Insight into the mechanism of methanol assistance with syngas conversion over partially hydroxylated γ-Al2O3(110D) surface in slurry bed.

Despite numerous studies devoted to the various properties of γ-Al2O3, the explorations of its catalytic activity remain scarce. In this study, density functional theory calculations are performed to study the elementary adsorption and reaction mechanisms for syngas conversion on partially hydroxylated γ-Al2O3(110D) surface in liquid paraffin. It is found that the partially hydroxylated γ-Al2O3(110D) surface with the hydroxyl coverage of 8.9 OH nm-2 is formed by two dissociative adsorptions of H2O on the dry γ-Al2O3(110D) surface. The hydroxyl coverage conditions play a key role in determining the dominant reaction mechanism on account of the existence of strong hydrogen bonds. The preferential pathway for syngas conversion with assistance of methanol over the partially hydroxylated γ-Al2O3(110D) surface in liquid paraffin has been proven to be CH3OH → CH3O + H → CH3 + OH, CH3 + CO → CH3CO. C2H5OH is then formed by successive hydrogenation via the pathway CH3CO + 3H → CH3CHO + 2H → CH3CH2O + H → C2H5OH. Here, CH3CHO formation by CH3CO hydrogenation is not inhibited. Actually, with the assistance of partially hydroxylated γ-Al2O3, CH3CHO has been synthesized with high selectivity in our previous experiment by the reaction of methanol and syngas, which provides favorable evidence for our results. The rate-limiting step is the formation of CH3O from CH3OH dehydrogenation with an activation barrier of 122.2 kJ mol-1. Moreover, the reaction barrier of CO insertion into the adsorbed CH3 group is at least 89.4 kJ mol-1, lower than those of CH4, C2H6, and CH3OCH3 formations. ADCH charge and ESP analyses indicate that the typical (Al, O) Lewis acid-base pair may have a significant effect upon the initial C-C chain formation. Thus, the present study provides a new approach for the rational tailoring and designing of new catalysts with superior reactivity involved in syngas conversion.

Identification of the protopanaxatriol synthase gene CYP6H for ginsenoside biosynthesis in Panax quinquefolius.

Panax quinquefolius is one of perennial herbs and well known for its outstanding pharmacological activity. Ginsenosides are thought to be the main active ingredients in P. quinquefolius and exist in many kinds of plant genus Panax (ginseng). Protopanaxatriol synthase, which is considered cytochrome P450 (CYP450) in ginsenoside biosynthesis pathway can convert protopanaxadiol into protopanaxatriol. However, the protopanaxatriol synthase gene in P. quinquefolius has not been identified. Here, we cloned and identified a protopanaxatriol synthase gene from P. quinquefolius (CYP6H, GenBank accession no. KC190491) at the first time, reverse transcription-PCR (RT-PCR) analysis showed no obvious transcription change of CYP6H in methyl jasmonate (MeJA)-induced hairy roots. Ectopic expression of CYP6H in Saccharomyces cerevisiae resulted in the production of protopanaxatriol with added exogenous protopanaxadiol and confirmed by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (LC/APCIMS). Moreover, high-performance liquid chromatography (HPLC) analysis shows that RNA interferences of CYP6H in transgenic hairy roots could increase the accumulation of protopanaxadiol-type ginsenosides and decrease the accumulation of protopanaxatriol-type ginsenosides, whereas the effect of overexpression CYP6H in transgenic hairy roots was contrary. Our study indicated that CYP6H is a gene encoding protopanaxadiol 6-hydroxylase which could convert protopanaxadiol into protopanaxatriol in P. quinquefolius ginsenoside biosynthesis, we also have confirmed the function of CYP6H on effect accumulation of ginsenosides.

The isolation and characterization of dammarenediol synthase gene from Panax quinquefolius and its heterologous co-expression with cytochrome P450 gene PqD12H in yeast.

Panax quinquefolius is one of perennial herbs and well known for its outstanding pharmacological activity. Ginsenosides are thought to be the main active ingredients in Panax quinquefolius and exist in many kinds of plant genus Panax (ginseng). Dammarenediol synthase, which is considered as a key enzyme in ginsenoside biosynthesis pathway can convert 2, 3-oxidosqualene into dammarenediol-II. However, the dammarenediol synthase gene in Panax quinquefolius has not been identified. Here, we cloned and identified a dammarenediol synthase gene from Panax quinquefolius (PqDS, GenBank accession No. KC316048) at the first time, and reverse transcription-PCR (RT-PCR) analysis also showed an obvious transcription increase of PqDS in the methyl jasmonate (MeJA)-induced hairy roots. Ectopic expression of PqDS in yeast resulted in the production of dammarenediol-II was confirmed by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (LC/APCIMS). Moreover, overexpression of PqDS in transgenic hairy roots could increase the transcription of gene PqDS and another P450 gene PqD12H (encoding protopanaxadiol synthase in Panax quinquefolius), the accumulation of ginsenosides also increased at the same time. In addition, both PqDS and PqD12H gene co-expressed in recombinant yeast result in the production of protopanaxadiol was detected by LC/APCIMS; this result also provides a new strategy for the abundant production of protopanaxadiol in vitro.