The equilibria for core Ca2+ replacement by Ln3+ in copper(II) 15-MC-5 complexes have been investigated using a series of visible spectrophotometric titrations of calcium(II) metallacrowns ({CaII[15-MCCuII(N)(L)-5]}2+) with Ln3+ ions (H2L = pheha, (S)-R-phenylalaninehydroxamic acid, or trpha, (S)-R-tryptophanhydroxamic acid). These studies allowed the determination of the equilibrium constants for the reaction {CaII[15-MCCuII(N)(L)-5]}2+ + Ln3+ = {LnIII[15- MCCuII(N)(L)- 5]}3++Ca2+ in methanol/water 9:1 (Ln3+ = La3+, Gd3+, Dy3+, Er3+) or 99:1 (Ln3+ = La3+, Nd3+, Gd3+, Dy3+, Er3+, Yb3+), respectively. The log K for these reactions decreases with increasing atomic number of the lanthanide(III), ranging from 6.1 to 3.91 in methanol/water 9:1. The same behavior is observed in methanol/water 99:1, although the constants are uniformly lower (log K = 4.09-2.52). A significant thermodynamic selectivity was observed for the later lanthanides (Gd3+-Yb3+) while a smaller selectivity is present throughout the beginning of the series (La3+-Gd3+). This observation has been interpreted on the basis of the size correspondence between the metal ions and the metallacrown cavity. The overall stability of the {CaII[15-MCCuII(N)(L)-5]}2+ in methanol/water 9:1 has been determined by pH-spectrophotometric titrations with HCl. The resulting log K values are 63.46(12) and 65.05(13) for pheha and trpha, respectively (Ca2+ + 5Cu2+ + 5HL- = {CaII[15- MCCuII(N)(L)-5]}2+ +5H+). The stability of both the La3+ and Ca2+ 15-metallacrown-5 complexes in the presence of high Na+ concentrations has also been demonstrated by spectophotometric studies. Based upon these observations, the preference of the 15-MC-5 for Ca2+ complexation compared to crown ethers has been quantitatively demonstrated for the first time.

Thermodynamics of Core Metal Replacement and Self-Assembly of Ca2+ 15-Metallacrown-5 / Tegoni, Matteo; M., Furlotti; M., Tropiano; C. S., Lim; V. L., Pecoraro. - In: INORGANIC CHEMISTRY. - ISSN 0020-1669. - 49:(2010), pp. 5190-5201. [10.1021/ic100315u]

Thermodynamics of Core Metal Replacement and Self-Assembly of Ca2+ 15-Metallacrown-5

TEGONI, Matteo;
2010-01-01

Abstract

The equilibria for core Ca2+ replacement by Ln3+ in copper(II) 15-MC-5 complexes have been investigated using a series of visible spectrophotometric titrations of calcium(II) metallacrowns ({CaII[15-MCCuII(N)(L)-5]}2+) with Ln3+ ions (H2L = pheha, (S)-R-phenylalaninehydroxamic acid, or trpha, (S)-R-tryptophanhydroxamic acid). These studies allowed the determination of the equilibrium constants for the reaction {CaII[15-MCCuII(N)(L)-5]}2+ + Ln3+ = {LnIII[15- MCCuII(N)(L)- 5]}3++Ca2+ in methanol/water 9:1 (Ln3+ = La3+, Gd3+, Dy3+, Er3+) or 99:1 (Ln3+ = La3+, Nd3+, Gd3+, Dy3+, Er3+, Yb3+), respectively. The log K for these reactions decreases with increasing atomic number of the lanthanide(III), ranging from 6.1 to 3.91 in methanol/water 9:1. The same behavior is observed in methanol/water 99:1, although the constants are uniformly lower (log K = 4.09-2.52). A significant thermodynamic selectivity was observed for the later lanthanides (Gd3+-Yb3+) while a smaller selectivity is present throughout the beginning of the series (La3+-Gd3+). This observation has been interpreted on the basis of the size correspondence between the metal ions and the metallacrown cavity. The overall stability of the {CaII[15-MCCuII(N)(L)-5]}2+ in methanol/water 9:1 has been determined by pH-spectrophotometric titrations with HCl. The resulting log K values are 63.46(12) and 65.05(13) for pheha and trpha, respectively (Ca2+ + 5Cu2+ + 5HL- = {CaII[15- MCCuII(N)(L)-5]}2+ +5H+). The stability of both the La3+ and Ca2+ 15-metallacrown-5 complexes in the presence of high Na+ concentrations has also been demonstrated by spectophotometric studies. Based upon these observations, the preference of the 15-MC-5 for Ca2+ complexation compared to crown ethers has been quantitatively demonstrated for the first time.
2010
Thermodynamics of Core Metal Replacement and Self-Assembly of Ca2+ 15-Metallacrown-5 / Tegoni, Matteo; M., Furlotti; M., Tropiano; C. S., Lim; V. L., Pecoraro. - In: INORGANIC CHEMISTRY. - ISSN 0020-1669. - 49:(2010), pp. 5190-5201. [10.1021/ic100315u]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11381/2307297
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