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    Home > Breaking the boundary between host and guest

    Breaking the boundary between host and guest

    • Last Update: 2018-05-17
    • Source: Internet
    • Author: User
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    In the history of human civilization, there are many amazing buildings, such as the great wall of China, the pyramids of Egypt, etc the construction of these buildings needs not only careful design, but also various structural units to achieve various functions There are also similar phenomena in the field of Science - the construction of molecular devices Like the macrostructure, micro molecular devices can not be built without various structural units, which can be small molecular object compounds with simple structure, or they can be Large size main compounds with special recognition ability, such as cyclodextrin, calixarene, crown ether, cyclopentane, columnar aromatic, organometallic polyhedron, etc Through the assembly of these molecules, scientists have prepared a series of different functional molecular devices, such as optical sensors, drug transport carriers, molecular electronic devices and molecular machines In recent years, cucurbitamide, a kind of main compound derived from glycylurea, has a high degree of selectivity and affinity for guest molecules, and can form a host guest inclusion compound with stimulus response with guest molecules, so it is widely used in the construction of molecular machines Fig 1 a) structural formula of cucurbitamide and M1; b) synthesis diagram of 6; c) synthesis diagram of 1 (picture source: angelw Chem Int ed 2018, Recently, Professor Lyle Isaacs of the University of Maryland at Park in the United States prepared a kind of iridoine modified open-loop cucurbit (1) on the basis of its development of the open-loop cucurbit (M1), and found that this compound plays the role of both the host and guest molecules when combined with other molecules In 2009, Professor Isaac first reported this new type of cucurbitamide homologue, open-loop cucurbitamide, at the 238th annual meeting of American Chemistry After that, the research team of Isaac carried out a detailed study on this type of cucurbitamide and found that it has properties that traditional cucurbitamide does not have in molecular recognition, drug transport, drug solubilization, etc After being modified by pterene, the host compound can not only recognize some traditional guest molecules, but also form stable inclusion complexes with large-scale molecules such as blue box and Fujita square This achievement was published in German Applied Chemistry (DOI: 10.1002 / anie 201803132) under the title of "blurring the lines between host and guest: a Chinese receiver derived from curubituril and triptycene" Fig 2 6 (left) and Fig 1 (right) (picture source: angelw Chem Int ed 2018, accepted) the author first obtained compound 4 through D-A addition reaction and aromatization reaction of anthracene and benzoquinone, and then 4 and 1, 3-propane sulfonic acid lactone reacts to obtain butterfly derivative 6 (Fig 1b) Finally, 6 reacts with glycourea tetramer 7 to obtain butterfly modified open-loop cucurbituril 1 (Fig 1c) The author is very lucky to get the crystal structure of compound 6 and compound 1 (Fig 2) From the crystal structure, it can be seen that two diene derivatives 6 can be overlapped by π - π stacking interaction between substituted benzene rings (Fig 2, left); and an unsubstituted benzene ring on the diene substituent of 1 will fold and extend into the cavity (Fig 2, right) Therefore, compared with the unmodified open-loop cucurbitamide, 1 has lower symmetry and smaller cavity size Fig 3 molecular structure of the object (top) and its ITC titration results (bottom) (picture source: angelw Chem Int ed 2018, Accepted) from the stacking diagram of 1, the author found that trimer can be formed between three open-loop cucurbitamide, so the author wanted to know whether it has the same properties in the solution However, the dilution experiment and DOSY experiment showed that 1 only exists in the form of monomer in the solution After that, the author carried out a study on the recognition of new host molecules By selecting the typical guest molecules of Cucurbit [6], cucurbit [7] and cucurbit [8], the author found that the modification of iridoine did not have a great impact on the recognition properties of cucurbit These typical cucurbit guest molecules still maintain a high affinity with the host compounds (Figure 3, bottom) Fig 4 Schematic diagram (left) and nuclear magnetic spectrum (right) (picture source: angel Chem Int ed 2018, accepted) In addition, the author also studied the recognition behavior between 1 and the traditional main compounds bluebox and Fujita square The abnormal proton movement on NMR shows that these ring-shaped molecules are not completely bound by 1, but show a phenomenon of mutual binding: a viologen unit of the ring-shaped molecule enters into the cavity of open-loop cucurbit urea, while the benzene ring of butterfly on Cucurbit urea is located in the inner part of the ring-shaped molecule There is another difference between blue box and Fujita square The distance between the two viologen units of the former is not enough to accommodate two benzene rings, so only one end of the pterene structure at both ends of 1 can enter into its interior (FIG 4A) The latter has a larger cavity, so it can accommodate two pterene structures of 1 (Fig 4b) This kind of host guest structure breaks the traditional mode of host guest structure in host guest system This host guest system can further enrich the function of supramolecular devices and help to build more complex molecular devices All authors: Xiaoyong Lu, Soumen K samanta, Peter yzavalij, and Lyle Isaac corresponding author: lyleisacs
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