title: Iron incorporation in biosilica of the marine diatom Stephanopyxis turris: dispersed or clustered?
abstract: Iron incorporation into diatom biosilica was investigated for the species Stephanopyxis turris. It is known that several "foreign" elements (e.g., germanium, titanium, aluminum, zinc, iron) can be incorporated into the siliceous cell walls of diatoms in addition to silicon dioxide (SiO2). In order to examine the amount and form of iron incorporation, the iron content in the growth medium was varied during cultivation. Fe:Si ratios of isolated cell walls were measured by ICP-OES. SEM studies were performed to examine of a possible influence of excess iron during diatom growth upon cell wall formation. The chemical state of biosilica-attached iron was characterized by a combination of infrared,29Si MAS NMR, and EPR spectroscopy. For comparison, synthetic silicagels of variable iron content were studied. Our investigations show that iron incorporation in biosilica is limited. More than 95% of biosilica-attached iron is found in the form of iron clusters/nanoparticles. In contrast, iron is preferentially dispersedly incorporated within the silica framework in synthetic silicagels leading to Si-O-Fe bond formation.
authors.affiliation: School of Mathematics and Science, TU Dresden, 01062, Dresden, Germany.
authors.forename: Janine
authors.initials: J
authors.lastname: Kaden
authors.affiliation: School of Mathematics and Science, TU Dresden, 01062, Dresden, Germany.
authors.forename: Stephan I
authors.initials: SI
authors.lastname: Brückner
authors.affiliation: School of Mathematics and Science, TU Dresden, 01062, Dresden, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Machill
authors.affiliation: Leibniz Institute of Photonic Technologies (IPHT) Jena, 07745, Jena, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Krafft
authors.affiliation: Faculty of Physics and Earth Sciences, University Leipzig, 04103, Leipzig, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Pöppl
authors.affiliation: School of Mathematics and Science, TU Dresden, 01062, Dresden, Germany. eike.brunner@chemie.tu-dresden.de.
authors.forename: Eike
authors.identifier: 0000-0003-3511-9899
authors.initials: E
authors.lastname: Brunner
mesh_terms: D002473:Cell Wall / Q000737:chemistry*; D003470:Culture Media; D017377:Diatoms / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D053758:Nanoparticles / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry*; D014025:Titanium / Q000737:chemistry
chemical_list: D003470:Culture Media; D012822:Silicon Dioxide; D014025:Titanium; D007501:Iron
keywords: 29Si MAS NMR; Biosilica; EPR; Infrared spectroscopy; Iron incorporation