Combinatorial Approaches to Peptide-Encapsulated CdS Nanoclusters

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Abstract
As many properties of group II-VI semiconductor nanocrystallites arise from their quantum confined nature, the synthesis of these clusters is of great interest. The challenge of synthesizing functional nanoclusters is, however, complicated by the limited stability of metalchalcogen surfaces under highly oxidizing conditions and Ostwald ripening. Our objectives are to develop methods for the synthesis of biogenic CdS semiconductor nanocrystallites that address the following issues: (1) What properties of the ligand peptide are important in stabilizing and producing CdS particles of any desired size? (2) Will hybrid peptides using nonnatural amino acids stabilize the nanoclusters while incorporating new surface functionality? (3) Is it possible to use novel peptides to modify the particle surface, thereby, controlling the photophysical properties of the CdS cluster? Our approach consists of parallel combinatorial techniques and computational methods for the discovery and optimization of peptide and peptidomimetic ligands to stabilize size-defined clusters of CdS. The effects of cysteine separation on CdS particle size by varying the number of bonds with rotational freedom within the spacer amino acids is examined. Furthermore, the properties of the resulting CdS nanoclusters are reported.