A lipid particle comprising: (a) a lipid; and (b) a therapeutic agent; the lipid having the structure or a salt thereof, wherein R 3 is optionally substituted di(alkyl)aminoalkyl; E is C O or OC; R 1 and R 2 and R x are each independently for each occurrence H, optionally substituted C 1 -C 10 alkyl, optionally substituted C 10 -C 30 alkyl, optionally substituted C 10 -C 30 alkenyl, optionally substituted C 10 -C 30 alkynyl, or optionally substituted C 10 -C 30 acyl, provided that at least one of R 1, R 2 and R x is not H; and n is 0, 1, 2, or 3; wherein the term "substituted" refers to the replacement of one or more hydrogen radicals in a given structure with the radical of a specified substituent selected from the group consisting of halo, alkyl, alkenyl, alkynyl, aryl, heterocyclyl, thiol, alkylthio, oxo, thioxy, arylthio, alkylthioalkyl, arylthioalkyl, alkylsulfonyl, alkylsulfonylalkyl, arylsulfonylalkyl, alkoxy, aryloxy, aralkoxy, aminocarbonyl, alkylaminocarbonyl, arylaminocarbonyl, alkoxycarbonyl, aryloxycarbonyl, haloalkyl, amino, trifluoromethyl, cyano, nitro, alkylamino, arylamino, alkylaminoalkyl, arylaminoalkyl, aminoalkylamino, hydroxy, alkoxyalkyl, carboxyalkyl, alkoxycarbonylalkyl, aminocarbonylalkyl, acyl, aralkoxycarbonyl, carboxylic acid, sulfonic acid, sulfonyl, phosphonic acid, aryl, heteroaryl, heterocyclic, and aliphatic, and wherein the specified substituent may be further substituted by replacement of one or more hydrogen radicals in a given structure with the radical of a further substituent selected from the group consisting of halo, alkyl, alkenyl, alkynyl, aryl, heterocyclyl, thiol, alkylthio, oxo, thioxy, arylthio, alkylthioalkyl, arylthioalkyl, alkylsulfonyl, alkylsulfonylalkyl, arylsulfonylalkyl, alkoxy, aryloxy, aralkoxy, aminocarbonyl, alkylaminocarbonyl, arylaminocarbonyl, alkoxycarbonyl, aryloxycarbonyl, haloalkyl, amino, trifluoromethyl, cyano, nitro, alkylamino, arylamino, alkylaminoalkyl, arylaminoalkyl, aminoalkylamino, hydroxy, alkoxyalkyl, carboxyalkyl, alkoxycarbonylalkyl, aminocarbonylalkyl, acyl, aralkoxycarbonyl, carboxylic acid, sulfonic acid, sulfonyl, phosphonic acid, aryl, heteroaryl, heterocyclic, and aliphatic; and provided that when E is C O, R 3 is and one of R 1, R 2, or R x is H, then the remaining of R 1, R 2, or R x are not both linoleyl. or a salt thereof, wherein R 3 is optionally substituted di(alkyl)aminoalkyl; E is C O or OC; R 1 and R 2 and R x are each independently for each occurrence H, optionally substituted C 1 -C 10 alkyl, optionally substituted C 10 -C 30 alkyl, optionally substituted C 10 -C 30 alkenyl, optionally substituted C 10 -C 30 alkynyl, or optionally substituted C 10 -C 30 acyl, provided that at least one of R 1, R 2 and R x is not H; and n is 0, 1, 2, or 3; wherein the term "substituted" refers to the replacement of one or more hydrogen radicals in a given structure with the radical of a specified substituent selected from the group consisting of halo, alkyl, alkenyl, alkynyl, aryl, heterocyclyl, thiol, alkylthio, oxo, thioxy, arylthio, alkylthioalkyl, arylthioalkyl, alkylsulfonyl, alkylsulfonylalkyl, arylsulfonylalkyl, alkoxy, aryloxy, aralkoxy, aminocarbonyl, alkylaminocarbonyl, arylaminocarbonyl, alkoxycarbonyl, aryloxycarbonyl, haloalkyl, amino, trifluoromethyl, cyano, nitro, alkylamino, arylamino, alkylaminoalkyl, arylaminoalkyl, aminoalkylamino, hydroxy, alkoxyalkyl, carboxyalkyl, alkoxycarbonylalkyl, aminocarbonylalkyl, acyl, aralkoxycarbonyl, carboxylic acid, sulfonic acid, sulfonyl, phosphonic acid, aryl, heteroaryl, heterocyclic, and aliphatic, and wherein the specified substituent may be further substituted by replacement of one or more hydrogen radicals in a given structure with the radical of a further substituent selected from the group consisting of halo, alkyl, alkenyl, alkynyl, aryl, heterocyclyl, thiol, alkylthio, oxo, thioxy, arylthio, alkylthioalkyl, arylthioalkyl, alkylsulfonyl, alkylsulfonylalkyl, arylsulfonylalkyl, alkoxy, aryloxy, aralkoxy, aminocarbonyl, alkylaminocarbonyl, arylaminocarbonyl, alkoxycarbonyl, aryloxycarbonyl, haloalkyl, amino, trifluoromethyl, cyano, nitro, alkylamino, arylamino, alkylaminoalkyl, arylaminoalkyl, aminoalkylamino, hydroxy, alkoxyalkyl, carboxyalkyl, alkoxycarbonylalkyl, aminocarbonylalkyl, acyl, aralkoxycarbonyl, carboxylic acid, sulfonic acid, sulfonyl, phosphonic acid, aryl, heteroaryl, heterocyclic, and aliphatic; and provided that when E is C O, R 3 is and one of R 1, R 2, or R x is H, then the remaining of R 1, R 2, or R x are not both linoleyl.