Issue 5, 2010

Specificity of the zinc(ii), magnesium(ii) and calcium(ii) complexation by (pyridin-2-yl)aminomethane-1,1-diphosphonic acids and related 1,3-(thiazol-2-yl) and 1,3-(benzothiazol-2-yl) derivatives

Abstract

The solution properties of a series of (pyridin-2-yl)aminomethane-1,1-diphosphonic acids 1–4 as well as closely related compounds 5 and 6 with 1,3-thiazolyl or 1,3-benzothiazolyl side chains and their influence on the complexation of Zn(II), Mg(II) and Ca(II) were studied by means of the 31P and 1H NMR spectroscopy, pH-potentiometry and ESI-MS methods. The crystal structures of 5 and 6 were determined by X-ray analysis. All the studied compounds exist in solution as mixtures of the Z and E isomers with respect to the C2–Namino bond. Compounds 1 and 2 exhibit higher overall basicities compared to 3–6 and have exceptionally basic pyridyl nitrogen (pK2 = 7.88 and 8.18, respectively). Dynamic NMR studies revealed that the nature of the aromatic side chain as well as the specificity and topology of the ring substituent account for the rotational barrier for the Z/E interconversion, which decreases in the order of 12 > 345 (6). This is particularly important for aggregational properties of 1–6 in solution and for the complex-formation equilibria. Overall, compounds 1–6 demonstrate a strong tendency for the formation of protonated multinuclear complexes. Their formation is unexpectedly slow on the NMR time scale compared to previously studied bisphosphonate complexes. The stepwise release of protons upon the rise of pH leads to mononuclear species. The Z ligand conformation is preferred in multinuclear complexes of Zn(II), Mg(II) and Ca(II) with 1 and 2 whereas in the case of 3–6 the complexation processes are affected by the intramolecular Z/E interconversion.

Graphical abstract: Specificity of the zinc(ii), magnesium(ii) and calcium(ii) complexation by (pyridin-2-yl)aminomethane-1,1-diphosphonic acids and related 1,3-(thiazol-2-yl) and 1,3-(benzothiazol-2-yl) derivatives

Supplementary files

Article information

Article type
Paper
Submitted
20 Jul 2009
Accepted
12 Oct 2009
First published
19 Nov 2009

Dalton Trans., 2010,39, 1207-1221

Specificity of the zinc(II), magnesium(II) and calcium(II) complexation by (pyridin-2-yl)aminomethane-1,1-diphosphonic acids and related 1,3-(thiazol-2-yl) and 1,3-(benzothiazol-2-yl) derivatives

E. Matczak-Jon, T. Kowalik-Jankowska, K. Ślepokura, P. Kafarski and A. Rajewska, Dalton Trans., 2010, 39, 1207 DOI: 10.1039/B914647D

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements