The order / disorder transition of the phospholipid 1,2-dihexadecyl-sn-glycero-3-phosphocholine and its derivatives was stud-Millipore filtered water is used throughout the experiment.
ied by X-ray reflection and thermodynamic measurements. We 1,2-Dihexadecyl-sn-glycero-3-phosphocholine (DHPC) was find that increasing the length of an ethylene oxide spacer ( zero obtained chromatographically pure from Fluka, Switzerland to three EO groups ) between the phosphate group and the hyand used as delivered without further purification.
drophobic chains ( i ) induces a slight shift of the main transition, ( ii ) reduces the influence of the head groups on the chain lattice,
The racemic one-to three-spacer derivatives DH(EO) 1 PC, and ( iii ) increases the head group length and promotes its hy-DH(EO) 2 PC, and DH(EO) 3 PC were kindly synthesized by dration. For DH ( EO ) 3 PC in the ordered phase we find that the B. Rattay at the Institute of Pharmaceutical Chemistry, Marsmall phosphate groups ( which are the main source of contrast tin Luther University, Halle, Germany. They are chromatoin X-ray reflectivity ) are homogeneously distributed within the graphically pure. head group region. In the fluid phase the phosphate groups are
The chemical structure of the molecules is given in Fig. .
preferentially oriented toward the air / water interface. ᭧ 1996
The substances are vacuum-dried and dissolved in chloro-Academic Press, Inc.