Molecular proton detector, reaction

V. The Reaction of the Proton with a Molecular Proton Detector. 43... 

V. THE REACTION OF THE PROTON WITH A MOLECULAR PROTON DETECTOR... 

The slower reaction, where the proton reacts with a ground-state molecular proton detector, widens the observation range. It can detect charge modulation of a protein, and the state of the water on an interface. The submicrosecond time resolution can discriminate proton exchange between donor-acceptor moieties located on the same structure from reaction with bulk proton. Similarly, it can resolve a complex proton-binding dynamics into initial and postprotonation events and it determines the contribution of each step to the overall measured equilibrium constants. 

MS condition — An API 4000 equipped with a Turbo Ionspray from Applied Biosystems was used as the mass detector and [M + NH4]+ was chosen as the precursor ion for multiple reaction monitoring (MRM) due to the lack of protonated molecular ions. A transition of m/z 434.4 — 273.2 was chosen for paricalcitol and m/z 450.5 —> 379.2 was selected for the structure analog internal standard. 

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