The Structure of the Protonated Serine Octamer

The
amino acid serine has long been known to form a protonated
“magic-number” cluster containing eight monomer units
that shows an unusually high abundance in mass spectra and has a remarkable
homochiral preference. Despite many experimental and theoretical studies,
there is no consensus on a Ser8H+ structure
that is in agreement with all experimental observations. Here, we
present the structure of Ser8H+ determined by
a combination of infrared spectroscopy and ab initio molecular dynamics
simulations. The three-dimensional structure that we determine is
∼25 kcal mol–1 more stable than the previous
most stable published structure and explains both the homochiral preference
and the experimentally observed facile replacement of two serine units.