Ultraviolet photodissociation spectroscopy of protonated adenosine and its hydrogen-bonded clusters with amino acid enantiomers

The effects of hydrogen bonding on the photochemical properties of nucleosides were investigated using ultraviolet photodissociation spectroscopy at 8 K in the gas phase. Photoinduced glycosidic bond cleavage of protonated adenosine is inhibited by hydrogen bonding with histidine. In the spectrum of protonated adenosine, a distinct band at 288 nm and broad bands were observed. The broad bands were similar to those of protonated adenosine hydrogen-bonded to d-histidine. In the spectrum of protonated adenosine hydrogen-bonded with l-histidine, the relative intensity increased gradually with increasing excitation energy, with the absorption onset at 285 nm. The protonation sites of protonated adenosine and its hydrogen-bonded cluster with d-histidine were located at the N3 position of the adenine moiety. The protonation site of protonated adenosine hydrogen-bonded with l-histidine was N1. The S₁–S₀ transition of N3-protonated adenosine was red-shifted compared to that of N1-protonated adenosine. Adenosine recognizes enantiomers through protonation and its electronic structure.