| Abstract | Kobalt je esencijalan mikronutrijent u morskoj vodi. U morskom okolišu prisutan je u otopljenoj
frakciji u vrlo niskim koncentracijama, <10-9 mol dm-3. Vezan za organske ligande stvara stabilne komplekse u
otopljenoj frakciji morske vode koji su slabo istraženi. U karakterizaciji organskih kompleksa kobalta u
uvjetima morske vode korištena je adsorpcijska voltametrija katodnog otapanja. Metoda se temelji na adsorpciji
formiranih kompleksa kobalta s odabranim organskim ligandima prisutnim u moru (kateholi,humusna kiselina,
fosfolipidi) na površini elektrode živina kap, te njihovoj redukciji. Osim elektrokemijski, kompleksi su
istraživani i metodom spektrofotometrije. S obzirom da su neki od korištenih liganada (fosfolipidi) amfifilne
molekule, kompleksiranje kobalta praćeno je i na granici faza voda/zrak Langmuir-Blodgett metodom te
mikroskopijom atomskih sila. Kobalt s ispitanim ligandima stvara stabilne komplekse visokih uvjetnih konstanti
stabilnosti log KCo(II)-4NC2 = 21,86 (pH = 8,2) i log KCo(II)-4NC2 = 21,11 (pH = 6,5), te log KCo(II)HA2 = 11,32, log
KCo(II)Phen2PC = 23,02 i log KCo(II)Phen2PC2 = 29,31 (pH = 8,2) nastale na hidrofobnoj elektrodi živina kap u
modelnoj otopini morske vode (NaCl, pH = 8,2, Ic = 0,55 mol dm-3). Spektrofotometrijski su detektirani
kompleksi kobalta topljivi u vodenoj otopini te su izračunate ravnotežne konstante stabilnosti kompleksa log
KCo(II)-4NC = 5,76 ± 0,40 (pH = 6,5), log KCo(II)-4NC = 3,98 ± 0,17 (pH = 8,2) i log KCo(II)-HA= 3,80±0,29 (pH =
8,2). Langmuir-Blodgett metoda ukazuje na vezanje 1,10-fenantrolina i kobalta na monosloj PC-a. Određena
konstanta stabilnosti takvog sloja je iznimno niska i iznosi K1 = 2,4 x 10-2 m3 mol-1, dok dodatkom 1,10-
fenantrolina dolazi do nastajanja sloja velike stabilnosti i konstante K2 = 4,86 x 1010 m2 mol-1. Mikroskopijom
atomskih sila pokazano je kako smjesa fenantrolina i fosfolipida, kako standarda tako i realnih uzoraka,
pokazuje stvaranja vezikula, dok dodatak kobalta u smjesu dovodi do stvaranja “terasa” zbog pretpostavljenog
povezivanja molekula. Istraživanje provedeno u svrhu izrade ove doktorske disertacije, istaknulo je važnost
poznavanja specijacije kobalta i razumijevanja biogeokemijskih procesa u kojim sudjeluje u morskom okolišu. |
| Abstract (english) | Cobalt is an essential micronutrient in seawater. In the marine environment, it is present in the
dissolved fraction at very low concentrations, < 10-9 mol dm-3. Bound to organic ligands, it forms stable
complexes in the dissolved fraction of seawater, which have been poorly investigated. Adsorption cathodic
stripping voltammetry was used to characterise cobalt complexes with organic ligands under seawater
conditions. The method is based on the adsorption of formed complexes with selected organic ligands present
in the sea (catechols, humic acid, phospholipids) on the surface of the mercury drop electrode and their
reduction. In addition to the electrochemical studies, the complexes were also investigated by the
spectrophotometry method. Since some of the ligands used (phospholipids) are amphiphilic molecules, cobalt
complexation was also monitored at the water/air phase boundary using the Langmuir-Blodgett method and
Atomic force microscopy. Cobalt formed stable complexes with the ligands with high conditional stability
constants log KCo(II)-4NC2 = 21.86 (pH = 8.2) and log KCo(II)-4NC2 = 21.11 (pH = 6.5), and log KCo(II)HA2 = 11.32,
log KCo(II)Phen2PC = 23.02, and log KCo(II)Phen2PC2 = 29.31 (pH = 8.2) formed at a hydrophobic mercury drop
electrode in a model seawater solution (NaCl, pH = 8.2, Ic = 0.55 mol dm-3). Cobalt complexes soluble in
aqueous solution were detected spectrophotometrically as well, and the equilibrium stability constants of the
complex log KCo(II)-4NC = 5.76±0.40 (pH = 6.5), log KCo(II)-4NC = 3.98 ± 0.17 were calculated. (pH = 8.2) and log
KCo(II)- HA = 3.80±0.29 (pH = 8.2). The Langmuir-Blodgett method shows the binding of 1,10-phenanthroline
and cobalt to the PC monolayer. The determined layer stability constant is extremely low and amounts to K1 =
2.4 x 10-2 m3 mol-1 , while the addition of 1,10-phenanthroline leads to the formation of a layer of high stability
with constant K2 = 4.86 x 1010 m2 mol-1. Atomic force microscopy showed that the mixture of phenanthroline
and phospholipids of both standard and real samples, shows the formation of vesicles, while the addition of
cobalt to the mixture leads to the formation of "terraces" due to the connection of molecules. The studies carried
out in this dissertation have shown the importance of knowing the speciation of cobalt and understanding the
biogeochemical processes in which it is involved in the marine environment. |
