Studies on Langmuir monolayers of polyprenyl phosphates towards a possible scenario for origin of life

Although some biological components such as RNA are believed to play a crucial role in the processes which led to the formation of the first living systems, we cannot ignore the importance of lipids in the genesis of cell membranes. To answer the fundamental question of what the oldest cell-forming components were the Ourisson/Nakatani group has extensively investigated the origin of lipids and they have proposed polyprenyl phosphates and related molecules as plausible candidates for precursors of modern lipids. These molecules have been demonstrated as being capable of forming vesicle structures, and this feature has been extended to preparation of Langmuir monolayers of polyprenyl phosphates in collaboration with the Ourisson/Nakatani group. In this review, after a brief outline of chemical evolution of cell components, we summarize research on Langmuir monolayers of polyprenyl phosphates and related molecules. Two topics are described: the evaluation of any reinforcing effects and the determination of interfacial acid dissociation. Rules governing reinforcing effects in molecular structures and unusual shifts of acid dissociation constants at interfaces were established. Finally, we propose a revised possible scenario of how the first cell-like membranes formed based on the former results.