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摘要
Electrospray ionization mass spectrometry was used to investigate the intrinsic chemical properties of beta-carbolines: Eudistomin U (as EU) and 5-Br-Eudistomin U (as BrEU) yielding self-association in negative ion mode. It was observed that the deprotonated homodimer of EU was more stable in the gas phase than BrEU. Indeed, BrEU presents a higher polarizability that could influence the dimerization energy. On the contrary, the stability energies calculated at B3LYP/6-31 G/AM1 level showed a small difference for these two dimers. To understand the experimental stability variation, the experimental and theoretical gas phase acidities of these two beta-carbolines have been estimated. It has been shown that EU is less acidic than BrEU in the gas phase, which could explain the lower stability of the [2BrEU-H](-) dimer. In addition, the investigation of non-covalent interaction of beta-carbolines and nucleobases has been carried out. It was experimentally demonstrated that the deprotonated heterodimer's relative stability scale was [Gua M-H](-) >> [Thy M-H](-) > [Ade M-H](-), but the Cyt/beta-carboline complexes were not observed. However, the absence of Cyt/beta-carboline complexes could be explained by the great acidity difference between Cyt and beta-carbolines, yielding unstable non-covalent complexes. The studied beta-carbolines showed a particular affinity with guanine which suggested a strong interaction, from a structural and reactivity point of view. Calculated reaction pathways rationalize the set of experimental results concerning the heterodimer stabilisation reflected by the V(1/2) value of breakdown curves of deprotonated heterodimers.
- 出版日期2009-9-15
- 单位复旦大学
