X is a member selected from the group consisting of ???O??? and ???NH???; R1 and R2 are each members independently selected from the group consisting of (C2-C24)acyl; R3 is a member selected from the group consisting of ???H and ???PO3R11R12, wherein R11 and R12 are each members independently selected from the group consisting of ???H and (C1-C4)alkyl; R4 is a member selected from the group consis