Biotechnological application of homo- and heterotrinuclear iron(III) furoates for cultivation of iron-enriched Spirulina

New trinuclear iron(III) furoates with the general formula [Fe3O(α-fur)6(R–OH)3]X, where α-fur C4H3OCOO, R = CH3 (1), C2H5 (2), n-C3H7 (3), n-C4H9 (4), X = NO3− (1–4); [Fe3O(α-Fur)6(DMF)(CH3OH)2]NO3 (5); [Fe3O(α-Fur)6(H2O)(CH3OH)2]Cl (6); [Fe2MO(α-Fur)6(L)(H2O)2], where L = THF (7–9), DMF (10–12), M = Mn2+ (7, 10), Co2+ (8, 11), Ni2+ (9, 12) and [Fe2MO(α-Fur)6(3Cl-Py)3], where M = Mn2+ (13), Co2+ (14), Ni2+ (15); have been prepared and investigated by Mössbauer and IR spectroscopy. The X-ray crystal structure for the 1·2CH3OH complex indicates that it crystallizes in the monoclinic crystal system (P21/n) and has a structure typical of μ3-O-bridged trinuclear iron(III) compounds. Coordination compounds 1, 4, 7, 8 can be used as regulators of the biochemical composition of cyanobacterium Spirulina platensis biomass. The supplementation of these compounds, in concentrations exceeding 5–10 mg/l, increases the content of iron, amino acids, peptides and carbohydrates in Spirulina.