Here described are compounds of formula I: wherein R1 and R2 is independently selected from a group consisting of C10 to C18 alkyl, C12 to C18 alkenyl, and oleyl group; wherein R3 and R4 are independently selected from a group consisting of C1 to C6 alkyl, and C2 to C6 alkanol; wherein X is selected from a group consisting of —CH2—, —S—, and —O— or absent; wherein Y is selected from —(CH2)n, —S(CH2)n, —O(CH2)n—, thiophene, —SO2(CH2)n—, and ester, wherein n=1-4; wherein a=1-4; wherein b=1-4; wherein c=1-4; and wherein Z is a counterion; as well as compositions and pharmaceutical formulations including compounds of formula I which are useful for the delivery of therapeutic agents; and methods of using these compositions and formulations.