Cyanobacterial copper-binding ligands isolated from artificial seawater cultures

This paper demonstrates a method to isolate and characterise strong biogenic copper-binding ligands from an artificial seawater matrix. Pseudo-polarography is used to detect the ligands, determine their ionic strength-corrected binding constants, and track them through each step of the extraction process. Two ligand types are found, one strong and one relatively weak, with log K′ values of 49.4 ± 1.1 and 19.8 ± 5.5 respectively, assuming that the metal is bound as copper(II). If a copper(I) complex, the log K′ of the strong copper-binding ligand would be 25. Pseudo-polarography is then used to assess different resins for ligand extraction and to determine the eluent fraction in which the strong ligand is recovered. XAD-16 is found to be a suitable resin for extracting the strong binding ligand from salt water into methanol, suggesting that the ligand is weakly hydrophobic. As ligands are identified by their complexation of copper, no assumptions are made regarding the functional groups of these natural ligands. The copper-binding ligands are successfully extracted into solvents suitable for mass spectrometric analysis using soft ionisation methods such as electrospray and MALDI.