TRENPYPOLS: A new water-soluble iron chelator (both Fe-III and Fe-II) involving six-membered coordination rings

An eight-step synthesis of a new water-soluble tripodal ligand TRENPYPOLS ( tris[2- (2-hydroxy-3-(2-pyridinyl)-5-sulfo-benzamido)ethyl]amine) is descri bed. TRENPYPOLS is built by connecting the TREN spacer through a tris-amide moiety to the ortho phenolic position of three 2-(2-hydroxyphenyl) pyridin e chelating subunits, (followed by the sulfonation of the 5-positions). The three [O,N-pyr] bidentate subunits of TRENPYPOLS involve six-membered coor dination rings. The solution coordination chemistry of the ligand and its i ron complexes have been studied by means of pH potentiometric, spectrophoto metric and voltammetric methods. The stability constants, log beta(110) are 30.1 for the ferric complex and 17.7 for the ferrous complex (pFe(III) and pFe(II) values are 23.6 and 11.2 respectively at pH = 7.4, [L](tot) = 10(- 5) M, [Fe](tot) = 10(-6) M). Comparison with the data of o-trensox (8-hydro xyquinoline subunits with a 5-membered chelate ring) corroborates the usual rules concerning the influence of the chelate ring size on complexation ab ility. Fe-III-TRENPYPOLs has been tested as a single source of iron in nutr itional experiments with Arabidopsis thaliana plant cells. The efficiency t owards growth and resistance to iron chlorosis is good, comparable to that of Fem-EDTA, the most commonly used complex for in vitro cell cultures.