Die E.‐coli‐Siderophore Enterobactin und Salmochelin bilden sechsfach koordinierte Siliciumkomplexe bei physiologischen pH‐Werten

Abstract

Die hohe Affinität der bakteriellen Eisensiderophore Enterobactin und Salmochelin für Fe3+, das sie über ihre Catecholgruppen als Chelatoren binden, ist wohlbekannt. Nun wurde entdeckt, dass beide Siderophore auch Silicium mit hoher Affinität binden. Dabei entstehen die ersten bekannten Siliciumkomplexe von Naturstoffen, die unter physiologischen Bedingungen stabil sind. Untersuchungen der isolierten Siliciumkomplexe deuten zudem an, dass darin SiIV in sechsfach koordiniertem Zustand vorliegt (siehe Bild).

Synthesis and Structural Characterization of Hexacoordinate Silicon, Germanium, and Titanium Complexes of the E. coli Siderophore Enterobactin

“…To assess whether or not M–binding is reversible, the above mentioned M–Ent complexes (M=Si, Ge, Ti, V, Fe, Ga) were each treated with Si(OMe) 4 , Ge(OMe) 4 , Ti(O i Pr) 4 , and Fe(acac) 3 solutions and incubated for 24 h at room temperature (see the Supporting Information). Similarly to our previous observations for Si IV –Ent and Si IV –Sal,5 all six complexes were stable in aqueous solution and no exchange of the bound metal could be detected, suggesting that the M–Ent binding is irreversible under normal conditions. However, the Fe III – and Ga III –Ent complexes could be converted into the corresponding Ge IV – and Ti IV –Ent complexes upon treatment with Ge(OMe) 4 and Ti(O i Pr) 4 in MeOH.…”

“…As we showed previously, Ent reacts with SiA C H T U N G T R E N N U N G (OMe) 4 even without addition of base to afford the protonated form H 2 A C H T U N G T R E N N U N G [2 a]. [5] To compare the rate of formation of 2 a-c, three NMR experiments were performed (see the Supporting Information). 4 , respectively.…”

“…To study the reactions of enterobactin with Si, Ge, and Ti, time‐dependent NMR studies were performed. As we showed previously, Ent reacts with Si(OMe) 4 even without addition of base to afford the protonated form H 2 [ 2 a ] 5. To compare the rate of formation of 2 a – c , three NMR experiments were performed (see the Supporting Information).…”

“…Although the main biological function of enterobactin is to effectively transport Fe III , it was found to bind many other metal ions with varying affinities 4. Recently, we found that Ent binds silicon to form the hexacoordinate complex Si IV –Ent ( 2 a ) at physiological pH,5 representing the first example of a natural product bound to silicon under physiological conditions, which makes it an interesting model for comparison with other hexacoordinate silicon complexes 6. Along with the interest in higher coordinate silicon compounds, many studies have focused on the synthesis and characterization of hexacoordinate catecholate germanium and titanium complexes 7–9.…”