title: In-beam electron impact mass spectrometry of N-carbobenzoxy derivatives of oligopeptides composed of leucine and isoleucine.
abstract: The characteristics of the in-beam electron impact mass spectra of 13 N-carbobenzoxyoligopeptides (up to pentapeptides) composed mainly of leucine and isoleucine, and their alkyl and N-hydroxysuccinimide esters are described. In the cases of di- and tripeptide derivatives, each in-beam electron impact spectrum exhibited an abundant [M + 1]+ peak as well as amino-acyl fragments. However, in the case of pentapeptides the in-beam spectra measured under the routine conditions corresponded to the conventional electron impact spectra of the cyclopeptide derivatives formed by thermal cyclization in the mass spectrometer and few [M + 1]+ ions of the original peptides were observed. From the studies on temperature spectral change of in-beam electron impact spectra it became clear that rapid heating of the sample over the temperature range 200-300 degrees C gave abundant [M + 1]+ ions as well as fragment ions originating from the thermally intact peptide as the major peaks in the spectrum.
mesh_terms: D007532:Isoleucine / Q000032:analysis; D007930:Leucine / Q000032:analysis; D013058:Mass Spectrometry; D009842:Oligopeptides / Q000032:analysis*
chemical_list: D009842:Oligopeptides; D007532:Isoleucine; D007930:Leucine