In the ribozyme from the hepatitis delta virus (HDV) genomic strand RNA, a cytosine side chain is proposed to facilitate proton transfer in the transition state of the reaction and, thus, act as a general acid-base catalyst. Mutation of this active-site cytosine (C75) reduced RNA cleavage rates by as much as one million-fold, but addition of exogenous cytosine and certain nucleobase or imidazol...

An experimental and theoretical study of the reactivity mechanism non-catalyzed catalyzed Povarov reaction for preparation a 4-ethoxy-2,3,4,4a-tetrahydro-2-phenylquinoline as biological active quinoline derivative has been performed. The optimization conditions indicate that use catalyst, namely Lewis acid with an electron-releasing group, creates best this kind reaction. chemical structure was...

In this work, some physical mixtures of Nb2O5·nH2O and NbOPO4 were prepared to study the role phosphate groups in total acidity samples two reactions involving carbohydrate biomass: hydrolysis polyfructane dehydration fructose/glucose 5-hydroxymethylfurfural (HMF). The acid catalytic properties dominated by group enrichment. Lewis Brønsted sites detected FT-IR experiments with pyridine adsorpti...

Coke formation on n-butene cracking catalyst is the main reason for reducing of its lifetime. To study effects acidity and textural properties coke process, a series HY zeolite-type catalysts were prepared by ammonium hexafluorosilicate treatment (AHFS). NH3-TPD Py-IR-TPD used to systematically change law zeolite acidity. It was found that with increase AHFS concentration, acid density decrease...

A stereocontrolled synthesis of benzannulated spiroketals has been developed using solvent-dependent Sc(OTf)3-mediated spirocyclizations of exo-glycal epoxides having alcohol side chains. In THF, the reaction proceeds via Lewis acid catalysis under kinetic control with inversion of configuration at the anomeric carbon. In contrast, in CH2Cl2, Brønsted acid catalysis under thermodynamic control ...

This review focuses on the development of acid catalysis for selective organic transformations conducted in our laboratories for the past 30 years. Several important concepts in designing of catalysts are described with some examples. Further, recent developments in super Brønsted acid and their applications in a one-pot procedure to construct complex molecules with high diastereoselectivities ...

Several sulfonated polymers, which are typical Brønsted acid catalysts, have been employed in the production of two biofuels: 5-ethoxymethylfurfural (EMF) and ethyl levulinate (EL) as main byproduct, catalytic results attributed to their different chemical morphological properties. The Purolite CT275DR attained best from 5-hydroxymethylfurfural (HMF) with a 63% EMF yield after 16 h at 100 °C th...

Despite the huge success of enantioselective Brønsted acid catalysis, experimental data about structures and activation modes of substrate/catalyst complexes in solution are very rare. Here, for the first time, detailed insights into the structures of imine/Brønsted acid catalyst complexes are presented on the basis of NMR data and underpinned by theoretical calculations. The chiral Brønsted ac...