ACS catalyst: hydrolysis of dioxolane mediated by cucurbit [7] urea

Efficient chemical reaction has always been one of the goals pursued by chemists In addition to the appropriate concentration, reaction pressure and reaction temperature, the use of catalyst is a kind of "lazy" behavior, but this does not mean that the design and application of catalyst is a simple thing Although nature has given us a very successful example enzyme, there is a big gap between the selectivity and catalytic performance of today's catalyst and enzyme With the development of supramolecular chemistry, scholars began to use zeolites and cyclodextrins to regulate some chemical reactions and made a series of achievements Among them, cucurbitamide, a kind of cyclic compound formed by condensation of glycourea and formaldehyde under acidic conditions, has been widely concerned by scholars because it can change the substrate PKA Fig 1 Cucurbita [7] (cb7) urea participates in the hydrolysis of dioxolane and the molecular structure of the substrate (source: ACS catalyst) Recently, Faruk Nome of the Federal University of Santa Catalina in Brazil and Luis Garc í A-R í o of the University of Santiago in Spain jointly studied the regulatory effect of Cucurbita [7] (cb7) urea on the hydrolysis of dioxolane (Fig 1) The effect of cb7 on the hydrolysis of dioxolane was studied in detail by means of NMR and computer simulation The research results were published in ACS Catalysis (DOI: 10.1021 / acscalal 8b03605) under the title of "cubic mediatedcatalytic Hydrology: a kinetic and computational study with neutral and catorial dioxolanes in cb7" Firstly, the author selected several substrates containing dioxolane (Fig 1), among which MFD, BFD and HFD are neutral dioxolane with different length of alkyl chain, while tmafd and teafd are cationic dioxolane Then, the author added different amount of cb7 to the reaction system to explore the effect of the macrocyclic compound on the hydrolysis reaction of the substrate The results showed that the addition of cb7 would increase the hydrolysis rate of the substrate (Fig 2), but the rate increase of different substrates was not the same The catalytic effect of cucurbitamide on neutral molecular substrates increased with the increase of alkyl chain length, but it also had a similar trend for cationic substrates However, when the concentration of CB7 is 1 mM, the catalytic effect of cucurbit on the cationic substrate is almost saturated, and the catalytic effect on the neutral molecule is far more than that After that, the author added the competitive object to the system, which made it compete with the substrate The results showed that the acceleration effect of cb7 on the reaction was greatly reduced after the addition of the competitive object molecules, which indicated that the combination of cb7 and the substrate molecules was the key point of the acceleration of the whole reaction, and the higher the binding strength, the better the reaction Fig 2 Hydrolysis process of dioxolane catalyzed by cucurbitamide and its rate constant (picture source: ACS catalyst.) further, in order to explain the reason why cb7 accelerates the hydrolysis of dioxolane, the author carried out computer simulation calculation for this process (Fig 3) In the hydrolysis process of dioxolane, the formation of carbon positive ion is the decisive step of the whole reaction, while the ternary complex formed by cb7, dioxolane and hydronium ion can effectively promote the reaction, and the hydrogen bond formed by carbonyl oxygen in cb7 and various reaction intermediates or even products can play a certain role in the whole process Therefore, cb7 shows good catalytic effect For neutral substrates, although the distance between cb7 carbonyl and dioxolane has nothing to do with the alkyl chain length of the substrate, the distance between cb7 and dioxolane will increase with the increase of the alkyl chain length when they form the ternary complex of dioxolane @ cb7 @ H3O +, and the increase of the distance will make the stability of cb7 disappear and the catalytic efficiency decrease There are two binding modes between organic cations and cb7, so the reaction can be accelerated effectively only when they form the close configuration of dioxolane and carbonyl oxygen Fig 3 Energy of intermediate products in the hydrolysis process of dioxolane catalyzed by cucurbit urea (picture source: ACS catalyst) Full text highlight: the author studied the effect of Cucurbit [7] urea (cb7) on the hydrolysis reaction of dioxolane, and analyzed the causes of different catalytic effects through computer simulation Full text authors: Leandro scorsin, Juliano a Roehrs, Roberta R campedelli, Giovanni f caramori, Alexandre OSMAR Ortolan, Renato Luis tame Parreira, Haidi d.fieldler, angel ACU ñ a, Luis Garc í A-R í o, and Faruk Nome.