Gene delivery agents

A compound of Formula I:

• in which
• YA is H or C1-C4 alkyl;
• ZA is C1-C30 amino, C1-C30 amido, C1-C30 carbonyl, C1-C30 carboxylate, or triazolyl;
• ZB is
• each of LC or LD is O;
• ZC is ZC2-XC-XC-ZC3, in which XC is S, ZC2 is C4-C10 alkylene, and ZC3 is C6-C12 alkyl or alkenyl;
• ZD is C4-C10 alkylene substituted with C6-C12 disulfanyl, in which disulfanyl contains C6-C12 alkyl or alkenyl;
• LK1 is
• or C3-C8 alkylene;
• LK2 is a bond or C1-C8 alkylene;
• each of LK3 and LK4 is —(CH2)2—;
• and
• wherein the compound has 40 to 100 carbon atoms.