1,021 research outputs found
Synthesis of Chiral Amines via a Bi-Enzymatic Cascade Using an Ene-Reductase and Amine Dehydrogenase
No full textAccess to chiral amines with more than one stereocentre remains challenging, although an increasing number of methods are emerging. Here we developed a proof-of-concept bi-enzymatic cascade, consisting of an ene reductase and amine dehydrogenase (AmDH), to afford chiral diastereomerically enriched amines in one pot. The asymmetric reduction of unsaturated ketones and aldehydes by ene reductases from the Old Yellow Enzyme family (OYE) was adapted to reaction conditions for the reductive amination by amine dehydrogenases. By studying the substrate profiles of both reported biocatalysts, thirteen unsaturated carbonyl substrates were assayed against the best duo OYE/AmDH. Low (5 %) to high (97 %) conversion rates were obtained with enantiomeric and diastereomeric excess of up to 99 %. We expect our established bi-enzymatic cascade to allow access to chiral amines with both high enantiomeric and diastereomeric excess from varying alkene substrates depending on the combination of enzymes.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.BT/Biocatalysi
Biocatalytic reduction of alkenes in micro-aqueous organic solvent catalysed by an immobilised ene reductase
No full textBiocatalytic asymmetric reduction of alkenes in organic solvent is attractive for enantiopurity and product isolation, yet remains under developed. Herein we demonstrate the robustness of an ene reductase immobilised on Celite for the reduction of activated alkenes in micro-aqueous organic solvent. Full conversion was obtained in methyl t-butyl ether, avoiding hydrolysis and racemisation of products. The immobilised ene reductase showed reusability and a scale-up demonstrated its applicability.BT/Biocatalysi
Thiol-ene polymer beads via liquid–liquid printing: armored interfaces and photopolymerization via graphitic carbon nitride
No full textPolymerization of multifunctional thiol-ene molecules is attractive as a proof of concept in photopolymerization, yet the formation of a bead structure is highly restricted. This manuscript will show graphitic carbon nitride based liquid–liquid printing and subsequent photopolymerization to form thiol-ene polymer beads with extreme simplicity and potential scalability.Aerospace Manufacturing Technologie
Rhodococcus strains as source for ene-reductase activity
No full textRhodococcus strains are ubiquitous in nature and known to metabolise a wide variety of compounds. At the same time, asymmetric reduction of C=C bonds is important in the production of high-valued chiral building blocks. In order to evaluate if Rhodococci can be used for this task, we have probed several Rhodococcus rhodochrous and R. erythropolis strains for ene-reductase activity. A series of substrates including activated ketones, an aldehyde, an imide and nitro-compound were screened using whole cells of seven Rhodococcus strains. This revealed that whole cells of all Rhodococcus strains showed apparent (S)-selectivity towards ketoisophorone, while most other organisms show (R)-selectivity for this compound. Three putative ene-reductases from R. rhodochrous ATCC 17895 were heterologously expressed in Escherichia coli. One protein was purified and its biocatalytic and biochemical properties were characterised, showing typical (enantioselective) properties for class 3 ene-reductases of the old yellow enzyme family.BT/Biocatalysi
Vapor Pressure of Hydrofluoroolefins: Critical Review of Experimental Data and Models
No full textThis paper critically reviews vapor pressure data and vapor pressure models for seventeen hydrofluoroolefins, including R1234yf and R1234ze(E), and presents Wagner-type vapor pressure correlations for the seventeen hydrofluoroolefins
Determination and potential importance of diterpene (kaur-16-ene) emitted from dominant coniferous trees in Japan
No full textReactive volatile organic compounds (VOCs) are known to affect atmospheric chemistry. Biogenic VOCs (BVOCs) have a significant impact on regional air quality due to their large emission rates and high reactivities. Diterpenes (most particularly, kaur-16-ene) were detected in all of the 205 enclosure air samples collected over multiple seasons at two different sites from Cryptomeria japonica and Chamaecyparis obtusa trees, the dominant coniferous trees in Japan,. The emission rate of kaur-16-ene, was determined to be from 0.01 to 7.1 μg dwg^[-1] h^[-1] (average: 0.61 μg dwg^[-1] h^[-1]) employing branch enclosure measurements using adsorbent sampling followed by solid phase-liquid extraction techniques. The emission rate was comparable to that of monoterpenes, which is known major BVOC emissions, collected from the same branches. In addition, total emission of kaur-16-ene at 30℃ was estimated to exceed that of total anthropogenic VOC emissions
Home and Mortgage Ownership of the Dutch Elderly: Explaining Cohort, Time and Age Effects
No full textThe relationship between home ownership of Dutch elderly households and age is strongly negative. Other studies suggest that this age gradient should be attributed to a cohort effect. In this paper we investigate where those cohort effects come from. We also observe that mortgage ownership among elderly home-owners increased considerably during the nineties. Using panel data we estimate models explaining home and mortgage ownership by age, cohort, and time effects, as well as other factors. Cohort and time effects are modelled explicitly using macro economic and housing market related variables. We find that the level of GDP per capita when the household head was young is the main factor explaining generation effects in home ownership among the elderly. After accounting for cohort effects it also appears that home ownership decreases slightly with age. Mortgage ownership among elderly home owners rose considerably during the nineties due to house price increases and due to financial innovation in the mortgage market. Cohort effects are also important. A supplementary analysis suggests that those cohort effects are due to the fact that the accidental bequest motive is becoming less important.home ownership, mortgages, cohort effects
Synthetic and mechanistic studies of ene reactions of carbonyl enophiles
No full textItem marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:56:05Z
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Reason: ETDs are only available to UIUC Users without author permissionETDs are only available to UIUC Users without author permissionU of I OnlyIn a synthetic study of a new carbonyl enophile, the ene reactions of dimethyl dioxosuccinate (81) with olefins were investigated and it was found the 81 reacts smoothly with most of the olefins investigated under thermal conditions to give the expected products in good yields. Sequential ene reactions to form cyclic products were also investigated and it was found that under catalysis with tin tetrachloride, the ene reaction product from methylenecyclohexane (8) and 81, dimethyl 2-oxo-3-hydroxyl-3-(1\sp\prime-cyclohexenylmethyl)succinate (89) undergoes another intramolecular ene reaction to give substituted cyclopentane products in moderate yield. The thermal ene reaction of 81 with vinyl heteroatom-substituted olefins, vinyl ethers, vinyl acetates, enamines, enols were also investigated.The mechanism of ene reactions of a selected group of carbonyl enophiles with 8 and 1-methylenetetralin (129) were studied by measurement of inter- and intramolecular hydrogen-deuterium isotope effects. In the thermal ene reactions of both 81 and diethyl oxomalonate (3) with 8, both inter- and intramolecular isotope effects are primary and substantial, consistent with concerted mechanisms. In the tin tetrachloride catalyzed reaction of 3 with 8, and in the reaction of acetylium hexachloroantimonate (CH\sb3CO\sp{+}SbCl\sb{6-}) with 8, the observed isotope effects are small in both inter- and intramolecular cases, which is inconsistent with either simple stepwise or concerted mechanism. To account for the observed anomalous isotope effects, a general quantitative kinetic model is proposed in which the starting materials form an intermediate which can partition between product formation, dissociation back to starting materials, and equilibration. The model predicts that depending on the extent of reversal in the formation of the intermediate and extent of equilibration of the intermediate between its different isomers, a range of inter- and intramolecular isotope effects can be observed even when the real isotope effect in the hydrogen transfer step is primary and substantial. Application and test of this model in the ene reaction of acetic anhydride with 129 catalyzed by zinc chloride was demonstrated.Made available in DSpace on 2011-05-07T13:32:39Z (GMT). No. of bitstreams: 2
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Previous issue date: 199
Changes in Ureteral Stone Treatment During COVID-19: A Single-Center Emergency Department Study
No full textAdrian Militaru,1,2 Catalin Andrei Bulai,1,2 Cosmin Victor Ene,1,2 Razvan Ionut Popescu,1,3 Cristian Mares,1,2 Stefan Marian Balacescu,1,2 Razvan Dragos Multescu,1,2 Dragos Adrian Georgescu,1,2 Petrisor Aurelian Geavlete,1,2 Bogdan Florin Geavlete1,2 1Department of Urology, “Carol Davila” University of Medicine and Pharmacy, Bucharest, Romania; 2Department of Urology, “Saint John” Clinical Emergency Hospital, Bucharest, Romania; 3Department of Urology, “Prof. Dr. Th. Burghele” Clinical Hospital, Bucharest, RomaniaCorrespondence: Catalin Andrei Bulai, Department of Urology, “Saint John” Clinical Emergency Hospital, 13 Vitan-Barzesti str, Bucharest, 042122, Romania, Tel +40749184205, Email [email protected]: We evaluated the hospitalization rate, length of stay, and management of patients with ureteric lithiasis admitted under emergency conditions at a single institution during the COVID-19 pandemic.Patients and Methods: A retrospective study was conducted on 219 patients with ureteral lithiasis, divided into pre-COVID-19 (1.10.2019– 29.02.2020) and COVID-19 groups (1.10.2020– 29.02.2021). The study examined patient and stone characteristics, hospitalization duration, surgical interventions, creatinine levels, and associated urinary tract infections. It also evaluated the complications related to delayed treatment during the pandemic.Results: The study found a 73.41% reduction in admissions for obstructive ureteral lithiasis during the COVID-19 pandemic compared to the pre-pandemic period. Notable differences were observed in age (61.5 vs 46 years, p=0.000), gender (p=0.046), stone laterality (p=0.024), location (p=0.002), serum creatinine levels (1.59 vs 1.09 mg/dL, p=0.000), and urine cultures (45.65% vs 23.12%, p=0.002). During the pandemic period, the rate of primary stone extraction procedures decreased (32.6% vs 59%, p< 0.001), while operative time (52.89 vs 39.84 minutes, p< 0.001) and hospital stay significantly increased (13.09 vs 3.76 days, p< 0.001).Conclusion: The pandemic resulted in fewer hospitalizations for ureteral lithiasis and an increase in complications, likely due to reduced access to medical care and a greater tendency for upper urinary tract drainage.Keywords: COVID-19, urolithiasis, ureteroscopy, double J stent, ureteral stone, percutaneous nephrostom
Asymmetric Reduction of (R)-Carvone through a Thermostable and Organic-Solvent-Tolerant Ene-Reductase
No full textEne-reductases allow regio- and stereoselective reduction of activated C=C double bonds at the expense of nicotinamide adenine dinucleotide cofactors [NAD(P)H]. Biological NAD(P)H can be replaced by synthetic mimics to facilitate enzyme screening and process optimization. The ene-reductase FOYE-1, originating from an acidophilic iron oxidizer, has been described as a promising candidate and is now being explored for applied biocatalysis. Biological and synthetic nicotinamide cofactors were evaluated to fuel FOYE-1 to produce valuable compounds. A maximum activity of (319.7±3.2) U mg−1 with NADPH or of (206.7±3.4) U mg−1 with 1-benzyl-1,4-dihydronicotinamide (BNAH) for the reduction of N-methylmaleimide was observed at 30 °C. Notably, BNAH was found to be a promising reductant but exhibits poor solubility in water. Different organic solvents were therefore assayed: FOYE-1 showed excellent performance in most systems with up to 20 vol% solvent and at temperatures up to 40 °C. Purification and application strategies were evaluated on a small scale to optimize the process. Finally, a 200 mL biotransformation of 750 mg (R)-carvone afforded 495 mg of (2R,5R)-dihydrocarvone (>95 % ee), demonstrating the simplicity of handling and application of FOYE-1.BT/Biocatalysi
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