Lipid nanoparticles

A lipid nanoparticle comprising a pH-sensitive cationic lipid represented by the formula (I):

• [Chem. 1]
• (R1)(R2)C(OH)—(CH2)a—(O—CO)b—X (1)
• [in the formula (I), a denotes an integer from 3 to 5;
• b denotes 0 or 1;
• R1 and R2 each independently denote a group represented by the following general formula (A):
• [Chem. 2]
• (R11)(R12)HC—(CH2)o—(CO—O)—(CH2)e- (A)
• (in the formula (A), R11 and R12 each independently denote a linear or branched C1-15 alkyl group;
• c denotes an integer from 1 to 7;
• and e denotes an integer from 4 to 12;
• provided that R11 and R12 may be joined to each other to form a ring);
• X denotes a group represented by the following general formula (B):
• [Chem. 3]
• —(CH2)d—N(R3)(R4) (B)
• (in formula (B), d denotes an integer from 0 to 3;
• R3 and R4 each independently denote a C1-4 alkyl group or a C2-4 alkenyl group (in the C1-4 alkyl group or the C2-4 alkenyl group, one or two hydrogen atoms may be substituted by a phenyl group), or R3 and R4 may be joined to each other to form a 5- to 7-membered non-aromatic heterocycle (in the heterocycle, one or two hydrogen atoms may be substituted by a C14 alkyl group or C2-4 alkenyl group),
• or a 5- to 7-membered non-aromatic heterocyclic group (provided that the group is bound to (O—CO)b- via a carbon atom, and one or two hydrogen atoms of the ring may be substituted by a C1-4 alkyl group or a C2-4 alkenyl group)].