Selective complexation of divalent cations by a cyclic α,β-peptoid hexamer: a spectroscopic and computational study.

E. De Santis (1) , A. A. Edwards (1) , B. D. Alexander (2) , S. J. Holder (3) , A.-S. Biesse-Martin (4) , B. V. Nielsen (2) , D. Mistry (5) , L. Waters (5) , G. Siligardi (6) , R. Hussain (6) , S. Faure (4) , C. Taillefumier (4)

1 Medway School of Pharmacy
2 School of Science, University of Greenwich
3 Functional Materials Group, School of Physical Sciences, University of Kent
4 ICCF - Institut de Chimie de Clermont-Ferrand
5 University of Huddersfield
6 DIAMOND Light source

We describe the qualitative and quantitative analysis of the complexation properties towards cations of a cyclic peptoid hexamer composed of alternating α- and β-peptoid monomers, which bear exclusively chiral (S)-phenylethyl side chains (spe) that have no noticeable chelating properties. The binding of a series of monovalent and divalent cations was assessed by 1H NMR, circular dichroism, fluorescence and molecular modelling. In contrast to previous studies on cations binding by 18-membered α-cyclopeptoid hexamers, the 21-membered cyclopeptoid cP1 did not complex monovalent cations (Na+, K+, Ag+) but showed selectivity for divalent cations (Ca2+, Ba2+, Sr2+ and Mg2+). Hexacoordinated C-3 symmetrical complexes were demonstrated for divalent cations with ionic radii around 1 Å (Ca2+ and Ba2+), while 5-coordination is preferred for divalent cations with larger (Ba2+) or smaller ionic radii (Mg2+).

Domaines: Chimie

E. De Santis, A. A. Edwards, B. D. Alexander, S. J. Holder, A.-S. Biesse-Martin, et al.. Selective complexation of divalent cations by a cyclic α,β-peptoid hexamer: a spectroscopic and computational study.. Organic & Biomolecular Chemistry, 2016, 14, pp.11371-11380. ⟨hal-01479200⟩