Department of Chemistry, Chungbuk National University, Chungbuk 28644, Korea.
Phys Chem Chem Phys. 2021 Mar 21;23(11):6783-6790. doi: 10.1039/d1cp00312g. Epub 2021 Mar 15.
Cryogenic ion spectroscopy was used to characterize adenine complexes containing alkali metal cations (MA, M = Cs, Rb, K, Na, and Li) produced by electrospray ionization. The ultraviolet (UV) photodissociation spectra of the complexes stored in a cryogenic ion trap exhibited well-resolved vibronic bands near their origin bands of the S-S transition. The UV-UV hole-burning and infrared ion-dip spectra showed that all the MA ions in the ion trap were single isomers of MA7a, where the M ion was not bound to canonical 9H-adenine (A9) but bound to a rare tautomer, 7H-adenine (A7). Density functional theory calculations showed lower tautomerization barriers for MA9 than for bare A9 in aqueous solution. We suggest that M ions not only play a catalytic role in the tautomerization of A9 to A7 but also increase the tautomerization yield by forming stable MA7a isomers.
低温离子光谱学被用于通过电喷雾电离来表征包含碱金属阳离子（MA，M = Cs，Rb，K，Na 和 Li）的腺嘌呤配合物。在低温离子阱中储存的配合物的紫外（UV）光解光谱在 S-S 跃迁的其起源带附近表现出很好分辨的振子带。UV-UV 空穴烧蚀和红外离子陷波光谱表明，离子阱中的所有 MA 离子都是 MA7a 的单异构体，其中 M 离子不与规范的 9H-腺嘌呤（A9）结合，而是与罕见的互变异构体 7H-腺嘌呤（A7）结合。密度泛函理论计算表明，在水溶液中，MA9 的互变异构化势垒低于裸露的 A9。我们认为，M 离子不仅在 A9 到 A7 的互变异构化中起催化作用，而且通过形成稳定的 MA7a 异构体来增加互变异构化产率。
