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Enzymatic transformations of the nitrile group are important in biology as well as in synthetic chemistry. The enzyme QueF catalyses the conversion of 7-cyano-7-deazaguanine (preQ0) to 7-aminomethyl-7-deazaguanine (preQ1), a unique approach towards biological four-electron reduction of a nitrile to an amine. The catalytic reaction involves a QueF–preQ0 thioimidate adduct that is converted to preQ1 in two NADPH dependent reduction steps via an imine intermediate. The QueF active site comprises a cysteine nucleophile flanked by an aspartic acid and additionally contains a histidine. Here, we used mutagenesis of E. coli QueF (C190A, C190S, D197A, D197H, and H229A) to study the functional interplay between these enzyme residues in covalent catalysis. Substitution of Cys190 or Asp197 annihilates preQ0 covalent binding and largely disrupts the nitrile-to-amine reductase activity. The H229A variant readily forms the thioimidate adduct and is 24-fold less active for preQ0 reduction than wild-type ecQueF (kcat = 7.2 min−1). Using isothermal titration calorimetry, we show that the non-covalent step of preQ0 binding involves proton uptake mediated by Asp197 with His229 as the likely protonated group. Catalytic proton transfer from the Cys190 thiol via Asp197 to the nitrile nitrogen promotes the covalent intermediate. We suggest that protonated (charged) His229 facilitates the polarization of the substrate nitrile for nucleophilic attack on carbon by Cys190, and through proton relay via Asp197, it could provide the proton for re-protonating Cys190 during the formation of the imine intermediate.

The hydroisomerization of ethylbenzene is an important industrial reaction to maximize the production of xylenes, and in particular, para-xylene. Zeolite EU-1 (with EUO topology) is commercially utilized in a physical mixture with a metallic phase (Pt/Al2O3). Herein, we have developed a micro-mesoporous EUO zeolite with a significant volume of intercrystalline mesoporosity to improve its catalytic performance in the industrial hydroisomerization of ethylbenzene. The use of a multivalent cationic surfactant as a capping agent was ideal to prevent uniform crystal growth and their aggregation, and to ensure the potential industrial applicability of the strategy. The corresponding mesoporosity and textural properties of nanosponge-like EUO were tuned according to the amount of the capping agent. The catalytic performance reflected the remarkable impact of a large exposed surface area (up to 55%) and a high amount of easily accessible Bronsted acid sites (up to 29%) in the EU-1 nanosponge on the catalytic yield. Our best catalyst revealed a three-fold increase in the conversion of ethylbenzene with no detrimental effects on the attained hydroisomerization yield. This approach presents a potential industrial capability in a wide range of catalytic applications as evidenced here in the hydroisomerization of ethylbenzene.

The gas-phase hydroconversion of ethylbenzene was investigated in the presence of intimate mixtures of *MRE, MFI and MTW-type zeolite nanosponges and a hydrogenating component (Pt/Al2O3). The nanomorphic zeolites were prepared using multiammonium surfactants acting as dual-porogenic agents directing the formation of micro- and mesopores simultaneously. The effects of the zeolite topology (pore size and dimensionality) and crystal thickness on the product selectivity of ultra-thin zeolite frameworks (