Premium
The Challenge of Deciphering Linkage Isomers in Mixtures of Oligomeric Complexes Derived from 9‐Methyladenine and trans ‐(NH 3 ) 2 Pt II Units
Author(s) -
Ibáñez Susana,
Mihály Béla,
Sanz Miguel Pablo J.,
Steinborn Dirk,
Pretzer Irene,
Hiller Wolf,
Lippert Bernhard
Publication year - 2015
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.201406378
Subject(s) - linkage isomerism , chemistry , conformational isomerism , nucleobase , stereochemistry , metal , oligomer , crystallography , cis–trans isomerism , nuclear magnetic resonance spectroscopy , ligand (biochemistry) , molecule , dna , polymer chemistry , biochemistry , receptor , organic chemistry
Metal coordination to N9‐substituted adenines, such as the model nucleobase 9‐methyladenine (9MeA), under neutral or weakly acidic pH conditions in water preferably occurs at N1 and/or N7. This leads, not only to mononuclear linkage isomers with N1 or N7 binding, but also to species that involve both N1 and N7 metal binding in the form of dinuclear or oligomeric species. Application of a trans ‐(NH 3 ) 2 Pt II unit and restriction of metal coordination to the N1 and N7 sites and the size of the oligomer to four metal entities generates over 50 possible isomers, which display different feasible connectivities. Slowly interconverting rotamers are not included in this number. Based on 1 H NMR spectroscopic analysis, a qualitative assessment of the spectroscopic features of N1,N7‐bridged species was attempted. By studying the solution behavior of selected isolated and structurally characterized compounds, such as trans ‐[PtCl(9MeA‐ N7 )(NH 3 ) 2 ]ClO 4 ⋅ 2H 2 O or trans , trans ‐[{PtCl(NH 3 ) 2 } 2 (9MeA‐ N1 , N7 )][ClO 4 ] 2 ⋅ H 2 O, and also by application of a 9MeA complex with an (NH 3 ) 3 Pt II entity at N7, [Pt(9MeA‐ N7 )(NH 3 ) 3 ][NO 3 ] 2 , which blocks further cross‐link formation at the N7 site, basic NMR spectroscopic signatures of N1,N7‐bridged Pt II complexes were identified. Among others, the trinuclear complex trans ‐[Pt(NH 3 ) 2 {μ‐( N1 ‐9MeA‐ N7 )Pt(NH 3 ) 3 } 2 ][ClO 4 ] 6 ⋅ 2H 2 O was crystallized and its rotational isomerism in aqueous solution was studied by NMR spectroscopy and DFT calculations. Interestingly, simultaneous Pt II coordination to N1 and N7 acidifies the exocyclic amino group of the two 9MeA ligands sufficiently to permit replacement of one proton each by a bridging heterometal ion, Hg II or Cu II , under mild conditions in water.