Synthesis and recognition of water soluble organometallic tetrahedral cage compounds

Organometallic cages are special supramolecular bodies, which are similar to metal organic frameworks and are formed by the assembly of metal and organic ligands The difference is that organometallic cages are not as large as the latter, which can be regarded as a small unit in the organometallic framework Organometallic cages have special cavity structure and can hold specific guest molecules In addition, due to the presence of metal sites in the structure, organometallic cages can also be used as catalysts to accelerate specific chemical reactions However, the solubility of many excellent organometallic cages in water is not high, so their application is limited Although the modification of some hydrophilic groups can increase the solubility of organometallic cage compounds, this method will lead to cumbersome organic synthesis operations and may reduce the recognition performance of cage compounds Figure 1 Synthesis and solubility transformation of metal cage compound 1 (picture source: angelw Chem Int ed.) Recently, Professor Jonathan R Nitschke and his collaborators from the Department of chemistry, Cambridge University, UK synthesized a water-soluble tetrahedral cage compound 1 (1.bf 4 and 1.so 4) through substructure self-assembly By introducing a fluorescent dye into the organic ligand structure of cage compounds, they not only increase the cavity size and electric charge of cage compounds 1, but also make 1 have a fluorescent response to specific anions This achievement was published in German Applied Chemistry (DOI: 10.1002 / anie 201814149) under the title of "fluorometric nuclear recognition within a water solubletherahedral capsule" The self-assembly process of tetrahedral cage compound 1 is shown in Figure 1 In order to introduce the Tata + structure with fluorescence characteristics, the author first obtained the ligand a containing aldehyde group by several steps of reaction, and then added a and tris (2-aminoethyl) amine (tran) into the solution containing zinc salt to obtain the corresponding cage compound 1 Specifically, when a and tren are added to the acetonitrile solution of zinc tetrafluoroborate, 1 · BF 4 with good solubility in organic phase can be obtained; when a and tren are added to the acetonitrile / aqueous solution of zinc sulfate, 1 · so 4 with good solubility in aqueous phase can be obtained In addition, 1.bf 4 and 1.so 4 can be converted to each other under the action of tetrabutylammonium sulfate or lithium tetrafluoroborate Fig 2 Recognition of 1 · BF 4 and Mo 6O 19 2 - (picture source: Angel W chem Int ed.) to obtain cage like compounds, the author first studied the ability of 1 · BF 4 to combine anions in organic phase As a large-scale anion, hexamolybdate ion (mo6o192 -) can not be combined with conventional small-scale cation main body, so the author studies the recognition ability of 1 · BF 4 to large-scale anion on behalf of it (Fig 2) The results of NMR titration showed that some new peaks appeared when Mo 6O 19 2 - was added into acetonitrile solution of 1 · BF 4, while the intensity of proton peak of 1 · BF 4 decreased gradually, which indicated that the combination of 1 · BF 4 and Mo 6O 19 2 - showed slow exchange in NMR In addition, the results of fluorescence titration showed that the fluorescence intensity of 1 · BF 4 decreased significantly with the addition of Mo 6O 19 2 - By fitting the fluorescence data, we calculated that the binding constant of 1 · BF 4 and Mo 6O 192 - is about (2.59 ± 0.06) × 105m-1, and the binding has certain selectivity BF 4 -, ClO 4 -, TF 2n -, TFO - and some neutral molecules such as fullerene and naphthalene do not cause similar changes in the fluorescence of 1 · BF 4 Fig 3.1.so4 recognition of anions (picture source: angelw Chem Int ed.), the author tried to study the recognition ability of 1.so4 to anions in aqueous phase, and found that 1.so4 preferred to combine anions in aqueous solution, and showed high affinity for phosphorylated nucleoside acids The authors speculate that this is because the positive Tata + in 1 · so 4 has a certain affinity for anions, and the cavity size of 1 · so 4 matches the nucleotide Highlights: a tetrahedral organometallic cage compound has been synthesized by self-assembly of sub components The compound has fluorescence properties and can recognize specific anions The author: Alex J plajer, Edmundo g perc á stegui, Marco Santella, Felix J Rizzuto, Quan Gan, Bo w Laursen and Jonathan R Nitschke.