| 1. |
- Ren, Yansong, 1988-, et al.
(author)
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Multienzymatic cascade synthesis of an enantiopure (2R,5R)-1,3-oxathiolane anti-HIV agent precursor
- 2019
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In: Molecular Catalysis. - : Elsevier. - 2468-8274 .- 2468-8231. ; 468, s. 52-56
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Journal article (peer-reviewed)abstract
- An enantiopure (2R,5R)-1,3-oxathiolane was obtained using a multienzymatic cascade protocol. By employing a combination of surfactant-treated subtilisin Carlsberg and Candida antarctica lipase B, the absolute configuration of the resulting 1,3-oxathiolane ring was efficiently controlled, resulting in an excellent enantiomeric excess (> 99%). This enantiopure 1,3-oxathiolane derivative is a key precursor to anti-HIV agents, such as lamivudine, through subsequent N-glycosylation.
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| 2. |
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| 3. |
- Andonova, Stanislava, 1977, et al.
(author)
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Micro-calorimetric studies of NO2 adsorption on Pt/BaO-supported on gamma-Al2O3 NOx storage and reduction (NSR) catalysts-Impact of CO2
- 2017
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In: Molecular Catalysis. - : Elsevier BV. - 2468-8231. ; 436, s. 43-52
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Journal article (peer-reviewed)abstract
- The adsorption of NO2 on Pt/BaO/gamma Al2O3 catalyst has been investigated by micro calorimetry at atmospheric pressure, NOx storage tests and temperature-programmed desorption (TPD). The heat of adsorption of NO2 (Delta H-ads(NO2)) was determined over a wide range of NOx coverages, as the catalyst was exposed to 500/900 ppm NO2 in the absence/presence of 5% CO2 in the range of 423-773 K. The temperature dependent changes of Delta H-ads(NO2) verified the presence of energetically different NOx storage sites with different binding strength. The Delta H-ads(NO2) was found to follow a linear correlation versus temperature, ranging for example from -134.5 to -178.8 kJ/mol for NOx storage over Pt/BaO/gamma Al2O3 at 423-673 K. Thus, at high temperature mostly strongly bound nitrates were formed, while at lower temperature more loosely bound species were also present. Interestingly, the heat of adsorption was higher when using higher NO2 concentration, indicating more bulk barium nitrate formation. This is consistent with the TPD data where a clear high temperature peak was visible after adsorption using 900 ppm NO2 at 423 and 473 K, which was not the case for 500 ppm NO2. Moreover, the micro-calorimetric data also provided evidence in support of the detrimental effect of CO2 on the NOx uptake process. The heat released during the NOx storage in 500 ppm NO2 + 5% CO2 was determined to be significantly reduced ca. -97.8 kJ mol(-1) at 423 K, but ca. -134.5 kJ mol(-1) without CO2. Furthermore, our results show that it is critical to measure heat of adsorption for surface compounds since they are significantly different compared to thermodynamic data for bulk materials.
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| 4. |
- Chen, Shan, et al.
(author)
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The effect of phosphate group binding cup coordination on the stability of the amine transaminase from Chromobacterium violaceum
- 2018
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In: Molecular Catalysis. - : Elsevier. - 2468-8231. ; 446, s. 115-123
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Journal article (peer-reviewed)abstract
- The amine transaminase from Chromobacterium violaceum (Cv-ATA) is a pyridoxal-5’-phosphate (PLP)dependent enzyme. The biological activity of this enzyme requires the formation of a holo homo dimer.The operational stability of Cv-ATA is, however, low due to dimer dissociation. At the enzyme dimeric interface, two phosphate group binding cups (PGBC) are located. Each cup coordinates the phosphate group of PLP by hydrogen bonds originating from both subunits. Hypothetically, molecular coordination of phosphate groups (PLP or free inorganic phosphate) into the PGBC can affect both dimer stabilization and enzyme activity. To test this assumption, the influence of phosphate (as a functional group in PLP or as free inorganic anions) on the stability and activity of Cv-ATA was explored by various biophysical techniques. The results show that Cv-ATA has a relatively low affinity towards PLP, which results in an excess of apo dimeric enzyme after enzyme purification. Incubation of the apo dimer in buffer solution supplemented with PLP restored the active holo dimer. The addition of PLP or inorganic phosphate into the enzyme storage solutions protected Cv-ATA from both chemical and long term storage unfolding. The use of phosphate buffer leads to faster inactivation of the holo enzyme, compared to the use of HEPES buffer. These results open up for new perspectives on how to improve the stability of PLP-dependent enzymes.
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| 5. |
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| 6. |
- Verziu, Marian, et al.
(author)
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Hydrogenolysis of lignin over Ru-based catalysts : the role of the ruthenium in a lignin fragmentation process
- 2018
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In: Molecular Catalysis. - : Elsevier. - 2468-8231. ; 450, s. 65-76
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Journal article (peer-reviewed)abstract
- The catalytic performances of two different classes of catalysts containing nickel or/and ruthenium as the active sites were studied in the depolymerisation of lignin isolated from Miscanthus × giganteus. The catalysts were prepared either by coprecipitation (ie, (RuNiMgAlO)x, (RuNiAlO)x, (NiAlO)x, (NiMgAlO)x) or by wet impregnation (ie, Ru/Al2O3) and characterized by nitrogen physisorption (BET), XRD, XPS, NH3-TPD, Raman and H2-TPR techniques. The experimental results indicate that the presence of ruthenium led to dimers as dominant products.
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| 7. |
- Wang, Yuwen, et al.
(author)
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Fast room-temperature hydrogenation of nitroaromatics on Pd nanocrystal-boron cluster/graphene oxide nanosheets
- 2022
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In: Molecular Catalysis. - : Elsevier. - 2468-8231. ; 529
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Journal article (peer-reviewed)abstract
- The reduction of nitroaromatics to aminoaromatics is essential for fine chemical production and effective sewage treatment. However, the activity of an external catalyst is essential for the reaction. In this study, Pd nanocrystals were anchored in situ on two-dimensional graphene oxide (GO), which acted as a catalyst support with high specific surface area. The oxygen-containing groups on the surface of GO bonded to the functionally rich boron clusters through hydrogen bonding interactions. A mildly reducible closed-dodecahydrododecaboric acid anion cluster (closo‑[B12H12]2–) was employed as the target site. The mild reducibility of closo‑[B12H12]2– resulted in a wide dispersion of ultrafine Pd nanocrystals on GO. Under ambient conditions, Pd/BGO rapidly hydrogenated nitroaromatics, such as 4-nitrophenol, to aminoaromatics with approximately 100% efficiency. Moreover, Pd/BGO retained its high catalytic activity for the hydrogenation/reduction of 4-nitrophenol after five catalytic cycles. Therefore, Pd/BGO could be a promising and economically viable candidate for various practical applications. The proposed innovative preparation strategy and highly efficient catalytic activity suggested the effective performance of closo‑[B12H12]2– as nanometal nucleation target sites. In addition to providing an alternate route for preparing supported nanometals, this study presents a stable and efficient catalyst for the hydrogenation of nitroaromatics.
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| 8. |
- Xu, Zheyuan, et al.
(author)
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Mechanistic study on the photo carboxylation of benzylic C-H bonds by xanthone and Ni(0) catalysts
- 2021
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In: MOLECULAR CATALYSIS. - : Elsevier BV. - 2468-8231. ; 514
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Journal article (peer-reviewed)abstract
- The photo carboxylation of the benzylic C(sp3)-H bond catalyzed by xanthone/nickel were examined by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. This study corroborates the previous proposal that light promotes the H-transfer from benzylic C(sp3)-H bond of the p-methoxytoluene to excited state of photocatalyst xanthone. Meanwhile, Ni(0) catalyst could mediate the H-transfer to occur via an electroncoupled-proton transfer manner, and then remarkably facilitates the carboxylation step (compared to the Niabsent systems). After that, the generated Ni(I) intermediate and ketyl radical anion complete the carboxylation and electron transfer processes independently.
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| 9. |
- Yang, Jinqin, et al.
(author)
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Computational insight into the hydrogenation of CO2 and carbamic acids to methanol by a ruthenium(II)-based catalyst : The role of amino (NH) ligand group
- 2021
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In: Molecular catalysis. - : Elsevier BV. - 2468-8231. ; 506
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Journal article (peer-reviewed)abstract
- Methanol is a liquid hydrogen carrier and potential platform molecule, and significant efforts are currently devoted to hydrogenate CO2 to methanol. In this work, hydrogenations of CO2 and captured CO2 (as dimethyl-carbamic acid, DMCA, and methylcarbamic acid, MCA) to methanol over Ru-MACHO (pre)catalysts were studied with a Ru-II-catalyst model by Density Functional Theory (DFT) calculations. For the hydrogenation of CO2, the concerted reaction was the rate-determining step involving a synchronous hydride transfer and proton transfer from the Ru-II-catalyst to coordinatively saturated intermediate methanediol. In the hydrogenation cycles of DMCA and MCA, the first hydride transfer reactions were more difficult than the concerted hydride and proton transfer from the Ru-II-catalyst to the aldehyde group of intermediate formaldehyde. These first hydride transfer reactions were identified as the rate-determining steps. The hydrogenations of DMCA and MCA were found much more favourable in methanol production than the direct CO2 hydrogenation, however, formamides could be main intermediate products due to the easier C-O breakage than C-N breakage in gem diols, and during the further hydrogenation of formamides, formaldehyde could be the main intermediate due to the easier C-N breakage than C-O breakage in alkanolamines. In all three hydrogenation cases, the amino (NH) ligand of the Ru-II-catalyst initially remained chemically innocent, and intermediates were stabilized by N-H center dot O hydrogenbonding interactions (HBIs) facilitating the continuation of catalytic hydrogenation cycles, but the NH ligand took part in multi-bond concerted reactions to produce eventually methanol.
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