Complete sequencing of mono—deprotonated peptide nucleic acids by sustained off-resonance irradiation collision—induced dissociation

Complete peptide nucleic acids (PNAs) sequence information is obtained from the unimolecular decomposition of singly-charged PNA oligomers in the negative-ion mode using electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) and sustained off-resonance irradiation collision induced dissociation. The 4-mers, n-CATT-c, n-AGCT-c, n-AACT-c, and n-acetylated-AACT-c and two 6-mers, n-AAAAAA-c and n-CCCCCC-c, were investigated to explore the unimolecular decomposition of mixed-nucleobase and homopolymer PNAs representing purine and pyrimidine oligomers, respectively. PNA decomposition is explored using a product-ion appearance curve and double resonance experiments. A decomposition mechanism for sequence ion formation (PNA amide bond cleavage) is proposed.