20 nm diameter, were prepared for the first time a hexagonal grid supramolecular
In nature, a plurality of different members of spontaneous self-assembly is a common phenomenon. Wherein many of the functional proteins and protein complexes based on the above phenomena is formed. Inspired by this phenomenon, in recent years, supramolecular chemists have to build a variety of metal with a highly predictable and directional characteristics of the metal complex – supramolecular structure. However, these methods are mainly the bottom discrete components or can be prepared less than 10 nm based on infinite coordination polymers. Few reports discrete architectures having a particular size and shape of a medium size of (10-100 nm), it may be difficult to design and because they, as well as complex self-assembly process required for the synthesis is too complicated and difficult to characterize reliably synthesized. Based on this, Xiaopeng Li of the University of South Florida, the United States and Yiming Li, Saw Wai Hla of Ohio University, Yuan Zhang Dominion University in Europe and Jonathan L. Sessler Shanghai University (co-author) a joint report a binding by intramolecular and intermolecular metal-mediated self-assembly strategy, and facilitates the strategy for constructing a series of diameter of about 20 nm, greater than 65 kDa molecular weight supramolecular giant hexagonal grid . Meanwhile, researchers characterized the imaging self-assembled hexagonal grid architecture and the resulting intermediate by a scanning tunneling microscope (STM) resolution sub molecules. Determining 14 kinds of atomic scale hexagonal grid facilitates the characterization of isomers (scanning tunneling spectroscopy (STS), etc.) can be scenic. The research results entitled \”Intra- and intermolecular self-assembly of a 20-nm-wide supramolecular hexagonal grid\” published in internationally renowned journals Nature Chemistry on.
1. Synthesis of supramolecular hexagonal grid
First, the researchers in a stepwise manner using a closure Suzuki coupling strategy and the metal-free terpyridine (TPY) a structural unit prepared by combining3. Wherein, in the presence of three open coordination sites allowing Fe (II) and intermolecular self-assembly occurs in step programmably mediated molecules. Self-assembled within an appropriate amount of Fe (II) molecules contribute to metal-mediated and nearly quantitative yield of 4 is formed. Relatively rigid twice 4 equivalents of Fe (II) in the presence of further self-assemble into a two-dimensional (2D) 5 construct, which contains 13 hexagons and 18 Fe (II) 36 and Ru (II) metal 108 and center counterion.
2. Characterization of the solution [ 123] Next, the researchers conducive electrospray ionization mass spectrometry (ESI-MS), ion mobility mass traveling wave (TWIM-MS) and nuclear magnetic resonance spectroscopy (NMR) characterization of the 5 molecules intramolecular and intermolecular self-assembly process as well. In the 1H NMR spectrum for the terpyridine H3 \’, 5\’ end of the resonance offset was observed, whereas for H6,6 \”signal has gone offset is observed .ESI-MS and TWIM-MS spectra confirmed the molecular composition according to these findings can be drawn in the complex formation between molecules 4, no detectable levels of other assembly is formed. Further, when two equivalents conducive Fe (II) form a grid of 4 treated 5, which calculates a molecular weight of 65790 Da, is one of the largest 2D discrete supramolecular metal current produced by 5 TWIM-MS analysis gives a set signal for this highly rigid systems are contemplated.
3, surface characterization
then, the researchers used ultra low temperature under high vacuum scanning tunneling microscope () further characterized the grid 5. in-depth understanding of molecules at two levels of such super-subgrid: (1) the composition of intra- and intermolecular self-assembled structures imaging; (2) determining the presence of isomers in the first study, the flexible ligand 3 was dissolved in acetonitrile (MeCN) and drop-casting onto the surface of Ag (111) due to the octahedral structure and a metal. higher electron density around the ions, unit generates a relatively strong signal in the form of leaf bright. Since the C-C single bond around freely rotating on the surface 3 are also generated conformation. However, only 4 hexagonal ring observe a conformation which conformation is formed by the same equivalent of Fe (II) by adding a solution of 3. For molecular grid 5, each leaf was observed to light
having a pistachio-shaped form in the STM image. More importantly, we can see a uniform hexagonal ring 13. Further, the diameter of the entire structure is about 20 nm, a height of about 6Å.
4, isomers identified
Finally, researchers dI / dV-V STS of grid molecule is present isomer 5. By positioning the STM tip (111) of each lobe above the upper surface 5 complex Ag, in the case of a fixed height, the offset range of 2 V to measure the tunneling spectra. Distinguished Fe (II), and Ru (II) from the center of each of the unit provides different energy gaps of the tunnel spectral measurements. Due to the symmetry of the damage on the surface 4 in the complex Ag (111) form two separate isomers, which are different Fe (II) a position on the surface. In these seven sites, HOMO-LUMO gap of each site a given isomer is 2.5 eV, and the gap in each of the remaining six isomers site is 2.8 eV. Therefore, having a smaller gap (2.5 eV) is designated as the site of Fe (II), having a large gap (2.8 eV) is designated as the site of Ru (II) sites. Density functional theory conducive (DFT) further confirmed the calculated distribution, calculations reveal that the density of states matches the expected results Fe (II), and Ru (II) centers. Since the Fe (II) typically have a higher magnetic moment compared with the Ru (II), so for 4 present in Fe (II) center, can expect to have a stronger effect Kondo, in order to further differentiate. Using a similar procedure, a total of 63 molecules STS analysis of atomic level, so that data can be collected by all 14 isomers. After statistical analysis of the results, it was confirmed that the probability of occurrence of each isomer matches according to the results of theoretical predictions.