The browser you are using is not supported by this website. All versions of Internet Explorer are no longer supported, either by us or Microsoft (read more here: https://www.microsoft.com/en-us/microsoft-365/windows/end-of-ie-support).

Please use a modern browser to fully experience our website, such as the newest versions of Edge, Chrome, Firefox or Safari etc.

Photo Mikael Lund

Mikael Lund

Professor

Photo Mikael Lund

Counterintuitive Electrostatics upon Metal Ion Coordination to a Receptor with Two Homotopic Binding Sites

Author

  • Vidar Aspelin
  • Anna Lidskog
  • Carlos Solano Arribas
  • Stefan Hervø-Hansen
  • Björn Stenqvist
  • Richard Chudoba
  • Kenneth Wärnmark
  • Mikael Lund

Summary, in English

The consecutive binding of two potassium ions to a bis(18-crown-6) analogue of Tröger’s base (BCETB) in water was studied by isothermal titration calorimetry using four different salts, KCl, KI, KSCN, and K2SO4. A counterintuitive result was observed: the enthalpy change associated with the binding of the second ion is more negative than that of the first (ΔH°bind,2 < ΔH°bind,1). This remarkable finding is supported by continuum electrostatic theory as well as by atomic scale replica exchange molecular dynamics simulations, where the latter robustly reproduces experimental trends for all simulated salts, KCl, KI, and KSCN, using multiple force fields. While an enthalpic K+–K+attraction in water poses a small, but fundamentally important, contribution to the overall interaction, the probability of the collapsed conformation (COL) of BCETB, where both crown ether moieties (CEs) of BCETB are bent in toward the cavity, was found to increase successively upon binding of the first and second potassium ions. The promotion of the COL conformation reveals favorable intrinsic interactions between the potassium coordinated CEs, which further contribute to the observation that ΔH°bind,2 < ΔH°bind,1. While the observed trend is independent of the counterion, the origin of the significantly larger magnitude of the difference ΔH°bind,2 - ΔH°bind,1 observed experimentally for KSCN was studied in light of the weaker hydration of the thiocyanate anion, resulting in an enrichment of thiocyanate ions close to BCETB compared to the other studied counterions.

Department/s

  • Computational Chemistry
  • Centre for Analysis and Synthesis
  • Physical Chemistry
  • NanoLund: Centre for Nanoscience
  • LINXS - Institute of advanced Neutron and X-ray Science
  • eSSENCE: The e-Science Collaboration

Publishing year

2022-02-10

Language

English

Pages

2921-2932

Publication/Series

Journal of the American Chemical Society

Volume

144

Issue

7

Document type

Journal article

Publisher

The American Chemical Society (ACS)

Topic

  • Physical Chemistry (including Surface- and Colloid Chemistry)

Status

Published

ISBN/ISSN/Other

  • ISSN: 1520-5126