- In Situ Electrosynthesis of Peroxydicarbonate Anion in Ionic Liquid Media Using Carbon Dioxide/Superoxide System. [Journal Article]
- AAACS Appl Mater Interfaces 2019 Jul 15
- Climate engineering solutions with emphasis on CO2 removal remain a global open challenge to balancing atmospheric CO2 equilibrium levels. As a result, warnings of impending climate disasters are gro…
Climate engineering solutions with emphasis on CO2 removal remain a global open challenge to balancing atmospheric CO2 equilibrium levels. As a result, warnings of impending climate disasters are growing every day in urgency. Beyond ordinary CO2 removal through natural CO2 sinks such as oceans and forest vegetation, direct CO2 conversion into valuable intermediaries is necessary. Here, a direct electrosynthesis of the peroxydicarbonate anion (C2O62-) was investigated by the reaction of CO2 with the superoxide ion (O2·-), electrochemically generated from O2 reduction in bis(trifluoromethylsulfonyl)imide [TFSI-] anion derived ionic liquid (IL) media. This is the first time that the IL media were employed successfully for CO2 conversion into C2O62-. Moreover, the charge transfer coefficient for the O2·- generation process in the ILs was less than 0.5, indicating that the process was irreversible. Voltammetry experiments coupled with global electrophilicity index analysis revealed that, when CO2/O2 was contacted simultaneously in the IL medium, O2·- was generated in situ first at a potential of approximately -1.0 V. Also, CO2 was more susceptible to attack by O2·- before any possible interaction with the IL except for [PMIm+][TFSI-]. This was because CO2 has a higher global electrophilicity index (ωCO2 = 0.489 eV) than those for the [EDMPAmm+][TFSI-] and [MOEMMor+][TFSI-]. By further COSMO-RS modeling, CO2 absorption was proven feasible at the COSMO-surface of the [TFSI-] IL-anion where the charge densities were σ = -1.100 and 1.1097 e/nm2. Therefore, the susceptible competitiveness of either IL cations or CO2 to the nucleophilic effects of O2·- was a function of their positive character as estimated by their electrophilicity indices. As determined by experimental attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and DFT-FTIR computation, the reaction yielded C2O62- in the ILs. Consequently, the presence of O=O symmetric stretching FTIR vibrational mode at ∼844 cm-1 coupled with the disappearance of the oxidative cyclic voltammetry waves when sparging CO2 and O2 confirmed the presence of C2O62-. Moreover, based on DFT/B3LYP/6-31G, pure C2O62- has symmetric O=O stretching at ∼805 and ∼844 cm-1 when it is in association with the IL-cation. This was the first spectroscopic observation of C2O62- in ILs, and the O=O symmetric stretching vibration has peculiarity for identifying C2O62- in ILs. This will open new doors to utilize CO2 in industrial applications with the aid of reactive oxygen species.
- Improved synthesis of icosahedral carboranes containing exopolyhedral B-C and C-C bonds. [Journal Article]
- TTetrahedron 2019 Jan 11; 75(2):187-191
- Carboranes are boron-rich molecular clusters possessing electronic characteristics that allow for orthogonal approaches to vertex-selective modifications. We report improved functionalization methods…
Carboranes are boron-rich molecular clusters possessing electronic characteristics that allow for orthogonal approaches to vertex-selective modifications. We report improved functionalization methods utilizing orthogonal chemistry to achieve efficient substitution at electron-rich B-vertices and electron-poor C-vertices of carborane. Functionalization of B-vertices with alkyl and (hetero)aryl groups using the corresponding Grignard reagents has been improved through the use of a Pd-based precatalyst featuring an electron-rich biaryl phosphine ligand, resulting in reduced reaction times. Importantly, this method is tolerant towards alkyl-based Grignard reagents containing β-hydrogens. Furthermore, a transition metal-free approach to the substitution of carborane C-vertices with (hetero)aryl substrates has been developed under nucleophilic aromatic substitution (SNAr) conditions. The selective substitution of carboranes afforded by these methods holds potential for the rational synthesis of heterofunctionalized boron clusters with substituents on both boron and carbon-based vertices.
- Green chemical synthesis of new chelating fiber and its mechanism for recovery gold from aqueous solution. [Journal Article]
- JHJ Hazard Mater 2019 May 27; 378:120674
- A novel environmentally-friendly polyacrylonitrile-2-amino-2-thiazoline chelating fiber (PANF-ATL) with good adsorption performance and thermal stability was synthesized in one step by nucleophilic a…
A novel environmentally-friendly polyacrylonitrile-2-amino-2-thiazoline chelating fiber (PANF-ATL) with good adsorption performance and thermal stability was synthesized in one step by nucleophilic addition reaction using water as a solvent. The optimum synthesis conditions for the chelating fibers are determined by controlling the synthesis temperature and the molar ratio of the reagents. The sulfur content and functional group capacity of the finally synthesized PANF-ATL were 3.82% and 1.19 mmol/g, respectively. PANF-ATL was characterized by elemental analysis, FTIR, TGA, SEM and XPS. Meanwhile, the adsorption characteristics and mechanism of PANF-ATL were evaluated. The Langmuir model and the pseudo-second-order model well described the adsorption of Au(Ⅲ) by PANF-ATL. The adsorption capacity of PANF-ATL obtained from Langmuir isotherm model towards Au(Ⅲ) was 130.58 mg/g (298 K). In addition, Au(Ⅲ) adsorbed on the fibers was completely eluted using a mixed solution of 4 mol/L HCl and 12% thiourea. It still has good adsorption performance after 5 adsorption-desorption cycles. Overall, PANF-ATL is a cost-effective adsorbent that can effectively adsorb Au(Ⅲ) in aqueous solution.
- Template-directed Nonenzymatic Primer Extension Using 2-methylimidazole-activated Morpholino Derivatives of Guanosine and Cytidine. [Journal Article]
- JAJ Am Chem Soc 2019 Jul 12
- Efforts to develop self-replicating nucleic acids have led to insights into the origin of life, and have also suggested potential pathways to the design of artificial life forms based on non-natural …
Efforts to develop self-replicating nucleic acids have led to insights into the origin of life, and have also suggested potential pathways to the design of artificial life forms based on non-natural nucleic acids. The template-directed nonenzymatic polymerization of activated ribonucleotide monomers is generally slow because of the relatively weak nucleophilicity of the primer 3'-hydroxyl. To circumvent this problem, several nucleic acids based on amino-sugar nucleotides have been studied, and as expected the more nucleophilic amine generally results in faster primer extension. Extending this logic, we have chosen to study morpholino nucleic acid (MoNA), because the secondary amine of the morpholino nucleotides is expected to be highly nucleophilic. We describe the synthesis of 2-methylimidazole activated MoNA monomers from their corresponding ribonucleoside 5'-monophosphates, and the synthesis of an RNA primer with a terminal MoNA nucleotide. We show that the activated G and C MoNA monomers enable rapid and efficient extension of the morpholino-terminated primer on homopolymeric and mixed-sequenced RNA templates. Our results show that MoNA is a non-natural informational polymer that is worthy of further study as a candidate self-replicating material.
- Neuronal proteins as targets of 3-hydroxykynurenine: Implications in neurodegenerative diseases. [Journal Article]
- ACACS Chem Neurosci 2019 Jul 12
- The neurotoxic activity of the tryptophan metabolite 3-hydroxykynurenine (3OHKyn) in neurodegenerative disorders as Parkinson's and Alzheimer's diseases, is related to oxidative stress and 3OHKyn int…
The neurotoxic activity of the tryptophan metabolite 3-hydroxykynurenine (3OHKyn) in neurodegenerative disorders as Parkinson's and Alzheimer's diseases, is related to oxidative stress and 3OHKyn interaction with cellular proteins. The pattern of protein modification induced by 3OHKyn involves the nucleophilic side chains of Cys, His, and Lys residues, similarly to the one promoted by dopamine and other catecholamines. In the present work, we have analyzed the reactivity of 3OHKyn towards the neuronal targets α-synuclein (and its N-terminal fragments 1-6 and 1-15) and amyloid-β peptides (1-16 and 1-28), and characterized the resulting conjugates through spectrometric (LC-MS/MS) and spectroscopic (UV-Vis, fluorescence, NMR) techniques. The amino acid residues of α-synuclein and amyloid-β peptides involved in derivatizations by 3OHKyn and its autoxidation products (belonging to the xanthommatin family) are Lys and His, respectively. The pattern of protein modification is expanded in the conjugates obtained in the presence of the metal ions copper(II) or iron(III), reflecting a more oxidizing environment that in addition to adducts with protein/peptide residues also favors the fragmentation of the protein. These results open the perspective to using the 3OHKyn-protein/peptide synthetic conjugates to explore their competence to activate microglia cell cultures as well as to unravel their role in neuroinflammatory conditions.
- Regiospecific formation of sugar-derived ketonitrone towards unconventional C-branched pyrrolizidines and indolizidines. [Journal Article]
- OBOrg Biomol Chem 2019 Jul 12
- The synthesis of unprecedented branched pyrrolizidines and indolizidines was accomplished via nitrone chemistry. The required ketonitrone, a known intermediate usually obtained as a mixture of regioi…
The synthesis of unprecedented branched pyrrolizidines and indolizidines was accomplished via nitrone chemistry. The required ketonitrone, a known intermediate usually obtained as a mixture of regioisomers, was prepared in a pure form from d-arabinose by a sequence of oximation/reduction/oxidation steps. Nucleophilic vinylation or allylation followed by ring-closing metathesis of the corresponding N-allylpyrrolidines furnished the targeted iminosugars, which proved potent and selective inhibitors of alpha-glucosidase from rice (GH31 family).
- DFT calculation and NMR data of novel aryloxymaleimides and the intermediates and transition states in the reaction. [Journal Article]
- DBData Brief 2019; 25:104110
- Maleimide ring is an important scaffold in organic chemistry, and tosyloxy group is a functional group widely used in organic synthesis. Nevertheless, tosyloxymaleimide compounds have been rarely rep…
Maleimide ring is an important scaffold in organic chemistry, and tosyloxy group is a functional group widely used in organic synthesis. Nevertheless, tosyloxymaleimide compounds have been rarely reported, and the reactivity properties and potential applications of tosyloxymaleimide in organic synthesis remain to be explored. This article presents the density functional theory (DFT) calculation data of the reaction mechanism of nucleophilic substitutions of tosyloxymaleimide with phenol, including the coordinate of all the stationary points (the reactant, transition states, intermediates, and product). All the structures had been geometrically optimized using M06-2X functional and 6-31+G** basis set; the reactant, intermediates and product had no imaginary frequencies, and each transition state has only one imaginary frequency in the vibration analysis at the same computation level. The intrinsic reaction coordinates (IRCs) of two steps of the reaction were calculated. 1H and 13C NMR spectra of the novel aryloxymaleimide compounds synthesized using this nucleophilic substitution reaction (doi: 10.1016/j.molstruc.2019.04.020 Yan et al.,) were also presented in this article.
- Transition-Metal-Free Oxidative Cross-Coupling of Triorganoindium Reagents with Tetrahydroisoquinolines. [Journal Article]
- JOJ Org Chem 2019 Jul 11
- Triorganoindium reagents (R3In) react with tetrahydroisoquinolines (THIQs) in the presence of Ph3CBF4 as oxidant to afford 1-substituted THIQs. The reaction proceeds in good yields at rt using 50 mol…
Triorganoindium reagents (R3In) react with tetrahydroisoquinolines (THIQs) in the presence of Ph3CBF4 as oxidant to afford 1-substituted THIQs. The reaction proceeds in good yields at rt using 50 mol % of R3In with a variety of organic groups. 1H NMR studies show the generation of an iminium ion intermediate supporting a two-step mechanism based on THIQ oxidation and R3In nucleophilic addition. This reaction was applied to the synthesis of the alkaloid Nuciferine in three steps.
- Acylation Reactions of Dibenzo-7-phosphanorbornadiene: DFT Mechanistic Insights. [Journal Article]
- CChemistryOpen 2019; 8(6):807-810
- Extensive DFT calculations provide deep mechanistic insights into the acylation reactions of tert-butyl dibenzo-7-phosphanobornadiene with PhCOX (X=Cl, Br, I, OTf) in CH2Cl2 solution. Such reactions …
Extensive DFT calculations provide deep mechanistic insights into the acylation reactions of tert-butyl dibenzo-7-phosphanobornadiene with PhCOX (X=Cl, Br, I, OTf) in CH2Cl2 solution. Such reactions are initialized by the nucleophilic P⋅⋅⋅C attack to the carbonyl group to form the acylphosphonium intermediate A+ together with X- anion, followed either by nucleophilic X-⋅⋅⋅P attack (X=Cl, Br, and I) toward A+ to eliminate anthracene or by slow rearrangement or decomposition of A+ (X=OTf). In contrast to the first case (X=Cl) that is rate-limited by the initial P⋅⋅⋅C attack, other reactions are rate-limited by the second X-⋅⋅⋅P attack for X=Br and I and even thermodynamically prevented for X=OTf, leading to isolable phosphonium salts. The rearrangement of phosphonium A+ is initiated by a P-C bond cleavage, followed either by sequential proton-shifts to form anthracenyl acylphosphonium or by deprotonation with additional base Et3N to form neutral anthracenyl acylphosphine. Our DFT results strongly support the separated acylphosphonium A+ as the key reaction intermediate that may be useful for the transfer of acylphosphenium in general.
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- Dye-sensitized photocathodes for oxygen reduction: efficient H2O2 production and aprotic redox reactions. [Journal Article]
- CSChem Sci 2019 Jun 07; 10(21):5519-5527
- Dye-sensitized photoelectrochemical cells (DSPECs) can be used to store solar energy in the form of chemical bonds. Hydrogen peroxide (H2O2) is a versatile energy carrier and can be produced by reduc…
Dye-sensitized photoelectrochemical cells (DSPECs) can be used to store solar energy in the form of chemical bonds. Hydrogen peroxide (H2O2) is a versatile energy carrier and can be produced by reduction of O2 on a dye-sensitized photocathode, in which the design of dye molecules is crucial for the conversion efficiency and electrode stability. Herein, using a hydrophobic donor-double-acceptor dye (denoted as BH4) sensitized NiO photocathode, hydrogen peroxide (H2O2) can be produced efficiently by reducing O2 with current density up to 600 μA cm-2 under 1 sun conditions (Xe lamp as sunlight simulator, λ > 400 nm). The DSPECs maintain currents greater than 200 μA cm-2 at low overpotential (0.42 V vs. RHE) for 18 h with no decrease in the rate of H2O2 production in aqueous electrolyte. Moreover, the BH4 sensitized NiO photocathode was for the first time applied in an aprotic electrolyte for oxygen reduction. In the absence of a proton source, the one-electron reduction of O2 generates stable, nucleophilic superoxide radicals that can then be synthetically utilized in the attack of an available electrophile, such as benzoyl chloride. The corresponding photocurrent generated by this photoelectrosynthesis is up to 1.8 mA cm-2. Transient absorption spectroscopy also proves that there is an effective electron transfer from reduced BH4 to O2 with a rate constant of 1.8 × 106 s-1. This work exhibits superior photocurrent in both aqueous and non-aqueous systems and reveals the oxygen/superoxide redox mediator mechanism in the aprotic chemical synthesis.