Photoinduced Processes within Noncovalent Complexes Involved in Molecular Recognition

Abstract

Investigating the intrinsic properties of molecular complexes is crucial for understanding the influence of noncovalent interactions on fundamental chemical reactions. Moreover, specific molecular recognition between a ligand and its receptor is a highly important biological process, but little is known about the effects of ionizing radiation on ligand–receptor complexes. The processes triggered by VUV photoabsorption on isolated noncovalent complexes between the glycopeptide antibiotic vancomycin and a mimic of its receptor have been probed by means of mass spectrometry and synchrotron radiation. In the case of protonated species, the glycosidic bond of vancomycin was cleaved with low activation energy, regardless of the molecular environment. In sharp contrast, for deprotonated species, electron photodetachment from carboxylate groups only triggered CO2 loss, whereas the glycosidic bond remained intact. Importantly, the noncovalent complex was also found to survive VUV photoabsorption only when the native structure is conserved in the gas phase.

Mass Spectral Signatures of Complex Post-Translational Modifications in Proteins: A Proof-of-Principle Based on X-ray Irradiated Vancomycin

“…S2). The same fragments as for VUV photons are observed, 11 but large fragments are less abundant, as in the case of isolated vancomycin (cf. Fig.…”

“…In the spectrum at 100 eV, we mainly observe the same species as we have previously observed after photoabsorption in the VUV range. 11 1). Note that the peak corresponding to the latter (at m/z 144) can also be attributed to , formed by cleavage of the…”

“…All relative yields have been obtained by calculating the area under each peak, normalizing by the precursor ion depletion, by the total yield of all cationic species formed by photoabsorption, and by detection efficiency. 11…”

Roadmap on dynamics of molecules and clusters in the gas phase

“…The coupling of this versatile ion source with spectroscopic techniques implies that the mass selected ions generated in the gas phase by an ESI source are collected in an ion trap and then excited with the radiation. The combination of ESI sources with tandem mass spectrometers and ion traps has been successfully used to measure partial ion yield NEXAFS spectra of systems with sizes up to a few thousands of amu and to address, for example, photo-induced processes in molecular recognition [36]. An improvement of the throughput of the sources is the challenge to be faced to perform electron spectroscopies on these systems.…”

“…3) have the great advantage of superior photon brilliance, a wide photon energy range (from infrared, through visible, vacuum ultra violet (VUV) up to X-rays) and, in the case of FELs, short intense pulses. More than a decade ago, the coupling of ESI tandem mass spectrometers at such light sources was introduced for a novel and unique way to investigate structure and dynamics of complex gas-phase biomolecules [29,36,[48][49][50][51]. In all the applied setups, the light interaction with a selected ion precursor takes place in ion traps to account for the low target density due to the space charge (see also Sect.…”