engleski

Voltametrija kobaltovih(II) kompleksa s prirodno prisutnim organskim ligandima u morskoj vodi

Cobalt (II) as an essential element and important for biochemical processes in the marine environment, is bioavailable in its dissolved form. At present it is known that cobalt in seawater is partially, but strongly complexed to natural organic ligands (binding place for cobalt is very possible a nitrogen- containing functional group). Dissolved cobalt(II) is biologically important element for marine organisms (for their biochemical and physiological functioning). Despite its abudance in oceans, dissolved Co2+ is present in low concentrations, <10-9 mol L-1, mostly as soluble organic complex. [1, 2] Electrochemical characterization of cobalt (II) complexes in model aqueous solution (0.55 mol dm-3 NaCl) was performed using square wave and cyclic voltammetry on mercury drop electrode. Results on complexation and electrochemical reaction mechanisms of cobalt (II) complexes with 4- nitrocatechol, humic acid, glutathione and 1, 10-phenanthroline, as ligands appearing in the marine system, will be presented. All used ligands are biologically important molecules. Catecholates, ortho-dihydroxybenzene and 4- nitro-dihydroxybenzene are present as a structural part of complex marine ligands (humic acid, siderophores, etc.). Humic substances as heterogeneous biomolecules are a characteristic component of the dissolved organic carbon (DOC) pool important for phytoplankton communities in seawater. [3] Glutathione is present in eukaryotes and some prokaryotes (cyanobacteria and purple bacteria) and makes up > 90 % of non-protein thiols in plants and algae [4], while 1, 10- phenanthroline is an inhibitor of metallopeptidases. [5] All of these Co(II) complexes are electroactive and give a reduction response on a voltammograms (square wave and cyclic) from Ep = -0.9 to -1.1 V. Mechanisms and stability constants of complexes were determined. While reduction reactions with 4-nitrocatechol and humic acid were irreversible, reduction reactions with glutathione and 1, 10-phenanthroline showed reversible/quasireversible behavior. Using CLE/ACSV method were calculated stability constants for Co(II)4NC and Co(II)HA2 complexes, (log KCo(II) (4NC)2 = 21.86 (pH = 8.2), log KCo(II) (4NC) 2 = 21.11 (pH )= 6.5), log KCo(II) (HA)2 = 11.32 (pH = 8.2)). For other complexes calculations are in process.

cobalt ; complexation ; voltammetry ; 4-nitrocatechol ; humic acid ; glutathione ; 1, 10-phenanthroline

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