Interaction of porphyrin/oligonucleotide complex with liposomes studied by drop coating deposition Raman spectroscopy

Drop coating deposition Raman (DCDR) microspectroscopy was used to investigate interaction of the complexed cationic copper 5,10,15,20-tetrakis(1-methyl-4-pyridyl) porphyrin (CuP) and phosphorothioate analog of dT(15) oligonucleotide with liposomes, the lipid composition of which imitated the natural plasmatic membrane. Great advantage of dried drops on DCDR plates over a solution sample is that the specific drying process on the special hydrophobic surface efficiently separates liposomes from small species in the solvent. In our case, liposomes with bound CuP/oligonucleotide complexes formed a ring at the edge part of the dried drop while dried solution of this complex remained inside this ring. High quality spectra measured from the ring by using Raman confocal microspectrometer revealed unperturbed arrangement of lipid chains by the drying process, partial binding of the CuP/oligonucleotide complexes to liposomes, and a certain reorientation of lipid chains as a consequence of this interaction.