Predictionof the Apparent p<i>K</i>_a Value of Lipid Nanoparticlesby Density Functional Theory

One of the most important parameters for the development of novel ionizable lipids (ILs) for use in lipid nanoparticle (LNP) drug carriers is their p<i>K</i>_a value. Ideally, the LNP should be deprotonated outside the cell to prevent cytotoxicity and protonated inside the endosome, where pH is lower. To achieve this switch, the LNP’s p<i>K</i>_a value, the so-called “apparent p<i>K</i>_a value”, should range generally between 5.5 and 7. For specific applications, the range is narrower. We present a straightforward approach to computationally estimate this apparent p<i>K</i>_a value of LNPs using density functional theory (DFT). This method uses “surrogates” of the ILs, which are hypothetical derivatives featuring an <i>N</i>,<i>N</i>-dimethylethylaminium side group attached to the lipid’s nitrogen atom.