Single-photon absorption of isolated collagen mimetic peptides and triple-helix models in the VUV-X energy range

Abstract

(2017). Single-photon absorption of isolated collagen mimetic peptides and triple-helix models in the VUV-X energy range. Physical Chemistry Chemical Physics, 19(28) Cartilage and tendons owe their special mechanical properties to the fibrous collagen structure. These strong fibrils are aggregates of a sub-unit consisting of three collagen proteins wound around each other in a triple helix. Even though collagen is the most abundant protein in the human body, the response of this protein complex to ionizing radiation has never been studied. In this work, we probe the direct effects of VUV and soft X-ray photons on isolated models of the collagen triple helix, by coupling a tandem mass spectrometer to a synchrotron beamline. Single-photon absorption is found to induce electronic excitation, ionization and conversion into internal energy leading to inter-and intra-molecular fragmentation, mainly due to Gly-Pro peptide bond cleavages. Our results indicate that increasing the photon energy from 14 to 22 eV reduces fragmentation. We explain this surprising behavior by a smooth transition from excitation to ionization occurring with increasing photon energy. Moreover, our data support the assumption of a stabilization of the triple helix models by proline hydroxylation via intra-complex stereoelectronic effects, instead of the influence of solvent.

Photoinduced Processes within Noncovalent Complexes Involved in Molecular Recognition

“…[6] After electron detachment from R, these charge-dipole interactions do not exist anymore, thus decreasing the complex bindinge nergy, whereas little structurale ffect is expected after electron detachment from the CO 2 À group of vancomycin,b ecause it is not bound to R, and thus can leave the complex without breakingi t, leading to [V+ +RÀ2HÀCO 2 ] À .T he influence of the native structure is also supported by the much lower intensity of the peak attributed to further loss of CO 2 ,l eading to [V+ +RÀ2HÀ2CO 2 ] À :t he loss of both CO 2 groupsm ostlyl eads to dissociation of the complex.W hen photon energy rises from 16 to 24 eV (cf. Figure 6), we observe an increaseo f [VÀHÀCO 2 ] À and [RÀHÀCO 2 ] À .I nt his energy range, we have previously demonstrated that the amount of transferred vibra-tional energy increases, [13,25] it is therefore in line with our hypothesis of [VÀHÀCO 2 ] À and [RÀHÀCO 2 ] À being due to internal conversion and intramolecular vibrationale nergy redistribution after electron detachment.…”

“…Figure ), we observe an increase of [V−H−CO 2 ] − and [R−H−CO 2 ] − . In this energy range, we have previously demonstrated that the amount of transferred vibrational energy increases, it is therefore in line with our hypothesis of [V−H−CO 2 ] − and [R−H−CO 2 ] − being due to internal conversion and intramolecular vibrational energy redistribution after electron detachment.…”

Irradiation of isolated collagen mimetic peptides by x rays and carbon ions at the Bragg-peak energy

“…However, a noticeable difference is the presence of peaks assigned to peptide monomers with charge states 2+, 3+, and 4+. They are due to intermolecular dissociation of the triple helix, which is mainly composed of two M 2+ and one M 3+ , as we reported earlier [34]. Therefore, the observation of M 4+ indicates nondissociative ionization of a M 3+ within the triple helix, followed by dissociation into monomers.…”

“…Figure 3 shows a comparison between mass spectra of the [(PHypG) 10 + 3H] 3+ after irradiation by an x-ray photon beam at 150 eV, and by a C 4+ ion beam at 0.98 MeV/u. The main observation is the striking similarity of the two spectra: For both, the main product cations are [(PHypG) 10 + 3H] 4+ with m/z = 673.5, due to nondissociative ionization (NDI), and backbone fragments, as we recently reported [34]. The latter are mainly singly charged b 3n and y 3n (1 n 4 being a positive integer) fragments coming from glycine-proline peptide bond cleavages, but also b 2 , y 2 , b 4 , y 5 and below m/z = 250, mainly internal fragments formed by at least two backbone cleavages.…”

Enabling liquid vapor analysis using synchrotron VUV single photon ionization mass spectrometry with a microfluidic interface

“…7 Furthermore, tunable VUV ionization has been shown to be a selective, yet universal technique in elucidating molecule-specific information since it can distinguish isomers via ionization energy (IE) and absorption cross-sections following rules that are quantifiable. This has allowed its applications in biology, 8,9 combustion chemistry, 10 and atmospheric chemistry. 3 However, liquids have not been often used thus far in single photon ionization mass spectrometry (SPI-MS) applications, because some of them are highly volatile and difficult to retain in vacuum; for a successful VUV SPI-MS measurement, the main chamber vacuum 2 is preferably maintained at 10 -7 Torr.…”