Recently, we demonstrated that Pt catalyst complexes dissolved in the ionic liquid (IL) [C4C1Im][PF6] can be deliberately enriched at the IL surface by introducing perfluorinated substituents, which act like buoys dragging the metal complex towards the surface. Herein, we extend our angle-resolved X-ray photoelectron spectroscopy (ARXPS) studies at complex concentrations between 30 and 5%mol down to 1%mol and present complementary surface tension pendant drop (PD) measurements under ultra clean vacuum conditions. This combination allows for connecting the microscopic information on the IL/gas interface from ARXPS with the macroscopic property surface tension. The surface enrichment of the Pt complexes is found to be most pronounced at 1%mol. It also displays a strong temperature dependence, which was not observed for 5%mol and above, where the surface is already saturated with the complex. The surface enrichment deduced from ARXPS is also reflected by the pronounced decrease in surface tension with increasing concentration of the catalyst. We furthermore observe by ARXPS and PD a much stronger surface affinity of the buoy-complex as compared to the free ligands in solution. Our results are highly interesting for an optimum design of ionic catalyst solutions contact areas with a surrounding reactant/product phase, such as in SILP catalysis.
Inclusion Complexes of a Metastable‐State Photoacid with High Acidity and Chemical Stability
Metastable-state photoacid MCH1 (see image) and cyclodextrins (CDs) can form inclusion complexes [MCH1 ⋅ (CD)2] [CD=2-hydroxypropyl-β-CD (HP-β-CD), γ-CD,β-CD and HP-γ-CD] with stronger ground and metastable-state acidity and slower thermal relaxation (SP1→trans-MCH1) rates than free MCH1. The inclusion complexes except [MCH1 ⋅ (HP-γ-CD)2] have better stability against hydrolysis than free MCH1. Appropriate host molecules can regulate the properties of metastable-state photoacids to meet various needs.
Abstract
Metastable-state merocyanine photoacids (MCHs) have been widely applied to various chemical, material and biomedical areas to drive or control chemical processes with light. In this work, stoichiometry and association constants have been determined for inclusion complexes of a photoacid MCH1 ((E)-3-(2-(2-hydroxystyryl)-3,3-dimethyl-3H-indol-1-ium-1-yl)propane-1-sulfonate) with β-cyclodextrin (β-CD), 2-hydroxypropyl-β-CD (HP-β-CD), γ-CD and HP-γ-CD by means of UV-Vis absorption spectroscopic titrations. The inclusion complexes were studied to enhance acidity and chemical stability. Kinetic study showed that CDs stabilized the acidic metastable state and slowed its thermal relaxation. The acidity of the ground and metastable state (pK a GS and pK a MS) increased upon addition of CDs. The pK a MS of [MCH1 ⋅ (γ-CD)2] is as low as 0.92 in comparison with 2.24 for MCH1, which is close to the lowest pK a MS values (1.20 and 1.03) reported previously, in which case the MCH1 was structurally modified with alkylammonium side chains. Addition of CDs also significantly enhanced the chemical stability of MCH1 against hydrolysis, which is one of the major concerns for the application of MCHs. In particular, the addition of HP-β-CD increased the half-life of MCH1 in aqueous solution more than four-fold. Moreover, the quantum chemical calculations confirmed the stoichiometry and analyzed the binding sites and hydrogen bonds of the inclusion complexes.
Chromatographic and Biological Screening of Chosen Species of Schisandraceae Family: Schisandra chinensis, S. rubriflora, S. sphenanthera, S. henryi and Kadsura japonica
Abstract
HPLC and TLC profiling was carried out for leaf and fruit extracts of five Schisandraceae species: Schisandra chinensis, S. rubriflora, S. spehenanthera, S. henryi and Kadsura japonica. HPLC measurements confirmed presence of lignans and phenolic compounds in fruits and leaves of all tested species. The most abundant in lignans was S. chinensis fruit extract in which 15 compounds were detected (e. g.: schisandrol A, schisanhenol, γ-schisandrin, gomisin N). The effect-directed detection, i. e., TLC-direct bioautography against Bacillus subtilis, showed exceptionally high activity for S. chinensis and S. rubriflora fruit extracts. On the other hand, TLC-DB enzyme tests (α-glucosidase, lipase, tyrosinase and acetylcholinesterase (AChE) inhibition assays) showed that all fruit and leaf extracts have ability to inhibit the above-mentioned enzymes (except for the K. japonica fruit). The leaf extracts showed much stronger antioxidant activity than the fruit ones, which were assessed and compared using both TLC-direct bioautography and spectrophotometric measurements based on ABTS, DPPH and FRAP tests.
Autocatalysis and CO2: carbon capture and utilization (CCU) meets natural processes
Autocatalytic reactions were proposed to play a key role at the beginning of life starting from the first reduction of CO2 to formate, acetate and C1-C4 hydrocarbons. In carbon capture and utilization (CCU) processes, the same reactions were demonstrated to be autocatalytic and, in some cases, promoted by catalysts of the same composition. Through evolution, CO2 reduction then turned into complex autocatalytic networks such as photosynthesis, where CCU chemists found inspiration for the development of more advanced systems for the synthesis of value-added chemicals. Less evolved systems than photosynthesis, however, may be easier to emulate and provide valuable inspiration into CO2 reduction chemistry for CCU. Other manmade systems were also demonstrated to be autocatalytic demonstrating that CO2 reactions and autocatalysis are closely connected. In this concept article, the relationship between natural, artificial and bio-inspired autocatalytic CO2 reduction processes is summarized and discussed. The accomplishments resulting from the integration of autocatalysis and CCU strategies, along with their inherent benefits and future prospectives are also outlined.
Fe Electron Center Local Regulation of CoFe‐Layered Double Hydroxides Nanosheets for Enhancing the Electrocatalytic Oxidation of Benzyl Alcohol
Replacing sluggish oxygen evolution reaction (OER) with electrocatalytic oxidation (ECO) of alcohols was a promising hotspot due to its advantages of requiring low potential, inhibiting mixing of gases, and forming value-added products. In the ECO of alcohols process, Fe electron centers of Fe-based layered double hydroxides (LDHs) can regulate the d band of LDHs overlap, optimize the active local structure of LDHs, and then enhance the electrocatalytic oxidation performance. In this work, CoxFey-LDHs nanosheets with different ratios of Co/Fe were prepared for selective ECO of benzyl alcohol (BA) to benzoic acid (BAC). Comprehensive characterizations revealed that the adjustment of bandgap and OH species adsorption of CoxFey-LDHs resulted in the appropriate thermodynamic driving force, which improved the electrical conductivity of CoxFey-LDHs and enhanced their ECO of BA. Especially, the as-prepared Co3Fe1-LDH showed intriguing electrocatalytic activity and only required a potential of 1.51 V (vs. RHE) to achieve a total current density of 50 mA cm−2 in alkaline solution containing 10 mM BA with a conversion (96.79%) of BA and selectivity (94.93%) of BAC, which was 60 mV lower than that of OER. After six cycles, Co3Fe1-LDH still achieved 94.74% conversion of BA and 92.10% selectivity of BAC without significant degradation.
[ASAP] Functional Alkali Metal-Based Ternary Chalcogenides: Design, Properties, and Opportunities
Chemistry of Materials
DOI: 10.1021/acs.chemmater.3c01652
Toward accurate modeling of structure and energetics of bulk hexagonal boron nitride
This work centers around the evaluation of various computational DFT-based methods in their ability to correctly predict equilibrium lattice constants while at the same time producing reliable interaction energies for h-BN as a prime example of both a covalent as well as weakly bound system. The state-of-the-art fixed-node diffusion quantum Monte Carlo method provided a reference estimate of the bulk h-BN exfoliation energy.
Abstract
Materials that exhibit both strong covalent and weak van der Waals interactions pose a considerable challenge to many computational methods, such as DFT. This makes assessing the accuracy of calculated properties, such as exfoliation energies in layered materials like hexagonal boron nitride (h-BN) problematic, when experimental data are not available. In this paper, we investigate the accuracy of equilibrium lattice constants and exfoliation energy calculation for various DFT-based computational approaches in bulk h-BN. We contrast these results with available experiments and reference fixed-node diffusion quantum Monte Carlo (QMC) results. From our reference QMC calculation, we obtained an exfoliation energy of −33±$$ -33\pm $$2 meV/atom (-0.38±$$ \pm $$0.02 J/m2$$ {}^2 $$).
Probe Beam Dichroism and Birefringence in Stimulated Raman Scattering in Polyatomic Molecules
The contributions of the dichroism and birefringence to the SRS signal depend strongly on the energy level structure of the molecular sample. They can be separated experimentally by using an appropriate probe beam polarization analyzer installed in front of the photodetector (D).
Abstract
Dichroism and birefringence in Stimulated Raman Scattering (SRS) in polyatomic molecules were studied theoretically. General expressions describing the change of the polarization matrix of the probe laser beam transmitted through initially isotropic molecular sample excited by the pump laser beam have been derived. Arbitrary polarization states and propagation directions of the incoming pump and probe beams were considered. The expressions were written in terms of spherical tensor operators that allowed for separation of the field polarization tensor and the molecular part containing three scalar values of nonlinear optical susceptibility with =0,1,2. The geometry of almost collinear propagation of the pump and probe beams through the molecular sample was considered in greater details. It was shown that the dichroism and birefringence refer to the nonlinear optical susceptibility element and that their contributions to the SRS signal can be separated experimentally by using an appropriate probe beam polarization analyzer installed in front of the photodetector. Particular cases of the off-resonant SRS and resonant SRS have been considered. The results obtained were expressed in terms of the Stokes polarization parameters of the pump and probe beams.
Palladium‐Catalyzed Regioselective C‐H Oxidative Arylation of 7‐Azaindazole N‐Oxide at the C6 Position
A new strategy is reported for the C-H/C-H functionalization of 7-azaindazoles at the C6 position via a regioselective oxidative arylation using N-oxide activation. This methodology allowed selective and original access to C6-arylated 7-azaindazoles with different substituted arenes and heteroarenes.
Photolysis of Phosphaketenyltetrylenes with a Carbazolyl Substituent
Carbazolyl-stabilised phosphaketenyltetrylenes were prepared and photolytically decarbonylated. The germylene and stannylene derivatives afforded diphosphene-type dimers, while the plumbylene displayed an unexpected isomerisation reaction and incomplete decarbonylation.
Abstract
Phosphaketenes of divalent group 14 compounds can potentially serve as precursors for the synthesis of heavy multiple-bond systems. We have employed the dtbpCbz substituent (dtbpCbz=1,8-bis(3,5-ditertbutylphenyl)-3,6-ditertbutylcarbazolyl) to prepare such phosphaketenyltetrylenes [(dtbpCbz)EPCO] (E=Ge, Sn, Pb). While the phosphaketenyltetrylenes are stable at ambient conditions, they can be readily decarbonylated photolytically. For the germylene and stannylene derivatives, dimeric diphosphene-type products [(dtbpCbz)EP]2 (E=Ge, Sn) were obtained. In contrast, photolysis of the phosphaketenylplumbylene, via isomerisation of the [(dtbpCbz)PbP] intermediate to [(dtbpCbz)PPb], afforded an unsymmetric and incompletely decarbonylated product [(dtbpCbz)2Pb2P2CO] formally comprising a [(dtbpCbz)PPb] and a [(dtbpCbz)PbPCO] moiety.