Structural Investigation of L Phases Formed by 1-Palmitoyl-2-oleoylphosphatidylnucleosides

¹ University of Florence and CSGI, Italy
² Hahn-Meitner-Institut, TU-Darmstadt, Germany

^* To whom correspondence should be addressed. E-mail: debora.berti{at}unifi.it.

Submitted on June 1, 2005
Revised on June 28, 2005
Accepted on 31 October 2005

	Abstract

Bilayers of palmitoyl-oleoyl phosphatidylnucleoside derivatives (POP-Adenosine and POP-Uridine) have been investigated in the low-water content regime by a combination of neutron diffraction and linear FTIR dichroism. Attention has been focused on the modulation of structural properties operated by the presence and the kind of nucleic acid base (either adenosine or uridine, a complementary pair in RNA). Base substitution causes major differences in phase behavior of the phospholipids, i.e. water sorption from a controlled humidity atmosphere and smectic periodicity. The profile of scattering length density of the lamellar phase can be inferred from five diffraction orders for POP-Uridine. POP-Adenosine is characterized by a lower hydration degree and a powder like nature of the sample. A LD-FTIR investigation on the same lamellar phases has been undertaken with the purpose to gather details at submolecular level on different portions of the molecule. POPC bilayers have been also investigated with the same technique for the sake of comparison. Besides a confirmation of the diffraction data, FTIR has also provided evidence that the same chemical groups at the bilayer interface (namely the sugar-phosphate) have a different orientation depending if the base is a purine or a pyrimidine. A very simple geometrical optimization agrees with this observation. This indicates that a different pattern of base interaction is operating in the two cases and that base substitution acts as a modulator of the phase properties.

Key Words: FTIR linear dichroism, lipid membranes, neutron diffraction, phosphatidylnucleosides