Internal structure of 15 nm 3-helix micelle revealed by small-angle neutron scattering and coarse-grained MD simulation

Transcription

1 Internal structure of 15 nm 3-helix micelle revealed by small-angle neutron scattering and coarse-grained MD simulation JooChuan Ang 1, Dan Ma, Reidar Lund 3, Sinan Keten, and Ting Xu *1,4,5 1 Department of Materials Science and Engineering, University of California, Berkeley 9470, USA Department of Civil and Environmental Engineering and Department of Mechanical Engineering, Northwestern University, Evanston, Illinois 6008, USA 3 Department of Chemistry, University of Oslo, P.O.Box 1033, Blindern, N-0315 Oslo, Norway 4 Department of Chemistry, University of California, Berkeley 9470, USA 5 Material Science Division, Lawrence Berkeley National Laboratory, Berkeley 9470, USA *Corresponding author: tingxu@berkeley.edu 1

2 Supplementary Information SANS modeling and fitting A core- model was used to describe the radial SLD profile of 3HM. The total scattering intensity can be written as: I C S φ ( = PV tot ( P V + P( P F(0)) V V sp core core + P V sp + V F ( ) where P is the aggregation number, = + is the total volume of a single amphiphile, = +, and =. The scattering amplitude of the layers can be described by: = 1/ Vsp ( Vp p p+ V ) The radial density profile is: (,, )= ( ) n(r) = 1 for j=id n(r) pep = n(r,, ) for j=peptide n(r) = n(r,, ) for j= where r is the distance from the center of the micelle, is the outer smearing factor for the component j, and = + is the cutoff thickness. = ⅓ = where M j is the molecular weight, N A is Avogadro s number, and d j is the density of the component j. The scattering amplitude of the individual components can be calculated according to: For id: =0, = =, =0 () = () 4 () For peptide: =1, = =, = = For : =, =, = The effective form factor 1, F(, can be calculated from the form factor of a single, P(, according to the following equation: F ( = P( /(1+ υp( ) P( = exp( Q R g / 3)+ d f /R g d f Γ(d f /) (erf(r g Q 1.06/.44948) 3 / d f Small-Angle X-ray Scattering (SAXS)

3 SAXS experiments were carried out at the SAXS/WAXS beamline 7.3.3, Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory (LBNL). The instrument was operated using an X-ray energy of 10 kev and a sample detector distance of 1.9 m, providing a Q-range of to 0.4 Å 1, where Q = ((4π)/λ)sin(θ/), θ = scattering angle, and λ = 1.4 Å. The instrument was equipped with a 1 M Pilatus detector. The samples were loaded in standard boron-quartz capillaries (Charles Supper) held in a customized sample holder that permitted the sample to be filled and removed using a syringe. In this way, background subtraction could be made quantitatively and absolute intensity calibration was possible using water as a primary standard. The sample was dissolved in phosphate buffer (5 mm, ph = 7.4) at concentrations of 0.8 mm. The sample was filtered through a 0. µm nylon filter and monitored closely to account for possible beam damage. It was found that no radiation damage was visible for 5 s acquisition times. Matrix-Assisted Laser Desorption Ionization (MALDI) 1 µl of dc16-1cw(d) (1 mg/ml) was added to an equal volume of α-cyano-4- hydroxycinnamic acid (10 mg/ml) matrix solution, the mixture was spotted and dried for 15 minutes on a stainless steel MALDI plate and the spectrum was collected on a MALDI-TOF (Applied Biosystems). 000 Intensity g/mol 594 g/mol m/z SI Figure 1. MALDI of dc16-1cw(d), m/z of 48 g/mol indicates the presence of deuterated ethylene oxide repeat units. 3

4 SI Figure. a) SAXS profile of 3HM with at the 14 position. b) Radial density profiles of the different components of 3HM. SI Figure 3. The aggregation number for the micelle selected for all the analyses in CGMD as a function of simulation time. SI Table 1. Repulsion parameter used for the interactions between the different bead-types in MD DPD model. water alkyl peptide 4

5 water alkyl peptide SI Table. Thicknesses of peptide,, and alkyl layers within 3HM from SANS and CGMD, reported in two different ways: (1) full-width at half maximum (FWHM) and () range of the distribution representing 95% of each component. FWHM 95% Thickness of component SANS (Å) CGMD (Å) SANS (Å) CGMD (Å) alkyl peptide References 1. Pedersen, J. S.; Svaneborg, C.; Almdal, K.; Hamley, I. W.; Young, R. N., A small-angle neutron and X-ray contrast variation scattering study of the structure of block copolymer micelles: Corona shape and excluded volume interactions. Macromolecules 003, 36, (), Beaucage, G., Small-angle scattering from polymeric mass fractals of arbitrary massfractal dimension. Journal of Applied Crystallography 1996, 9,