posted on 2021-10-12, 21:14authored byWyatt Zagorec-Marks, Leah G. Dodson, Patrick Weis, Erik K. Schneider, Manfred M. Kappes, J. Mathias Weber
We investigated the structural and
spectroscopic properties of
singly deprotonated biliverdin anions in vacuo, using
a combination of cryogenic ion spectroscopy, ion mobility spectrometry,
and density functional theory. The ion mobility results show that
at least two conformers are populated, with the dominant conformer
at 75–90% relative abundance. The vibrational NH stretching
signatures are sensitive to the tetrapyrrole structure, and they indicate
that the tetrapyrrole system is in a helical conformation, consistent
with simulated ion mobility collision cross sections. The vibrational
spectrum in the fingerprint region of this singly deprotonated species
shows that the two propionate groups share the remaining acidic proton.
The S1 band of the electronic spectrum in vacuo is broad, despite ion trap temperatures of 20 K during ion preparation,
with a congested Franck–Condon envelope showing partially resolved
vibrational features. The vertical transition exhibits a small solvatochromic
red shift (−320 cm–1) in aqueous solution.