Properties of phytochelatin-coated CdS nanocrystallites formed in a marine phytoplanktonic alga (Phaeodactylum tricornutum, Bohlin) in response to Cd

Phytochelatins (PC) are (-Glu–Cys)nGly peptides involved in the cellular detoxification mechanism of plants, algae and yeasts for their capability to form stable metal–PC complexes. Phaeodactylum tricornutum exposed to Cd forms Cd–PC complexes in which sulfide ions (S2-) can be incorporated to stabilize PC-coated CdS nanocrystallites. Native CdS particles exhibited differences in their particle size, sulfide content and optical spectroscopic properties. The max of the UV transition ranged from 290 to 260 nm. The radii were predicted to vary from 9 to 11 Å. The sulfide/Cd molar ratio ranged from 0.89 to 0.26. Low sulfide particles showed propensity to in vitro sulfide mediated accretion. Characterization of these complexes showed that CdS nanoparticles were mainly coated with -glutamyl peptides with n value from 3 to 5. The PC2 oligopeptide was not found as coating peptide. CdS particles were stable in the pH range from 8 to 6 and showed half-dissociation at pH 4.9. In vitro reaction with S2- easily converted native, sulfide-free Cd–PC complexes to PC-coated CdS nanocrystallites, but was less effective to restrict particles accretion.