Flavin-related compounds: 3-Ethyl-lumiflavin. Combined DFT, NMR, X-ray and EI mass spectral study

3-Ethyl-lumiflavin was characterized by a variety of methods. Laser flash photolysis measurements in methanol solutions yielded a triplet state living 9.5 μs and a radical species living 91 μs, with steady-state photolysis quantum yields below 10-5. Fluorescence lifetime of 4.5 ns and quantum yield of 0.16 was recorded in aqueous solutions. Crystal structure determined by X-ray diffraction was quite similar to the geometry of an isolated molecule calculated using the DFT approach, with the observed differences attributable to a nonlinear hydrogen bond existing in the crystal solid. EI mass spectra revealed a fragmentation path specific to this compound and inexistent in lumiflavin or other similar compounds, due to ejection of a C 2H5-N=C=O molecule, containing the ethyl substituent of the parent molecule.