21184-74-7Relevant academic research and scientific papers
Tunable NIR-II emitting silver chalcogenide quantum dots using thio/selenourea precursors: Preparation of an MRI/NIR-II multimodal imaging agent
Basel, Siddhant,Bhardwaj, Karishma,Borthakur, Sukanya,Brito, Beatriz,Clarke, Mitchell,Pariyar, Anand,Pradhan, Sajan,Roy, Pankaj,Saikia, Lakshi,Shankar, Amit,Stasiuk, Graeme J.,Tamang, Sudarsan,Thapa, Surakcha
supporting information, p. 15425 - 15432 (2020/11/18)
Aqueous-stable, Cd- and Pb-free colloidal quantum dots with fluorescence properties in the second near-infrared region (NIR-II, 1000-1400) are highly desirable for non-invasive deep-tissue optical imaging and biosensing. The low band-gap semiconductor, silver chalcogenide, offers a non-toxic and stable alternative to existing Pd, As, Hg and Cd-based NIR-II colloidal quantum dots (QDs). We report facile access to NIR-II emission windows with Ag2X (X = S, Se) QDs using easy-to-prepare thio/selenourea precursors and their analogues. The aqueous phase transfer of these QDs with a high conservation of fluorescence quantum yield (retention up to ～90%) and colloidal stability is demonstrated. A bimodal NIR-II/MRI contrast agent with a tunable fluorescence and high T1 relaxivity of 408 mM-1 s-1 per QD (size ～ 2.2 nm) and 990 mM-1 s-1 per QD (size ～ 4.2 nm) has been prepared by grafting 50 and 120 monoaqua Gd(iii) complexes respectively to two differently sized Ag2S QDs. The size of the nanocrystals is crucial for tuning the Gd payload and the relaxivity.
The reactions of O-(4-nitrophenyl) S-aryl dithiocarbonates with anilines: Effects on the relative nucleofugality
Santos, José G.,Gazitúa, Marcela
supporting information, (2019/01/03)
Kinetic and high-performance liquid chromatography studies were investigated for the reactions of S-phenyl, S-(4-chlorophenyl), and S-(4-nitrophenyl) O-(4-nitrophenyl) dithiocarbonates with anilines. These were performed in the presence of 0.1M borate buffer in 44?wt% aqueous ethanol. For reactions of the 3 substrates, the mechanism is stepwise with 2 tetrahedral intermediates, one zwitterionic (T±), and the other anionic (T?), where the intermediate T? is formed by proton transfer from T± to the borate buffer. The nonleaving group is not passive, playing an important role in the relative nucleofugality of the groups, which depend largely on its electron withdrawing capability. The nucleofugacity of 4-nitrophenolate ion and of 4-nitrophenylthiolate from the same tetrahedral intermediate is similar, despite the differences in their basicities (3 pKa units). In the reactions of S-(4-nitrophenyl) O-(4-nitrophenyl) dithiocarbonate, the change of nucleophile from pyridines (only 4-nitrophenolate ion is nucleofuge) to anilines (2 nucleofuges) shows that the nature of the amine impacts on the relative nucleofugality of groups.
