Premium
Diffusion and NOE NMR Studies on Multicationic DAB‐Organoruthenium Dendrimers: Size‐Dependent Noncovalent Self‐Assembly to Megamers and Ion Pairing
Author(s) -
Pettirossi Stefania,
Bellachioma Gianfranco,
Ciancaleoni Gianluca,
Zuccaccia Cristiano,
Zuccaccia Daniele,
Macchioni Alceo
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200802585
Subject(s) - dendrimer , heteronuclear molecule , chemistry , supramolecular chemistry , nuclear magnetic resonance spectroscopy , crystallography , proton nmr , nuclear overhauser effect , stereochemistry , crystal structure , polymer chemistry
Supra‐mega ion pairing : Multicationic organoruthenium dendrimers show a notable tendency to self‐aggregate when the concentration is increased, leading to megamers. This tendency increases with the generation. The self‐aggregation of dendrimers to megamers is coupled with a decrease in the extent of ion pairing, as illustrated.New multicationic organoruthenium dendrimers ( RuPF 6 ‐Dab n , n =2, 4, 8, 16) have been synthesized by coupling of [Ru(η 6 ‐ p ‐cymene)(κ 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(η 6 ‐ p ‐cymene)(κ 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 ‐Dab n 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 Å depending on the dendrimer generation) is much greater than the diameter of 1PF 6 (9.9 Å). 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 ‐Dab n 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 ( α ) and a consequent reduction in ion‐paired ruthenium centers. Graphs of α 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.