The surfaces of two algae species (Cyclotella
cryptica,
diatom; Chlamydomonas reinhardtii, green alga) were
characterized with regard to their interactions with copper.
Chemical and spectroscopic methods (FT-IR, continuous-wave EPR, and two-pulse ESEEM) gave information about
the kinds of functional groups (-NH2, R-COOH, R-OH, and
Si-OH) on the surfaces of the algae. Maximum proton
binding
capacities of 9.7 × 10-4 and 9.1 ×
10-4 mol/g algae (dry
weight) were determined for C. cryptica and C.
reinhardtii,
respectively. The maximum Cu(II) binding capacity was
7.6
× 10-7 mol/g for the diatom and 6.2 ×
10-6 mol/g for the
green alga with [Cu2+] =
10-13−10-11 in
solution (at pH
6.9). Less than 1% of the total proton binding sites are
occupied
by copper under these conditions. The high
conditional
stability constants (log K = 11.9 for C.
cryptica and log K =
11.3 for C. reinhardtii, at pH 6.9) demonstrate the
strong
binding of copper to the algae surfaces. These results
are
confirmed by the CW-EPR and two-pulse ESEEM spectroscopy, which indicate binding to N-ligands, with
histidine
being one of the possible ligands for copper. The
binding
sites on algae surfaces represent a buffer capacity for
Cu2+ in natural waters.
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