Self-pairing of 1-methylthymine mediated by two and three Ag(I) ions: a gas phase study using infrared dissociation spectroscopy and density functional theory.

Yevgeniy Nosenko,Gereon Niedner-Schatteburg,Christoph Riehn

doi:10.1039/c5cp07016c

Abstract

Metal base pairs of Ag(I) cations and 1-methylthymine (1MT) or deprotonated 1-methylthymine (1MT-H) are produced and analyzed by electrospray ionization mass spectrometry (ESI-MS). Mass-selected ions of type [Ag2(1MT)(1MT-H)](+) and [Ag3(1MT-H)2](+) are interrogated by infrared multiple-photon dissociation (IRMPD) in an ion trap in the range of 1200-3700 cm(-1). Supporting spectroscopic data were obtained from the investigation of the analogous 2'-deoxy-thymidine complexes which exhibit advantageously high fragment yields. By comparison with calculated linear IR spectra (obtained by density functional theory, DFT) we assign the structures and the possible isomeric forms of these metal base pairs and their dependence on the number of mediating Ag(I) ions. Based on the observed Ag(+)/1MT complexes and related polarizable continuum model DFT calculations we describe the probable formation pathways in aqueous solution. The present findings pave the way for subsequent UV investigations of the multi-metal mediated base pairs.

Highlights

DNA molecules have been recognized for a while as promising templates for atomic scale metal structures due to their ability to bind transition metal ions between their oligonucleotide strands and because of the advanced level of their synthetic structural control.[1]
In the current study we report on the structure of the cationic BP of 1MT mediated by two and three AgI ions investigated using infrared multiple-photon dissociation (IRMPD) spectroscopy
The number of AgI ions involved in the different complexes is readily discernible from their isotope patterns

Summary

Introduction

DNA molecules have been recognized for a while as promising templates for atomic scale metal structures due to their ability to bind transition metal ions between their oligonucleotide strands and because of the advanced level of their synthetic structural control.[1]. The gas phase structure of the DDA–(Ag)2–(1MT-H) MBP (1MT = 1-methylthymine) has been recently investigated by one- and two-color IR multiple photon dissociation (1C-/2C-IRMPD) spectroscopy in an electrospray ionization ion trap experiment.[9] In that study, vibrational analysis by DFT led to the assignment of a reversed Hoogsteen base pairing topology mediated by two silver coordinative bridges with likely argentophilic interactions due to the close proximity of the metal units.[20]

Results

Conclusion