Ligand size distribution of phenanthroline-functionalized polyethylene glycol-iron(II) complexes determined by electrospray ionization mass spectrometry and computer simulation.

The complex formation in solution, and the gas-phase dissociation of a phenanthrolineterminated poly(ethylene glycol) with Fe(2+) ions were investigated. The size distribution of poly(ethylene glycol)-α-monomethyl-ω-5-[1,10]phenanthroline (mPEG_phen) was determined by electrospray ionization mass spectrometry (ESI-MS). Based on the measured ligand size distribution of mPEG_phen by ESI-MS, the 1:3 complex formation (Fe(2+)/mPEG_Phen) was computer-simulated as a pure random assembly process. The simulated distribution fits excellently to that of the complex Fe(mPEG_phen) 3 (2+) determined from the ESI-MS intensities. In addition, the collision-induced dissociation (CID) of the Fe(mPEG_phen) 3 (2+) complex was also studied by tandem mass spectrometry (ESI-MS/MS) and by computer simulation, as well. The ESI-MS/MS intensity distribution of the Fe(mPEG_phen) 2 (2+) formed from Fe(mPEG_phen) 3 (2+) by the loss of an mPEG_phen ligand under CID conditions fits quite well to the calculated one.