122nd General Meeting of the KCS

Type Poster Presentation
Area Physical Chemistry
Room No. Grand Ballroom
Time 10월 19일 (금요일) 11:00~12:30
Code PHYS.P-220
Subject Evaporation of hydrogen-bonded guanine dimers upon collisional activation of Na+-bound G-quartets
Authors Yoonkyung Choi, Sang Yun Han*
Department of Nano Chemistry, Gachon University Global Campus, Korea
Abstract Na+-bound G-quartets exhibits intriguing square planar structures formed by non-covalent interactions including ion-dipole interactions and multiple hydrogen bonding. In this study, energy-resolved collision-induced dissociation (ER-CID) of Na+-bound complexes of G-quartets with mixed ligands of guanine (G) and 9-methylguanine (9mG), [Na∙Gm∙9mGn]+ (m + n = 4) were investigated using tandem mass spectrometry in a combined approach with quantum chemical calculations. Theoretical study suggested that all five Na+-bound G-quartets investigated in this study possess square planar structures. The mass spectrum of [Na∙Gm∙9mGn]+ produced by electrospray ionization (ESI) exhibited generation of mixed clusters of Na+-bound dimers and G-quartets, wherein Na+-bound trimers (m + n = 3) were essentially missing. In addition, CID of G-quartets hardly produced fragments of Na+-bound trimers from the square planar complexes, while formation of dimeric fragments was pronounced These suggest that a great stability is achieved by forming a complete hydrogen bonding network in G-quartets, which agrees well with a large predicted stepwise enthalpy gained by complexation with the fourth ligand, which is as high as 55 kcal/mol. The stability by hydrogen bonding network between G moieties in G-quartets further suggests that Na+-bound dimeric fragments may arise from neighboring, hydrogen-bonded ligands; it allowed to address the stereochemistry of G-quartets, of which population for cis- and trans-conformers of [Na∙G2∙9mG2]+ can be assessed to be 50:50 in the gas phase. The ratio of 50:50 also suggests that the G-quartets were likely to be formed in the solution due to thermochemical stability rather than in the course of electrospray ionization via kinetic trapping.
E-mail choiyk5@naver.com