These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Aryl-substituted C3-bridged oligopyrroles as anion receptors for formation of supramolecular organogels.
    Author: Maeda H, Haketa Y, Nakanishi T.
    Journal: J Am Chem Soc; 2007 Nov 07; 129(44):13661-74. PubMed ID: 17927182.
    Abstract:
    BF2 complexes of aryl-substituted dipyrrolyldiketones (3a-c, 5a-d) have been synthesized by the condensation of arylpyrroles obtained by Suzuki cross-coupling reactions with malonyl chloride, followed by treatment with BF3.OEt2. The binding constants (Ka11) of the BF2 complexes (3a-c) for various anions (Cl-, Br-, CH3CO2-, H2PO4-, and HSO4-) in CH2Cl2 decrease in the order Ph (3a) > o-tolyl (3b) > 2,6-Me2Ph (3c), possibly because of differences in the planarity and the number of interacting o-CH units at the binding sites. Aryl-substituted receptors exhibit a [1+1] binding mode with Cl- as well as a [2+1] binding mode under conditions of high concentration and low temperature, as suggested by 1H NMR studies in CD2Cl2. These receptors, especially phenyl-substituted (3a) and o-tolyl (3b), exhibit drastic colorimetric and fluorescent changes in the presence of F- due to extended pi-conjugation, as compared to 2,6-dimethylphenyl (3c) and the previously reported derivatives (1a-c). Aryl-substitution at the alpha-positions of pyrrole is an excellent means for the introduction of various substituents at the periphery of the anion receptors. For example, derivatives with long alkoxy chains at 3,4,5-positions of the substituent aryl rings (5b-d) afford emissive gel structures in hydrocarbon solvents, such as octane, based on the stacking of slipped H- and J-aggregates at the core pi-plane. The structural organization of the supramolecular gels was investigated by AFM, SEM, and XRD measurements as well as by considering the solid-state packing of crystalline derivatives. The slow transformation of the gel to the solution phase by the addition of various anions, possibly except for F-, is correlated with the unique properties of these acyclic receptors where inversions of pyrrole rings are required for anion binding. Boron complexes of 1,3-dipyrrolyl-1,3-propanediones with aryl-substituents, as a new class of acyclic anion receptors, have shown efficient binding due to the interacting o-CH units and, in the case of the derivative with long aliphatic chains, afforded the emissive supramolecular organogels using stacking of core pi-planes controlled by external chemical stimuli.
    [Abstract] [Full Text] [Related] [New Search]