D-Amino acid analysis in solution using the photochemical properties of protonated adenosine

The chiral-recognition ability of protonated adenosine was investigated using a tandem mass spectrometer equipped with an electrospray ionization source and cold ion trap. The ultraviolet photodissociation spectra of the hydrogen-bonded protonated clusters of adenosine and histidine enantiomers at 100 K revealed that H⁺(adenosine)(D-histidine) exhibited a relative intensity at 278 nm that was more than double that of H⁺(adenosine)(L-histidine). Histidine enantiomers were identified by probing the electronic excited state of the adenine moiety in protonated adenosine in the gas phase. The adenine moiety acquires the ability to recognize chirality via its glycosidic bond with D-ribose in protonated adenosine. This ability, which was discovered in the gas phase, was used in quantitative-analysis applications in solution. The molar fractions of L-histidine and D-histidine in solution were determined by measuring the relative abundance of the precursor and product ions in the single product-ion spectrum of the hydrogen-bonded clusters generated from solution and with reference to a calibration curve.