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

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.

Advancing Inorganic Coordination Chemistry by Spectroscopy of Isolated Molecules: Methods and Applications

“…Inevitably, the one colour IR-PD and IR-MPD efficiencies of untagged complexes decline exponentially towards low photon energies. Whereas in early work the onset of siginificant nonlinear damping of IR-MPD yield versus expected (and sometimes computed) IR activities was found to set in at about 3000 cm À 1 , [101] improved table top laser instrumentation shifted this operational limit to below 1200 cm À 1 [102][103] and in the most favourable cases as low as 660 cm À 1 . [104] Nevertheless, the required balance between weakest bond energy, oscillator strength and necessary photon flux (total energy per few nanosec laser pulse) oftentimes remains unpredictable and often causes weak IR bands to disappear in IR-MPD spectra.…”

“…Early application examples of this two‐colour infrared photo dissociation (2cIR‐PD) method were the characterization of a dimeric silver complex uncovering a Hoogsteen‐type, nucleobase‐mimic coordination motif (Figure 5 ) [105] as well as a study of dimeric silver complexes of 1‐methylthymine. [102] Also, a multi method characterization of a Ruthenium transfer hydrogenation catalyst of the type [(η 6 ‐cym)RuX(pympyr)] + , benefitted from 2cIR‐PD spectra of precursors (before HCl loss) and of activated complexes (after HCl loss), and it eventually become possible to elucidate C−H activation as the key step in the activation mechanism. [106] Likewise, the structural characterization of Thymine‐Uracil‐Tetracyano‐Pt II ‐Aggregates benefitted strongly from 2cIR‐PD spectra together with DFT modelling that revealed decisive bands below 1500 cm −1 , as opposed to previous 1cIR‐PD attempts.…”

From Preassociation to Chelation: A Survey of Cisplatin Interaction with Methionine at Molecular Level by IR Ion Spectroscopy and Computations

“…It is worthy of note that the species is assayed in the gas phase, in the absence of solvent and associated band-broadening effects. IRMPD spectroscopy has been extensively used for the vibrational and structural characterization of transition metal complexes of both catalytic and biological relevance. − In particular, cisplatin related platinum­(II) complexes have been characterized. − Previous reports have highlighted the versatility of ESI-MS together with the specificity of IRMPD spectroscopy in delivering detailed structural information on the monofunctional complexes cis -[PtCl­(NH 3 ) 2 (AA)] + , where AA is either Met or His. − Furthermore, solutions of cisplatin and a simple ligand (L, chosen to model the nucleophilic functionalities of amino acids and nucleobases), assayed by ESI-MS and IRMPD spectroscopy have revealed the presence and role of the encounter complexes { cis -[PtCl­(NH 3 ) 2 (H 2 O)] + ·L}. , These species are formed by the diffusion controlled encounter of the aqua complex of cisplatin with the incoming ligand L and are the early actors in the substitution reaction of metal complexes in aqueous media, conforming to the Eigen–Wilkins reactant preassociation model. − In the reported cases, the role of the encounter complex along the substitution reaction path of the cisplatin aqua complex with model ligands was assessed by observing the reaction to occur in the isolated species after collisional- or photoactivation, while IRMPD spectroscopy has afforded its vibrational and structural features. Moving one step further in assaying the cisplatin reaction with nucleophiles approaching the biomolecular targets, herein is reported the isolation and characterization of the adduct formally obtained by the preassociation of cisplatin aqua complex with methionine, [PtCl­(NH 3 ) 2 (H 2 O)­(Met)] + .…”