Theoretical investigation of 3,5-dihydroxybenzylalcohol based dendrimer generations 1-5 using Molecular Mechanics (MM+) method and the PM3 Semi-Empirical Molecular Orbital Theory

The structures of 3,5-dihydroxybenzyl alcohol (DHBA) based dendrimer generations 1-5 (DG1-5) were optimized using the Molecular Mechanics, MM+ method. The PM3 Semi-Empirical Molecular Orbital Theory was used to optimize the structures of DHBA-based dendrimer generations 1-3 (DG1-3). By comparing the results, it was established that the MM+ molecular modelling results for DG1-3 had identical conformations to the PM3 global minimum structures, and therefore were reliable and predictive for DG4 and 5 structures. Single point PM3 calculations were performed on MM+ optimized DG4 and 5 structures, and the energies and wave functions obtained. The peripheral molecular wave functions of DG1-5 are reactive, and were found to be a degenerate set with the similar eigenvalues. The reactivities of the peripheral orbitals allow the synthesis of larger generations. However, the structures start to close up on each other and the steric hindrance prevents the formation of larger generations than DG5, in agreement with the experiment. The bond lengths, shapes, sizes of the DG1-5 structures and the size of the internal cavities in the 3D structures were obtained.