The influence of adenine content on the properties of Q-CdS clusters stabilized by polynucleotides

Abstract In this work the nature of the interaction between quantum-confined cadmium sulfide (Q-CdS) clusters and either single or double-stranded polynucleotide stabilizers of varying nucleic acid base composition is investigated. We specifically focus here on the influence of adenine content on cluster size, photoluminescence behavior, and the relative ability of these small particles to increase in average diameter upon conditions of mild heating. Thermolysis of Q-CdS/polynucleotide samples affects the interfacial interaction between cluster and stabilizer giving rise to a shift in the emission maximum, a change in luminescence quantum yield, and in some cases an increase in average size. For a fixed set of reactant concentrations, Q-CdS stabilized by polyadenylic acid (Poly[A]) and other adenine-rich polynucleotides are unique in stabilizing the formation of smaller clusters with an average diameter near 38 A under ambient conditions, but Poly[A]-stabilized Q-CdS clusters readily fuse to larger (about 60 A) clusters upon mild heating. In contrast, Q-CdS stabilized by other types of single-stranded hompolymers (Poly[U], [G], and [C]) as well as double-stranded calf thymus and Escherichia coli deoxyribonucleic acids form somewhat larger clusters during intitial synthesis and typically exhibit greater protection against radical changes in size upon thermolysis.