24421-05-4Relevant articles and documents
Precursor reaction kinetics control compositional grading and size of CdSe1-: XSx nanocrystal heterostructures
Hamachi, Leslie S.,Yang, Haoran,Jen-La Plante, Ilan,Saenz, Natalie,Qian, Kevin,Campos, Michael P.,Cleveland, Gregory T.,Rreza, Iva,Oza, Aisha,Walravens, Willem,Chan, Emory M.,Hens, Zeger,Crowther, Andrew C.,Owen, Jonathan S.
, p. 6539 - 6552 (2019/07/10)
We report a method to control the composition and microstructure of CdSe1-xSx nanocrystals by the simultaneous injection of sulfide and selenide precursors into a solution of cadmium oleate and oleic acid at 240 °C. Pairs of substituted thio- and selenoureas were selected from a library of compounds with conversion reaction reactivity exponents (kE) spanning 1.3 × 10-5 s-1 to 2.0 × 10-1 s-1. Depending on the relative reactivity (kSe/kS), core/shell and alloyed architectures were obtained. Growth of a thick outer CdS shell using a syringe pump method provides gram quantities of brightly photoluminescent quantum dots (PLQY = 67 to 90%) in a single reaction vessel. Kinetics simulations predict that relative precursor reactivity ratios of less than 10 result in alloyed compositions, while larger reactivity differences lead to abrupt interfaces. CdSe1-xSx alloys (kSe/kS = 2.4) display two longitudinal optical phonon modes with composition dependent frequencies characteristic of the alloy microstructure. When one precursor is more reactive than the other, its conversion reactivity and mole fraction control the number of nuclei, the final nanocrystal size at full conversion, and the elemental composition. The utility of controlled reactivity for adjusting alloy microstructure is discussed.
Cyclic Urea and Thiourea Derivatives as Inducers of Murine Erythroleukemia Differentiation
Li, Chau-der,Mella, Sharon L.,Sartorelli, Alan C.
, p. 1089 - 1092 (2007/10/02)
A series of derivatives of tetramethylurea, a known inducer of the differentiation of Friend erythroleukemia cells, has been synthesized and tested for its capacity to induce erythroid maturation, as measured by the synthesis of hemoglobin.Cyclic urea and thiourea derivatives consisting of five-, six-, and seven-membered ring systems containing N-alkyl substituents were prepared.Most of these agents were relatively effective inducers of differentiation, with N-alkyl substitution appearing to be essential for maximum response.The most potent agents developed wereN,N'-dimethyl cyclic ureas.Exposure to concentrations of 2 to 4 mM of these derivatives resulted in more than 90percent of the cell population achieving a differentiated state.Under these conditions, the parent compound, tetramethylurea, was slightly less efficacious, causing differentiation of only 68percent of the population at its maximum effective level of 4 mM.