The Structure of Phosphor Lipid Membranes Embedded with

n-Alcohols Investigated by SAXS and MD-Simulations

Ulf Rørbæk Pedersen (RUC)

Supervisors

Dorthe Posselt (RUC)Peter Westh (RUC)

Güenter Peters (DTU)

Introduction

Method:● Small angle x-ray scattering (SAXS)● Molecular Dynamics Simulations (MD-simulations)

System: DMPC/hexanol (MD-simulations)and similar systems (SAXS)

SAXS Model

Smearing from line shaped beamin Kratky camera ( )

q = |kin - kout|

SAXS data

DMPC/hexanolDMPC

DMPC

DMPC/hexanol

elek

tron

den

city

[a.

u.]

SAXS data

Molecular Dynamic Simulations

Program: NAMD

Force Field: CHARMM27

with modified charges in headgroup , RHF 6-31G*.

TIP3 water

Constant NPT, P=1 atm (Nosé-Hoover Langevin piston)

Periodic boundary conditions

Full electrostatics(Particle Mesh Ewald)

Time step: 1 fs(velocity Verlet integration method)

Membrane area

A=59.6 Ų (30˚C)

Density profile

Voronoi Volumes

number carbon in acyl chain

mea

n vo

rono

i vol

ume

[ų]

VDMPC=1101 ų

Order parameter

carbon number in acyl chain

Flip-flop event

t = 0.4 ns

Summary

Alcohol molecules intercalate with the hydroxy group in the hydrophilic part and the acyl chain parallel to

the fatty acids

n-hexanol in a membrane introduces● a reduction of the thickness (SAXS) ● a condensations of the area (MD)● a softer membrane (MD)● more free volume in inner part of membrane (MD)● more order in outer part of membrane (MD)● less order in inner part of membrane (MD)

Perspectives

● How can we modify the properties of a membrane by doping?● Permeability● Concentration dependence● The dependence of alcohol length● Other doping molecules (cholesterol, other anesthesia)● MD-Pulling experiment

Equations

SAXS of MLV

Distribution of Voronoi Volumes

Density profile

Literature