Confinement and step-wise reopening of channels in an artificial cell/inorganic capsule: a 7Li NMR study.
Confinement and step-wise reopening of channels in an artificial cell/inorganic capsule: a 7Li NMR study.
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DOI：
10.1002/chem.200801122
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发表时间：
2008-10
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影响因子：
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通讯作者：
E. Haupt;Claudia Wontorra;D. Rehder;Alice Merca;A. Müller
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文献类型：
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作者：
E. Haupt;Claudia Wontorra;D. Rehder;Alice Merca;A. Müller
在以前的文献中，我们已经证明了阴离子多孔氧化钼基胶囊[Lin {（Mo）Mo 5 O21 ACHTUNGTRENNUNG（H2O）6} 12 ACHTUNGTRENNUNG {Mo V2 O 4 ACHTUNGTRENNUNG（SO 4）}30] 72 n化合物[（CH 3）2NH 2] 44 Li 28 n·1a·250 H2O的（1a ; n 5）（1;图1）可以被认为是细胞阳离子运输的模型，特别是关于胶囊内部和周围溶液之间的锂离子交换。此外，我们可以证明，适当的阳离子有机物种，如甲脒阳离子（FA·H），可以作为“软木塞”/客人;也就是说，他们能够关闭，在一个超分子的方式，显示冠醚功能的孔，并从外部分离的内部。从Li NMR光谱可以推断，对于存在的各种锂物质，可以观察到单独的信号。然而，内部锂阳离子的特征（Li被限制在胶囊的空腔中）只是间接推导出来的，因为Li离子参与了交换过程（图1，底部）。在这里，我们提出了一个NMR研究，允许一个精确的解释与胶囊相关的锂阳离子的交换和限制的过程。特别是，我们表明，逐步重新开放的孔（部分释放的formamidinium插头）是可能的，通过添加限定量的水，一个事件模型配体门控离子通道。外部和内部锂阳离子之间的差异的第一个指示产生从系统的扩散行为的研究所描绘的Li NMR信号。如果在Li DOSY实验中研究1（根据参考文献[1]制备）的二甲亚砜（DMSO）溶液并用FA·HCl处理，则与溶剂化Li（[LiACHTUNGTRENNUNG（dmso）nACHTUNGTRENNUNG（H2O）4 n]）相比，预期随胶囊（Li 1a）移动的包封锂阳离子的扩散系数存在显著差异。事实上可以观察到这一点（图2）。根据扩散系数（9.3？）获得1a的斯托克斯（“流体动力学”）半径。10 11 ms）为1.2 nm。考虑到扩散实验校准的模糊性，确定的值与从1的单晶X射线结构分析获得的r=1.5 nm合理一致。[a]Dr. E. T. K.奥普特角Wontorra，Prof. D. Hamburg（德国）20146 Hamburg（University Ft Hamburg 20146 Hamburg）Fax：（+49）40428382893 E-mail：埃哈德.奥普特rehder@chemie.uni-hamburg.de [B] Dr. A. chemie.uni-hamburg.de马尔卡教授，A. MJller FakultFt fJr Chemie der UniversitFt Postfach 100131，33501比勒费尔德（德国）图1。上图：通过高电荷阴离子胶囊1a（Mo蓝，O红）的孔吸收和释放阳离子（反离子转运）的空间填充示意图。下图：1a的20个孔中的两个孔的视图（五角单元的MoO 6八面体为蓝色，{Mo 2}型连接基团为红色;详细信息参见参考文献[1]）。通过X射线晶体学观察到的硫酸盐的无序（S黄色，O红色）是由（不能直接观察到的）Li离子引起的。
In previous contributions we have demonstrated that the anionic porous molybdenum oxide based capsule(s) [Lin {(Mo)Mo5O21 ACHTUNGTRENNUNG(H2O)6}12ACHTUNGTRENNUNG{Mo V 2O4ACHTUNGTRENNUNG(SO4)}30] 72 n (1a ; n 5) of the compound [(CH3)2NH2]44Li28 n·1a· 250H2O (1; Figure 1) can be considered as models for cellular cation transport, in particular with respect to the exchange of lithium ions between the interior of the capsules and the surrounding solution. Additionally, we could show that appropriate cationic organic species, such as formamidinium cations (FA·H), can act as “corks”/guests; that is, they are able to close, in a supramolecular fashion, the pores exhibiting crown-ether function, and separate the interior from the exterior. From Li NMR spectra it has been deduced that separate signals can be observed for the various lithium species present. However, the characteristics of the internal lithium cations (Li confined in the cavity of the capsule) were only deduced indirectly, because Li ions are involved in exchange processes (Figure 1, bottom). Here, we present an NMR study that allows for a precise interpretation of the processes associated with the exchange and confinement of capsule associated lithium cations. In particular we show that stepwise re-opening of the pores (partial release of the formamidinium plugs) is possible by addition of defined amounts of water, an incident which models ligand-gated ion channels. A first indication of the differentiation between external and internal lithium cations arises from the study of the diffusion behaviour of the system as depicted by the Li NMR signals. If a solution of 1 (preparation according to reference [1]) in dimethyl sulfoxide (DMSO) and treated with FA·HCl is investigated in a Li DOSY experiment, a substantial difference in the diffusion coefficients of encapsulated lithium cations moving with the capsule (Li 1a) as compared to solvated Li ([LiACHTUNGTRENNUNG(dmso)nACHTUNGTRENNUNG(H2O)4 n] ) is to be expected. This is in fact observed (Figure 2). The Stokes (”hydrodynamic”) radius obtained for 1a from the diffusion coefficient (9.3?10 11 ms ) is 1.2 nm. Keeping in mind the ambiguities with the calibration of the diffusion experiments, the determined value is in reasonable agreement to r=1.5 nm obtained from the single-crystal X-ray structure analysis of 1. [a] Dr. E. T. K. Haupt, C. Wontorra, Prof. Dr. D. Rehder Department Chemie, UniversitFt Hamburg 20146 Hamburg (Germany) Fax: (+49)40428382893 E-mail : erhard.haupt@chemie.uni-hamburg.de rehder@chemie.uni-hamburg.de [b] Dr. A. Merca, Prof. Dr. A. MJller FakultFt fJr Chemie der UniversitFt Postfach 100131, 33501 Bielefeld (Germany) Figure 1. Top: Schematic space-filling representation of the uptake and release of cations (counterion transport) through the pores of the highly charged anionic capsule 1a (Mo blue, O red). Bottom: View of two of the 20 pores of 1a (MoO6 octahedra of the pentagonal units blue and of the {Mo2} type linker groups red; for details see reference [1]). The disorder of the sulfates observed by X-ray crystallography (S yellow, O red) comes about by the (not directly observable) Li ions.