Mass spectrometric studies on the effect of sidechains of N-acetylamino acid methyl esters and N-methylamides on their photoionisation

✍ Scribed by V. M. Orlov; Ya. M. Varshavsky; A. I. Miroshnikov

• Publisher: John Wiley and Sons
• Year: 1974
• Tongue: English
• Weight: 472 KB
• Volume: 9
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/oms.1210090809

✦ Synopsis

Abstract

Photoionisation mass spectra of N‐methylamides of N‐acetyl derivatives of the following amino acids have been studied: alanine, valine, leucine, serine, threonine, phenylalanine, tyrosine, tryptophan and proline. The study also included methyl esters of N‐acetyl tyrosine, N‐acetyl phenyl alanine and N‐trideuteroacetyl phenylalanine. The photon energies were within the range of 7.5 to 13.0 eV. The appearance potentials of the main ions were also determined. The compounds under study contain CHCO, CONH and NC~α~ bonds as well as sidechains and may therefore be regarded as models of short peptides.

Under photoionisation conditions, decomposition of compounds containing aliphatic sidechains involves mainly CHCO bonds; the appearance potentials of the corresponding fragments decrease with an increase in the size of sidechain. The presence of hydroxyl in the sidechain results in an increase in the appearance potential of a fragment formed due to CHCO bond rupture, whereas the presence of an aromatic moiety favours an even greater increase in the appearance potential and results in predominant rupture of the NC~α~ bond.

Analysis of the mass spectra obtained confirms the conclusion made previously that application of the photoionisation technique enables one to increase considerably the relative intensity of characteristic peaks and to suppress secondary process taking place upon ionisation by the electrons with energy values of the order of 70 eV.