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Metal‐Ion‐Coordinating Properties of the Dinucleotide 2′‐Deoxyguanylyl(5′→3′)‐2′‐deoxy‐5′‐guanylate (d(pGpG) 3− ): Isomeric Equilibria Including Macrochelated Complexes Relevant for Nucleic Acids
Author(s) -
Knobloch Bernd,
Sigel Helmut,
Okruszek Andrzej,
Sigel Roland K. O.
Publication year - 2007
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.200600744
Subject(s) - chemistry , metal , metal ions in aqueous solution , phosphate , chelation , divalent metal , potentiometric titration , ion , inorganic chemistry , nucleic acid , intramolecular force , crystallography , divalent , stereochemistry , organic chemistry , biochemistry
The interaction between divalent metal ions and nucleic acids is well known, yet knowledge about the strength of binding of labile metal ions at the various sites is very scarce. We have therefore studied the stabilities of complexes formed between the nucleic acid model d(pGpG) and the essential metal ions Mg 2+ and Zn 2+ as well as with the generally toxic ions Cd 2+ and Pb 2+ by potentiometric pH titrations; all four ions are of relevance in ribozyme chemistry. A comparison of the present results with earlier data obtained for M(pUpU) − complexes allows the conclusion that phosphate‐bound Mg 2+ and Cd 2+ form macrochelates by interaction with N7, whereas the also phosphate‐coordinated Pb 2+ forms a 10‐membered chelate with the neighboring phosphate diester bridge. Zn 2+ forms both types of chelates with formation degrees of about 91 % and 2.4 % for Zn[d(pGpG)] ${{{- \hfill \atop {\rm cl}/{\rm N7}\hfill}}}$ and Zn[d(pGpG)] ${{{- \hfill \atop {\rm cl}/{\rm PO}\hfill}}}$ , respectively; the open form with Zn 2+ bound only to the terminal phosphate group, Zn[d(pGpG)] ${{{- \hfill \atop {\rm op}\hfill}}}$ , amounts to about 6.8 %. The various intramolecular equilibria have also been quantified for the other metal ions. Zn 2+ , Cu 2+ , and Cd 2+ also form macrochelates in the monoprotonated M[H;d(pGpG)] species (the proton being at the terminal phosphate group), that is, the metal ion at N7 interacts to some extent with the P(O) 2 (OH) − group. Thus, this study demonstrates that the coordinating properties of the various metal ions toward a pGpG unit in a nucleic acid differ: Mg 2+ , Zn 2+ , and Cd 2+ have a significant tendency to bridge the distance between N7 and the phosphate group of a (d)GMP unit, although to various extents, whereas Pb 2+ (and possibly Ca 2+ ) prefer a pure phosphate coordination.