2 research outputs found
Does the Residues Chirality Modify the Conformation of a Cyclo-Dipeptide? Vibrational Spectroscopy of Protonated Cyclo-diphenylalanine in the Gas Phase
The
structure of a protonated diketopiperazine dipeptide, cyclo-diphenylalanine,
is studied by means of infrared multiple photon dissociation spectroscopy
combined with quantum chemical calculations. Protonation exclusively
occurs on the oxygen site and, in the most stable conformer, results
to an intramolecular OH路路路蟺 interaction, accompanied
by a CH路路路蟺 interaction. Higher-energy conformers
with free OH and NH路路路蟺 interactions are observed
as well, due to kinetic trapping. Optimization of the intramolecular
interactions involving the aromatic ring dictates the geometry of
the benzyl substituents. Changing the chirality of one of the residues
has consequences on the CH路路路蟺 interaction, which
is of C<sub>伪</sub>H路路路蟺 nature for LD,
while LL shows a C<sub>尾</sub>H路路路蟺 interaction.
Higher-energy conformers also display some differences in the nature
of the intramolecular interactions
Exotic Protonated Species Produced by UV-Induced Photofragmentation of a Protonated Dimer: Metastable Protonated Cinchonidine
A metastable protonated cinchona
alkaloid was produced in the gas
phase by UV-induced photodissociation (UVPD) of its protonated dimer
in a Paul ion trap. The infrared multiple photon dissociation (IRMPD)
spectrum of the molecular ion formed by UVPD was obtained and compared
to DFT calculations to characterize its structure. The protonation
site obtained thereby is not accessible by classical protonation ways.
The protonated monomer directly formed in the ESI source or by collision-induced
dissociation (CID) of the dimer undergoes protonation at the most
basic alkaloid nitrogen. In contrast, protonation occurs at the quinoline
aromatic ring nitrogen in the UVPD-formed monomer