Stereospecific collision-induced dissociation and vibrational spectroscopy of protonated cyclo (Tyr-Pro)

The protonated cyclo (LTyr-LPro) and (LTyr-DPro) dipeptides based on a diketopiperazine (DKP) ring are studied by tandem mass spectrometry in Fourier transform ion cyclotron resonance (FT-ICR) spectrometer. Collision-induced dissociation (CID) infrared multiple-photon (IRMPD) spectroscopy results interpreted with the aid of quantum chemical calculations dynamics simulations. All conformers identified for each diastereomer, denoted c-LLH+ c-LDH+, respectively, carbonyl group tyrosine. most stable form has an extended structure aromatic oriented outside DKP ring; it is stabilized OH+…? interaction. Distinct IR signatures obtained which differ strength interaction, much stronger c-LLH+. Less species folded over kinetically trapped our experimental conditions, but their spectrum identical c-LDH+. main collision-induced products analyzed using More efficient CID observed particular formation iminium In contrast to monomers, dimers c-LDH+ show spectra. This explained terms involving single strong OH+…O interaction between subunits not sensitive absolute configuration residues, i.e., from monomer neutral monomer.