Ferroverdin
Ferroverdin refers to three different coordination compounds that were first isolated in 1955 by Chain, Tonolo, and Carilli. It consists of three p-vinylphenyl-3-nitroso-4-hydroxybenzoate ligands complexed with a ferrous ion. Ferroverdin is a green pigment produced in the mycelium of species of Streptomyces. It is claimed to be the “first stable ferrous compound to be found in nature.” There are three types of ferroverdin: A, B, and C. In ferroverdin A, both R groups are hydrogens. In ferroverdin B, R1 is a hydroxyl group (OH) and R2 is a hydrogen (according to a diagram in the paper, the R-groups are on the vinyl group, on the carbon opposite the phenyl; they are respectively trans and cis relative to the phenyl group). In ferroverdin C, R1 is a hydrogen while R2 is a carboxyl group (COOH). Ferroverdin is immune to chelating and oxidizing agents due to the strong interaction between the ligands and ferrous ion. However, it can be broken down by reductive processes.1 The presence of ferroverdin peaks when there are four to eight μg/mL of Fe in the media usually in the form of a salt.