title: Interaction of Cu(+) with cytosine and formation of i-motif-like C-M(+)-C complexes: alkali versus coinage metals.
abstract: The Watson-Crick structure of DNA is among the most well-known molecular structures of our time. However, alternative base-pairing motifs are also known to occur, often depending on base sequence, pH, or the presence of cations. Pairing of cytosine (C) bases induced by the sharing of a single proton (C-H(+)-C) may give rise to the so-called i-motif, which occurs primarily in expanded trinucleotide repeats and the telomeric region of DNA, particularly at low pH. At physiological pH, silver cations were recently found to stabilize C dimers in a C-Ag(+)-C structure analogous to the hemiprotonated C-dimer. Here we use infrared ion spectroscopy in combination with density functional theory calculations at the B3LYP/6-311G+(2df,2p) level to show that copper in the 1+ oxidation state induces an analogous formation of C-Cu(+)-C structures. In contrast to protons and these transition metal ions, alkali metal ions induce a different dimer structure, where each ligand coordinates the alkali metal ion in a bidentate fashion in which the N3 and O2 atoms of both cytosine ligands coordinate to the metal ion, sacrificing hydrogen-bonding interactions between the ligands for improved chelation of the metal cation.
authors.affiliation: Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525 ED Nijmegen, The Netherlands. joso@science.ru.nl.
authors.forename: Juehan
authors.initials: J
authors.lastname: Gao
authors.forename: Giel
authors.initials: G
authors.lastname: Berden
authors.forename: M T
authors.initials: MT
authors.lastname: Rodgers
authors.forename: Jos
authors.initials: J
authors.lastname: Oomens
mesh_terms: D000468:Alkalies / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D003596:Cytosine / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D000468:Alkalies; D003300:Copper; D003596:Cytosine