Issue 39, 2020

Al(iii)-NTA-fluoride: a simple model system for Al–F binding with interesting thermodynamics

Abstract

Al(III) complexes are extensively studied as [18F]fluoride carriers in positron emission tomography. However, our limited knowledge on their thermodynamic and kinetic properties has hindered efforts to easily prepare radiochemically pure compounds while simultaneously reducing the overall labeling time. Thus, to improve our understanding of fluoride binding to coordinatively unsaturated Al(III) complexes, we investigated the ternary system Al(III)–H3NTA–F (H3NTA = nitrilo-triacetic acid) by NMR, potentiometry and X-ray diffraction. Our results show that the [Al(NTA)] complex binds two water molecules, which are replaced by fluorides. Individual species and isomers show separate 19F NMR signals and different stability constants. The two available positions on the [Al(NTA)] complex feature significantly different properties in terms of basicity of the coordinated water molecules and preferential binding of fluoride anions. Fluorides are effectively bound in weakly acidic or neutral solutions, whereas hydroxido species are preferentially formed in alkaline solutions. Our experimental observations were rationalized by theoretical calculations: predictions of the energy ordering of complexes and isomers, interpretation of 19F NMR chemical shifts, and natural bonding orbital analysis. Radiolabeling of [Al(NTA)] with [18F]fluoride gave low yields that confirmed a high affinity of the complex for hydroxide anions.

Graphical abstract: Al(iii)-NTA-fluoride: a simple model system for Al–F binding with interesting thermodynamics

Supplementary files

Article information

Article type
Paper
Submitted
28 Jul 2020
Accepted
21 Sep 2020
First published
22 Sep 2020

Dalton Trans., 2020,49, 13726-13736

Al(III)-NTA-fluoride: a simple model system for Al–F binding with interesting thermodynamics

E. Hacaperková, A. Jaroš, J. Kotek, J. Notni, M. Straka, V. Kubíček and P. Hermann, Dalton Trans., 2020, 49, 13726 DOI: 10.1039/D0DT02644A

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