Laser Desorption/Ionization Time-of-flight Mass Spectrometric Analysis of Some Synthetic Flavonoids and Their Complexes with Zn and Fe

Abstract

Three antioxidants: flavonol (3-hydroxyflavone) (L1), 4’-(N,N-dimethylamino)flavonol (L2), 4’-[N,N-di(2-
hydroxyethylamino)]flavonol (L3) and their complexes with Zn and Fe prepared in aqeous-alcoholic solutions were
examined by means of UV-Vis spectroscopy and laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF
MS) using the standard stainless steel targets. It was possible to obtain the protonated molecules in the mass spectra of
all flavonoids under study, practically no fragmentation being achieved in the case of unsubstituted flavonol. The
identified positively charged ions in the mass spectra of L1-metal complexes correspond to the ligand:metal ratio 2:1, 3:2
for L1-Zn and 2:1, 3:2, 4:2 for L1-Fe. The presence of the electron donating substituent in 4’-position of flavonol
molecule enhanced fragmentation and affected the contribution and ligand:metal stoichiometry of the minor ions in the
LDI mass spectra. Namely, the compounds with ligand:metal ratio 2:1, 3:2 for L2-Zn, 2:1, 3:2, 4:2 for L2-Fe, 1:1, 2:1,
3:2 for L3-Zn, 2:1, 3:1, 4:2 for L3-Fe, respectively, were identified. The discrepancy in the composition of the complexes
derived from the spectroscopic data (ligand:metal ratio 1:1) and MS analysis may be attributed to differences in the
environment for the complexes in solution and in solid state, as well as to peculiarities of laser desorption/ionization
from the solid sample condensed on steel target.