A structural study of carbosilane dendrimers versus polyamidoamine

Several types of substituted carbosilane-based dendrimers are studied in co mparison with polyamidoamine (PAMAM), using molecular mechanics approach, t o evaluate the shape and steric interactions when the generation number (G) increases. A scaled van der Waals energy parameter: the scaled steric ener gy, is defined, and used, to compare the steric repulsion in these dendrime rs. Our calculations indicate that the steric repulsions, between the end g roups at the surface of dendrimers, do not increase for higher generations of such macromolecules. Density calculations show that this property decrea ses with the increase of G. The moment of inertia calculations show that th e shape of the considered dendrimers is asymmetrical for lower generations and becomes spherical at higher generations. The shape of the carbosilane d endrimers is more spherical than PAMAM. The results show that higher genera tions can afford the increased number of terminal groups at the surface of the macromolecules, without increase of the density in this region, therefo r these factors (steric repulsion between the end,groups at the surface, or high density) would not impede the chemistry to build higher generations o f completely branched dendrimers. (C) 2000 Elsevier Science Ltd. All rights reserved.