Enzymatic transformation of platycosides and one‐step separation of platycodin D by high‐speed countercurrent chromatography

Platycosides, the saponins found in the roots of Platycodon grandiflorum (Platycodi Radix), are typically composed of oleanane triterpenes with two side chains. In platycosides, platycodin D, a glucose unit at C‐3, is a major component, which has several pharmacological activities. Because of the high demand for this compound, we attempted to enzymatically convert platycodin D₃ and platycoside E, having two and three glucose units at C‐3, respectively, into platycodin D. In this study, we tested the ability of several glycosidases to transform platycosides, or more specifically, the ability to transform platycoside E and platycodin D₃ into platycodin D. To obtain pure platycodin D on a preparative scale, high‐speed countercurrent chromatography with a solvent system of ethyl acetate/n‐butanol/water (1.2:1:2, v/v/v) was used for the separation of the enzymatically transformed product. Approximately 39.4 mg of platycodin D (99.8% purity) was obtained from 200 mg of the product in a one‐step separation. The results strongly support the advantage of enzymatic transformation of the platycosides for the efficient enrichment of platycodin D in the complicated extract of the medicinal plant.     

Determination of partition coefficient and analysis of nitrophenols by three‐phase liquid‐phase microextraction coupled with capillary electrophoresis

A three‐phase hollow fiber liquid‐phase microextraction method coupled with CE was developed and used for the determination of partition coefficients and analysis of selected nitrophenols in water samples. The selected nitrophenols were extracted from 14 mL of aqueous solution (donor solution) with the pH adjusted to pH 3 into an organic phase (1‐octanol) immobilized in the pores of the hollow fiber and finally backextracted into 40.0 μL of the acceptor phase (NaOH) at pH 12.0 located inside the lumen of the hollow fiber. The extractions were carried out under the following optimum conditions: donor solution, 0.05 M H₃PO₄, pH 3.0; organic solvent, 1‐octanol; acceptor solution, 40 μL of 0.1 M NaOH, pH 12.0; agitation rate, 1050 rpm; extraction time, 15 min. Under optimized conditions, the calibration curves for the analytes were linear in the range of 0.05–0.30 mg/L with r²>0.9900 and LODs were in the range of 0.01–0.04 mg/L with RSDs of 1.25–2.32%. Excellent enrichment factors of up to 398‐folds were obtained. It was found that the partition coefficient (K_a/d) values were high for 2‐nitrophenol, 3‐nitrophenol, 4‐nitrophenol, 2,4‐dinitrophenol and 2,6‐dinitrophenol and that the individual partition coefficients (K_org/d and K_a/org) promoted efficient simultaneous extraction from the donor through the organic phase and further into the acceptor phase. The developed method was successfully applied for the analysis of water samples.     

Two cationic metal-organic frameworks based on cadmium and α,ω-alkanedisulfonate anions and their photoluminescent properties

We have successfully synthesized three cadmium-based metal-organic frameworks by utilizing two separate organic linkers to direct the structure. The first material is a three-dimensional neutral framework based on 2D cadmium ethanedisulfonate layers pillared by a 4,4'-bipyridine linker. The other two materials are 3D cationic frameworks and are the first with propanedisulfonate and butanedisulfonate as extraframework charge balancing anions. Both structures occupy a high symmetry hexagonal crystal system where Cd-bipy chains are arranged into three crystallographically distinct layers that stack spirally along [001]. The framework is stabilized by alkanesulfonate anions that are electrostatically and hydrogen bonded to the framework. Each material was characterized by single-crystal and powder X-ray diffraction. The thermal and luminescent properties were also investigated by thermogravimetric analysis and photoluminescence spectroscopy, respectively. All three materials exhibit high thermal stability to above 300 °C and efficient blue emissive photoluminescence centered at 425 nm to 450 nm upon 350 nm excitation.     

Interaction proteomics of synapse protein complexes

The brain integrates complex types of information, and executes a wide range of physiological and behavioral processes. Trillions of tiny organelles, the synapses, are central to neuronal communication and information processing in the brain. Synaptic transmission involves an intricate network of synaptic proteins that forms the molecular machinery underlying transmitter release, activation, and modulation of transmitter receptors and signal transduction cascades. These processes are dynamically regulated and underlie neuroplasticity, crucial to learning and memory formation. In recent years, interaction proteomics has increasingly been used to elucidate the constituents of synaptic protein complexes. Unlike classic hypothesis-based assays, interaction proteomics detects both known and novel interactors without bias. In this trend article, we focus on the technical aspects of recent proteomics to identify synapse protein complexes, and the complementary methods used to verify the protein–protein interaction. Moreover, we discuss the experimental feasibility of performing global analysis of the synapse protein interactome.     

Ionic liquid-modified silica as a new stationary phase for chromatographic separation

A new stationary phase based on silica modified with 1-methyl-3-propylimidazolium chloride was synthesized and characterized in this paper. A derivative of 1-methyl-3-propylimidazolium chloride was used to chemically modify the surface of silica particles to act as the stationary phase for HPLC. The modified particles were characterized by Fourier Transform Infrared (FT-IR), ¹³C NMR spectroscopy and thermogravimetric analysis (TGA). The surface modification procedure rendered particles with a surface coverage of 0.89 μmol/m² of alkylimidazolium chloride. Columns packed with the modified silica and blank silica particles were tested under HPLC conditions. Preliminary evaluation of the stationary phase for HPLC was performed using aromatic compounds as model compounds. The separation mechanism appears to involve multiple interactions including ion exchange, hydrophobic and electrostatic interactions.     

An experimental and computational investigation on the fragmentation behavior of enaminones in electrospray ionization mass spectrometry

The dissociation pathways of protonated enaminones with different substituents were investigated by electrospray ionization tandem mass spectrometry (ESI‐MS/MS) in positive ion mode. In mass spectrometry of the enaminones, Ar? CO? CH?CH? N(CH₃)₂, the proton transfers from the thermodynamically favored site at the carbonyl oxygen to the dissociative protonation site at ipso‐position of the phenyl ring or the double bond carbon atom adjacent to the carbonyl leading to the loss of a benzene or elimination of C₄H₉N, respectively. And the hydrogen? deuterium (H/D) exchange between the added proton and the proton of the phenyl ring via a 1,4‐H shift followed by hydrogen ring‐walk was witnessed by the D‐labeling experiments. The elemental compositions of all the ions were confirmed by ultrahigh resolution Fourier transform ion cyclotron resonance tandem mass spectrometry (FTICR‐MS/MS). The enaminones studied here were para‐monosubstituted on the phenyl ring and the electron‐donating groups were in favor of losing the benzene, whereas the electron‐attracting groups strongly favored the competing proton transfer reaction leading to the loss of C₄H₉N to form a benzoyl cation, Ar‐CO⁺. The abundance ratios of the two competitive product ions were relatively well‐correlated with the σ_p⁺ substituent constants. The mechanisms of these reactions were further investigated by density functional theory (DFT) calculations. Copyright © 2010 John Wiley & Sons, Ltd.     

Effects of carbon coating on the temperature-dependent electrochemical properties of Li3V2(PO4)3

Carbon coated and carbon free Li₃V₂(PO₄)₃ cathode materials were prepared by carbothermal reduction and H₂ reduction methods, respectively. The carbon free material had a grain size about 1 μm whereas the carbon coated material was less than 100 nm. The surface carbon layer enhanced the electronic conductivity of Li₃V₂(PO₄)₃ by five orders of magnitude. In addition, the surface carbon layer also prevented the formation of SEI film, decreased the charge transfer resistance and increased the chemical diffusion coefficient of Li⁺ ions. All of these advantages improved the electrochemical performance of Li₃V₂(PO₄)₃. As most of intercalation materials, the low temperature performance of Li₃V₂(PO₄)₃ was poorer than that at room temperature. This was attributed to the electrochemical sluggish kinetics which caused higher charge transfer resistance and smaller chemical diffusion coefficient. The carbon coating technique was effective to eliminate these sluggish kinetics, and then improved the low temperature performance of Li₃V₂(PO₄)₃.     

Excited state structural dynamics and Herzberg–Teller coupling of tetraphenylporphine explored via resonance Raman spectroscopy and density functional theory calculation

Resonance Raman spectra of free-base tetraphenylporphine (TPP) were obtained with 397.9, 416, and 435.7 nm excitation wavelengths and density functional calculations were done to elucidate the electronic transitions and the resonance Raman spectra (RRs) of TPP. The RRs indicate that the Franck–Condon region photodynamics for S₀ → S₄ electronic state is predominantly along the C_m–ph stretch while that for S₀ → S₃ electronic state is predominantly along the porphin ring C_βC_β stretch. Non-totally symmetric vibrational modes were regularly presented in resonance Raman spectra: the shorter the excitation wavelengths were, the stronger intensity the modes had, which can be interpreted in terms of electric dipole transition moments caused by Franck–Condon and Herzberg–Teller coupling.Four non-total symmetry vibrational mode υ_52, υ₆₄, υ₉₇ and υ₁₃₀ in A₂ irreducible representative of TPP were observed in 397.9, 416 and 435.7 nm resonance Raman spectrum. With the shorter wavelength laser excitations at 416 or 397.9 nm, the A₂ vibrational modes show more enhanced Raman intensity by comparison with those in the TPP spectrum excited at 435.7 nm.     

Photoinduced charge transfer in porphyrin-C60 oligomer

Photoinduced electron transfer (ET) between C₆₀ and porphyrin (P) in a new polymer containing porphyrin, poly(p-phenylenevinylene), and pendant fullerene units has been investigated by nanosecond transient absorption and phosphorescence spectroscopy. Compared to the physically doping material systems, binding porphyrin/C₆₀ through chemical bonds in a polymer detains the formation of the triplet states of porphyrins and C₆₀. The formation of intermediate charge transfer state (CSS) of P⁺-C₆₀ ^? was observed, which led to the delayed formation of triplet states of porphyrins and C₆₀. The reduced opto-electronic properties, such as optical limiting performance, were also observed, which resulted from the delayed formation of triplet states. The results presented in this article are significant in understanding the complicated spectral characteristics of the triplet state and charge transfer of the porphyrin and C₆₀ complexes, and are therefore related to the controllable performance of the new materials in applications.     

羊抗人IgG在金纳米通道中的迁移

以聚碳酸酯超滤膜为基板,用化学镀的方法在超滤膜上沉积金,制得直径在45nm左右的金纳米通道阵列,利用制得的金纳米通道阵列搭建离子电流测量平台,可实现对羊抗人IgG分子的浓度检测.当羊抗人IgG分子通过直径45nm的金纳米通道时,由于物理占位及表面电荷的影响,会引起离子电流发生变化;在KCl浓度为0.15mol/L(pH7.48)溶液中,IgG分子的物理占位对离子电流有阻塞作用,会导致电流减小,IgG浓度在1.8～18ng/mL范围内,减小量与浓度成线性关系;实现了对IgG的定量检测.KCl浓度降低到0.025mol/L时,由于IgG分子扩散层内反离子对通道内离子浓度的贡献占主导地位,从而造成离子电流随着IgG浓度增大而增大.