Shen Lei, Soong Ronald, Wang Mingfeng, Lee Anna, Wu Chi, Scholes Gregory D, Macdonald Peter M, Winnik Mitchell A
Department of Chemistry, University of Toronto, Toronto, Ontario, Canada.
J Phys Chem B. 2008 Feb 14;112(6):1626-33. doi: 10.1021/jp0768975. Epub 2008 Jan 18.
Pulsed field gradient nuclear magnetic resonance (PFG NMR) experiments have been used to examine ligand exchange between poly(2-(N,N-dimethylamino)ethyl methacrylate) (PDMA) (Mn = 12,000, Mw/Mn = 1.20, Nn = 78) and trioctylphosphine oxide (TOPO) bound to the surface of CdSe/TOPO quantum dots (QDs). We show that PFG 1H NMR can quantify the displacement of TOPO by PDMA through its ability to differentiate signals due to TOPO bound to the QDs versus those from TOPO molecules free in solution. For CdSe QDs with a band edge absorption maximum at 558 nm (diameter 2.7 nm by transmission electron microscopy), we determined that, at saturation, 8 polymer chains on average displace greater than 90% of the surface TOPO groups. At partial saturation, with an average of 6 polymer chains/QD, each TOPO displaced requires 28 DMA repeat units. Assuming that one Me2N- group binds to a surface Cd2+ for each TOPO displaced, we infer that only about 3% of the DMA units are directly bound to the surface. The remaining groups are present as loops or tails that protrude into the solvent and increase the hydrodynamic diameter of the particles.
脉冲场梯度核磁共振（PFG NMR）实验已被用于研究聚（甲基丙烯酸2-（N，N-二甲基氨基）乙酯）（PDMA）（Mn = 12,000，Mw/Mn = 1.20，Nn = 78）与结合在CdSe/TOPO量子点（QD）表面的三辛基氧化膦（TOPO）之间的配体交换。我们表明，PFG 1H NMR能够通过区分与量子点结合的TOPO信号和溶液中游离的TOPO分子信号的能力，来量化PDMA对TOPO的取代。对于在558 nm处具有最大带边吸收的CdSe量子点（通过透射电子显微镜测得直径为2.7 nm），我们确定，在饱和状态下，平均8条聚合物链取代了超过90%的表面TOPO基团。在部分饱和状态下，平均每条量子点有6条聚合物链，每个被取代的TOPO需要28个DMA重复单元。假设每取代一个TOPO，有一个Me2N-基团与表面的Cd2+结合，我们推断只有约3%的DMA单元直接与表面结合。其余的基团以环或尾的形式存在，伸向溶剂中，增加了颗粒的流体动力学直径。
