The parent anion of the RGD tripeptide: Photoelectron spectroscopyand quantum chemistry calculations

摘要

The gas-phase conformation of the intact (parent) unprotected RGD~-peptide anion has beeninvestigated using a combination of anion photoelectron spectroscopy and quantum chemistrycalculations of its low-energy stable structures. The experimentally observed RGD~-speciescorrespond to a conformation in which the guanidinium group is protonated, the C-terminus isneutral, the aspartic acid carboxyl is deprotonated, and the anion's excess electron orbital islocalized on the protonated guanidinium. This structure is reminiscent of the RGD loop, which is thepeptide motif recognized by trans-membrane integrins. The parent RGD~-radical anion was generated using a unique infrared desorption-photoemission-helium jet ion source, whose ability toproduce radical anions of peptides may also have analytical mass spectrometric implications.