The K2(9-ethylguanine)122+ quadruplex is more stable to unimolecular dissociation than the K(9-ethylguanine)8+ quadruplex in the gas phase: a BIRD, energy resolved SORI-CID, IRMPD spectroscopic, and computational study

Authors

Mohammad Azargun, Memorial University of Newfoundland
Paul J. Meister, University of Windsor
James Gauld, University of Windsor
Travis D. Fridgen, Memorial University of Newfoundland

Document Type

Article

Publication Date

6-19-2019

Publication Title

Physical Chemistry Chemical Physics

First Page

1

Last Page

8

Abstract

A combination of experimental trapped-ion mass spectrometric studies and computational chemistry has been used in the present work to assess the intrinsic properties of the potassiated 9-ethylguanine (9eG) self-assembled quadruplex, K₂(9eG)₁₂²⁺, in the gas phase. Infrared multiple photon dissociation (IRMPD) spectroscopy in the N–H/C–H stretching region (2700–3800 cm⁻¹) revealed that this G-quadruplex is a sandwich-type structure with two G-tetrads sandwiching each of the two K⁺, very similar to the structure determined previously for the K(9eG)₈⁺ complexes. The stability of K₂(9eG)₁₂²⁺ toward unimolecular dissociation and its binding energy were examined using energy-resolved sustained off-resonance collision induced dissociation (SORI-CID) and blackbody infrared radiative dissociation (BIRD) kinetics experiments. SORI-CID experiments showed that the self-assembled K₂(9eG)₁₂²⁺ complex undergoes charge separation forming K(9eG)₈⁺ and K(9eG)₄⁺ compared to K(9eG)₈⁺ which loses neutral 9eG. More interestingly, K₂(9eG)₁₂²⁺ is more stable toward unimolecular dissociation activated by SORI-CID than the K(9eG)₈⁺ complex. Temperature dependent BIRD kinetics for K₂(9eG)₁₂²⁺ were consistent with energy-resolved SORI-CID results showing K₂(9eG)₁₂²⁺ to have an activation energy of 225 ± 15 kJ mol⁻¹, approximately 50 kJ mol⁻¹ greater than that determined for K(9eG)₈⁺. The extra stability of K₂(9eG)₁₂²⁺ is apparently not thermodynamic stability, but most likely due to an energy barrier for dissociation.

DOI

10.1039/c9cp01651a

Recommended Citation

Azargun, Mohammad; Meister, Paul J.; Gauld, James; and Fridgen, Travis D.. (2019). The K2(9-ethylguanine)122+ quadruplex is more stable to unimolecular dissociation than the K(9-ethylguanine)8+ quadruplex in the gas phase: a BIRD, energy resolved SORI-CID, IRMPD spectroscopic, and computational study. Physical Chemistry Chemical Physics, 1-8.
https://scholar.uwindsor.ca/chemistrybiochemistrypub/136