Heteropoly acid catalysts in upgrading of biorenewables: Synthesis of para-menthenic fragrance compounds from α-pinene oxide

© 2018 Elsevier B.V. The isomerization of α-pinene oxide in the presence of Cs2.5H0.5PW12O40 (CsPW) heteropolysalt as solid acid catalyst is reported. The reactions were performed in various solvents, which allowed to obtain trans-carveol, trans-sobrerol and pinol in 60–80% yield each, which exceed the yields reported so far. The CsPW catalyst could be recovered and reused without loss of its activity and selectivity

Isomerization of Cyclohexane over Bifunctional Pt-, Au-, and PtAu-Heteropoly Acid Catalysts

© 2019 American Chemical Society. Isomerization of cyclohexane was investigated in the presence of monofunctional acid and bifunctional metal-acid catalysts based on Keggin-type heteropoly acid H3PW12O40 and Pt and Au as the metal components using a differential fixed-bed microreactor at 180-300 °C, ambient pressure and a C6H12/H2 partial pressure ratio of 0.04-0.14. Particular emphasis was placed on the acidic Cs salt, Cs2.5H0.5PW12O40 (CsPW) as the acid catalyst and Pt/CsPW, Au/CsPW, and PtAu/CsPW as the bifunctional catalysts. Pt/CsPW and Au/CsPW were more efficient than the monofunctional acid catalyst CsPW, and Pt/CsPW was more active than Au/CsPW with both giving >99% selectivity to methylcyclopentane. It was found with Pt/CsPW that the cyclohexane dehydrogenation step equilibrated at a molar ratio of Pt and H+ surface sites Pt/H+ ≥ 0.7, which is much higher than for Pt/zeolite. PtAu/CsPW bimetallic catalyst exhibited a 2-fold higher activity in cyclohexane isomerization and a 3.5-fold higher activity in the accompanying dehydrogenation of cyclohexane to benzene than the mixture of Pt/CsPW and Au/CsPW with the same metal loading. The enhancing effect of gold is assigned to PtAu bimetallic particles, which had a higher Pt dispersion than the Pt in Pt/CsPW. Scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX) revealed bimetallic PtAu particles in PtAu/CsPW with a wide range of Pt/Au atomic ratios. No enhancing effect of gold was found in the case of carbon-supported catalyst PtAu/C physically mixed with CsPW, and the STEM-EDX analysis revealed no modification of Pt sites by Au in this catalyst

Different characteristics and nucleotide binding properties of Inosine Monophosphate Dehydrogenase (IMPDH) isoforms

We recently reported that Inosine Monophosphate Dehydrogenase (IMPDH), a rate-limiting enzyme in de novo guanine nucleotide biosynthesis, clustered into macrostructures in response to decreased nucleotide levels and that there were differences between the IMPDH isoforms, IMPDH1 and IMPDH2. We hypothesised that the Bateman domains, which are present in both isoforms and serve as energy-sensing/allosteric modules in unrelated proteins, would contribute to isoform-specific differences and that mutations situated in and around this domain in IMPDH1 which give rise to retinitis pigmentosa (RP) would compromise regulation. We employed immuno-electron microscopy to investigate the ultrastructure of IMPDH macrostructures and live-cell imaging to follow clustering of an IMPDH2-GFP chimera in real-time. Using a series of IMPDH1/IMPDH2 chimera we demonstrated that the propensity to cluster was conferred by the N-terminal 244 amino acids, which includes the Bateman domain. A protease protection assay suggested isoform-specific purine nucleotide binding characteristics, with ATP protecting IMPDH1 and AMP protecting IMPDH2, via a mechanism involving conformational changes upon nucleotide binding to the Bateman domain without affecting IMPDH catalytic activity. ATP binding to IMPDH1 was confirmed in a nucleotide binding assay. The RP-causing mutation, R224P, abolished ATP binding and nucleotide protection and this correlated with an altered propensity to cluster. Collectively these data demonstrate that (i) the isoforms are differentially regulated by AMP and ATP by a mechanism involving the Bateman domain, (ii) communication occurs between the Bateman and catalytic domains and (iii) the RP-causing mutations compromise such regulation. These findings support the idea that the IMPDH isoforms are subject to distinct regulation and that regulatory defects contribute to human disease