Study of the cyclen derivative 2-[1,4,7,10-tetraazacyclododecan-1-yl]-ethanethiol and its complexation behaviour towards d-transition metal ions

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• 作者：Sara Lacerda ; Maria Paula Campello ; Isabel C. Santos ; Isabel Santos ; Rita Delgado
• 关键词：2-Ethanethiol-cyclen derivative ; Protonation constants ; Stability constants ; Protonation sequence ; ¹³C NMR titration ; EPR
• 刊名：Polyhedron
• 出版年：2007
• 期刊代码：87_02775387
• 类别：ch
• 出版时间：31 August 2007
• 卷：26
• 期：14
• 页码：3763-3773
• 文件大小：569 K

摘要

The compound 2-[1,4,7,10-tetraazacyclododecan-1-yl]-ethanethiol (L2) has been synthesized and characterized by multinuclear NMR spectroscopy and mass spectrometry. Its thiol-protected precursor L1 has also been isolated and characterized, including by X-ray structural analysis. The protonation constants of L2 were determined by potentiometric methods at 25.0 °C and 0.10 mol dm⁻³ KNO₃ ionic strength. ¹³C NMR studies and 2D NMR spectra recorded at different pD values have been used to analyse its protonation scheme. Stability constants of L2 with Cu²⁺, Zn²⁺ and Cd²⁺ were also determined by potentiometry, and the Zn(II) and Cu(II) complexes were studied in solution by NMR, UV–Vis, and EPR spectroscopies. The pM values (pH 7.4) calculated for the metal complexes of L2 are higher than the corresponding values found for cyclen and cyclam, but the selectivity of L2 for Cu²⁺ is low.