Structure and conformation of DAB dendrimers in solution via multidimensional NMR techniques

NOESY-HSQC 3D-NMR and NOESY 2D-NMR techniques have been used on a 750 MHz s pectrometer to study the chain conformations of different generation DAB de ndrimers (poly[propylene imine] dendrimers) in chloroform and benzene solut ions. The high-field multidimensional NMR techniques provided the chemical shift dispersion needed to resolve all of the unique resonances in the dend rimers, By studying the NOE interactions among dendritic chain protons, inf ormation about through space interactions between protons on different part s of the dendrimer chain is obtained, which is directly related to the conf ormation of the dendrimer, These experiments also give further proof of the chemical shift assignments obtained from the HMQC-TOCSY 2D and 3D NMR expe riments. The concentration effects on chemical shifts have also been observ ed, revealing information about the interactions between solvent and differ ent parts of dendrimer molecules, These studies clearly show for DAB dendri mers, that folded chain conformations can occur in nonpolar solvents such a s benzene and extended chain conformations are predominant in polar solvent s such as chloroform.