X-ray photoabsorption-induced processes within protonated rifamycin sodium salts in the gas phase

Up to now, the response of antibiotics upon ionizing radiation has been very scarcely reported. Here, we present the results of X-ray photoabsorption experiments on isolated rifamycin, a broad-range antibiotic against Gram-positive and Gram-negative bacteria. A mass spectrometer has been coupled to a synchrotron beamline to analyze cationic products of photoabsorption on protonated rifamycin dimer and monomer sodium salts. Absorption of a single photon in the 100–300eV energy range leads to ionization of the molecular system, followed by vibrational energy deposition and subsequent inter- and/or intramolecular fragmentation. Interestingly, we observe a proton transfer from sodiated rifamycin to rifamycin, a widely observed process in ionized molecular systems in the gas phase. Moreover, we show that another charge-transfer process occurs in both dimer and monomer: intramolecular sodium transfer, which has not been reported yet, to the best of our knowledge.