Channel: Article http://journal15.magtechjournal.com/Jwk3_hxs_new/hxxb EN-US http://journal15.magtechjournal.com/Jwk3_hxs_new/hxxb/EN/0567-7351/current.shtml http://journal15.magtechjournal.com/Jwk3_hxs_new/hxxb 0567-7351 http://journal15.magtechjournal.com/Jwk3_hxs_new/hxxb/EN/10.6023/A19060233 Apigenin-7-O-β-D-glucuronide (1) and scutellarin (scutellarein-7-O-β-D-glucuronide, 2) are two major flavone glucuronide components occurring in breviscapines, which are prepared from the traditional Chinese herb Erigeron breviscapus. These two flavone glycosides show potent anti-oxidative, anti-inflammatory and neuroprotective activities in various evaluations. Synthesis of these natural glycosides in an efficiently manner would facilitate studies on their structure activity relationships. As a persistent effort on the chemical syntheses of the diverse glycoconjugates from traditional Chinese herbs in our group, we report herein the synthesis of these two representative flavone O-glucuronides. It is known that the solubility of flavone compounds is rather low and this property would greatly hinder their glycosylation reactions. In order to increase the solubility of the flavone derivatives in the glycosylation solvents, hexanoyl and benzyl groups were selected as the permanent protecting groups for the hydroxyl groups of apigenin (7) and scutellarein (8). The construction of the phenolic O-glucuronide is known to be a difficult task, especially the glycosylation of the poorly nucleophilic 7-hydroxyl group which locates at the para-position of the flavone carbonyl group. We achieved the glycosylation of the flavone 7-OH with 2,3,4-tri-O-benzoyl-6-O-TBDPS-glucopyranosyl ortho-alkynylbenzoate (9) under the catalysis of Ph₃PAuNTf₂ (0.2 equiv., 4 ? MS, CH₂Cl₂, r.t., 5 h) in excellent yields. After that, the 6-O-TBDPS groups were removed, and the requisite glucuronides were then elaborated by oxidation of the resulting 6-OH under the conditions of DAIB/TEMPO (CH₂Cl₂/H₂O, V∶V=2∶1, r.t.) in good yields. After global deprotection, the desired products apigenin-7-O-β-D-glucuronide (1) and scutellarin (2) were obtained in overall yields of 36% (5 steps) and 7% (9 steps), respectively, from the starting flavone aglycones. Following the same strategy, four naturally occurring flavone-7-O-glycosides, namely apigetrin (3), plantaginin (4), apigenin 7-O-β-D-xylopyranoside (5) and apigenin 7-O-α-L-rhamnopyranoside (6), were smoothly synthesized in 4~7 steps with the overall yields of 61%, 13%, 58% and 61%, respectively.

]]> http://journal15.magtechjournal.com/Jwk3_hxs_new/hxxb/EN/10.6023/A19050191 In recent years, food safety problems caused by illegal additions in infant foods have received widespread attention. Surface-enhanced Raman scattering (SERS) technique is used to rapidly and non-destructively detect the banned RhB that is usually added in food. In this study, we have prepared g-C₃N₄/Ag composites via a simple method successfully, their morphology and structure were characterized by transmission electron microscope (TEM), ultraviolet-visible (UV-Vis), X-ray diffraction (XRD), fluorescence spectrophotometer and confocal micro-Raman spectrometer (Raman). The g-C₃N₄ nanosheet possesses good adsorption performance due to its highly delocalized π-conjugated system, which acts as a carrier for Ag nanoparticles. Therefore, Ag nanoparticles are more uniformly and stably distributed on the surface of g-C₃N₄ nanosheets to form g-C₃N₄/Ag nanocomposite, which can be used for rapid adsorption and trace detection of RhB. In the experiment, the pH of the test and the absorbed time between the substrate and RhB were optimized. The influence of pH on the SPR of the substrate and the SERS intensity of the probe molecule were investigated in detail. As g-C₃N₄/Ag nanocomposite shows a significant higher absorption in the visible region around 500 nm than Ag nanoparticles, g-C₃N₄/Ag nanocomposite is more favorable for SPR absorption. A wide SPR absorption range is achieved due to the synergy between g-C₃N₄ and Ag nanoparticles, providing an improved SERS enhancement performance. Under the optimal experimental conditions by using RhB as probe molecule, an enhancement factor of 7.6×10 ⁵ is achieved. Due to the electrostatic interaction and π-π interaction between the substrate and the probe molecules, the substrate can enrich in a large amount of cationic dyes, offering a detection of RhB. The g-C₃N₄/Ag SERS substrate can be used to detect RhB with a linear relationship from 1.0×10 ^–9 to 1.0×10 ^–6 mol/L and a detection limit as low as 0.39 nmol/L. In addition, the g-C₃N₄/Ag nanocomposite SERS substrate can also detect trace amounts of RhB molecules in the commercially available rainbow lollipops with a high sensitivity, and the recovery were 93.6%~95.04%. In summary, the g-C₃N₄/Ag nanocomposite is not only a SERS substrate with high sensitivity, uniformity and stability, but also can be used as a rapid trace detection method of Rhodamine B in real food and environment.

]]> http://journal15.magtechjournal.com/Jwk3_hxs_new/hxxb/EN/10.6023/A19060219 The mesoporous SBA-15 molecular sieves doped in situ by W with channels parallel to the short axis (W-s-SBA-15) were synthesized by using decane as cosolvent and trimethylbenzene (TMB) as pore-expanding agent, which were used as the supports for the preparation of the Pt/W-s-SBA-15 catalysts. The effect of the loadings of Pt and W on the catalytic performance in glycerol hydrogenolysis to 1,3-propanediol (1,3-PDO) was investigated. The morphology, chemical states of Pt and W, and acidity of the catalysts were systematically characterized by using Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), CO pulsed adsorption, X-ray photoelectron spectroscopy (XPS), Raman, ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS), Fourier transform infrared spectroscopy (FT-IR) and FT-IR of adsorbed pyridine analysis (Py-IR). The BET and TEM results revealed that there are two kinds of pores in the structure: the mesoporous channels parallel to the short axis and honeycomb-like macropores. The Pt dispersion and active surface area calculated from CO chemical adsorption, firstly increased and then decreased with the increase in the Pt and W loadings. The highly dispersed tungsten species were assigned to the single-site WO₄ on the basis of the characterization results of Raman, UV-Vis DRS, and FT-IR. The XPS results indicated that the amount of the Pt-O-Si/W linkages and the Pt ^δ+/(Pt ⁰+Pt ^δ+) ratio are the highest on the 4Pt/W-s-SBA-15(1/480) catalyst which promote the dispersion of the Pt particles on the catalyst surface. With the increase in the loadings of Pt and W, the conversion of glycerol and the conversion of glycerol to liquid products (CTL) increased monotonically, while the selectivity to 1,3-PDO experienced a volcanic-type evolution. At the reaction temperature of 433 K, H₂ pressure of 4.0 MPa, and reaction time of 24 h, the highest yield of 1,3-PDO of 49.0% was resulted on the 4Pt/W-s-SBA-15(1/480) catalyst. It is identified that the conversion of glycerol on the Pt/W-s-SBA-15 catalysts is proportional to the active surface area of Pt on the catalyst, while the small Pt particle size and the strong synergy between Pt and the highly dispersed WO₄ species are advantageous to the formation of 1,3-PDO.

]]> http://journal15.magtechjournal.com/Jwk3_hxs_new/hxxb/EN/10.6023/A19050192 We demonstrate in this work that the performance of self-assembled monolayer (SAM) molecular devices can be modulated by the composition and supramolecular structure of the molecular layer using mixed self-assembled monolayer strategy. We prepared the mixed monolayer on gold surface (with ca. 1 nm roughness) by co-adsorption of 11-(ferrocenyl)- undecanethiol (FUT, rectifier) and 1-undecanethiol (C11-SH, diluent). Micrometer scale molecular junctions were formed by using indium gallium eutectic alloy (EGaIn) as the top electrode. Electrical characterization of the junction found that the ratio of FUT and C11-SH molecules can tune the rectifying performance of the monolayer device: the higher the proportion of ferrocene is, the better the rectifying performance is. To our surprise, mixed monolayer prepared by 20% C11-SH and 80% FUT mixed solution exhibited higher rectification ratio than pure FUT monolayer, due to reduced leaking current. Surface reflective IR spectroscopy and the monolayer thickness characterization by the ellipsometer revealed loosely packed molecules on the surface in the pure FUT monolayer due to the bulky head group of the FUT and the rough gold substrate. FUT that partially lied down on the surface, or buried in the layer therefore created defects, which in turn become the origin of the leakage current. Upon insertion of C11-SH molecules in between the ferrocene molecules, the molecules in the monolayer become more ordered with the support of the C11-SH, as evidenced by decreased wave number of the C—H stretching mode of methylene group by reflective IR spectroscopy. Meanwhile, an increase in thickness for 80% FUT monolayer relative to pure FUT monolayer implied a better orientation of the FUT molecule in mixed monolayer. The ordered structure and better orientation largely improved the stability and reproducibility of the molecular device, reduced the leaking current and afforded higher rectification ratio. Our approach therefore provides a facile and effective strategy for regulating the performance of monolayer devices by molecule aggregation state.

]]> http://journal15.magtechjournal.com/Jwk3_hxs_new/hxxb/EN/10.6023/A19060197 Pesticides and their metabolites often coexist in the real environment. The combined toxicity (synergism or antagonism) between pesticide and metabolites directly affects the environment risk assessment of pesticide. Dichlorvos (A) has three main metabolites, 2,2-dichloroethanol (B), 2,2-dichloroacetic acid (C) and dimethyl phosphate (D), in water and soil environment. Under different environmental conditions, metabolites with various concentration compositions form a variety of mixtures with dichlorvos. In this paper, five mixture rays with different mixture ratios were selected by optimal experimental design method. A typical aquatic (Vibrio qinghaiensis sp. -Q67) and a soil organisms (Caenorhabditis elegans) were selected as the tested organisms. The photoluminescence inhibitory toxicity (IT) of parent A and its metabolites B, C and D as well as their mixtures to Q67 and the lethal toxicity (LT) to C. elegans at different exposure time and concentration levels were determined by microplate toxicity analysis. The combination index with 95% observation-based confidence intervals was used to evaluate the change of combined toxicity of each mixture ray under different exposure times and the concentration levels. The results showed that the ITs of parent A and two metabolites C and D to Q67 do not change with the exposure time, but the IT of metabolite B at 12 h is significantly larger than that at 0.25 h. However, at two exposure times, the IT of parent A is greater than that of any of metabolites. The LTs of A and B, C and D to C. elegans do not change with the exposure time. The LTs of A, C and D to C. elegans are basically the same and significantly greater than that of B. The ITs of five mixture rays to Q67 at 12 h are significantly greater than those at 0.25 h at various concentration levels. The combined toxicities of the mixture rays to Q67 are concentration additive at low concentration levels and antagonistic at high concentration levels whether at 0.25 h or 12 h. For C. elegans, the LTs of five mixture rays at various concentration levels do not basically change with the exposure time. At two exposure times (12 h and 24 h), the combined toxicities of mixture rays are concentration additive except for the slight antagonism in the rays of R2 and R5.

]]> http://journal15.magtechjournal.com/Jwk3_hxs_new/hxxb/EN/10.6023/A19060226 In recent years, fluorescent bioimaging technology has great advantages in the fields of life science research and medical diagnosis because of its advantages of fast and effective, high sensitivity, easy realization of multi-channel imaging and economic efficiency. Organic fluorescent dyes have been widely used as biological imaging reagents due to their excellent photoelectric properties, functional modification, adjustable optical properties, and good biocompatibility. However, conventional organic fluorescent molecules cause aggregation-caused quenching (ACQ) due to π-π stacking in the aggregated state, limiting their bioimaging applications in aggregated or high concentrations. Since the discovery of the unique luminescence phenomenon of aggregation-induced emission (AIE), the ACQ phenomenon of traditional fluorescent materials has been eliminated. Stimulating responsive polymer nanoparticles have been widely used in the life sciences due to their combination of nanoparticle and polymer advantages and their ability to respond intelligently with environmental changes. Therefore, nanomaterials with excellent aggregation-induced emission (AIE) property, environmental stimuli responsiveness and biocompatibility based on AIE molecules and smart responsive polymers have shown attractive application prospects in the life sciences. A kind of multi-responsive AIE-active polymer nanospheres, which were composed of tetraphenylethylene (TPE) and stimuli-responsive poly[N]-2-(diethylamino)-ethyl]acrylamide (PDEAEAM), were constructed in this study. Firstly, a multi-stimulation responsive monomer N-[2-(diethylamino)ethyl]acrylamide (DEAEAM) and TPE derivative tetraphenylethene-4-(12-hydroxydodecyl-2-methylpropionyl) (TPE-BIB) with propionyl bromide were synthesized, respectively, and a multi-stimuli-responsive amphiphilic polymer of tetraphenylethene-graft-poly[N-[2-(diethylamino)ethyl]acrylamide] (TPE-g-PDEAEAM) was then successfully synthesized by atom transfer radical polymerization (ATRP) using TPE-BIB as initiator. Lastly, polymer nanospheres TPE-g-PDEAEAM of approximately 200 nm were formed by a self-assembling pro-cess. The results of the performed experiments showed that the LCST of TPE-g-PDEAEAM in aqueous solution is about 60 ℃. Meanwhile, the luminescence change of TPE-g-PDEAEAM at different temperatures from 20 to 66 ℃ was observed. The fluorescence intensity of TPE-g-PDEAEAM firstly decreased with increasing temperature from 20 to 58 ℃, and the fluorescence intensity increased with increasing temperature from 58 to 66 ℃. The phase transfer of PDEAEAM in TPE-g-PDEAEAM may be the reason of luminescence change which may lead to the fluorescent temperature response. Moreover, the fluorescence intensity of TPE-g-PDEAEAM nanospheres in aqueous solution increased with increasing temperature pH. Besides, the fluorescence intensity of TPE-g-PDEAEAM decreased dramatically when the volume of CO₂ increased from 0.0 to 1.2 mL. Therefore, TPE-g-PDEAEAM was a new temperature and pH/CO₂ responsive materials and might be used as multi-functional smart fluorescent sensors. More importantly, the fluorescent signals were significantly strong in HeLa cells after cells were incubated with TPE-g-PDEAEAM for 24 h based on the characteristic of AIE fluorescence and low cytotoxicity. The resultant nanospheres were able to be internalized by the cancer cells and effectively track the HeLa cells for as long as 11 passages. So, the polymer nanomaterial is an ideal living cell fluorescent tracer probe, which is expected to be applied as biosensors, long-term cell traces and medical biomaterials.

]]> http://journal15.magtechjournal.com/Jwk3_hxs_new/hxxb/EN/10.6023/A19060205 The surface potential of the liquid-vapor interface of water plays a critical role in electrochemistry, interfacial reactivity, and solvation thermodynamics. However, direct experimental measurement of the surface potential of pure water is exceedingly challenging. Here we present a methodology to explore the effect of external electric field on the water surface potential. The methodology contains constant electrostatic potential molecular dynamics simulation[J. Chem. Phys., 126, 084704(2007)], in which, the electrode charges are allowed to fluctuate to keep the potential fixed, as well as a recently developed probe and average method[J. Phys.: Cond. Matter, 28, 464006(2016)] to accurately map out the electrostatic potential across the water surfaces. The methodology is applied to the coexistence of the vapor phase and the liquid phase of the room temperature pure water (described by a simple SPC/E water model) under different magnitudes of E-fields generated from the nearby electrodes, yielding a first-time calculation of the external E-field dependent water surface potential profiles, and the relationship between the water surface potential and the external E-field strength which has been rarely reported. We found an asymmetric effect of external E-field on the surface potential, i.e., the surface potential decreases with increasing the external E-field strength for the water surface close to the cathode, while the surface potential increases with increasing field strength for the surface close to the anode. The water surfaces are also characterized by calculating the number density and dipole polarization density profiles, which depict the presence of the external E-fields induced bulk polarization under high strength field. By comparing the dipole polarization density profiles and the potential profiles, we conclude that the asymmetric effect of external E-field on the surface potential is due to the asymmetric behavior in surface polarization under external E-field for the water surfaces near cathode or anode, and is also due to the polarization within bulk part of the liquid water. The methodology presented in the current study can be easily applied to more advanced water models such as polarizable water models which are beyond the SPC/E used in current work. The achievement of the fundamental data and the physics relationship between the surface potential of water and the applied external E-field could potentially facilitate the advancements in electrodynamics and thermodynamics of the liquid-vapor interfaces.

]]> http://journal15.magtechjournal.com/Jwk3_hxs_new/hxxb/EN/10.6023/A19060203 The chemical transformation of ZVI micro-surface and the degradation mechanism in the process of synergistic removal of copper ions and methylene blue pollutants by ZVI-Fenton system were studied systematically. The samples of ZVI, before and after reaction in the ZVI/H₂O₂ and ZVI/H₂O₂-Cu systems, were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and Fourier Transform infrared spectroscopy (FTIR) to research the changes of ZVI surface structure, Fe and Cu species’ chemical conversion. The results showed that the residual corrosion products on the surface of ZVI were more and the corrosion products were mainly Fe₃O₄ and Fe₂O₃ after reaction in the ZVI/H₂O₂ system. However, in the ZVI/H₂O₂-Cu system, the corrosion effect of ZVI was more significant, but the residual corrosion products of ZVI surface were less, and the proportion of Fe₃O₄ increased. In addition, the main reduction product of Cu ²⁺ was Cu ⁰, which was accompanied by the generation of CuO. Furthermore, the effects of pH on the removal of pollutants from the five systems (ZVI, ZVI-Cu, H₂O₂-Cu, ZVI/H₂O₂ and ZVI/H₂O₂-Cu) were compared and the changes in TCu and TFe concentrations under different pH conditions were monitored. The results indicated that the ZVI/H₂O₂-Cu system not only simultaneous effectively remove MB and TCu compared with other three systems, but also enlarged the effective pH range (pH=2.5~5.5) of ZVI-Fenton system. In addition, free radical capture experiments showed that hydroxyl radicals played an important role in the oxidative degradation of methylene blue, and 10 mmol/L tert-butanol could completely capture hydroxyl radicals in the system. Finally, the mechanism of synergistic removal of TCu and MB degradation by ZVI-Fenton system was revealed. The substitution reaction between ZVI and Cu ²⁺, the action of Cu ⁰ and ZVI galvanic cells, the acid corrosion effect, and the redox cycle of iron and copper together accelerate the degradation of MB by the system and promote the conversion of ZVI surface substances. This study provides a theoretical basis for collaborative treatment of industrial complex pollutants.

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