Copper-binding ligands in the NE Pacific

Whitby, H ORCID: 0000-0002-0064-3052, Posacka, AM, Maldonado, MT and van den Berg, CMG (2018) Copper-binding ligands in the NE Pacific Marine Chemistry, 204. pp. 36-48. ISSN 0304-4203, 1872-7581

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Abstract

Copper distribution and speciation were determined at stations P4 and P26 along Line P as part of a GEOTRACES Process Study in the Northeast Pacific, at depths between 10 and 1400 m. Two ligand classes (L<inf>1</inf> and L<inf>2</inf>) were detected at both stations: the stronger L<inf>1</inf> ligand pool with log K’<inf>Cu2+L1</inf> 15.0–16.5 and the weaker L<inf>2</inf> ligand pool with log K’<inf>Cu2+L2</inf> 11.6–13.6. The L<inf>1</inf> class bound on average 94% of dCu, with the ratio between L<inf>1</inf> and dCu constant and close to unity (1.15 = [L<inf>1</inf>]:[dCu]). The concentrations of total ligands exceeded those of dCu at all depths, buffering Cu²⁺ concentrations ([Cu²⁺]) to femtomolar levels (i.e. pCu 14.1–15.7). Measurements using cathodic stripping voltammetry also identified natural copper-responsive peaks, which were attributed to thiourea- and glutathione-like thiols (TU and GSH, respectively), and Cu-binding humic substances (HS<inf>Cu</inf>). Concentrations of TU, GSH and HS<inf>Cu</inf> were determined by standard addition of model compounds in an attempt to identify Cu-binding ligands. HS<inf>Cu</inf> concentrations were generally higher at P26 than at P4, consistent with a marine origin of the humic material. Overall, HS<inf>Cu</inf> contributed to 1–27% of the total L concentration (L<inf>T</inf>) and when combined with the two thiols contributed to up to 32% of L<inf>T</inf>. This suggests other ligand types are responsible for the majority of dCu complexation in these waters, such as other thiols. Some potential candidates for detected, but unidentified, thiols are cysteine, 3-mercaptopropionic acid and 2-mercaptoethanol, all of which bind Cu. Significant correlation between the concentrations of TU-like thiols and L<inf>1</inf>, along with the high log K’<inf>Cu2+L1</inf> values, tentatively suggest that the electrochemical TU-type peak could be part of a larger, unidentified, high-affinity Cu compound, such as a methanobactin or porphyrin, with a stronger binding capability than typical thiols. This could imply that chalkophores may play a greater role in oceanic dCu complexation than previously considered.

Item Type:	Article
Uncontrolled Keywords:	Copper speciation, Seawater, Thiols, Humic substances, Cathodic stripping voltammetry, Thiourea, Glutathione, Organic ligands
Depositing User:	Symplectic Admin
Date Deposited:	13 Mar 2019 14:42
Last Modified:	01 Mar 2026 04:20
DOI:	10.1016/j.marchem.2018.05.008
Open Access URL:	https://doi.org/10.1016/j.marchem.2018.05.008
Related Websites:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3034188
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