Comprehensive Mechanism for CO Electroreduction on Dual-Atom-Catalyst-Anchored N-Doped Graphene

Carbon neutrality has drawn increasing attention for realizing the carbon cyclization and reducing the greenhouse effect. Although the C1 products, such as CO, can be achieved with a high Faraday efficiency, the targeted production of C2 fuels as well as the mechanism have not been systematically investigated. In this work, we carry out a first-principles study to screen dual-atom catalysts (DACs) for producing C2 fuels through the electrocatalytic carbon monoxide reduction reaction (e-CORR). We find that methanol, ethanol and ethylene can be produced on both DAC−Co and DAC−Cu, while acetate can be achieved on DAC−Cu only. Importantly, methanol and ethylene are preferred on DAC−Co, while acetate and ethylene on DAC−Cu. Furthermore, we show that the explicit solvent can enhance the adsorption and influence the protonation steps, which subsequently affects the protonation and dimerization behavior as well as the performance and selectivity of e-CORR on DACs. We further demonstrate that the C−C coupling is easy to be formed and stabilized if the Integrated Crystal Orbital Hamilton Population (ICOHP) is low because of the low energy barrier. Our findings provide not only guidance on the design of novel catalysts for e-CORR, but an insightful understanding on the reduction mechanism.     

Nitroimidazole and glucosamine conjugated heteroscorpionate ligands and related copper(II) complexes. Syntheses, biological activity and XAS studies

New nitroimidazole and glucosamine conjugated heteroscorpionate ligands, namely 2,2-bis(3,5-dimethyl-1H-pyrazol-1-yl)-N-(2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethyl)acetamide (L(MN)) and 1,3,4,6-tetra-O-acetyl-2-{[bis(3,5-dimethyl-1H-pyrazol-1-yl)acetyl]amino}-2-deoxy-β-D-glucopyranose (L(DAC)), respectively, were synthesized by direct coupling of preformed side chain acid and amine components. The related copper(II) complexes {[(L(MN))(2)Cu]Cl(2)}, and {[(L(DAC))(2)Cu]Cl(2)} have been prepared from the reaction of CuCl(2)*2H(2)O with L(MN) or L(DAC) ligand in methanol solution. Single crystal structural characterization was undertaken for the L(MN) ligand. In the absence of a coordinated metal core, the overall arrangement of the ligand is determined by some loose intra- and inter-molecular nonbonding contacts. X-Ray Absorption Spectroscopy (XAS) has been used to probe the local structure of the two copper(II) complexes, {[(L(MN))(2)Cu]Cl(2)} and {[(L(DAC))(2)Cu]Cl(2)}. The EXAFS analysis has permitted the identification of the local environment of the copper site. Copper interacts with 2 units of ligand in both complexes, and it is found to be 6-fold coordinated. Its local structure is described by four Cu-N and two Cu-O interactions to form a pseudo-octahedron core, with a 0.14 ? lengthening of the Cu-O bond length in the case of L(DAC) complex with respect to the L(MN) one, likely due to the higher steric hindrance of the glucosamine moiety. The XANES analysis agrees with these results, also confirming the Cu(II) formal copper oxidation state for both complexes. The new copper(II) complexes {[(L(MN))(2)Cu]Cl(2)} and {[(L(DAC))(2)Cu]Cl(2)} as well as the corresponding uncoordinated ligands were evaluated for their cytotoxic activity towards a panel of several human tumour cell lines. The results reported here indicate that both copper(II) complexes show similar spectra of cytotoxicity and very low resistance factors (RF < 2) against C13* ovarian cancer cells which have acquired resistance to cisplatin.     

Probing shapes of bichromophoric metal-organic complexes using ion mobility mass spectrometry

Ion mobility mass spectrometry (IM-MS) was used to probe the structures of several metal complexes carrying pendant chromophores. The three complexes investigated were the copper(II) complex Cu(DAC)2+ (DAC = 1,8-bis(9-methylanthracyl)cyclam, cyclam = 1,4,8,11-tetraazacyclotetradecane), the N-nitrosylated ligand DAC-NO, and the Roussin's red salt ester (mu-S,mu-S')-protoporphyrin-IX-bis(2-thioethyl ester)tetranitrosyldiiron (PPIX-RSE). From the IM-MS data coupled with theoretical calculations, it was found that [Cu(II)(DAC - H)]+ exists as a single conformer, with one anthracenyl group above the cyclam and the other below, similar to the crystal structure of Cu(II)(DAC)2+. The metal-free N-nitrosylated ligand (DAC-NO + H)+ has two conformations: one family of structures has one anthracenyl group above the cyclam and one below, while the other has both anthracenyl groups on the same side of the cyclam. These observations are consistent with 1H NMR data for the neutral DAC-NO complex that indicate the presence of two geometric isomers in solution. The third species, PPIX-RSE, has a porphyrin chromophore covalently linked to an Fe2S2(NO)4 cluster for use as a precursor for the photochemical delivery of nitric oxide in single- and two-photon excitation processes. Ion mobility indicates the presence of two (PPIX-RSE + H)+ conformations, consistent with the previous interpretation of the bimodal fluorescence lifetime decay seen for PPIX-RSE. DFT structures, in good agreement with the IM-MS cross sections, indicate two "bent" conformations with the planes of the porphyrin and Fe2S2 rings at different angles with respect to each other.     

Pressure-induced buckling of spin ladder in SrCu2O3

Pressure-induced structural phase transition of spin ladder compound SrCu2O3 was investigated by synchrotron X-ray powder diffraction with a diamond anvil cell (DAC). The change was characterized by a buckling of the Cu2O3 plane in the rung direction of the ladder. The structure of the high-pressure phase was found to be essentially the same as that of CaCu2O3. Application of an external pressure of 3.4 GPa therefore affected the structure in the same manner that the chemical (internal) pressure does.     

固定化脲酶催化作用下双醛纤维素对尿素氮的吸附平衡和动力学

研究了在固定化脲酶催化作用下双醛纤维素对尿素氮的吸附平衡和动力学. 吸附过程符合Langmuir方程, 为单分子层化学吸附. 考察了双醛纤维素的氧化度、初始尿素氮浓度、双醛纤维素与固定化脲酶的质量比和温度等对双醛纤维素吸附尿素氮的影响, 结果表明上述因素对尿素氮的吸附均有较显著的影响. 实验数据能很好地拟合准二级吸附速率方程, 说明该吸附过程遵从二级动力学模型. 当氧化度为88%的双醛纤维素与固定化脲酶的质量比为10∶1, 尿素氮浓度为638.3 mg•L^－1时, 由Arrhenius方程求得表观吸附活化能为6.0 kJ•mol^－1, 该吸附过程为吸热反应.     

Dual-Atom Catalysts Derived from a Preorganized Covalent Organic Framework for Enhanced Electrochemical Oxygen Reduction

Dual-atom catalysts (DAC) are deemed as promising electrocatalysts due to the abundant active sites and adjustable electronic structure, but the fabrication of well-defined DAC is still full of challenges. Herein, bonded Fe dual-atom catalysts (Fe₂DAC) with Fe₂N₆C₈O₂ configuration were developed through one-step carbonization of a preorganized covalent organic framework with bimetallic Fe chelation sites (Fe₂COF). The transition from Fe₂COF to Fe₂DAC involved the dissociation of the nanoparticles and the capture of atoms by carbon defects. Benefitting from the optimized d-band center and enhanced adsorption of OOH* intermediates, Fe₂DAC exhibited outstanding oxygen reduction activity with a half-wave potential of 0.898 V vs. RHE. This work will guide more fabrication of dual-atom and even cluster catalysts from preorganized COF in the future.     

Amine nitrosation via NO reduction of the polyamine copper(II) complex Cu(DAC)2+

The reaction of the fluorescent macrocyclic ligand 1,8-bis(anthracen-9-ylmethyl)-1,4,8,11-tetraazacyclotetradecane with copper(II) salts leads to formation of the Cu(DAC)2+ cation (I), which is not luminescent. However, when aqueous methanol solutions of I are allowed to react with NO, fluorescence again develops, owing to the formation of the strongly luminescent N-nitrosated ligand DAC-NO (II), which is released from the copper center. This reaction is relatively slow in neutral media, and kinetics studies show it to be first order in the concentrations of NO and base. In these contexts, it is proposed that the amine nitrosation occurs via NO attack at a coordinated amine that has been deprotonated and that this step occurs with concomitant reduction of the Cu(II) to Cu(I). DFT computations at the BP/LACVP* level support these mechanistic arguments. It is further proposed that such nitrosation of electron-rich ligands coordinated to redox-active metal centers is a mechanistic pathway that may find greater generality in the biochemical formation of nitrosothiols and nitrosoamines.     

Photochemically-Driven CO2 Release Using a Metastable-State Photoacid for Energy Efficient Direct Air Capture

One of the grand challenges underlying current direct air capture (DAC) technologies relates to the intensive energy cost for sorbent regeneration and CO₂ release, making the massive scale (GtCO₂/year) deployment required to have a positive impact on climate change economically unfeasible. This challenge underscores the critical need to develop new DAC processes with substantially reduced regeneration energies. Here, we report a photochemically-driven approach for CO₂ release by exploiting the unique properties of an indazole metastable-state photoacid (mPAH). Our measurements on simulated and amino acid-based DAC systems revealed the potential of mPAH to be used for CO₂ release cycles by regulating pH changes and associated isomers driven by light. Upon irradiating with moderate intensity light, a ≈55 % and ≈68 % to ≈78 % conversion of total inorganic carbon to CO₂ was found for the simulated and amino acid-based DAC systems, respectively. Our results confirm the feasibility of on-demand CO₂ release under ambient conditions using light instead of heat, thereby providing an energy efficient pathway for the regeneration of DAC sorbents.     

The influence of dodecylamine hydrochloride on the dissolution kinetics of heat-treated hydroxyapatite samples

The influence of dodecylamine hydrochloride (DAC) on the dissolution rate behavior of hydroxyapatite (HAP) samples prepared by digestion at 100°C and heated to various temperatures was investigated. The dissolution rates of HAP samples heated to temperatures of 300, 500, 750, 900, 1000, and 1200°C were determined at various levels of DAC in an acetate buffer having a pH of 4.50 and an ionic strength of 0.10. DAC adsorption isotherms for these different HAP samples and the specific surface areas were also determined. The initial dissolution rates (IDR) for all preparations generally decreased with increasing DAC levels with an approximately inverse relationship between IDR and DAC adsorption. For HAP samples heated at 1000°C and higher, the dissolution rates at 3.0 mM DAC were completely inhibited, while for samples heated at 900°C or less, there was a significant residual IDR at 3.0 mM DAC. This residual rate was approximately 20% of the zero DAC rate for all samples treated between 300 and 900°C. These results are in agreement with the concept that HAP prepared by precipitation and digestion at 100°C has two or more kinds of sites for dissolution and that heat treatment at around 1000°C or greater causes the elimination of one or more of these sites.     

Effect of additives on electrokinetic properties of colloidal alumina suspension

Additive interactions and their effects on electrokinetic properties of colloidal alumina suspension are presented in this study. Dibasic ammonium citrate (DAC), natural egg albumin, and octanol-2 are chosen as additives. The surface charge behavior of a 5% (w/v) colloidal alumina suspension in the presence of these additives has been studied in detail. The optimum dosage of DAC to have a stable suspension is found to be 3 mg/g of alumina whereas it is 105 and 164 mg/g of alumina for albumin and octanol-2, respectively. Albumin was found to be a better dispersant than DAC and interacts more strongly than DAC with the surface of alumina, while octanol-2 shows physisorbing characteristics. Turbidity measurements indicate that albumin and DAC interact. When the DAC : albumin molar ratio exceeds 10, the turbidity of the solution is higher than the turbidity of pure albumin, indicating the formation of complexes.     

Hantzsch Ester as a Visible-Light Photoredox Catalyst for Transition-Metal-Free Coupling of Arylhalides and Arylsulfinates

Diethyl 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (HEH) has been utilized as a visible-light photoredox catalyst for the cross coupling of arylhalides and arylsulfinates without transition metal, sacrificial agent, and mediator. This method is compatible with various functional groups and provides diaryl sulfones in good to high yields. Mechanistic studies indicate that this reaction undergoes the stepwise light irradiation of HE⁻, single electron transfer (SET) in donor–acceptor complex (DAC) from *HE⁻ to arylhalide, trapping of aryl radical with sulfinate, and SET oxidation of sulfone radical anion by HE^. to sulfone by the DAC method.     

Synthesis and properties of novel photosensitive polyimides containing chalcone moiety in the main chain

Two chalcone-derivative isomers, 4,4′-diaminochalcone ( 4DAC ) and 3,3′-diaminochalcone ( 3DAC ), were synthesized and used as monomers together with tetracarboxylic dianhydrides to prepare novel photosensitive polyimides that contain a chalcone moiety in the main chain. The polyimides were characterized and their photochemical behavior was investigated as thin films and in solutions with the aid of ultraviolet and infrared spectroscopy. Compared with 4DAC -based polyimides, the 3DAC -based polyimides exhibited lower glass transition temperatures and higher photocrosslinking rates of the carbon–carbon double bond as well as higher photosensitivities obtained from the exposure characteristic curves, suggesting that an increase in the photoreactivity of the 3DAC -based polyimides might arise from the improved flexibility of their backbones. The polyimide from 3DAC and 6FDA (2,2-bis[3,4-dicarboxypheny]hexa-fluoropropane dianhydride) showed a photosensitivity of 33 mJ/cm² with a contrast of 1.5 upon light irradiation using a Xenon lamp. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 685–693, 1998     

Miscibilities of methanol and ethanol with dodecylammonium chloride in the adsorbed film and micelle

The surface tension of the aqueous solutions of methanol– dodecylammonium chloride (DAC) and ethanol–DAC mixtures has been measured as a function of the total molality of the mixture m^ and the mole fraction of DAC X^₂ in the mixture at 298.15?K under atmospheric pressure. The compositions of the adsorbed film at 50, 40, and 30?mN?m^-1, and that of the micelle at the critical micelle concentration (CMC) have been evaluated by applying the thermodynamic equations derived previously and shown in the form of phase diagrams of adsorption and micelle formation. It has been found that (i) methanol is hardly miscible in M28.8nthe adsorbed film and micelle, and (ii) ethanol molecules are very slightly incorporated into adsorbed film of DAC at high-surface tension and into the micelle, although hardly miscible in the adsorbed film at low-surface tension. By comparing the corresponding phase diagrams of ethanol-2- (octylsulfinyl)ethanol (OSE) mixture, furthermore, it has been shown that there exists a difference in the miscibility of ethanol between DAC and OSE.     

Nonideal mixing of alkylammonium chloride and decyldimethylphosphine oxide surfactants in adsorbed films and micelles

Miscibility and interaction of decyldimethylphosphine oxide (DePO) with ammonium chloride (AC), hexylammonium chloride (HAC), and dodecylammonium chloride (DAC) in adsorbed films and micelles were studied by surface tension measurements. Phase diagrams were drawn for the mixed adsorption, mixed micelle formation, and equilibrium between adsorbed films and micelles. Nonideal mixing of DAC and DePO was characterized by a negative excess Gibbs free energy and positive excess area of adsorption and negative excess Gibbs free energy of micelle formation. It is concluded that the interaction between DAC and DePO in adsorbed films and micelles is larger than those between the same surfactants alone due to two factors: ion-dipole interactions between the head groups of DAC and DePO and alkyl-chain/alkyl-chain interactions.     

二乙酰化甲壳素包囊吸附树脂的制备及其血液相容性研究

研究了大孔吸附树脂用二乙酰化甲壳素(DAC)包囊的方法,对包囊树脂的膜层进行了考查,得到有意义的结果。动物血液灌流试验表明,树脂经DAC包囊后,灌流过程中血小板和血细胞的损失显著减少,吸附能力没有明显变化。     

Studies on the interaction of diacetylcurcumin with calf thymus-DNA

Ongoing research on curcumin and its structural derivatives are a subject of growing interest because of their demonstrated biological properties. Diacetylcurcumin (DAC), a synthetic derivative of natural non-toxic curcumin has been shown to affect a host of activities ranging from wound healing to life threatening diseases like AIDS, cancer etc. The interaction of diacetylcurcumin (DAC) with calf thymus-DNA (ct-DNA) has been investigated by spectroscopic and viscometric techniques. The fluorescence intensity of DAC was quenched by ct-DNA. The mean binding constant obtained from the spectroscopic techniques was 3.97 ± 0.31 × 10⁵ M⁻¹. Circular dichroism studies did not reveal any unwinding of the DNA helix on interaction with DAC, implying no conformational changes. The binding mode was analyzed by competitive binding between ethidium bromide (EB) and DAC for ct-DNA and also by viscometric studies. DAC was found to be a minor groove binder with a preference for the A-T region compared to the G-C region. This was substantiated by displacement studies with Hoechst 33258, a known minor groove binder. Docking studies were found to corroborate the experimental results.     

Synthesis,crystal structure,and antimicrobial activity of silver(I) complexes derived from 3-nitrobenzoic acid and diamines

Russian Journal of Coordination Chemistry - Two new silver(I) complexes, [Ag2(NBA)2(DAC)] (I) and [Ag2(NBA)2(DAB)] (II), where NBA, DAC, and DAB are 3-nitrobenzoate, 1,2-diaminocyclohexane, and...     

Pencil Graphite Electrode Decorated with Xylenol Orange Flakes for Studying Possible Pharmacokinetic Interaction Between Vardenafil and Daclatasvir

The main aim of the current work is to investigate possible pharmacokinetic interactions between vardenafil hydrochloride (VAR), which is used for the treatment of erectile dysfunction and daclatasvir dihydrochloride (DAC), which is used for the treatment of chronic hepatitis C viral infection when they are concomitantly administered. Therefore, a sensitive and selective square‐wave voltammetric method was developed and validated for simultaneous determination of VAR and DAC using disposable pencil graphite electrode (PGE) modified with xylenol orange (X.O.) flakes as an electrochemical sensor. A full investigation of the experimental parameters for obtaining the highest electroanalytical signal with sufficient resolution between the oxidation peaks of two compounds was performed. It was found that VAR and DAC were resolved on X.O./PGE with different potentials at 1.4 V and 0.9 V, respectively using Britton‐Robinson buffer (pH 2.2) and 0.1 mol L^?1 KCl as a supporting electrolyte. In addition, with the aid of cyclic voltammetry, a mechanistic scheme for the oxidation behaviour of both VAR and DAC was suggested. The proposed square wave voltammetric method was successfully applied for trace quantification of VAR and DAC in male rabbits. The suggested approach shows detection and quantification limits in rabbit plasma samples of 0.06 and 0.17 μmol L^?1, respectively for VAR and 0.13 and 0.39 μmol L^?1, respectively for DAC. The pharmacokinetic parameters of VAR alone and in combination with DAC after oral administration to rabbits were successfully estimated. The obtained results confirm that when DAC is co‐administered with VAR, plasma concentration of VAR increases, which necessitates dose adjustment for VAR to prevent toxicological consequences in patients.     

Size exclusion chromatography of polypeptides on Bio-Gel P2 in the dynamic axial compression mode

The effect of dynamic axial compression (DAC) upon the structure of a bed packed with semirigid Bio-Gel P2 and its chromatographic parameters was studied in the separation of peptides of various mass. In the studied range of DAC pressure, 0–5 bar, a decrease in the retention times of the studied substances and the standard deviation of their peaks is observed. In spite of a reduced packed bed height and an increase in the linear velocity of the eluent, the height equivalent to the theoretical plate (HETP) does not rise. The resolution of the separated substances increases throughout the studied range of DAC pressure with the Bio-Gel P2 exclusion limit extended. According to the results obtained, DAC provides more efficient optimisation of the bed parameters in columns packed with Bio-Gel P2 than in columns packed with Sephadex G-25 due to the greater rigidity of the former packing.     

Dialdehyde cellulose as a niche material for versatile applications: an overview

Cellulose - Dialdehyde cellulose (DAC) has garnered substantial scientific interest, thanks to broad spectrum of possible chemical reactions offered by the aldehyde moieties in its backbone. In the...