14915-25-4Relevant articles and documents
A model reaction assesses contribution of H-tunneling and coupled motions to enzyme catalysis
Liu, Qi,Zhao, Yu,Hammann, Blake,Eilers, James,Lu, Yun,Kohen, Amnon
, p. 6825 - 6833 (2012)
To assess the contribution of physical features to enzyme catalysis, the enzymatic reaction has to be compared to a relevant uncatalyzed reaction. While such comparisons have been conducted for some hydrolytic and radical reactions, it is most challenging for biological hydride transfer and redox reactions in general. Here, the same experimental tools used to study the H-tunneling and coupled motions for enzymatic hydride transfer between two carbons were used in the study of an uncatalyzed model reaction. The enzymatic oxidations of benzyl alcohol and its substituted analogues mediated by alcohol dehydrogenases were compared to the oxidations by 9-phenylxanthylium cation (PhXn+). The PhXn+serves as an NAD+ model, while the solvent, acetonitrile, models the protein environment. Experimental comparisons included linear free energy relations with Hammett reaction constant (ρ) of zero versus -2.7; temperature-independent versus temperature-dependent primary KIEs; deflated secondary KIEs with deuteride transfer (i.e., primary-secondary coupled motion) versus no coupling between secondary KIEs and H- or D-transfer; and large versus small secondary KIEs for the enzymatic versus uncatalyzed alcohol oxidation. Some of the differences may come from differences in the order of microscopic steps between the catalyzed versus uncatalyzed reactions. However, several of these comparative experiments indicate that in contrast to the uncatalyzed reaction the transition state of the enzymatic reaction is better reorganized for H-tunneling and its H-donor is better rehybridized prior to the C-H→C transfer. These findings suggest an important role for these physical features in enzyme catalysis.
Electron and Hydrogen Atom Transfer Mechanisms for the Photoreduction of o-Quinones. Visible Light Induced Photoreaction of β-Lapachone with Amines, Alcohols, and Amino Alcohols
Ci, Xiaohong,Silva, Rosaly Silveira da,Nicodem, David,Whitten, David G.
, p. 1337 - 1343 (1989)
β-Lapachone (1), a substituted o-naphthoquinone absorbing into the visible (λmax=424 nm in benzene), is cleanly and efficiently reduced to the corresponding semiquinone radical upon photolysis in degassed solutions with alcohols, amines, and β-amino alcohols.The course and products of these photoreactions have been followed by NMR, ESR, fluorescence, and absorption spectroscopy.For all three types of reductant the overall reaction involves 2e- oxidation of the donor, and the quantum efficiencies show a dependence upon quinone concentration indicative of therole of a second dark reduction of 1 by products of the primary photolysis.For amines and amino alcohols the reaction is initiated by single electron transfer quenching of triplet 1.For triethylamine the mechanism is indicated to be a sequence of two electron transfer-proton transfer steps culminating in two semiquinone radicals and the enamine Et2NCH=CH2.For amino alcohols a C-C cleavage concurrent with deprotonation of the alcohol (oxidative photofragmentation) occurs, in competition with reverse electron transfer, following the quenching step.For both amines and amino alcohols, limiting efficiencies of reaction approach 2 (for QH. formation).In contrast, both 2-propanol and benzyl alcohol are oxidized by excited states of 1 with much lower efficiency.The probable mechanism for photooxidation of the alcohols involves a H atom abstraction quenching of the excited state followed by an electron transfer-proton transfer sequence in which a ground-state 1 is reduced.Lower limiting efficiencies for photoreduction of 1 by the alcohols are attributed to inefficiencies of net H-atom transfer in the quenching step.
Critical role of solvent-modulated hydrogen-binding strength in the catalytic hydrogenation of benzaldehyde on palladium
Cheng, Guanhua,Chin, Ya-Huei (Cathy),Gutiérrez, Oliver Y.,Jentys, Andreas,Lercher, Johannes A.,Liu, Yue
, p. 976 - 985 (2021/11/24)
Solvents not only disperse reactants to enhance mass transport in catalytic reactions but also alter the reaction kinetically. Here, we show that the rate of benzaldehyde hydrogenation on palladium differs by up to one order of magnitude in different solv
Cross β-arylmethylation of alcohols catalysed by recyclable Ti-Pd alloys not requiring pre-activation
Utsunomiya, Masayoshi,Kondo, Ryota,Oshima, Toshinori,Safumi, Masatoshi,Suzuki, Takeyuki,Obora, Yasushi
supporting information, p. 5139 - 5142 (2021/05/31)
Ti-Pd alloy catalysts were developed for the cross β-arylmethylation between arylmethylalcohols and different primary alcohols via a hydrogen autotransfer mechanism. The alloy catalysts could be reused multiple times without the need for pre-activation. Analysis of the reaction solution by inductively coupled plasma atomic absorption spectroscopy indicated that only a minimal amount of Ti and no Pd was leached from the catalyst.
