posted on 2021-03-25, 15:06authored byWenjin Cao, Hanhui Zhang, Qinqin Yuan, Xiaoguo Zhou, Steven R. Kass, Xue-Bin Wang
This
Letter reports a counterintuitive observation that methylation
of the glycine-iodide cluster leads to fewer conformations and spectroscopic
simplicity. Cryogenic “iodide-tagging” negative ion
photoelectron spectroscopy (NIPES) is used to probe specific binding
sites of three N-methylated glycine derivatives,
i.e., N-methylglycine (sarcosine), N,N-dimethylglycine, and N,N,N-trimethylglycine (glycine betaine).
NIPES reveals a progressive spectral simplification of the iodide
clusters with increasing methylation due to fewer contributing structures.
Low energy conformers and tautomers of each cluster are computationally
identified, and those observed in the experiments are assigned based
on excellent agreement between the NIPE spectra and theoretical simulations.
Zwitterionic cluster structures are found to be less stable than their
canonical forms and do not contribute to the observed spectra. This
work demonstrates the power of iodide-tagging NIPES in probing conformations
of amino acid-iodide clusters and provides a molecular level understanding
on the effect of methyl substitution on amino acid binding sites.