Circular dichroism (CD) spectra contain information about absolute configurations and conformations of chiral compounds. However, extracting this information from CD spectra in solution is challenging, because the spectra exhibit only the averaged CD values of all different conformers. CD spectroscopy of jet-cooled molecules can provide conformation-specific CD spectra, but its application to biomolecules has been limited due to the difficulty of their production in the gas phase. Here, we obtained the first CD spectra of chiral molecular ions produced by electrospray ionization (ESI) using cold ion CD spectroscopy. Protonated L-or D-phenylalanine ions produced by ESI were stored in a cold quadrupole ion trap and irradiated by multiple laser pulses with left or right circular polarization. The CD spectra exhibited well-resolved CD bands of two conformers, whose signs were opposite to each other. This study will broaden the scope of conformation-resolved CD spectroscopy to large molecular ions without size limitations.

We obtained ultraviolet photodissociation (UVPD) circular dichroism (CD) spectra of protonated L-phenylalanyl-L-alanine (L-H+PheAla) near the origin band of the S0-S1 transition using cryogenic ion spectroscopy. Infrared (IR) ion-dip, IR-UV hole...

Ultraviolet photodissociation (UVPD) spectra of protonated 9-methyladenine (H + 9MA), protonated 7-methyl adenine (H + 7MA), protonated 3-methyladenine (H + 3MA), and sodiated 7methyladenine (Na + 7MA) near the origin bands of the S 0 −S 1 transition were obtained using cryogenic ion spectroscopy. The UV− UV hole burning, infrared (IR) ion-dip, and IR-UV double resonance spectra showed that all the ions were present as single isomers in a cryogenic ion trap. The UVPD spectrum of H + 9MA exhibited only a broad absorption band, whereas the spectra of H + 7MA, H + 3MA, and Na + 7MA displayed moderately or well-resolved vibronic bands. Potential energy profiles were computed to understand the reason for the different bandwidths of the vibronic bands in the spectra. The broadening of the bands was correlated with the slopes between the Franck−Condon point and the conical intersection between the S 1 and S 0 states in the potential energy profiles, thus reflecting the deactivation rates in the S 1 state.