Amino Acid-Based Stabilization of Oxide Nanocrystals in Polar Media: From Insight in Ligand Exchange to Solution 1H NMR Probing of Short-Chained Adsorbates
Amino Acid-Based Stabilization of Oxide Nanocrystals in Polar Media: From Insight in Ligand Exchange to Solution 1H NMR Probing of Short-Chained Adsorbates
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DOI：
10.1021/acs.langmuir.5b04611
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发表时间：
2016-03-01
期刊：
影响因子：
3.9
通讯作者：
Van Driessche, Isabel
中科院分区：
文献类型：
--
作者：
De Roo, Jonathan;Coucke, Sofie;Van Driessche, Isabel
配体交换是手性合成和手性应用之间的关键步骤。虽然胶体稳定性和配体交换在非极性介质中很容易建立，天然的，疏水性配体与极性配体的交换是不太系统的。在本文中，我们提出了一种通用的配体交换策略的羧酸封端的HfO 2和ZrO 2纳米晶体的相转移到各种极性溶剂，基于小的氨基酸作为传入的配体。为了深入了解交换的基本机制，我们结合FTIR，Zeta电位测量和溶液H-1 NMR技术研究了该系统。在这方面，用溶液NMR检测表面缔合的小配体证明具有挑战性。紧密结合的氨基酸是不可检测的，但它们的存在可以通过在滴定实验中与其他配体的置换来证明。或者，我们发现属于结合物种的甲基部分可以规避这些限制，因为它们由于内部流动性而具有更有利的弛豫特性。因此，我们的结果不限于氨基酸，但任何短链配体，因此将有利于严格的调查和了解各种配体交换过程。
Ligand exchange is a crucial step between nanocrystal synthesis and nanocrystal application. Although colloidal stability and ligand exchange in nonpolar media are readily established, the exchange of native, hydrophobic ligands with polar ligands is less systematic. In this paper, we present a versatile ligand exchange strategy for the phase transfer of carboxylic acid capped HfO2 and ZrO2 nanocrystals to various polar solvents, based on small amino acids as the incoming ligand. To gain insight in the fundamental mechanism of the exchange, we study this system with a combination of FTIR, zeta potential measurements, and solution H-1 NMR techniques. The detection of surface-associated, small ligands with solution NMR proves challenging in this respect. Tightly bound amino acids are undetectable, but their existence can be proven through displacement with other ligands in titration experiments. Alternatively, we find that methyl moieties belonging to bound species can circumvent these limitations because of their more favorable relaxation properties as a result of internal mobility. As such, our results are not limited to amino acids but to any short-chained ligand and will therefore facilitate the rigorous investigation and understanding of various ligand exchange processes.