Fragmentation of Bacteriochorophyll-a in a Mass Spectrometer: An Experimental and Theoretical Study

摘要

Motivation: In photosynthetic green sulfur bacteria, the process of light harvesting is mediated by a chlorosome which collects and transfers light energy to the FMO (Fenna-Matthews-Olsen) complex which in turn transfers the energy to the reaction center, in which the energy is used to drive chemical reactions [3,4]. Integral to the light harvesting apparatus are the bacteriochlorophylls. Bacteriochlorophyll-a plays a unique role is transferring light energy from the chlorosome to the FMO complex and the funneling of that energy in that complex to the reaction center. This compound consists of a bacteriochlorin ring related to a prophyrin ring featuring an aromatic 18 pi-electron system with side chains including phytyl alcohol esterified to the propionic acid side chain. Furthermore, the FMO complex hosts 8 bacteriochlorophylls, one which is more loosely bound and loses its phytyl group tail upon isolation [4a]. Goal: In a mass spectrometer, the major fragment is the loss of the phytyl side chain as [phytyl - H]. The focus of this study is to understand that fragmentation and its mechanism.