Synthetic iron complexes as models for natural iron-humic compounds: Synthesis, characterization and algal growth experiments.
A series of monomeric and dimeric FeIIIcomplexes with O,O-; O,N-; O,S-coordination motifs has been prepared and characterized by standard analytical methods in order to elucidate their potential to act as model compounds for aquatic humic acids. Due to the postulated reduction of iron in humic acids and following uptake by microorganisms, the redox behavior of the models was investigated with cyclic voltammetry. Most of the investigated compounds showed iron reduction potentials accessible to biological reducing agents. Additionally, observed reduction processes were predominantly irreversible, suggesting that subsequent reactions can take place after reduction of the iron center. Also the stability of the synthesized complexes in pure water and artificial seawater was monitored from 24h up to 21days by means of UV-Vis spectrometry. Several complexes remained stable even after 21days, showing only partially precipitation but some of them showed changes in UV-Vis spectra already after 24h which were connected to protonation/deprotonation processes as well as redox processes and degradation of the complexes. The ability to act as an iron source for primary producers was tested in algal growth experiments with two marine algae species Chlorella salina and Prymnesium parvum. Some of the compounds showed effects on the algal cultures, which are comparable with natural humic acids and better as for the samples kept under ideal conditions. Those findings help to understand which functional groups of humic acids could be responsible for the reversible iron binding and transport in aquatic humic substances.
Institute of Inorganic Chemistry, Faculty of Chemistry, University of Vienna, Waehringer Str. 42, A-1090 Vienna, Austria.
Ewelina
E
Orlowska
Institute of Inorganic Chemistry, Faculty of Chemistry, University of Vienna, Waehringer Str. 42, A-1090 Vienna, Austria.
Alexander
A
Roller
Department of Nutritional and Physiological Chemistry, Faculty of Chemistry, University of Vienna, Althanstr. 14/UZA II, A-1090 Vienna, Austria.
Marc
M
Pignitter
Institute of Inorganic Chemistry, Faculty of Chemistry, University of Vienna, Waehringer Str. 42, A-1090 Vienna, Austria; Department of Zoology, University of Johannesburg, Auckland Park 2006, South Africa.
Franz
F
Jirsa
Institute of Inorganic Chemistry, Faculty of Chemistry, University of Vienna, Waehringer Str. 42, A-1090 Vienna, Austria.
Regina
R
Krachler
Institute of Inorganic Chemistry, Faculty of Chemistry, University of Vienna, Waehringer Str. 42, A-1090 Vienna, Austria. Electronic address: wolfgang.kandioller@univie.ac.at.
Wolfgang
W
Kandioller
Institute of Inorganic Chemistry, Faculty of Chemistry, University of Vienna, Waehringer Str. 42, A-1090 Vienna, Austria.
Bernhard K
BK
Keppler
D002708:Chlorella / Q000254:growth & development*; D058087:Haptophyta / Q000254:growth & development*; D006812:Humic Substances / Q000032:analysis*; D007501:Iron; D058085:Iron Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction
D006812:Humic Substances; D058085:Iron Compounds; D007501:Iron
Algal growth experiments; Coordination compounds; Humic acids models; Iron complexes; Iron uptake