Nucleotide chain length and the morphology of complexes with cationic amphiphiles: P-31-NMR observations

P-31-NMR and UV spectroscopies were used to study the interactions between cationic amphiphile-containing lipid bilayers and either a phosphorothioate oligonucleotide (OligoS) (n = 21) or polyadenylic acid (PolyA) (n approxim ate to 18 000). Multilamellar vesicles (MLVs) were composed of 1-palmitoyl- 2-oleoyl-sn-glycero-3-phosphocholine (POPC) or 1,2-dioleoyl-sn-glycero-3-ph osphoethanolamine (DOPE) in binary mixture with either of the cationic lipi ds, N-[1-(2,3-dioleoyloxy)propyl]-N',N',N'-trimethylammonium chloride (DOTA P) or cetyltrimethylammonium bromide (CTAB). A UV-difference assay showed t hat OligoS binding ceased above a 1:1 anion/cation ratio, while PolyA bindi ng continued until a 2:1 ratio was reached, indicating a 'flat' conformatio n for bound OligoS, but not necessarily for PolyA. Cross-polarization P-31- NMR of the nucleotide chains bound to 100% DOTAP MLVs produced spectra virt ually identical to those of dry powders of OligoS or PolyA, indicating effe ctive immobilization of the surface-bound nucleotide chains. Hahn echo P-31 -NMR showed that MLVs composed of binary mixtures of POPC with DOTAP or CTA B retained a lamellar bilayer architecture upon adding nucleotide chains. A t less than stoichiometric anion/cation ratios little or no signal attribut able to free nucleotide chains was visible. A narrow signal at the chemical shift expected for phosphorothiodiesters or phosphodiesters became visible at greater levels of added OligoS or PolyA, respectively, indicating the p resence of mobile nucleotide chains. Salt addition caused complete desorpti on of the nucleotide chains. When POPC was replaced with DOPE, binding of O ligoS or PolyA produced non-bilayer lipid phases in the presence of DOTAP, but not in the presence of CTAB. (C) 2000 Elsevier Science B.V. All rights reserved.