Pereverzev, Aleksandr Y.Kopysov, Vladimir N.Boyarkin, Oleg V.2018-09-192018-09-192018-09-192018-08-2910.1021/acs.jpclett.8b02148https://infoscience.epfl.ch/handle/20.500.14299/148377Peptide-bond VUV absorption is inherent to all proteins and peptides. Although widely exploited in top-down proteomics for photodissociation, this absorption has never been spectroscopically characterized in the gas phase. We have measured VUV/UV photofragmentation spectrum of a single peptide bond in a cryogenically cold protonated dipeptide. Although the spectrum appears to be very broadband and structureless, vibrational pre-excitation of this and even larger cold peptides significantly increases the UV dissociation yield for some of their photofragments. We use this effect to extend the technique of IR−UV photofragmentation vibrational spectroscopy, developed for aromatic peptides, to nonaromatic ones and demonstrate measurements of conformation-specific and nonspecific IR spectra for di- to hexa-peptides.text::journal::journal article::research article