[en] The parameters that influence the conformation of poly(propylene imine) dendrimers were investigated by molecular simulations using molecular mechanics and simulated annealing methods. Dendrimers with two types of peripheral units able to communicate via hydrogen bonding-amine and amide moieties-were considered in order to study the role that secondary interactions among the end groups have in the spatial organization of the dendritic branches. Radial atomic density profiles and radial atomic probability distributions were used to extract global properties, such as the degree of packing of the branches, the distribution of the monomers throughout the molecular volume, and the extent and characteristics of the surface region. Information was also obtained about the nature, location, and extent of formation of the hydrogen bonds, as well as their evolution with dendrimer generation and their assembly into networks. The analyses were supported by a detailed investigation of the first two generations, with an emphasis on the relationship between hydrogen bonding and the compactness and stability of the molecules; this allowed us to account for the generational evolution of hydrogen bonding that is experimentally observed in several poly(propylene imine) dendrimers.
Lescanec, R. L.; Muthukumar, M. Macromolecules 1990, 23, 2280.
Mansfield, M. L.; Klushin, L. I. Macromolecules 1993, 26, 4262.
Boris, D.; Rubinstein, M. Macromolecules 1996, 29, 7251.
Mourey, T. H.; Turner, S. R.; Rubinstein, M.; Fréchet, J. M. J.; Hawker, C. J.; Wooley, K. L. Macromolecules 1992, 25, 2401.
Wooley, K. L.; Klug, C. A.; Tasaki, K.; Schaefer, J. J. Am. Chem. Soc. 1997, 119, 53.
De Backer, S.; Prinzie, Y.; Verheijen, W.; Smet, M.; Desmedt, K.; Dehaen, W.; De Schryver, F. C. J. Phys. Chem. A 1998, 102, 5451.
Gorman, C. B.; Hager, M. W.; Parkhurst, B. L.; Smith, J. C. Macromolecules 1998, 31, 815.
Jansen, J. F. G. A.; de Brabander-van den Berg, E. M. M.; Meijer, E. W. Science 1994, 266, 1226.
Jansen, J. F. G. A.; Peerlings, H. W. I.; de Brabander-van den Berg, E. M. M.; Meijer, E. W. Angew. Chem., Int. Ed. Engl. 1995, 34, 1206.
Peerlings, H. W. I.; Meijer, E. W. Chem. Eur. J. 1997, 3, 1563.
Bosman, A. W. Ph.D. Thesis: Dendrimers in action: structure, dynamics and functionalization of poly(propylene imine) dendrimers, University of Technology: Eindhoven, The Netherlands, 1999.
Cavallo, L.; Fraternali, F. Chem. Eur. J. 1998, 4, 927.
Miklis, P.; Cagin, T.; Goddard, W. A., III J. Am. Chem. Soc. 1997, 119, 7458.
Accelrys, formerly Molecular Simulation Inc., 9685 Scranton Road, San Diego, CA, 1997.
Mayo, S. L.; Olafson, B. D.; Goddard, W. A., III J. Phys. Chem. 1990, 94, 8897.
The data extracted from the SA simulations were preferred over those obtained from usual MD methods performed at room temperature, after comparative studies were made.
Rappé, A. K.; Goddard, W. A., III J. Phys. Chem. 1991, 95, 3358.
Typical charges calculated with the Qeq method for an extended conformer of an amine- and amide-terminated dendrimer of the first generation are available as Supporting Information.
Hoover, W. G. Phys. Rev. A 1985, 31, 1695.
Verlet, L. Phys. Rev. 1967, 159, 98.
Welch, P.; Muthukumar, M. Macromolecules 1998, 37, 5892.
Naylor, A. M.; Goddard, W. A., III; Kiefer, G. E.; Tomalia, D. A. J. Am. Chem. Soc. 1989, 111, 2339.
Figures describing the morphology/stability/hydrogen bond relationship for the G1 and G2 conformers of the amine- and amide-terminated dendrimers are available as Supporting Information.
Scherrenberg, R.; Coussens, B.; van Vliet, P.; Edouard, G.; Brackman, J.; de Brabander, E.; Mortensen, K. Macromolecules 1998, 31, 456.
The optimized NMA dimer was used as a standard for rating the stability of amide-amide hydrogen bonds, since the hydrogen bond takes place between amide moieties in the absence of any unfavorable orientation effect.