1. Determining Structure and Composition of a Model Phospholipid Bilayer ORANGE TEAM Monica Branco Suh Joon Han Matthew Helgeson Kathryn Krycka Jong Keun Park Chu Xiangiang

2. Phospholipid Bilayers Phospholipid bilayers serve as biomimetic membranes Lipids self-assemble into ordered, multi-layer structure Our system: DMPC –Phospho-choline head group –C 14 hydrocarbon chains

3. Advanced Neutron Diffractometer/Reflectometer Reflection of incident beam based on Bragg diffraction: Slit #2 Slit #1 Slit #3 Slit #4 monitor monocromator sample detector   θ 2θ2θ kiki krkr ktkt QzQz

4. Experiment Objectives Determine quantitative structural information –Bilayer thickness –Bilayer composition profiles –Solvent penetration –Extent of thermal fluctuation

5. Sample Preparation Deposition of lipid solution on glass slide Solvent evaporation Hydration of bilayer film in sample chamber (75% RH) Allow for sample equilibration at 37ºC I(Q) Q (Å -1 ) Glass slide

6. Determination of Bilayer Spacing Phase problem: 100% H 2 O 50/50 H 2 O/D 2 O 100% D 2 O I(Q) Q (Å -1 ) n=1 n=2 n=3 n=4 n=5 Phospholipid bilayer spacing: d = 49.3 Å

7. Solving the Phase Problem Variation of solvent conditions: H 2 O  D 2 O 100% H 2 O 50/50 H 2 O/D 2 O 100% D 2 O I(Q) Q (Å -1 )

8. Scattering Length Density Profiles SLD profiles for lipid C-H chains:

9. Bilayer Composition Determination Selective deuteration of solvent and lipid:

10. Water and Hydrocarbon Profiles Subtraction of profiles allows for identification of species profiles: V CH2 =27 Å 3 V CH3 =54 Å 3

11. Conclusions AND/R allows for detailed, quantitative structural and compositional characterization of biomimetic bilayers –Solving the phase problem –Selective contrast variation Further experiments –Site-specific D-labeling –Protein incorporation