PROPERTIES OF GLUTATHIONE-CAPPED AND PHYTOCHELATIN-CAPPED CDS BIONANOCRYSTALLITES

The incorporation of inorganic sulfide into cadmium-glutathione (GSH) led to the formation of a variety of GSH-capped CdS (GSH-CdS) complexe s that differed in sulfide/Cd(II) ratios, optical spectroscopic proper ties and Cd(II)-binding capacity of GSH. The size-fractionation of GSH -CdS complexes indicated that the Cd(II)/GSH molar ratio increased fro m a minimum of 0.3 to a maximum of 25 as sulfide/Cd(II) molar ratio in creased from 0 to similar to 1.0 equivalent. The absorption shoulders in the 290-400 nm range, photoluminescence in the 400-550 nm range and the ability to reduce methylviologen indicated that these GSH-CdS com plexes behaved like semiconductor nanocrystallites (NCs). The predicte d radii of (GSH-CdS) NCs varied from 10.8 to 17.3 Angstrom. Unlike GSH , phytochelatins (PCs) formed CdS crystallizes that appeared uniform i n size as was indicated by their similar optical properties. Although the properties of PC-capped CdS (PC-CdS) complexes were controllable b y altering the amounts of sulfide titrated, sulfide-induced transition s in the electronic absorption spectrum (indicative of the crystallite size) were limited to the blue of 318 nm. Thus, the maximum predicted radius of PC-capped crystallites was 11.8 Angstrom. The titration of PCs into GSH-CdS led to the replacement of GSH with PCs, Interestingly , the displacement of GSH by PCs did not alter the size of CdS particl es as indicated by lack of changes in emission lambda(max) or in the c haracteristic absorption shoulder at 358 nm. However, emission yields were quantitatively decreased upon displacement of GSH with PCs. (C) 1 998 Elsevier Science Inc. All rights reserved.