Self-assembled metallocycles with two interactive binding domains

Sung Youn Chang, Hye Young Jang, Kyu Sung Jeong

Research output: Contribution to journalArticle

24 Citations (Scopus)

Abstract

Five metallocycles 1a-e have been self-assembled from S-shaped bispyridyl ligands 2a-e and a palladium complex, [Pd(dppp)(OTf)2] (dppp = 1,3-bis(diphenylphosphanyl)propane), and have been characterized by elemental analysis and various spectroscopic methods including 1H NMR spectroscopy and electrospray ionization (ESI) mass spectrometry. These metallocycles all are monocyclic compounds, but can fold to generate two binding domains bearing hydrogen-bonding sites based on pyridine-2,6-dicarboxamide units. The binding properties of the metallocycles with N,N,N′,N′- tetramethylterephthalamide (G) have been probed by means of ESI mass spectrometry and 1H NMR spectroscopy. The results both in the gas phase and in solution are consistent with the fact that the metallocycles accommodate two molecules of the guest G. Thus, the ESI mass spectra clearly show fragments corresponding to the 1:2 complexes in all cases. 1H NMR studies on 1a and G support the formation of a 1:2 complex in solution; the titration curves are nicely fitted to a 1:2 binding isotherm, but not to a 1:1 binding isotherm. In addition, a Job plot also suggests a 1:2 binding mode between 1a and G, showing maximum complexation at ∼0.33 mol fraction of the metallocycle 1a in CDCl3. The binding constants K1 and K2 are calculated to be 1600 and 1400 M-1 (± 10%), respectively, at 25 °C in CDCl3, indicative of positively cooperative binding. This positive cooperativity was confirmed by the Hill equation, affording a Hill coefficient of n = 1.6. Owing to insufficient solubility in CDCl3, for comparison purposes the binding properties of the metallocycles 1b-e were investigated in a more polar medium, 3% CD 3CN/CDCl3. 1H NMR titrations revealed that the metallocycles all bind two molecules of the guest G with Hill coefficients ranging from 1.4 to 1.8. This positive cooperativity may be attributed to a structural reorganization of the second binding cavity when the first guest binds to either one of the subcavities present in the metallocycles.

Original languageEnglish
Pages (from-to)4358-4366
Number of pages9
JournalChemistry - A European Journal
Volume10
Issue number17
DOIs
Publication statusPublished - 2004 Sep 6

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Electrospray ionization
Titration
Nuclear magnetic resonance spectroscopy
Mass spectrometry
Isotherms
Bearings (structural)
Nuclear magnetic resonance
Propane
Molecules
Palladium
Complexation
Pyridine
Hydrogen bonds
Solubility
Gases
Ligands
Chemical analysis

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Organic Chemistry

Cite this

Chang, Sung Youn ; Jang, Hye Young ; Jeong, Kyu Sung. / Self-assembled metallocycles with two interactive binding domains. In: Chemistry - A European Journal. 2004 ; Vol. 10, No. 17. pp. 4358-4366.
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Self-assembled metallocycles with two interactive binding domains. / Chang, Sung Youn; Jang, Hye Young; Jeong, Kyu Sung.

In: Chemistry - A European Journal, Vol. 10, No. 17, 06.09.2004, p. 4358-4366.

Research output: Contribution to journalArticle

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N2 - Five metallocycles 1a-e have been self-assembled from S-shaped bispyridyl ligands 2a-e and a palladium complex, [Pd(dppp)(OTf)2] (dppp = 1,3-bis(diphenylphosphanyl)propane), and have been characterized by elemental analysis and various spectroscopic methods including 1H NMR spectroscopy and electrospray ionization (ESI) mass spectrometry. These metallocycles all are monocyclic compounds, but can fold to generate two binding domains bearing hydrogen-bonding sites based on pyridine-2,6-dicarboxamide units. The binding properties of the metallocycles with N,N,N′,N′- tetramethylterephthalamide (G) have been probed by means of ESI mass spectrometry and 1H NMR spectroscopy. The results both in the gas phase and in solution are consistent with the fact that the metallocycles accommodate two molecules of the guest G. Thus, the ESI mass spectra clearly show fragments corresponding to the 1:2 complexes in all cases. 1H NMR studies on 1a and G support the formation of a 1:2 complex in solution; the titration curves are nicely fitted to a 1:2 binding isotherm, but not to a 1:1 binding isotherm. In addition, a Job plot also suggests a 1:2 binding mode between 1a and G, showing maximum complexation at ∼0.33 mol fraction of the metallocycle 1a in CDCl3. The binding constants K1 and K2 are calculated to be 1600 and 1400 M-1 (± 10%), respectively, at 25 °C in CDCl3, indicative of positively cooperative binding. This positive cooperativity was confirmed by the Hill equation, affording a Hill coefficient of n = 1.6. Owing to insufficient solubility in CDCl3, for comparison purposes the binding properties of the metallocycles 1b-e were investigated in a more polar medium, 3% CD 3CN/CDCl3. 1H NMR titrations revealed that the metallocycles all bind two molecules of the guest G with Hill coefficients ranging from 1.4 to 1.8. This positive cooperativity may be attributed to a structural reorganization of the second binding cavity when the first guest binds to either one of the subcavities present in the metallocycles.

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