Pseudorotaxane complexes of naphthylpyridines and naphthylbipyridyl with β-cyclodextrin and hydroxypropyl-β-cyclodextrin |
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Authors: | V B Nazarov V G Avakyan S P Gromov M V Fomina T G Vershinnikova V Yu Rudyak M V Alfimov |
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Institution: | (1) Institute of Problems of Chemical Physics, Russian Academy of Sciences, 1 prosp. Akad. Semenova, 142432 Chernogolovka, Moscow Region, Russian Federation;(2) Photochemistry Center, Russian Academy of Sciences, 7a ul. Novatorov, 119421 Moscow, Russian Federation |
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Abstract: | The electronic absorption spectra and fluorescence spectra of 4-(2-naphthyl)pyridine (1), 2-(4-methyl-2-pyridyl)-4-(2-naphthyl)pyridine (2), and 4-(2-naphthyl)-2-phenylpyridine (3) in solutions and in complexes with β-cyclodextrin (β-CD) and well water-soluble hydroxy-propyl-β-cyclodextrin (HP-β-CD)
were studied. Fluorescence near 475 nm observed in aqueous solutions of compounds 1–3 arises from protonated forms of these compounds produced in the excited state. Results of DFT quantum chemical calculations
show an increase in proton affinity energies of excited-state naphthylpyridines 2 and 3. The formation of inclusion complexes with cyclodextrins makes protonation of compounds 2 and 3 more difficult, which manifests in large hypsochromic shifts of fluorescence band maxima. The stability constants of the
complexes 1·HP-β-CD and 2·HP-β-CD determined from their fluorescence spectra are 3425 and 3760 L mol−1, respectively. The stability constant of the complex 3·HP-β-CD (5500±600 L mol−1) was found from the changes in the solubility of naphthylpyridine 3 in water upon complexation. Semiempirical quantum chemical calculations of the molecular structures and thermodynamic characteristics
of pseudorotaxane inclusion complexes of trans-2, cis-2, and trans-2·H2O with HP-β-CD were carried out.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 272–280, February, 2007. |
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Keywords: | naphthylpyridines naphthylbipyridyl β -cyclodextrin hydroxypropyl-β -cyclodextrin pseudorotaxane complexes molecular structure quantum chemical calculations density functional theory PM3 method electronic absorption spectra fluorescence spectra |
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