The van der Waals interaction energy arising from the drug molecule, Doxorubicin (DOX), interacting with the finite units of peptide nanotubes is investigated. We model the DOX molecule as a hollow sphere, and a unit of peptide as a cylinder. There are three different types of the peptide nanotubes determined here, which are (i) cyclo[(-D-Ala-L-Ala)4-], (ii) cyclo[Gln-(D-Leu-Trp)4-D-Leu], and (iii) cyclo[(Gln-D-Ala-Glu-D-Ala)3]. The main outcome from this research is mathematical expressions for the relation between total energy of the system, radius of the drug molecule, and the size and numbers of peptide units.

The physical dimensions of the peptides are known then we aim to find a size of DOX that can be encapsulated inside the peptides. For cyclo[(-D-Ala-L-Ala)4-] peptide, we find the size of the drug that can enter into the peptide nanotubes, where it prefers to stay the space between the peptide subunits. Moreover, the energy behaviours at the first open-end of the tube, the interior of the peptide tube, and the free spacing between units are determined for all three peptides. Our findings may be considered as a first step to develop a deeper understanding for the studies of the peptide nanotube under drug and gene delivery systems.

**Reference****
**S. Putthikorn, P. Ruengrot and D. Baowan* (2020) Energy behaviour of Doxorubicin interacting with peptide nanotubes, Journal of Mathematical Chemistry, Vol. 58, pp. 382-392.