| abstract |
A lipid represented by the formula: n n nwherein each of R 1 and R 2 is an alkyl or alkenyl chain having between about 8 to about 24 carbon atoms; n=0-20; L is selected from the group consisting of (i) —X—(C═O)—Y—, (ii) —X—(C═O)—, and (iii) —X—CH 2 —, wherein X and Y are independently selected from oxygen, NH and a direct bond; and Z is a weakly basic moiety that has a pK of less than about 7.4 and greater than about 4.0 is described. |