Nagle, Y. Liu, R. L.
Headrick, E. Fontes, P. C. Mason, and J. F.
Nagle Physical Review E May 2000 61 5668-5677
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The Advantages of AFM

• It allows for direct visualization of the ripple
  phase on the nanometer length scale in fully
  hydrated lipid bilayers at the relevant
  temperatures.
• It facilitates studies of structural changes of
  dynamic processes that occur on the minute
  timescale, which is exactly the relevant
  timescale for the structural rearrangements that
  take place at the pretransition.

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Height mode
Deflection mode
AFM image of a DPPC double bilayer
Chad Leidy, Thomas Kaasgaard, John H. Crowe, Ole
G. Mouritsen, and Kent Jørgensen Biophys. J.
2002 83 2625-2633
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Height mode
Deflection mode
Different ripple phases in double bilayer at 37C
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Height mode AFM images of different ripple phases.
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• Periodicity and amplitude of different ripple
  phases in DPPC lipid bilayers

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Ripple disappearance at the pretransition
The times elapsed after cooling to 32C are (A)
20 min (B) 46 min (C) 49 min and (D) 84 min.
Height mode
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Ripple formation at the pretransition
The times elapsed after heating to 35C are (B)
7 min (C) 10 min (D) 13 min (E) 17 min (F) 21
min (G) 24 min (H) 28 min and (I) 32 min.
Deflection mode
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Two Different Mechanisms

• One possible mechanism is by a homogeneous and
  continuous reduction of the ripple amplitude
  occurring simultaneously in the entire
  ripple-phase lipid bilayer.
• On the other hand, a certain ripple amplitude
  corresponds to a minimum in the free energy, an
  abrupt ripple disappearance would be more likely.

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Height mode
Deflection mode
Images of the interfacial region between a
L/2-ripple domain and several L-ripple domains in
a 73 DMPC-DSPC lipid bilayer at 26.0C.
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27.0C
27.5C
Deflection mode
Height mode
Interfacial melting at the solidus phase line.
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29.0C
28.0C
32.5C
30.0C
Deflection mode
Further melting, domain growth, and structural
rearrangements
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Conclusion

• The temperature-controlled AFM images have
  provided several examples of the anisotropic
  nature of ripple phases.
• The amplitudes of the three ripple types were
  estimated to be 12 Å, 50 Å, and 110 Å.
• The L/2-ripples are the thermodynamically stable
  ripple variety.
• The ripple phase is characterized by long-range
  two-dimensional hexagonal order of the
  phospholipids, and is responsible for distorting
  the underlying hexagonal lattice in a way that
  has important consequences for the melting
  behavior of ripple-phase lipid bilayers.

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Acknowledgements

• J. Daniel Gezelter
• Matt Meineke
• Teng Lin
• Charles F. Vardeman II
• Chris Fennell
• Eli Barkai
• S. Alex Kandel