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    Home > The latest breakthrough of cucurbit urea as nano catalyst

    The latest breakthrough of cucurbit urea as nano catalyst

    • Last Update: 2018-05-05
    • Source: Internet
    • Author: User
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    As we all know, the enzyme in organism is the most active catalyst in nature This characteristic is not only related to its own nature, but also to its environment: Before the reaction, the enzyme and its environment can make the reaction substrate present a "reaction ready" state through weak interaction In this state, not only the collision probability of the substrate is greatly increased, but its spatial structure will also be induced into a conformation conducive to reaction Inspired by enzyme, scholars try to synthesize macrocyclic compounds with cavity structure to simulate this environment, so that they not only have the function of enzyme, but also have better environmental adaptability than enzyme With the in-depth study of enzyme properties and the emergence and development of host guest chemistry, the examples of supramolecular host compounds catalyzing organic reactions gradually appear in the field of chemistry and biology Since it was proposed, more and more attention has been paid to supramolecular catalysts because of their relatively flexible structure and excellent recognition properties, and some achievements have been made in the field of catalysis Recently, academician Zhang Xi, Department of chemistry, Tsinghua University, based on the research on the recognition properties of Cucurbit [7] urea, successfully catalyzed a series of alcohol oxidation reactions with the inclusion compound of Cucurbit [7] urea (CB [7]) and 2,2,6,6-tetramethylpiperidine oxide (tempo) as supramolecular catalyst Compared with the use of tempo alone, the inclusion compound can not only promote the formation of the intermediate TEMPO +, but also inhibit the side reactions to some extent This achievement was published in German Applied Chemistry (DOI: 10.1002 / anie 201713351) under the title of "highly efficient supramolecular catalyst by ending the reactionintermediate with adaptive reactivity" Figure 1 ITC (left) and EPR (right) maps of Cucurbit [7] urea combined with tempo (photo source: angelw Chem Int ed 2018, By simply mixing cucurbit [7] urea and tempo, the author obtained tempo / CB [7] supramolecular inclusion complex Then, the combination of the two was characterized by isothermal titration calorimetry (ITC) and electron paramagnetic resonance (EPR) It was found that the combination ratio of tempo and cucurbit [7] urea was 1:1, and the binding constant was 3.9 × 103 M-1 Although the structure of NMR can not reflect the position of N atom on tempo, EPR results show that the N-O group on tempo is in the cavity of Cucurbit [7] urea Because the binding between tempo and cucurbit [7] urea is driven by enthalpy, and the binding constant between them is not high, it needs excessive cucurbit [7] urea to completely encapsulate the tempo in the solution Fig 2 The effect of Cucurbit [7] urea on the chemical properties of tempo (picture source: angel Chem Int ed 2018, early view) After confirming that cucurbit [7] urea can be combined with tempo, the author found that the inclusion of Cucurbit [7] urea can activate tempo to a certain extent by cyclic voltammetry, making the latter more prone to oxidation-reduction reaction The author speculates that the reason is that cucurbit [7] urea has a higher affinity with the reaction intermediate TEMPO +, which will promote the reaction to move to the right In order to confirm this conjecture, EPR was used to monitor the reaction between NaCl and tempo, and it was found that the presence of Cucurbit [7] urea would accelerate the reaction by 10 times In addition, the active intermediate of TEMPO + is not stable, and there are many ways of reaction in water Among them, the reduction by water and the formation of by-products without catalytic activity will reduce the catalytic efficiency of tempo However, the high affinity between cucurbit [7] urea and TEMPO + will stabilize the active intermediate to a certain extent By means of NMR and other means, it was found that even in the presence of excessive oxidants, cucurbit [7] urea could prolong the life of TEMPO + Table 1 Effect of Cucurbit [7] urea on tempo catalyzed oxidation of a series of alcohols (picture source: angel Chem Int ed 2018, early view) Finally, the author found that the catalytic activity of TEMPO + can be restored after entering the organic phase, and the presence of Cucurbit [7] urea does not affect this process On this basis, the effects of Cucurbit [7] urea on tempo catalyzed oxidation of a series of alcohols were compared The results showed that although the presence of Cucurbit [7] urea increased the conversion of aromatic alcohol greatly, but for fatty alcohols with low reaction activity, cucurbit [7] urea increased the conversion only a little Full text author: Yang Jiang, Bohan Tang, Yucheng Zhang, Jiang Fei Xu, Zhiqiang Wang, and Xi Zhang correspondence Author: academician Zhang Xi
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