Ruthenium Catalyzed 2e -/2H + PCET - Characterizing the Catalyst-Substrate Interaction with High-Resolution Mass Spectrometry and Gas-Phase Vibrational Spectroscopy

CATTANEO, MAURICIO; PEREZ, EVAN H; JOHNSON, MARK; MENGES, FABIAN S; JAMES M. MAYER

Atlanta

Congreso; 67th ASMS Conference on Mass Spectrometry and Allied Topics; 2019

American Society for Mass Spectrometry

IntroductionProton-coupled electron transfer (PCET) is a ubiquitous mechanism for charge translocation and redox chemistry in biology. A particularly interesting aspect of this concerns the case where two protons and two electrons are involved in the oxidation of the ruthenium metal center from Ru II to Ru IV in a coordination compound that features an outer-shell NH group. Important questions regarding the mechanism of this process include whether the two protons are transferred in a concerted vs stepwise manner, and whether the key intermediates can be trapped in the act of this transformation. We address this using a new instrument that combines high resolution mass spectrometry based on the Orbitrap platform with cryogenic gas phase IR spectroscopy.MethodsThe high-resolution capability of the Orbitrap mass spectrometer allows for a distinction between different oxidation states of the catalyst-substrate complex. These catalyst-substrate complex ions can be formed in the commercial ESI spray of the Orbitrap Velos instrument as well as in the home-built ESI source of our time-of-flight based Cryogenic Ion Vibrational Spectrometer (CIVS). A reverse injection scheme of ions into the C-trap of the Orbitrap allows for a precise characterization of the ions formed in the CIVS. These are then sent alternatively into the cryogen-cooled 3D quadrupole ion trap and tagged with N 2. After cooling, the tagged ions are transferred to a Wiley-McLaren TOF and the focused ion packet is intercepted by a tunable OPO/OPA IR source.Preliminary DataHigh-resolution mass spectrometry shows the interconversion between the two oxidations states Ru II or Ru IV during the experiment. This results in a change of the acquired IR data dependent on the abundancy of the two species in an overlapping isotopic pattern. This problem can be overcome by selecting a specific range in the doubly charged, broad isotopic distribution of the Ru-catalyst-substrate ion which allows for oxidation state resolved IR spectra. These spectra show significant shifts of NH stretching frequencies upon binding to the RuII catalyst vs. binding to the RuIV species. The motifs of these interactions are currently under investigation using DFT calculations.Novel AspectHigh resolution Mass Spectrometry paired with cryogenic ion vibrational spectroscopy is a new tool for sequencing and chemical analysis