Self-Assembly of Binary Phospholipids Mixtures

1
Self-Assembly of Binary Phospholipids Mixtures

• Yellow Group
• Peter Bowerman
• Andrea Hamill
• Ashish Jha
• Theresa LaFollette
• Tiffany Wilson
• Chaofang Yue
• Summer School June 2006

2
Experimental Background

• Long and short tail lipids dissolved in solution
• Useful in aligning proteins in solution to aid in
  structural NMR characterization
• SANS can be used to characterize the structures
  formed by lipid mixture at low temperature

3
Experiment Objectives

• To determine the average dimensions of the
  self-assembled aggregate
• derived from a Guinier analysis of the scattering
  at low Q
• Determine the shape of the self-assembled
  aggregate
• analyzing the scattering curves with different
  models
• Determine the internal structure of the
  self-assembled aggregate
• using selective deuteration in order to highlight
  only one lipid in the lipid mixture
• Characterize the morphology of the lipid mixture
• fitting simultaneously scattering curves from
  mixtures of hydrogenated and deuterated lipids

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Experiment Details
DMPC C36H72NO8P DHPC C20H40NO8P
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Experiment Details

• Samples (ratio DMPC/DHPC is 3 to 1)
• 5 DMPC/DHPC in D2O
• 5 d-DMPC/DHPC in D2O
• 2 DMPC/DHPC in D2O
• 5 DMPC/DHPC in D2O with NaCl
• The 2 samples phase separated, no analysis
• Distance(1m, 4.5m, 15.3m)
• Measurements
• Neutrons scattered by sample
• Transmission (sample dependent)
• Empty Cell (distance and sample dependent)
• Blocked Beam (distance and sample dependent)

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Instrument- NG-7 SANS
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Instrument Characteristics
Source Neutron guide (NG-7), cross section 50 mm x 50 mm
Monochromator Mechanical velocity selector with variable speed and pitch
Wavelength Range 5.0 to 20.0 Å
Wavelength Resolution 10 to 22 ??/?(FWHM)
Source-to-Sample Distance 4 to 16 m in 1.5 m steps via insertion of guide sections
Sample-to-Detector Distance 1.0 to 15.3 m continuously variable
Collimation Circular pinhole collimation or focusing biconcave lenses
Sample Size 5 to 25 mm diameter
Q-range 0.008 to 7.0 Å-1
Size Regime 1 to 500 nm
Detector 640mm x 640 mm 3He position-sensitive proportional counter (5 mm x 5 mm resolution)
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Data
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Reasoning Different Shapes
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Core-Shell Cylinder
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Results - Hydrogenated
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Global AnalysisPolydispersed Core-Shell Cylinder
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Results - Deuterated
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Final Model
56 A
53 A
12 A
See physical model for better visualization
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Conclusion

• The mixture forms a bicelle shape common among
  surfactants with different tail lengths
• For NG-7 SANS testing information, refer to the
  website

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