Deformation of lipid membranes containing photoresponsive molecules in response to ultraviolet light

Recently, membrane deformation using photoresponsive molecules has been extensively studied toward controlling their shapes because light can supply energy without contacting the vesicles. In this study, photoresponsive pseudogem-bis(diphenylimidazole) [2.2]paracyclophane (pseudogem-bisDPI[2.2]PC) molecules were doped into dioleoylphosphatidylcholine (DOPC) membranes, and the deformation of the DOPC/pseudogem-bisDPI[2.2]PC vesicles was observed under ultraviolet (UV)-light irradiation. It was also found that the volume-to-surface area ratio of spherical vesicles was changed by UV irradiation. Further, we performed high performance liquid chromatography (HPLC) analysis of membrane components in order to clarify the absence of irreversible chemical reactions and UV-irradiation experiments under an osmotic pressure in order to investigate the volume change of the vesicles. Then, we calculated the time-correlation function of membrane fluctuation. Change in the relaxation time of the time-correlation function indicated that the photoisomerization of pseudogem-bisDPI[2.2]PC might decrease the membrane fluidity. We consider that decreasing fluidity is induced by physical entanglement between photochromic compounds and lipids. This technique of membrane deformation may be expected to be applied to various situations such as drug delivery systems (DDS).