Formation of a Unique 1:2 Calcium-Calixquinone Complex in Aqueous Media
- Authors
- Kang, Sun Kil; Lee, One-Sun; Chang, Suk-Kyu; Chung, Doo Soo; Kim, Hasuck; Chung, Taek Dong
- Issue Date
- Mar-2011
- Publisher
- WILEY-V C H VERLAG GMBH
- Keywords
- Calix[4]arenemonoquinone-triacid; Calcium ion; NMR titration; Binding constant; Monte Carlo simulation
- Citation
- BULLETIN OF THE KOREAN CHEMICAL SOCIETY, v.32, no.3, pp 793 - 799
- Pages
- 7
- Journal Title
- BULLETIN OF THE KOREAN CHEMICAL SOCIETY
- Volume
- 32
- Number
- 3
- Start Page
- 793
- End Page
- 799
- URI
- https://scholarworks.bwise.kr/cau/handle/2019.sw.cau/21669
- DOI
- 10.5012/bkcs.2011.32.3.793
- ISSN
- 1229-5949
1229-5949
- Abstract
- We report the complexation behavior of calix[4]arenemonoquinone-triacid (CTAQ), which is an electroactive and water-soluble receptor for calcium ion. UV-visible and NMR spectroscopic studies revealed that CTAQ in aqueous media forms 1:2 as well as 1:1 (metal ion:CTAQ) stoichiometric complexes with Ca2+, Sr2+, and Ba2+ ions. The nonlinear fitting of titration curves based on UV-visible absorption spectra showed that the binding constants of CTAQ for Ca2+ ion are 4 (+/- 2) x 10(6) M-1 for 1:1 and 1.4 (+/- 0.5) x 10(11) M-2 for 1:2 complex. NMR conformational studies and the titration curves corroborate that the Ca2+:CTAQ complex in aqueous solution is not present in the form of merely 1:1 one, being consistent with UV-visible spectrophotometric results. The Monte Carlo simulation supports the presence of a stable conformer of 1:2 complexes in which a Ca2+ ion is interposed between two CTAQs at the global minimum. This is the first model of 1:2 stoichiometric complex of calix[4]arene and alkaline earth ions in aqueous media.
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