PTERIN CHEMISTRY .94. ELECTROSPRAY-IONIZATION MASS-SPECTROMETRY - DETECTION OF A RADICAL CATION PRESENT IN SOLUTION - NEW RESULTS ON THE CHEMISTRY OF (TETRAHYDROPTERIDINONE)-METAL COMPLEXES

This paper marks the first reported detection of radical cations by Electrospray-Ionization Mass Spectrometry (ESI-MS). Electron Spin Resonance (ESR) measurements have proven that the detected radical cation existed already in solution and has not been generated by the electrospray ionization technique. However, we observed that the radical cation can be generated by changes in the ionization conditions. A molar mixture of 2-amino-5,6,7,8-tetrahydro-5-methylpterin-4(4H)-one dihydrochloride ( = 5,6,7,8-tetrahydro-N(5)-methylpterin . 2 HCl, N(5)-MTHP . 2 HCl), and tris(pentane-2,4-dionato)iron(III) in MeCN at pH 2-3 leads to the formation of a [bis(pentane-2,4-dionato)(2-amino-5,6,7,8-tetrahydro-5-methylpteridin-4(4H)-one)]iron complex ( = [bis(pentane-2,4-dionato)(5,6,7,8-tetrahydro-N(5)-methylpteridin)]iron complex) which can be detected by ESI-MS. The results suggest that this complex might be an Fell radical cation, which could possibly be a suitable model complex for the active center of the phenylalanine hydroxylase. In the same solution, the stable radical cation of N(5)-MTHP is identified by ESI-MS and ESR.