The Transport and Organization of Cholesterol in Planar Solid-Supported Lipid Bilayer Depend on the Phospholipid Flip-Flop Rate

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1 Supporting Information The Transport and Organization of Cholesterol in Planar Solid-Supported Lipid Bilayer Depend on the Phospholipid Flip-Flop Rate Ting Yu, 1,2 Guangnan Zhou, 1 Xia Hu, 1,2 Shuji Ye 1,2,* 1 Hefei National Laboratory for Physical Sciences at the Microscale, and Department of Chemical Physics, and 2 Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, nhui , China 1. SFG-VS Experiments. Details regarding SFG theories and instruments have been reported previously. 1-5 In briefly, SFG is composed of a fixed visible beam (532 nm) and tunable IR laser beam (1000~4000 nm). The energy of visible beam and IR beam at cm -1 and cm -1 is about 10 µj and 40~50µJ, respectively. The incidence angle at CaF 2 surface was 53 for the IR beam and 63 for the visible beam. The SFG setup is similar to that described in our earlier publications. 6, 7 2. Fitting of SFG-VS Signals. s described in detail elsewhere, the intensity of the SFG light is related to the square of the sample's second-order nonlinear susceptibility( χ ), and the intensity of the two input fields I( ωir ) and I ( ω vis ), see eq. (S1), which vanishes when a material has inversion symmetry ( SFG eff 1 vis 2 I ω ) χ I ( ω ) I ( ω ) (1) IR eff where ω = ω + ω. The frequency dependence of SFG IR vis χ eff is described by eq. (S2) S1

2 χ eff ( ω) = χ NR + χ Re s = χ NR + ω ω + iγ where, ω, and Γ are the strength, resonant frequency, and damping coefficient of the vibrational mode(ν), respectively. χ NR and χ Re s are the non-resonant background and the resonant signals of the vibrational mode(ν). could be either positive or negative depending on the phase of the vibrational mode. s the IR beam frequency is tuned over the vibrational resonance of surface/interface molecules, the resonant signals χ Re s can be enhanced. The plot of SFG signal vs. the IR input frequency shows a polarized vibrational spectrum of the molecules at surface or interface., ω, and Γ can be extracted by fitting the spectrum. 3. The possible forms in the organizations of cholesterol in lipid bilayer Figure S1. Six possible forms in the organizations of cholesterol in lipid bilayer in equilibrium. Because the organizations in head to tail and head to head manners don t favor the van der Waals interactions and facilitate the maximal molecular packing, we do not list them in the possible forms. S2

3 In Figure S1, cholesterol is a molecule comprising a flexible isooctyl hydrocarbon tail and a near planar steroid ring (denoted as the head of cholesterol). The plane of the steroid ring is asymmetric. We refer the flat and smooth side without substituents as the α face and the rough side with substituents of chiral methyl groups as β face. In Figure S1a, S1b and S1c, the cholesterol is only distributed in one leaflet of the bilayer, the ssp or ppp signals of methyl group in the isooctyl hydrocarbon tail cannot be cancelled. In Figure S1d, S1e, and S1f, cholesterol flips from one leaflet to another leaflet and organizes itself in tail to tail manner, the achiral ssp or ppp signals from the methyl groups in the tail can be effectively canceled. In Figure S1b, S1c, and S1d, the methyl substituents in the cholesterol pair orient in the opposite direction, therefore, the chiral psp signals from the methyl substituents of sterol ring can be effectively eliminated with the formation of α-α and β-β structures. In contrast, in Figure S1a, S1e and S1f, the cholesterol pair forms α-β structures, and the methyl substituents in the cholesterol pair orient in the same direction. Therefore, such α-β structures will have large chiral psp signals. Here, the side-by-side organizations of the α-α, β-β and α-β structures are α face by α face, β face by β face, and α face by β face, respectively. 4. The molecular structure of phospholipids. 1,2-dimyristoyl-sn-glycerol-3-phosphocholine (DMPC) 1,2-dipalmitoyl -sn-glycero-3- phosphocholine (DPPC) 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) S3

4 1,2-dimyristoyl-d 54 -sn-glycero-3-phosphocholine-1,1,2,2-d 4 -N,N,N-trimethyl-d 9 (d-dmpc) 1,2-dipalmitoyl-d 62 -sn-glycero-3-phosphocholine-1,1,2,2-d 4 -N,N,N-trimethyl-d 9 (d-dppc) 1,2-distearoyl-d 70 -sn-glycero-3-phosphocholine-1,1,2,2-d 4 -N,N,N-trimethyl-d 9 (d-dspc) 1,2-dimyristoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) (DMPG) 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) (DPPG) 1,2-distearoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) (DSPG) S4

5 1,2-dimyristoyl-d 54 -sn-glycero-3-[phospho-rac-(1-glycerol)] (sodium salt) (d-dmpg) 1,2-dipalmitoyl-d 62 -sn-glycero-3-[phospho-rac-(1-glycerol)] (sodium salt) (d-dppg) 1,2-distearoyl-d 70 -sn-glycero-3-[phospho-rac-(1-glycerol)] (sodium salt) (d-dspg) Figure S2. The molecular of cholesterol(chol), cholesterol-d 7 (d-chol) and all the used lipids. 5. The ssp spectra in the frequency range of cm -1 for the phospholipid monolayer in the air surface c) Wavenumber (cm -1 ) d) e) f) Wavenumber (cm -1 ) g) h) i) Wavenumber (cm -1 ) Figure S3. The ssp spectra in the frequency range of cm -1 for the phospholipid monolayer in the air surface. DMPC; DPPC; c) DSPC; d) d-dmpc; e) d-dppc; f) d-dspc; g) d-dmpg; h) d-dppg; i) d-dspg. S5

6 6. The SFG spectra from DXPC/(DPPC+d-Chol) and d-dxpc/(dppc+chol) B C 5 0 Time(min) Wavenumber(cm -1 ) Wavenumber(cm -1 ) Figure S4.) The time-dependence of the ssp SFG intensity at 2075 cm -1 during the formation of the lipid bilayer. B) The ssp SFG spectra in the frequency region from cm -1 after flip-flop reaches equilibrium. C) The ppp SFG spectra in the frequency region from cm -1 after flip-flop reaches equilibrium. DMPC/(DPPC+d-Chol); DPPC/(DPPC+d-Chol) Time(min) B Wavenumber(cm -1 ) C Wavenumber(cm -1 ) Figure S5.) The time-dependence of the ssp SFG intensity at 2075 cm -1 during the formation of the lipid bilayer. B) The ssp SFG spectra in the frequency region from cm -1 after flip-flop reaches equilibrium. C) The ppp SFG spectra in the frequency region from cm -1 after flip-flop reaches equilibrium. d-dmpc /(DPPC+Chol); d-dppc/(dppc+ Chol). S6

7 7. The surface pressure-area (π-) isotherms of d-dspc and DSPC at air/di water interface. Surface pressure (mn/m) DSPC d-dspc Mean molecular area( 2 /molecule) Figure S6. The surface pressure-area (π-) isotherms of d-dspc and DSPC at air/di water interface at 24 C. Because of isotopic effect, the surface molecular density of d-dspc is larger than DSPC at the surface pressure of 35 mn/m, at which the monolayer was deposited on CaF 2 surface. 8. The time-dependence of the ssp SFG intensity at 2075 cm -1 of d-dppc/(dppc+chol) and d-dppc/dppc. SFG intersity Time(min ) Figure S7. The time-dependence of the ssp SFG intensity at 2075 cm -1 from the CD 3 group of the lipid. d-dppc/(dppc+chol); d-dppc/dppc. From the picture, we can see the flip-flop rate of d-dppc in bilayer d-dppc/(dppc+chol) is much faster than the one in the bilayer of d-dppc/dppc, suggesting the cholesterol S7

8 facilitates the flip-flop of lipids in the neutral phospholipid bilayer. 9. The lipid and cholesterol show a synchronous flip-flop behavior in the bilayer. Time(min) Figure S8. The time-dependence of the ssp SFG intensity at 2075 cm -1 from the CD 3 group of the bilayer: DPPG/(DPPC+d-Chol); d-dppg/dppc. The intensity (red curve) from d-dppg is divided by The static spectra in equilibrium from d-chol after DPPG/(DMPC+d-Chol) and d-dppg/dmpc at the 0.05mol/L KCl subphase ssp ppp Wavenumber ( cm -1 ) B ssp ppp Wavenumber ( cm -1 ) Figure S9. ) The ssp and ppp SFG spectra from d-chol after DPPG/(DMPC+d-Chol) flip-flop reaches equilibrium at the 0.05mol/L KCl subphase. B) The ssp and ppp SFG spectra from d-dppg after d-dppg/dmpc flip-flop reaches equilibrium at the 0.05mol/L KCl subphase. S8

9 11. The time-dependence of the ssp SFG intensity at 2075 cm -1 of d-dxpg/dmpc and d-dxpg/(dmpc+chol) (Here, X=P or S) c) d) 0.0 Time ( min ) 0.0 Time ( min ) Figure S10. The time-dependence of the ssp SFG intensity at 2075 cm -1 from the CD 3 group in the bilayers of d-dxpg/dmpc and d-dxpg/(dmpc+chol).. d-dppg/dmpc;. d-dppg/(dmpc+chol); c). d-dspg/dmpc; d). d-dspg/(dmpc+chol) For d-dppg/dmpc and d-dppg/(dmpc+chol), the ssp SFG intensity at 2075 cm -1 from the CD 3 group of d-dppg in bilayers, the lipid d-dppg shows almost the same flip-flop rates in the bilayers of d-dppg/dmpc and d-dppg/(dmpc+chol). But it is different from the cholesterol in d-dxpc/(dxpc+chol) bilayer,the cholesterol does not accelerate the lipid flip-flop in negative lipid bilayer. The d-dspg/dmpc and d-dspg/(dmpc+chol) also shows the same conclusion. S9

10 12. The control experiments on the single component bilayer c) d) Wavenumber (cm -1 ) Figure S11. The chiral psp spectra for the control experiments on the single component bilayer. DMPC/DMPC; DPPC/DMPC; c) DMPC/DPPC; d) DPPC/DPPC. No chiral signal is detected. 13. The psp spectra from cm -1 of DMPC/(DMPC:d-Chol=1:2) psp Wavenumber ( cm -1 ) Figure S12. The psp SFG spectra from d-chol in PC: d-chol=1:2 mixtures. Reference: (1) Castellana, E. T.; Cremer, P. S. Solid Supported Lipid Bilayers: From Biophysical Studies to Sensor Design. Surf. Sci. Rep. 2006, 61, Shen, Y. R. The Principles of Nonlinear Optics; Wiley: New York, S10

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