Investigation by two-color IR dissociation spectroscopy of Hoogsteen-type binding in a metalated nucleobase pair mimic

Abstract

Two Ag^I ions, deprotonated 1-methyl-thymine (1MT-H)⁻ and 1,3-dideaza-adenine (DDA), self-assemble in methanolic solution to a cationic [(Ag)₂(1MT-H)(DDA)]⁺ complex as identified by electrospray ionization mass spectrometry. Assignment of vibrational bands and identification of the silver coordination pattern arise from comparison of one- and two-color Infrared Multiple Photon Dissociation (IRMPD) spectra (1000–4000 cm⁻¹) of isolated and trapped complexes to calculated spectra from density functional theory. This approach reveals two structurally and energetically close isomers that resemble a metalated Hoogsteen-like binding motif. The two color IR/IR double resonance scheme proved in particular useful to observe weakly absorbing or weakly fragmenting vibrational modes.