Energy transfer in artificial membrane systems. Singlet-singlet energy transfer from alloxazines to isolloxazines in dipamitoyl phosphatidylcholine liposomes and dialkylammonium chloride vesicles.

The singlet-singlet energy transfer from alloxazines to isoalloxazines has been investigated in dialmitoyl phosphatidylcholine (DPPC) liposomes and dioctadecyltrimethylammonium chloride (2C18NC) vesicles to clarify the role of the artificial membranes in the energy transfer phenomenon. The structures of the artificial membranes were divided into two types: the single-walled (sonicated DPPC) and the multi-compartment vesicles (unsonicated DPPC and sonicated 2C18NC). In the DPPC single-walled liposomes, the energy of the donor lost by quenching is efficiently transferred to the acceptor via the Förster-type dipoledipole interaction. In the case of multi-compartment liposomes of DPPC, the mean distance between donor and acceptor is so small because the external surface of a bilayer is in the vicinity of the internal surface of another bilayer. As a consequence, efficiencies both of energy transfer and of energy loss were greater than those in single-walled liposomes. The fluid property of the 2C18NC bilayer allowed the preferential collisional quenching. The marked reduction in the efficiencies of both energy transfer and energy loss were attributed to the elongation of donor-acceptor distances due to the increase of the size of liposome.