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Bilayer thickness and lipid interface area in unilamellar extruded 1,2-diacylphosphatidylcholine liposomes: a small-angle neutron scattering study

2001; Elsevier BV; Volume: 1512; Issue: 1 Linguagem: Inglês

10.1016/s0005-2736(01)00298-x

1879-2642

Pavol Balgavý, Martina Dubničková, Norbert Kučerka, М. А. Киселев, S. Yaradaikin, Daniela Uhrı́ková,

Spectroscopy and Quantum Chemical Studies

Small-angle neutron scattering (SANS) experiments have been performed on large unilamellar liposomes prepared from 1,2-dilauroylphosphatidylcholine (DLPC), 1,2-dimyristoyl-phosphatidylcholine (DMPC) and 1,2-distearoylphosphatidylcholine (DSPC) in heavy water by extrusion through polycarbonate filters with 500 Å pores. The neutron scattering intensity I(Q) in the region of scattering vectors Q corresponding to 0.0015 Å−2≤Q2≤0.0115 Å−2 was fitted using a step function model of bilayer neutron scattering length density and supposing that the liposomes are spherical and have a Gaussian distribution of radii. Using the lipid volumetric data, and supposing that the thickness of bilayer polar region equals to dH=9±1 Å and the water molecular volume intercalated in the bilayer polar region is the same as in the aqueous bulk aqueous phase, the steric bilayer thickness dL, the lipid surface area AL and the number of water molecules per lipid molecule N intercalated in the bilayer polar region were obtained: dL=41.58±1.93 Å, AL=57.18±1.00 Å2 and N=6.53±1.93 in DLPC at 20°C, dL=44.26±1.42 Å, AL=60.01±0.75 Å2 and N=7.37±1.94 in DMPC at 36°C, and dL=49.77±1.52 Å, AL=64.78±0.46 Å2 and N=8.67±1.97 in DSPC at 60°C. After correcting for area thermal expansivity α∼0.00417 K−1, the lipid surface area shows a decrease with the lipid acyl chain length at 60°C: AL=67.56±1.18 Å2 in DLPC, AL=66.33±0.83 Å2 in DMPC and AL=64.78±0.46 Å2 in DSPC. It is also shown that a joint evaluation of SANS and small-angle X-ray scattering on unilamellar liposomes can be used to obtain the value of dH and the distance of the lipid phosphate group from the bilayer hydrocarbon region dH1.