A molecular dynamics study of the first five generations of poly(propylene imine) dendrimers modified with N-tBoc-L-phenylalanine

A molecular dynamics study of poly(propylene imine)-based dendrimers, with end groups modified with tBoc-protected L-phenylalanyl amino acids, has been performed. Five generations of the dendrimer with 4, 8, 16, 32 and 64 amino acids were considered. The shape of the dendrimer was found to be generation-dependent, with higher generations more spherical. C^a atom radial distributions indicate that terminal amino acids are not confined to the surface, and density profiles show a hollowness for higher generations. These results suggest self-inclusion of the end groups in the inner shell and are in qualitative agreement with the experimentally proved encapsulating properties of the higher generations. Hydrogen-bond analysis indicates that a lower percentage of intraresidue hydrogen bonds occurs for higher generations. The φ and ψ torsional angle distributions of the amino acid end groups indicate that for higher generations an increased number of energy minima is populated. The experimentally observed decrease of the optical activity could be related to the large conformational disorder observed for higher generations.