Millicient A. Firestone, Amanda C. Wolf, and Sonke Seifert. Chris Bianchi 4/30/12

Transcription

1 Small-Angle X-ray Scattering of the Interaction of Poly(ethylene oxide)-b-poly(propylene oxide)-b- Poly(ethylene oxide)triblock Copolymers with Lipid Bilayers Millicient A. Firestone, Amanda C. Wolf, and Sonke Seifert Chris Bianchi 4/30/12

2 Background Polymer-a large molecule composed of repeating structural units. Copolymer-a polymer derived from two or more monomeric species. Lipid bilayer-cellular structure that acts as a barrier separating the outside of the cell from the inside.

3 Background eastman.com

4 What Was Studied? Mechanistic study of a commercial surfactant known as Pluronic on model lipid bilayers. Firestone, et al Specifically the interaction of structural variants of the triblock copolymer PEO-PP0- PEO with dimyristol-sn-glycero-3- phosphocholine (DMPC) lipid bilayers.

5 Why Study This? Potential pharmaceutical application by replacing lipid grafted polymers in liposomes. In addition for sealing damaged cell membranes in injuries such as heat shock, high dose radiation, and neurotoxic events.

6 Techniques Small-Angle X-ray Scattering at undulator 12ID-C of the Advanced Photon Source at Argonne National Laboratory were done on samples sealed in 1.5mm quartz capillaries. The sample-to-detector distance was such as to provide scattering vector range of /Å < q < 0.6/Å Thermal analysis was done using differential scanning calorimetry (DSC).

7 SAXS Theory Nielsen & McMorrow, 2010

8 SAXS Theory Sphere Long Wavelength Limit: QR<<1 Short Wavelength Limit: QR >>1

9 Results They first studied the affect of PPO chain length. Compared to SAXS profiles to two well characterized systems 1. Pure DMPC in solution 2. PEGlyated DMPE, DMPC, LDAO

10 Results The DMPC bilayer has two equally spaced Bragg peaks at q = 0.099/Å and q = 0.199/Å and d = 63 Å. PEG5000-DMPE has five distinct Bragg peaks at q = , , , , and Å and d = 257 Å. This is a swollen lamellar structure.

11 Results DMPC-Water PEG5000-DMPC Firestone, et al. 2003

12 Results Firestone, et al. 2003

13 PO Chain Length Effect Determined the effects of Pluronic F38, F68, F88, F98, and P85* Firestone, et al *This is a different physical form and was not used in first round of experiments

14 PO Chain Length Effect SAXS Pluronic # PO Repeat Units R g (Å) # Bragg Peaks q- Positions (1/Å) F , F , F , 0.094, 0.142, F , , 0.133, 0.174, d-spacing (Å) Summary 57 shallow insertion 57 shallow insertion 134 increased insertion from F38 F increased insertion from F38, F68, F88 *Bilayer hydrophobic moieties R g is 20 Å

15 PO Chain Length Effect SAXS DMPC-Water PEG5000-DMPC F38 F88 F68 F98 Firestone, et al. 2003

16 PO Chain Length Effect F38 and F68 F88 and F98 Firestone, et al. 2003

17 EO Chain Length Effect The authors hypothesize the PEO chain length and concentration are contributing factors to the structural properties of the bilayer. While the PPO chains integrate into the tail region of the bilayer the PEO moieties aggregate on the polar head region which produces a surface tension and leads to area expansion.

18 EO Chain Length Effect Pluronic # PO repeat units R g (Å) # EO repeat units # Bragg Peaks q- Positions ( 1/Å) P , 0.122, F , 0.094, 0.142, 0.189, d-spacing (Å) Summary 103 Swollen Lamellar Structure 134 Increase in long range ordering P85 F88 Firestone, et al. 2003

19 Concentration d-spacing (Å) 4 mol % mol % mol % mol % mol % Not sated (hexagonal phase emerges) EO Concentration Effect F98 *Reminder F98: #PO=47, #E0=117 commons/thumb/4/4d/micelle_scheme -en.svg/250px-micelle_schemeen.svg.png

20 EO Concentration Effect F98 Firestone, et al mol % 8 mol % 12 mol % 20 mol %

21 EO Concentration Effect F68 Insufficient number of PO molecular repeat units to span the bilayer. SAXS patterns were invariant under changes in concentration of F68. This suggest an interplay between both PO and EO chain length for d-spacing tuning and long range ordering of the bilayer.

22 Effect of Temperature F98 SAXS PPO block is more water soluble at lower temperatures. As temperature increases hydrophobicity increases and thus insertion of PPO block into the bilayer increases.

23 Effect of Temperature F98 SAXS Firestone, et al. 2003

24 Conclusions PEO-PPO-PEO can be used as alternatives to more costly and limited PEGlyated biomimetic nanostructures. When PPO block is less than bilayer thickness insertion is poor, but PEO chains adopt more of a flat orientation. If EO concentration is grater than 10 mol % a saturation limit is reached and micelles begin to form. Hydrophobicity of PPO block is dependent upon temperature.