Formation of a Unique 1:2 Calcium-Calixquinone Complex in Aqueous Media

• Published in: Bulletin of the Korean Chemical Society 2011, 32(3), , pp.793-799
• Main Authors: Kang, Sun-Kil, Lee, One-Sun, Chang, Suk-Kyu, Chung, Doo-Soo, Kim, Ha-Suck, Chung, Taek-Dong
• Format: Article
• Language: English
• Subjects: 화학
• ISSN: 0253-2964; 1229-5949
• DOI: 10.5012/bkcs.2011.32.3.793

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 Ca^(2+), Sr^(2+), and Ba^(2+)ions. The nonlinear fitting of titration curves based on UV-visible absorption spectra showed that the binding constants of CTAQ for Ca^(2+) ion are 4 (± 2) × 10^6 M^(–1) for 1:1 and 1.4 (± 0.5) × 10^11 M^(–2) for 1:2 complex. NMR conformational studies and the titration curves corroborate that the Ca^(2+):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 Ca^(2+) 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. KCI Citation Count: 1