A compound having a structure of Formula IA or IB: or a pharmaceutically acceptable salt, tautomer or stereoisomer thereof, wherein: L 1 and L 2 are each independently -O(C=O)-, -(C=O)O-, -C(=O)-, -O-, -S x -, -S-S-, -C(=O)S-, -SC(=O)-, -NR a C(=O)-, -C(=O)NR a -, -NR a C(=O)NR a -, -OC(=O)NR a -, -NR a C(=O)O- or a direct bond; G 3 is C 1 -C 6 alkylene; R a is H or C 1 -C 12 alkyl; R 1a and R 1b are, at each occurrence, independently either: (a) H or C 1 -C 12 alkyl; or (b) R 1a is H or C 1 -C 12 alkyl, and R 1b together with the carbon atom to which it is bound is taken together with an adjacent R 1b and the carbon atom to which it is bound to form a carbon-carbon double bond; R 2a and R 2b are, at each occurrence, independently either: (a) H or C 1 -C 12 alkyl; or (b) R 2a is H or C 1 -C 12 alkyl, and R 2b together with the carbon atom to which it is bound is taken together with an adjacent R 2b and the carbon atom to which it is bound to form a carbon-carbon double bond; R 3a and R 3b are, at each occurrence, independently either (a): H or C 1 -C 12 alkyl; or (b) R 3a is H or C 1 -C 12 alkyl, and R 3b together with the carbon atom to which it is bound is taken together with an adjacent R 3b and the carbon atom to which it is bound to form a carbon-carbon double bond; R 4a and R 4b are, at each occurrence, independently either: (a) H or C 1 -C 12 alkyl; or (b) R 4a is H or C 1 -C 12 alkyl, and R 4b together with the carbon atom to which it is bound is taken together with an adjacent R 4b and the carbon atom to which it is bound to form a carbon-carbon double bond; R 5 and R 6 are each independently H or methyl; R 7 is C 6 -C 16 alkyl; R 8 and R 9 are each independently C 1 -C 12 alkyl; or R 8 and R 9, together with the nitrogen atom to which they are attached, form a 5, 6 or 7-membered heterocyclic ring; a, b, c and d are each independently an integer from 1 to 24; and x is 0, 1 or 2, wherein alkyl refers to a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms, which is saturated or unsaturated and is optionally substituted, and wherein alkylene refers to a straight or branched divalent hydrocarbon chain linking the rest of the molecule to a radical group, consisting solely of carbon and hydrogen, which is saturated or unsaturated and is optionally substituted. L 1 and L 2 are each independently -O(C=O)-, -(C=O)O-, -C(=O)-, -O-, -S x -, -S-S-, -C(=O)S-, -SC(=O)-, -NR a C(=O)-, -C(=O)NR a -, -NR a C(=O)NR a -, -OC(=O)NR a -, -NR a C(=O)O- or a direct bond; G 3 is C 1 -C 6 alkylene; R a is H or C 1 -C 12 alkyl; R 1a and R 1b are, at each occurrence, independently either: (a) H or C 1 -C 12 alkyl; or (b) R 1a is H or C 1 -C 12 alkyl, and R 1b together with the carbon atom to which it is bound is taken together with an adjacent R 1b and the carbon atom to which it is bound to form a carbon-carbon double bond; R 2a and R 2b are, at each occurrence, independently either: (a) H or C 1 -C 12 alkyl; or (b) R 2a is H or C 1 -C 12 alkyl, and R 2b together with the carbon atom to which it is bound is taken together with an adjacent R 2b and the carbon atom to which it is bound to form a carbon-carbon double bond; R 3a and R 3b are, at each occurrence, independently either (a): H or C 1 -C 12 alkyl; or (b) R 3a is H or C 1 -C 12 alkyl, and R 3b together with the carbon atom to which it is bound is taken together with an adjacent R 3b and the carbon atom to which it is bound to form a carbon-carbon double bond; R 4a and R 4b are, at each occurrence, independently either: (a) H or C 1 -C 12 alkyl; or (b) R 4a is H or C 1 -C 12 alkyl, and R 4b together with the carbon atom to which it is bound is taken together with an adjacent R 4b and the carbon atom to which it is bound to form a carbon-carbon double bond; R 5 and R 6 are each independently H or methyl; R 7 is C 6 -C 16 alkyl; R 8 and R 9 are each independently C 1 -C 12 alkyl; or R 8 and R 9, together with the nitrogen atom to which they are attached, form a 5, 6 or 7-membered heterocyclic ring; a, b, c and d are each independently an integer from 1 to 24; and x is 0, 1 or 2, wherein alkyl refers to a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms, which is saturated or unsaturated and is optionally substituted, and wherein alkylene refers to a straight or branched divalent hydrocarbon chain linking the rest of the molecule to a radical group, consisting solely of carbon and hydrogen, which is saturated or unsaturated and is optionally substituted.