128337-08-6Relevant academic research and scientific papers
Functional mimicry of the active site of carboxypeptidase A by a molecular imprinting strategy: Cooperativity of an amidinium and a copper ion in a transition-state imprinted cavity giving rise to high catalytic activity
Liu, Jun-Qiu,Wulff, Guenter
, p. 7452 - 7453 (2004)
A model for the natural enzyme carboxypeptidase A was prepared by molecular imprinting in synthetic polymers. An unusually high activity and efficiency for carbonate hydrolysis could be obtained by imprinting with a stable transition-state analogue template and introducing an amidinium group and a Cu2+ ion-binding site in a defined orientation to each other into the active site. With substrates having a very similar structure to the template, extraordinarily high enhancements of rates of 110000-fold were obtained of catalyzed to uncatalyzed reaction kcat/kuncat. The efficiency kcat/Km of the molecularly imprinted catalysts compared to that of the nonimprinted control polymers containing the same functional groups was 790-fold higher, a clear indication of a very efficient imprinting procedure. Copyright
Kinetic study on aminolysis of phenyl 2-pyridyl carbonate in acetonitrile: Effect of intramolecular h-bonding interaction on reactivity and reaction mechanism
Song, Ji-Hyun,Lee, Jae-In,Um, Ik-Hwan
, p. 2081 - 2085 (2014/12/10)
Second-order rate constants (kN) have been measured spectrophotometrically for the reactions of phenyl 2- pyridyl carbonate (6) with a series of cyclic secondary amines in MeCN at 25.0 ± 0.1 °C. The Bronsted-type plot for the reaction of 6 is linear with βnuc = 0.54, which is typical for reactions reported previously to proceed through a concerted mechanism. Substrate 6 is over 103 times more reactive than 2-pyridyl benzoate (5), although the reactions of 6 and 5 proceed through the same mechanism. A combination of steric hindrance, inductive effect and resonance contribution is responsible for the kinetic results. The reactions of 6 and 5 proceed through a cyclic transition state (TS) in which H-bonding interactions increase the nucleofugality of the leaving group (i.e., 2-pyridiniumoxide). The enhanced nucleofugality forces the reactions of 6 and 5 to proceed through a concerted mechanism. In contrast, the corresponding reaction of 4-nitrophenyl 2-pyridyl carbonate (7) proceeds through a stepwise mechanism with quantitative liberation of 4-nitrophenoxide ion as the leaving group, indicating that replacement of the 4-nitrophenoxy group in 7 by the PhO group in 6 changes the reaction mechanism (i.e., from a stepwise mechanism to a concerted pathway) as well as the leaving group (i.e., from 4-nitrophenoxide to 2-pyridiniumoxide). The strong electron-withdrawing ability of the 4- nitrophenoxy group in 7 inhibits formation of a H-bonded cyclic TS. The presence or absence of a H-bonded cyclic TS governs the reaction mechanism (i.e., a concerted or stepwise mechanism) as well as the leaving group (i.e., 2-pyridiniumoxide or 4-nitrophenoxide).
