Synthesis of a tetranitrosyl iron complex with unique structure and properties as an inhibitor of phosphodiesterases.

A novel neutral tetranitrosyl iron complex {[Fe(H 2 O) 4 ] 2+ [FeR 2 (NO) 2 ] 2 2- }·4H 2 O (1) with R = 5-(3-pyridyl)-4 H -1,2,4-triazole-3-thiolyls (C 7 H 5 N 4 S), which is a supramolecular ensemble, has been synthesized and studied. As follows from X-ray diffraction analysis, this is an octahedral Fe 2+ complex (Lewis acid) with two monoanionic dinitrosyl groups [FeR 2 (NO) 2 ] - (Lewis base) and 4 water molecules as the ligands. As follows from Mössbauer spectra, the coordinating Fe 2+ ion is in a low-spin state S = 0, and the dinitrosyl Fe + ion is in a low-spin state S = 1/2. According to the data of EPR spectroscopy, mass-spectrometry and amperometry, complex 1 in solution forms dinitrosyl particles of [Fe(C 7 H 6 N 4 S-H) 2 (NO) 2 ] - composition, which are responsible for NO generation. In addition, complex 1 was shown to be a 5-6 times more efficient phosphodiesterase (PDE) inhibitor at 5 × 10 -5 M and 10 -4 M concentrations than its thioligand. Probable binding sites of the [FeR 2 (NO) 2 ] - ligand for the bovine PDE1B model have been determined by molecular docking and quantum-chemical calculations.