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Molecular Receptors for Adenine and Guanine Employing Metal Coordination, Hydrogen‐Bonding and π‐Stacking Interactions
Author(s) -
Kickham James E.,
Loeb Stephen J.,
Murphy Shan L.
Publication year - 1997
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.19970030807
Subject(s) - nucleobase , chemistry , stacking , hydrogen bond , coordination sphere , crystallography , guanine , ligand (biochemistry) , aromaticity , stereochemistry , coordination complex , molecule , metal , crystal structure , dna , nucleotide , organic chemistry , receptor , biochemistry , gene
Thiacyclophane ligands 1 and 2 , containing a meta ‐xylyldithiaether unit, an aromatic spacing unit and a polyether chain, were prepared in good yield in a three‐step synthesis. The macrocyclic organopalladium complexes [Pd(L)‐(MeCN)][BF 4 ] ( 3 : L = 1; 4 : L = 2 ) were prepared through palladation of the respective thiacyclophane ligand by reaction with [Pd(MeCN) 4 ][BF 4 ] 2 . These complexes act as metalloreceptors to aromatic amines such as p ‐aminopyridine (pap), m ‐aminopyridine (map) and the DNA nucleobases adenine and guanine. Binding occurs through simultaneous first‐ and second‐sphere coordination. This involves three separate interactions: first‐sphere σ donation from an aromatic N atom to the Pd centre, second‐sphere hydrogen bonds between the NH 2 group and polyether O atoms, and π stacking between the electron‐poor aromatic rings of the substrate and the electron‐rich aromatic spacing units of the receptor. 1 H NMR spectra exhibit chemical shift changes indicative of the H‐bonding and π‐stacking interactions in solution. X‐ray structures for thiacyclophane 1 , metalloreceptor [Pd( 1 )(MeCN)][BF 4 ] ( 3 ), metalloreceptor/model substrate complexes [Pd( 1 )(pap)][BF 4 ( 5 ) and [Pd( 2 )‐(pap)][BF 4 ] ( 7 ), and metalloreceptor/nucleobase complexes [Pd( 1 )(adenine)][BF 4 ] ( 13 ), [Pd( 2 )(adenine)][BF 4 ] ( 14 ) and [Pd( 1 )(guanine‐BF 3 )][BF 4 ] ( 15b ) show details of these interactions in the solid state.