Tautomer-Selective Spectroscopy of Nucleobases, Isolated in the Gas Phase

Tautomer-Selective Spectroscopy of Nucleobases, Isolated in the Gas Phase 

The rare imino and enol forms can lead to alternate base-pair combinations and thus cause mutations in replication. This type of mutation is called a tautomeric shift [2, 3]. Possible mismatches include iminoC-A, enolT-G, C-iminoA, and T-enolG. Tautomerization can occur in DNA by single or double proton transfer. In solution equilibrium, generally the keto form dominates, complicating efforts to study the properties of the individual forms. One approach to studying tautomeric properties is double-resonant gas-phase spectroscopy, as this technique offers isomeric selectivity. This chapter summarizes the results from such investigations. 

As molecules can exist in tautomeric equilibria, most experimental techniques need to address mixtures of tautomer populations. Double-resonant techniques in 

Tautomerism Methods and Theories, First Edition. Edited by Liudmil Antonov. 

For spectral hole-burning, the ionization step is preceded by a pulse from a tunable IR laser. This pulse resonantly alters a specific population in the beam, which is probed as a decrease in the ion signal [13-18]. This technique produces ground-state IR absorption spectra of optically selected as well as mass-selected molecules. The OH and NH stretching frequencies are especially highly specific for difierent tautomeric forms as well as for hydrogen-bonded structures. 

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