EHPG

Eig. 2. Stmctural representations of chelates where (8) corresponds to M(acac)2 (9) to ML2, L = S-sulfo-S-hydroxyquiaoline (10) to M-Trien (11) to a tetracoordinate metal bound to the hexadentate ligand EDTA and (12) to the Ee(III) chelate of EHPG. Stmcture (13), which emphasizes the spatial... 

Eor the many details of constmcting or interpreting stmctures and systematic names, the Hterature on nomenclature and indexing (6) can be consulted. Systematic nomenclature is illustrated by the Chemicaly hstracts name of the sodium iron(III) EHPG chelate sodium [[N,N -l,2-ethanediylbis[2-(2-hydroxyphenyl)glyciQatol]](4-)-N,N, 0,0, 0, 0 ]ferrate(l-) [16455-61-1], The ferrate anion (12) [20250-28-6] and the potassium salt [22569-56-8] are also Hsted ia Chemical Abstracts (7). 

Eor example, beryUium occurs at the bottom of a displacement series with NTA allowing this metal to be recovered as the hydroxide by pH adjustment of an ore processing solution all of the interfering metals remain sequestered by chelation (14). Additionally, because other metals present caimot displace iron in an iron—EHPG chelate, the chelate can be used in highly calcareous soils to supply iron as a trace nutrient in agriculture (15). 

The more stable the chelate, the higher the pM that it can maintain, and the higher the pH required to precipitate the metal hydroxide. From equation 22 it can be seen that the smaller the solubihty product ie, the more iusoluble the metal hydroxide, the higher the pM that a chelant must maintain to prevent precipitation. The stabiUty constant of the Fe(III)—EHPG complex (/2), is so large (10 ) that iron is not precipitated even ia strongly alkaline solutions. 

The racemic Fe(III) complex containing a hexadentate ligand, Fe(5-Br-ehpg) , can exist in racemic RR and SS) and meso (RS) forms (Structures 7a and 7b) which have different solubilities in methanol. 

In addition to different affinities for HSA in vitro, the two stereoisomers of Fe-EHPG have different distributions in vivo [133]. The meso-Fe-EHPG complex is cleared from the blood more slowly than rac-Fe-EHPG. The rate of liver uptake was also different for the two diastereomers. 

Croft et al. [15] reported significant increases in kt when iron was chelated by DTPA, ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and several aminophosphonic acids. Compared to aqueous Fe2+, increases in /cj from 1000-fold to 50,000-fold were indicated. They also note that DTPA inhibits reaction (3). Graf et al. [10] suggest that reaction (3) is completely inhibited by DTPA, EHPG, phytate, and desferal. These two studies are not entirely consistent in their findings, possibly due to the... 

Fig. 14. Derivatives oflV,N -ethylenebis-[2-(o-hydroxyphenyl)glycine] (EHPG)...

---