Biodegradable lipids for the delivery of active agents

A lipid consisting of a protonatable primary group and two hydrophobic tails that are directly bonded to the protonatable primary group, wherein

• each of the two hydrophobic tails are of the formula -(hydrophobic chain)-(C(O)O)-(hydrophobic chain);
• and
• each of the two hydrophobic tails has a total carbon atom content of from 17 to 26 carbon atoms, wherein
• at least one hydrophobic tail is of the formula:
• wherein R13 is a C1-C17 alkyl, wherein
• the maximum length of R13 from its attachment point to the ester group is 12 carbon atoms, and
• R13 comprises (i) a carbon atom that is directly bonded to the ester, (ii) two alkyl groups directly bonded to the carbon atom that is bonded to the ester, and (iii) a hydrogen atom directly bonded to the carbon atom that is bonded to the ester.