| 19350590 |
Pettirossi S, Bellachioma G, Ciancaleoni G, Zuccaccia C, Zuccaccia D, Macchioni A: Diffusion and NOE NMR studies on multicationic DAB-organoruthenium dendrimers: size-dependent noncovalent self-assembly to megamers and ion pairing. Chemistry. 2009;15(21):5337-47.
New multicationic organoruthenium dendrimers (RuPF (6)-Dabn, n = 2, 4, 8, 16) have been synthesized by coupling of [Ru (eta (6)-p-cymene)(kappa (3)-dpk-OCH (2) CH (2) OH)] X (1PF (6), dpk = 2,2'-dipyridyl ketone, X = PF (6)) with 1,4-diaminobutane (DAB) and polypropylenimine dendrimer DAB-dendr-(NH (2))(n) {n=4, 8, 16} mediated by 1,1'-carbonyldiimidazole (CDI). The intermediate in the synthesis, [Ru (eta (6)-p-cymene)(kappa (3)-dpk-OCH (2) CH (2) OC (O) Im] X (2PF (6), Im = imidazole, X = PF (6)) has been isolated and characterized by single-crystal XRD. The intra- and supramolecular structures in a solution of RuPF (6)-Dabn dendrimer have been investigated by multidimensional and multinuclear NMR techniques. Diffusion NMR experiments on dilute solutions indicated that the linear distance between two metal centers (14.9-22.1 A depending on the dendrimer generation) is much greater than the diameter of 1PF (6) (9.9 A). (19) F,(1) H-HOESY NMR experiments (HOESY = heteronuclear Overhauser effect spectroscopy) showed that the counterion is positioned on the surface of the dendrimers and assumes the same relative anion-cation orientation as in 2PF (6). Diffusion NMR experiments on RuPF (6)-Dabn dendrimers in CD (2) Cl (2) at different concentrations revealed a process of supramolecular assembly of dendrimers to megamers that is strongly favored for the highest generations. Megamer formation is coupled with an increased fraction of free ions (alpha) and a consequent reduction in ion-paired ruthenium centers. Graphs of alpha versus C (Ru) (the concentration of ruthenium centers) showed a minimum for RuPF (6)-Dab4, RuPF (6)-Dab8, and RuPF (6)-Dab16 at a position coinciding with the significant presence of supramolecular dendritic dimers. The tendency to ion pairing decreases as the dendrimer generation increases. |
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