Switching Ca2+/Ba2+ to Ba2+/Ca2+ Potentiometric Selectivities of Podands with Phosphoryl-containing Terminal Groups: A Molecular Modelling Study

• Published in: Journal of Inclusion Phenomena and Macrocyclic Chemistry Vol. 37; no. 1-4; pp. 407 - 421
• Main Authors: Varnek, A, Volkova, T, Petrukhin, O M, Wipff, G
• Format: Journal Article
• Language: English
• Published: 01.05.2000
• ISSN: 0923-0750; 1573-1111
• DOI: 10.1023/A:1008148116010

It has been shown experimentally that theCa/Ba potentiometric selectivity ofphosphoryl-containing podandR---O---(CH2---CH2---O)nndash; -R,R = ---C6H4---P(O)Ph2, n = 3 (I),switches to Ba/Ca when the ligand containsthe longer polyether chain, n = 5 (II). Here, we reportmolecular dynamics and free energy perturbation simulationsperformed using the amber 4.1 program on the complexesL M (M = Ca, Sr andBa, L = I and II) in the gas phase inorder to gain a microscopic insight into structural and energy bindingproperties of podands as a function of n. Mixed QM/MM (PM3/ amber) calculations were performed toanalyse the role of polarisation effects on the complexation selectivityof podands. It isshown that an increase of n does not affect the interactions ofM with phosphine oxide groups,but leads to less efficient interactions of small cations with the polyether chain. Calculatedpotentiometric selectivities of I (Ca > Ba)and II (Ba > Ca) are in agreement with the experimental data.