Table 3.
Attributes of Head and Fatty Acyl (Tail) Groups for Commonly Used Phospholipids
| Phospholipid Property | Effect on Liposome Membrane and Nanoparticle Characteristics | Functional Attributes |
|---|---|---|
| Head group | ||
| SPH/choline: –(CH2)2–N(CH2)3+ | Some surface hydration | Neutral charge |
| Ethanolamine: –(CH2)2–NH3+ | Minimal surface hydration | Neutral charge |
| Serine: –CH2–CH(COO–)–NH3+ | Some surface hydration | Negative charge |
| Glycerol: –CH2–CH(OH)–CH2OH | Some surface hydration | Negative charge |
| PEG (ethanolamine): –(CH2)2–NH-PEGa | Enhanced surface hydration and steric effect | Negative charge |
| Tail group—fatty acyl chains: R1 and R2 (C14–18 in length) | ||
| Increase in the degree of saturation | More rigidity; less fluidity | Elevated Tc |
| Increase in the chain length of R1 and R2 | Increased thickness of bilayer | Elevated Tc |
| Varying degree of saturation and chain length on R1 and R2 | Decreased order of membrane packing | Reduced Tc (compared with phospholipid with two identical fatty acyl tails) |
a
PEG: –[O–(CH2)2]n–OH.
Tc, lipid-phase transition temperature.