Multiple Bilayer Dipalmitoylphosphatidylserine LB Films Stabilized with Transition Metal Ions

Langmuir−Blodgett films of dipalmitoyl- dl -α-phosphatidyl- l -serine (DPPS) have been transferred from aqueous subphases containing the 0.1 mM transition metal compounds K 2 PdCl 4, K 2 PtCl 4, K 2 Pt(CN) 4, KAuCl 4, and Cd[ClO 4 ] 2 . This report provides a detailed description of the formation and structural characterization of the multiple bilayer films of DPPS that are formed. The films were characterized through a combination of attenuated total reflectance Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and solid-state 31 P NMR. The results show that the films are layered, there are two types of DPPS molecule in the films, and the metals are incorporated as positive ions that bridge phospholipids by complexing amines of the serine headgroups. Water molecules likely occupy the remaining coordination sites of the metal complexes, leading to a proposed stoichiometry of [Pt(DPPS - ) 2 (OH 2 ) 2 ](DPPS) 4 . The metal ions stabilize film formation by screening repulsive interactions between the serine headgroups through the formation of coordinate covalent bonds.