Determination of Protonation Constants of O-Phospho-<Emphasis Type="SmallCaps">l</Emphasis>-serine in Aqueous Solution: Potentiometry,Microcalorimetry, NMR Spectroscopy and Quantum Chemical Calculations

O-Phospho-l-serine is one of the naturally occurring phosphorylated amino acids, having important pharmacological activity and bioactivity. The protonation constants of O-phospho-l-serine were determined by means of potentiometric titrations at 25 °C and ionic strength of 0.5 mol·L^?1 (NaCl). The heat effects of the protonation reaction of the O-phospho-l-serine were measured by direct calorimetry. NMR spectroscopy has demonstrated that the first protonation site occurs at the nitrogen atom in the amino group, followed by one of the oxygen atoms in the phosphono group, and finally the carboxyl oxygen atom. This trend is in good agreement with the enthalpy of protonation and quantum chemical calculations. These data will help to predict the speciation of O-phospho-l-serine in physiological systems.     

Vulgarisins B–D,three novel diterpenoids with a rare skeleton isolated from Prunella vulgaris Linn

Three new diterpenoids, vulgarisins B–D (1–3), have been isolated from a medicinal plant Prunella vulgaris Linn. These diterpenoids contain a rare 5/6/4/5 fused tetracyclic ring skeleton. Their structures were determined through the analysis of spectroscopic data, and the absolute configuration were further confirmed by single crystal X-ray diffraction as well as CD analysis. All the compounds were evaluated for their cytotoxicity activity, vulgarisins B (1) and C (2) demonstrated modest cytotoxicity activity against human lung carcinoma A549 cell line.     

Synthesis and characterization of tetraoctyloxy substituted naphthalenophanedienes

Tetraoctyloxy-substituted naphthalenophanedienes were synthesized from tetraoctyloxy-substituted dithia[3.3]naphthalenophanes via sequential benzyne Stevens rearrangement, oxidation, and pyrolysis reactions. Surprisingly, only the pseudo-geminal isomer of tetraoctyloxy-substituted dithia[3.3]naphthalenophane was obtained after cyclization of the corresponding starting materials. The structures of the pseudo-geminal isomers of tetraoctyloxy-substituted dithia[3.3]naphthalenophane and tetraoctyloxy-substituted naphthalenophanediene were fully determined by nuclear magnetic resonance spectroscopy, high resolution mass spectrometry, and X-ray crystallography. The pseudo-geminal and pseudo-meta diastereomers of tetraoctyloxy-substituted naphthalenophanedienes were isolated by multiple fractional recrystallization from hexane at 5 °C. The solid state structure of the pseudo-geminal isomer of tetraoctyloxy-substituted naphthalenophanediene revealed strongly distorted naphthyl rings with high levels of ring strain.     

Use of a hydrophobic associative four-armed star anionic polymer to create a saline aqueous solution of CO2-switchability

A four-armed anionic star-shaped block polymer, containing an anionic polymer poly(2-Acrylamido-2-methylpropanesulfonic acid) (PAMPS) as the core group and poly(2-(Dimethylamino)ethyl methacrylate) (PDM) as the terminal group, was synthesized by using the Atom Transfer Radical Polymerization (ATRP) method. The (PAMPS₅₀-PDM₅₀)₄ aqueous solution exhibited both polyelectrolyte and hydrophobic associative characteristics, that is, a low concentration of NaCl results in decreasing viscosity but a high concentration of NaCl results in increasing viscosity. The four-armed anionic block polymer shows a CO₂-reversible property at high concentrations of brine. Viscosity, pH, and ζ potential demonstrate the switchability jointly; the values could be switched from relatively low to high cyclically. These transitions could actually be attributed to the protonation of tertiary amine groups in PDM blocks, and the mechanism was proved by ¹H NMR.     

Multiplicative Jordan Decomposition in Integral Group Ring of Group K_8×C_5

In this article,we present the multiplicative Jordan decomposition in integral group ring of group K8 × C5,where K8 is the quaternion group of order 8.Thus,we give a positive answer to the question raised by Hales A W,Passi I B S and Wilson L E in the paper "The multiplicative Jordan decomposition in group rings II.     

A Comparison of NO Reduction Over Mn–Cu/ZSM5 and Mn–Cu/MWCNTs Catalysts Assisted by Plasma at Ambient Temperature

Manganese–copper bimetal oxide catalysts supported on ZSM5 and acid-treated multi-walled carbon nanotubes (MWCNTs) were produced by incipient wetness impregnation for selective catalytic reduction of NO with dielectric barrier discharge plasma. Plasma can activate molecules even at ambient temperature, generating active oxygen species such as O, O₃, and HO₂ radicals, which can oxidize NO to NO₂ effectively. The SCR activity of Mn–Cu/MWCNTs was studied and compared to that of the Mn–Cu/ZSM5. The obtained samples were characterized by XRD, SEM, TEM, ICP, H₂-TPR, Raman spectroscopy, and XPS. The results show that Mn–Cu/MWCNTs catalyst possesses NO removal activity superior to that of the Mn–Cu/ZSM5 catalyst. MWCNTs-based catalyst attains NO removal efficiency of 88% at 480 J/L, while the ZSM5-supported catalyst achieves NO removal efficiency of 82% at the same energy density. The oxygen content increased from 3.33 to 19.07% on the nanotube surface after introducing Mn and Cu, which almost remained unchanged on ZSM5. The oxygen-containing functionalities are important for NO_x adsorption and removal. Moreover, the characterization revealed that CuO is the main phase of copper oxide, but copper dispersion decreases on Mn–Cu/ZSM5 surface because of the formation of copper dimer species. The manganese is well-dispersed on the catalysts, MnO₂ and Mn₂O₃ contents of Mn–Cu/MWCNTs are larger than that of Mn–Cu/ZSM5, MnO₂ is the predominant phase of manganese oxide.     

Effect of ultraviolet absorption reagent for determination of piperidinium ionic liquid cations by ion pair chromatography with indirect ultraviolet detection

Indirect ultraviolet detection method is a simple and effective method for the determination of ionic liquid cations without ultraviolet absorption group. This paper focused on the influence of different background ultraviolet absorption reagents on the determination of piperidinium ionic liquid cations by ion pair chromatography with indirect ultraviolet detection. Ultraviolet absorption reagents are divided into cationic (4-aminophenol hydrochloride, 1-ethyl-3-methylimidazolium tetrafluoroborate, and N-ethylpyridinium tetrafluoroborate), anionic (potassium biphthalate and 5-sulfosalicylic acid), and amphiprotic (p-aminobenzoic acid). The results showed that piperidinium cations can be separated and detected by cationic and anionic ultraviolet absorption reagents. In general, the cationic ultraviolet absorption reagents have the best effect for separation and detection of the piperidinium cations by ion pair chromatography with indirect ultraviolet detection.     

Hexagram-like CoS-MoS<Subscript>2</Subscript> composites with enhanced activity for hydrogen evolution reaction

Hexagram-like CoS-MoS₂ composites were prepared on indium tin oxide (ITO) conductive glasses via cyclic voltammetry electrodeposition using Co(NO₃)₂ and (NH₄)₂MoS₂ as precursors and tested for application in hydrogen evolution reaction (HER). The structure of CoS-MoS₂ composites was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectrum (XPS). Electrochemical characterizations indicate that CoS-MoS₂ composites exhibit more excellent catalytic activity and stability than MoS₂. Compared with pure MoS₂, the hexagram-like CoS-MoS₂ composites with increased specific surface area improved the density of exposed active sites, and the Co binding S edges in CoS-MoS₂ composites promote the number of highly catalytic edge sites and decreased the binding energy △G _H. Moreover, the effects of different substrates on the CoS-MoS₂ composites were also investigated. Our further understanding of this highly active hydrogen evolution catalyst can facilitate the development of economical electrochemical hydrogen production systems.     

Template synthesis of imine-based covalent organic framework core-shell structure and hollow sphere: a case of COF<Subscript>TTA-DHTA</Subscript>

Controllably synthesizing well-dispersed covalent organic frameworks (COFs) with uniform both morphology and size is still a challenge. Herein, we report the template-directed synthesis of COF_TTA-DHTA-based core-shell hybrids under solvothermal conditions by using amino-functionalized SiO₂ microspheres as templates coupled with stepwise addition of initial monomer molecules. The modified amino groups on the surfaces of SiO₂ templates play an important role in the formation of well-defined NH₂-f-SiO₂@COF_TTA-DHTA core-shell hybrids. COF_TTA-DHTA hollow spheres can be obtained by etching SiO₂ cores of NH₂-f-SiO₂@COF_TTA-DHTA. Both the NH₂-f-SiO₂@COF_TTA-DHTA and COF_TTA-DHTA hollow spheres possess the well-defined morphology, high crystallinity and porosity, excellent dispersion property and high chemical stability. The template synthesis method demonstrated in this work provides a general method for the shape-controlled synthesis of COF-based materials, which is important for the further applications in the fields such as energy storage, drug delivery and catalysis.     

A facile chemical reduction method for synthesis of platinum–iron catalysts on carbon fiber papers for methanol oxidation

To enhance catalytic activity and durability for methanol oxidation reaction (MOR), we have fabricated bimetallic Pt–Fe catalysts on carbon fiber papers (denoted as Pt–Fe@CFP) by a facile chemical reduction method using iron as the precursor, ascorbic acid and sodium hypophosphite as the reductants, respectively. When ascorbic acid is using as the reductant, the Pt–Fe@CFP catalysts are composed of platinum and disordered Pt–Fe phases. The atomic ratio between Pt and Fe can be adjusted by altering deposition conditions. The Pt–Fe@CFP catalysts with Pt/Fe ratio of 1.1, which deposited with surfactant CTAB in bath at room temperature, exhibit excellent catalytic activity and stability in MOR. However, when sodium hypophosphite is employed as the reductant, the co-deposition of phosphorus would lead to a decreased catalytic performance in MOR.