Observing the Hierarchical Self-Assembly and Architectural Bistability of Hybrid Molecular Metal Oxides Using Ion-Mobility Mass Spectrometry
Observing the Hierarchical Self-Assembly and Architectural Bistability of Hybrid Molecular Metal Oxides Using Ion-Mobility Mass Spectrometry
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DOI：
10.1002/anie.201102340
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发表时间：
2011-01-01
影响因子：
16.6
通讯作者：
Cronin, Leroy
中科院分区：
文献类型：
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作者：
Thiel, Johannes;Yang, Dongmei;Cronin, Leroy
多金属氧酸盐 (POM) 是一类存在于单体和基于 Mo、W 和 V 的大量无限氧化物之间的阴离子分子金属氧化物簇。 [1]虽然 POM 簇可以很好地定义，但存在一个巨大的结构库，其大小和电荷各不相同，并且它们在远离平衡反应条件下的组装甚至可以与蛋白质的一级、二级、三级和四级结构单元进行比较。 [2, 3] 这是因为金属氧化物多面体 [MOx] 的酸性缩合反应，导致寡聚 [MOx] n 单元（x= 4 至 7），可以与 POM 一级结构的组装有关。蛋白质。[4]然后，这些构建单元能够经历扩展的组装过程，产生各种高核团簇，这些团簇不仅在大小和电荷方面不同，[5]而且在形状和构象方面也不同，形成一系列超分子聚集体。 [6]这种结构灵活性在实际设计的潜力方面非常诱人，但考虑到溶液中存在过多的物种，理解并控制自组装是非常困难的。在这方面，我们最近采用电喷雾电离质谱 (ESIMS) 来表征 POM 团簇的一级、二级和三级结构。[7, 8] 此外，机理研究揭示了二级构建块级别的自组装过程。[9, 10] 传统 MS 允许通过质量和电荷（即 m/z 比）分离阴离子团簇，但超分子四级结构或具有相同大小和电荷的异构体，无法通过此方法拆分。[11]这是一个主要限制，因为 POM 构建模块库不仅涵盖广泛的质量和电荷，[12]，而且它们的尺寸和构象灵活性也表现出高度的多样性。[13]在此，我们描述了离子淌度质谱 (IMS/MS) 的使用，[14] 最近用于检查蛋白质结构和动力学以及对配位化合物的一些初步研究，[15] 作为探测金属氧化物系统的新工具，允许尺寸分离和研究超分子组装体以及簇结构的构象或折叠。我们还能够展示如何通过设计光可切换多金属氧酸盐杂化物来直接探测簇的构象，这些杂化物可以改变其构象，从而改变其横截面积。为了实现这些目标，我们选择研究有机-无机杂化 Mn-Anderson 簇的多分子聚集体，[MnMo6O18 ((OCH2) 3CR) 2] 3À（方案 1），
Polyoxometalates (POMs) are a class of anionic molecular metal oxide clusters existing between monomers and bulk infinite oxides based upon Mo, W, and V.[1] Although POM clusters can be well defined, there is a vast library of architectures varying in size and charge, and their assembly under far from equilibrium reaction conditions can even be compared to that of proteins in terms of primary, secondary, tertiary, and quaternary building blocks.[2, 3] This is because the acidic condensation reactions of metal oxide polyhedra [MOx], leading to oligomeric [MOx] n units (with x= 4 to 7), can be related to the assembly of the primary structure of a protein.[4] These building units are then able to undergo extended assembly processes, resulting in a variety of high nuclearity clusters that differ not only in terms of size and charge,[5] but also in shape and conformation, forming a range of supramolecular aggregates.[6] This structural flexibility is tantalizing in terms of the potential for real design but, given the plethora of species in solution, understanding and hence controlling self-assembly is extremely demanding. In this respect we have recently been employing electrospray ionization mass spectrometry (ESIMS) in the characterization of the primary, secondary, and tertiary structures of POM clusters.[7, 8] Additionally, mechanistic studies revealed self-assembly processes involved at the secondary building block level.[9, 10] Conventional MS allows for the separation of the anionic clusters by their mass and charge, that is, their m/z ratio, but the supramolecular quaternary structure, or isomers with the same size and charge, cannot be resolved by this method.[11] This is a major limitation since the libraries of POM building blocks not only cover a wide range of masses and charges,[12] but they also show a high level of diversity by their size and conformational flexibility.[13]Herein, we describe the use of ion-mobility mass spectrometry (IMS/MS),[14] recently used to examine protein structure and dynamics as well as some preliminary studies on coordination compounds,[15] as a new tool to probe metal oxide systems, allowing size separation and investigation of supramolecular assemblies as well as the conformation or folding of the cluster architectures. We are also able to show how the conformation of the clusters can be probed directly by engineering photoswitchable polyoxometalate hybrids that switch their conformation thereby changing their cross-sectional areas. To achieve these goals we chose to examine polymolecular aggregations of organic–inorganic hybrid Mn-Anderson clusters,[MnMo6O18 ((OCH2) 3CR) 2] 3À (Scheme 1),