Multienzymatic Stereoselective Reduction of Tetrasubstituted Cyclic Enones to Halohydrins with Three Contiguous Stereogenic Centers

The asymmetric hydrogenation of conjugated tetrasubstituted alkenes with transition-metal catalysts is a challenging reaction, especially for substrates bearing a halide substituent. We describe a two-step multienzymatic reduction of a series of α-halo β-alkyl tetrasubstituted cyclic enones, affording halohydrins with three contiguous stereogenic centers, in good yield and with a high stereoselectivity. The reduction is catalyzed by a stereospecific ene-reductase (OYE2-3 or NemA) and a highly enantioselective alcohol dehydrogenase (ADH). The use of two enantiodivergent ADHs allows the control of the diastereoselectivity. The absolute stereochemical configurations of the products have been determined from the analysis of single-crystal structures (Flack's parameter). The enantiomeric excess (ee) has been determined by derivatization of the products with (R) Mosher's acid. Lastly, we extended our methodology also to a nonhalogenated substrate: the α-methyl ketoisophorone was reduced by two distinct enantiodivergent ene-reductases (flavin mononucleotide- and F 420-dependent), affording each enantiomer of the saturated ketone with ee > 98%

Biodiesel Processing Using Sodium and Potassium Geopolymer Powders as Heterogeneous Catalysts

This work investigates the catalytic activity of geopolymers produced using two different alkali components (sodium or potassium) and four treatment temperatures (110 to 700 \ub0C) for the methyl transesterification of soybean oil. The geopolymers were prepared with metakaolin as an aluminosilicate source and alkaline activating solutions containing either sodium or potassium in the same molar oxide proportions. The potassium-based formulation displayed a higher specific surface area and lower average pore size (28.64-62.54 m\ub2/g; 9 nm) than the sodium formulation (6.34-32.62 m\ub2/g; 17 nm). The reduction in specific surface area (SSA) after the heat treatment was more severe for the sodium formulation due to the higher thermal shrinkage. The catalytic activity of the geopolymer powders was compared under the same reactional conditions (70-75 \ub0C, 150% methanol excess, 4 h reaction) and same weight amounts (3% to oil). The differences in performance were attributed to the influences of sodium and potassium on the geopolymerization process and to the accessibility of the reactants to the catalytic sites. The Na-based geopolymers performed better, with FAME contents in the biodiesel phase of 85.1% and 89.9% for samples treated at 500 and 300 \ub0C, respectively. These results are competitive in comparison with most heterogeneous base catalysts reported in the literature, considering the very mild conditions of temperature, excess methanol and catalyst amount and the short time spent in reactions

Applying CBM and PHM concepts with reliability approach for Blowout Preventer (BOP): a literature review

The sensibility originated by the Blowout Preventer (BOP) theme, due to all attention gathered after the Macondo event, established a high level of requirements from regulatory agencies, clients and Drilling Contractors themselves. Based on these pillars, the concept of reliability has been constantly applied in the oil industry, especially in the Well Safety and Control System, where it is extremely important for the equipment to be reliable and operational when required. In parallel, the Condition Based Maintenance (CBM) and Prognostic Health Management (PHM) concepts, widely used in critical industries, which require high reliability levels, are being pointed out as the future for the BOP system management. Within this context, the purpose of this paper is to review the literature on Condition Based Maintenance and Prognostic Health Management, integrated with reliability concepts, and to enable them to be applied in the BOP health management. The paper identifies different concepts needed to support the main theme and, through research and selection criteria, it brings together a set of publications to obtain consistent theoretical framework. This research outlines important techniques used in high reliability industries and the way they can be applied on the BOP system and it also provides many useful references and case studies to assist on further development works in terms of well control and operational safety