Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 16, Issue 8, Pages 2427-2441Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.200902575
Keywords
benzamide; dendrimers; gels; hydrogen bonds; self-assembly
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Funding
- National Research Foundation (NRF) through ERC [R11-2007-050-04001-0]
- NRL [R0A-2008-00020121-0]
- Ministry of Knowledge Economy, Republic of Korea
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A series of bis-dendritic gelators consisting of a benzamide dendron and an alkyl dendron were synthesized to investigate the dendritic effect on self-assembly. The gelators with a first-generation benzamide (benzamide-G1) dendron or a first-generation alkyl (alkyl-G1) dendron formed stable gels in most aromatic solvents, and their self-assembled fibrillar networks were imaged by electron microscopy. The unbranched molecule (GO-GO) or the molecule possessing a second-generation benzamide (benzamide-G2) dendron did not form gels. Differential scanning calorimetry, powder X-ray diffraction, and Fourier transform IR studies revealed that introduction of a dendritic branch strongly affected the molecular packing as well as the strength of intermolecular interactions. Furthermore, concentration-dependent diffusion coefficient measurements and the evaluation of association constants by H-1 NMR spectroscopy indicated that bis-dendritic gelators with a benzamide-G1 dendron possessed high association constants and formed large aggregates, whereas molecules with a single benzamide formed dimers in chloroform. The formation of self-assembled fibrillar networks was driven by the multivalent and cooperative hydrogen bonding observed in the benzamide-G1 dendrons. pi-pi stacking of aromatic groups and van der Waals interactions between alkyl chains also played roles in the self-assembly process, thus indicating that a spatial balance between two dendrons is important.
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