The present invention provides, in part, a biodegradable compound of formula I, and sub-formulas thereof:or a pharmaceutically acceptable salt thereof, where each X independently is O or S, each Y independently is O or S, and each R1 independently is defined herein； and a liposome composition comprising the cationic lipid of formula I or a sub-formula thereof, and methods of delivering agents, such as nucleic acids including mRNA, in vivo, by administering to a subject the liposome comprising the cationic lipid of formula I or a sub-formula thereof, where the agent is encapsulated within the liposome.
