| 1. |
- Alsoghier, H. M., et al.
(författare)
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NMR spectroscopic investigation of benzothiazolylacetonitrile azo dyes : CR7 substitution effect and semiempirical study
- 2021
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Ingår i: RESULTS IN CHEMISTRY. - : Elsevier. - 2211-7156. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- Ebead et al. had reported in the synthesis and the UV-Visible solvatochromism combined with semiempirical calculations to study the tautomerism of 1,3-benzothiazol-2-ylacetonitrile azo dyes [1]. In this study, 1,3-ben zothiazol-2-ylacetonitrile azo dyes (1-6) have been resynthesized, one and two dimensional H-1 and C-13 NMR, as well as absorption and emission spectra, were collected and interpreted. The obtained results were used to clarify the tautomerization phenomenon of these dyes. Predominantly, these dyes exist in Z-hydrazone form reinforced through intramolecular hydrogen bonding in deuterated chloroform. Substituents (R) in carbon7 (CR7) are the key player of the changes in H-1 and C-13 NMR chemical shifts, also in the absorption and emission wavelengths of benzothiazole azo dyes. Also, the relative photoluminescence quantum yields (PL QY) of these dyes (1-6) were estimated and related to the nature of substituents. Finally, PM6 semiempirical calculations were employed to confirm the preferred geometric structure and experimental NMR, absorption, and emission results.
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| 2. |
- Jafari, Sonia, et al.
(författare)
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QM/MM study of the stereospecific proton exchange of glutathiohydroxyacetone by glyoxalase I
- 2019
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Ingår i: Results in Chemistry. - : Elsevier BV. - 2211-7156. ; 1
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Tidskriftsartikel (refereegranskat)abstract
- We have performed quantum mechanics (QM), molecular mechanics (MM) and hybrid QM/MM calculations to study the stereospecific proton exchange of glutathiohydroxyacetone (HOC-SG) by glyoxalase I (GlxI). We did the QM/MM calculations with a large QM system (246 atoms) to investigate the proton-exchange mechanism. Moreover, single-point big-QM energies with 1303 atoms in the big QM system and 22,412 atoms in the MM sys- tem were used to compare the energy difference of the stationary structures. GlxI catalyzes the exchange of the pro-S, but not the pro-R hydroxymethyl proton of HOC-SG with a deuterium from the D2O solvent. Classical mo- lecular dynamics simulations with different protonation states of Glu99, Glu172 and HOC-SG led to the determi- nation of most stable species (Glu-172 is protonated and the alcoholic oxygen of HOC-SG is deprotonated). The QM/MM results showed that before binding of HOC-SG, both active-site glutamates are charged, whereas HOC- SG is protonated. When HOC-SG binds, its alcoholic proton (HO) can point toward either Glu-99 or Glu-172. How- ever, if the substrate binds so that HO is directed toward Glu-99, it is not transferred, whereas if it is directed to- ward Glu-172, the latter abstracts HO. The results showed that transferring HO to the glutamates from the reactant states is the key step to make the proton exchange reaction possible. Our calculations show that order of basicity of the glutamates and HOC-SG inside the enzyme is: Glu-172 N HOC-SG N Glu-99. The calculations allow us to propose a reaction mechanism for the stereospecific proton exchange of HOC-SG by GlxI with an over- all barrier of 14.1 kcal/mol.
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| 3. |
- Kumar Raul, Prasanta, et al.
(författare)
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Microwave assisted and in-situ generated palladium nanoparticles catalysed desulfitative synthesis of cross-biphenyls from arylsulfonyl chlorides and phenylboronic acids
- 2021
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Ingår i: Results in Chemistry. - : Elsevier. - 2211-7156. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- A microwave assisted reaction protocol for Suzuki–Miyaura cross-coupling has been developed. Substituted arylboronic acids and arylsulfonyl chlorides coupled under microwave irradiation (MWI) to produce cross-biphenyls in high yields under aerobic condition. The principal advantage of this protocol is that formation of cross-biphenyls was achieved within shorter time along with desulfurization of arylsulfonyl chloride. In-situ generated Pd nanoparticles (NPs) act as catalyst in the reaction. Substituents like methyl, halogens, cyano, amino and t-butyl groups in arylboronic acids tolerate the reaction condition. Pd NPs could be reused several times under chosen reaction conditions without losing its activity significantly. The product formation and the role of the catalyst for the cross-coupling reaction has been rationalised with the help of a proposed mechanism. This reaction is one of the examples of In-situ generated Nanoparticles-catalyzed Organic Synthesis Enhancement (i-NOSE) approach. The approach derives its importance in terms of catalyst’s (i) simple preparation method, (ii) stability under the chosen reaction condition, (iii) substrate specificity, (iv) simple filtration to recover the catalyst and (v) easy regeneracy which clearly indicate that the approach could be applicable for various types of catalytic transformations.
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| 4. |
- Lukato, Simon, et al.
(författare)
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Selective oxidation of benzyl alcohols with molecular oxygen as the oxidant using Ag-Cu catalysts supported on polyoxometalates
- 2021
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Ingår i: Results in Chemistry. - : Elsevier BV. - 2211-7156. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- We report an efficient process for the oxidation of benzyl alcohols using molecular oxygen as the oxidant catalyzed by Ag-Cu catalysts supported on polyoxometalates (Ag-Cu/POM). The Ag-Cu/POM catalyst was prepared by galvanic displacement in the presence of polyvinyl pyrrolidone and polyethylene glycol. The catalysts were characterized using Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–Vis), powder X-ray diffraction (PXRD), X-ray fluorescence (XRF), Brunauer-Emmett-Teller (BET) surface analysis, transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and thermogravimetric analysis (TGA). The oxidation reaction was carried out using a Schlenk– line setup, under ambient atmospheric pressure. Reaction products were identified by GC–MS and quantified with GC using an internal standard method. The Ag-Cu/POM catalyst gave close to 100% benzyl alcohol conversion in 5 h with >99% selectivity to benzaldehyde. When tested on various benzyl alcohol derivatives the Ag-Cu catalysts showed good conversions and >99% selectivity to the corresponding aldehydes. The Ag-Cu catalysts supported on the POM are highly stable, and don't show tendency to leach or deactivate. The catalysts are heterogeneous in nature and easy to recover after reactions, and could be reused at least 5 times without significant loss in activity and selectivity.
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| 5. |
- Mbabazi, Ruth, et al.
(författare)
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Advances in carbon dioxide and propylene oxide copolymerization to form poly(propylene carbonate) over heterogeneous catalysts
- 2022
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Ingår i: Results in Chemistry. - : Elsevier BV. - 2211-7156. ; 4
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Forskningsöversikt (refereegranskat)abstract
- Chemical conversion of carbon dioxide (CO2) into value-added products is an attractive industrial process because it offers several economic and environmental advantages. This review presents advances and challenges in the CO2 and propylene oxide (PO) co-polymerization using heterogeneous catalysts to form poly (propylene carbonate) (PPC), an environmentally friendly polymer with several applications. In the co-polymerization process, CO2 is employed as a green carbon source, an alternative to the toxic phosgene which has numerous negative environmental impacts. However, this route of polycarbonate production, is hindered by the chemical inertness of CO2, and to overcome this, various catalysts have been developed. A number of heterogeneous catalysts including carboxylates, double metal cyanides and composites, have achieved varying success in activating CO2 in the production of polycarbonates. The effect of different reaction conditions including pressure, temperature and solvent has been explored. The limitations faced by various heterogeneous catalysts and improvements made over the past decades have been highlighted. Mechanistic insights for the production of PPC from CO2 and PO have been presented and the differences in both the regioselectivity and stereochemistry of the resultant polymers discussed.
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