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The recently re-discovered 5-hydroxymethylcytosine (5hmC) is established as the sixth base and found in various mammalian tissues. Although the content of 5hmC is much lower than that of the best known epigenetic mark 5-methylcytosine (5mC), 5hmC plays key roles in nuclear reprogramming, regulates the gene activity, and initiates the DNA demethylation in mammals. The formation of 5hmC results from the oxidation of 5mC in genomic DNA, which is mediated by Tet (ten eleven translocation) family dioxygenases. The Tet-mediated 5mC oxidation has just been identified. The 5hmC formation can cause DNA replication-dependent and passive DNA demethylation, meanwhile, it can also induce active DNA demethylation by further oxidation forming 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC), which can be removed by base excision repair. Essentially, the discovery of 5fC and 5caC indicates the occurrence of active DNA demethylation mechanisms. The 5fC and 5caC have been detected in genomic DNA of mouse embryonic stem cells, but 5hmC has been found in various tissues. The 5hmC abundance in genomic DNA of certain tumors is found to be associated with the tumor process. However, the genome-wide distribution and sequence selectivity of 5hmC are not known yet. 5hmC cannot be discriminated from 5mC by the well-known bisulfite sequencing. Therefore, it is essential to develop new methods and technologies for detecting and sequencing 5hmC. To this purpose, the two or more of the technologies for modification of 5hmC by glucosylation or chemical labeling, restriction enzymatic digestion, affinity capture, liquid chromatography and mass spectrometry, and bisulfite sequencing are combined. The further combination with next-generation high-throughput DNA sequencing technologies may provide genome-wide information. The single molecule real time DNA sequencing is also of choice to detect 5hmC at the gene level or the genome level. Recently, oxidative bisulfite sequencing was for the first time developed for quantitative mapping of 5hmC in genomic DNA at single base resolution. The genome-wide 5hmC sequencing at single base resolution is also reported. Here we briefly review and discuss the detection and sequencing technologies for 5hmC analysis.
The most popular hypothesis of precellular life is the “RNA World”, which is utilizing RNA as both genetic as well as catalytic material. The chemical similarity between RNA and DNA leads researchers to investigate whether DNA has the catalytic function, although DNA is commonly viewed as a genetic carrier with a ubiquitous double-stranded architecture in living world. Nevertheless, the catalytic DNA has not been discovered in nature to date. In recent years, the catalytic function of DNA in nonbiological applications has aroused much interest to chemists in chemical synthesis such as DNA-templated organic synthesis and DNA-based asymmetric catalysis. However, the investigation of DNA as a direct catalyst for organic synthesis is largely elusive. Here we report that double-stranded DNA from herring sperm can catalyze the dithioacetalization in water for a wide range of aldehydes under mild reaction conditions. It is proposed that the phosphate groups of DNA together with the duplex architecture are responsible for the catalytic reaction.
A simple synthesis of ferrocenyloxazoline derived chiral N,P ligands and N,S ligands immobilized on a MeO- PEG-support is described. The metal complexes of chiral ligands have been successfully applied to 1,3-dipolar cycloaddition reaction of azomethine ylides and asymmetric allylic substitution reaction, providing the products with up to 97% ee and 90% ee, respectively. The MeO-PEG-supported metal complex catalysts can be recycled easily and reused.
Titania/titanate nanomaterials including rutile, anatase, brookite TiO2 and sodium dititanate and trititanate were obtained by regulating the acid/alkali concentration under hydrothermal treatment. A systematical investigation was established to uncover the phase transition and morphological evolution behaviors of TiO2/titanate nanomaterials by calcining the samples including rutile TiO2 nanorods, anatase TiO2 nanocrystallines, brookite TiO2 nanoflowers, acid washed dititanate H2Ti2O5 nanosheets and trititanate H2Ti3O7 nanowires at 400, 600, 800 or 1000 ℃ for 4 h in air with the heating rate of 2 ℃/min. After heat-treatment, the products were taken out from the oven and cooled down to the room temperature. Rietveld refinements of the powder X-ray diffraction (XRD) pattern were used to generally assess the phase composition of the different samples and their crystallite sizes, and to further investigate the phase transition behavior in company with the synthetic parameters. FESEM, TEM, and HRTEM were used to characterize the morphology evolution and to further elucidate the morphological evolution of the resulting products. The crystalline phase distributed diagram of TiO2/titanate nanostructures dominated by the two experimental parameters indcluding acid/alkali concentration and calcination temperature was presented in the current work based on our experimental results, in which revealed the 5 types of phase transition and morphological evolution behaviors of titania/titanate nanomaterials. 1. Rutile nanorods → rutile nanorod aggregations → rutile micro particles. 2. Anatase nanocrystallines → anatase nanoparticle aggregations → rutile micro particles. 3. Brookite nano- flowers → brookite nanoflower clusters → rutile micro clusters. 4. Dititanate H2Ti2O5 nanosheets →anatase nanoparticle aggregations → rutile micro clusters. 5. Trititanate H2Ti3O7 nanowires → TiO2-B nanowires → anatase nanowire aggregations → rutile micro clusters. The crystal growth and phase transition mechanism was discussed based on the Ostwald’s step rule. Moreover, morphological evolution mechanism was also discussed based on the thermodynamic equilibrium regime and oriented attachment growth model.
In different research fields nucleus independent chemical shift (NICS) has been used frequently as a convenient tool for obtaining information about induced dia-paratropic and paratropic ring currents, especially for the purpose of assigning aromaticity and anti-aromaticity to molecules, obviously, aromaticities and magnetic properties of molecules can be measured by NICS. This paper presents the investigation on some important features of benzene and heterobenzenes C5H5X (X=CH, N, P, As, Sb, Bi) based on the analyzing maximum value of NICS above the cycle planar about 0.8~0.9 Å. Compared with density functional theory (DFT), the calculated results by ab initio (HF) are more accurate and acceptable for the NICS of heterobenzenes. There are two primary reasons to explain the phenomenon. First, the correlation coefficient of the proton chemical shifts of 1H NMR between calculated and experimental data by HF method is larger than adopted DFT methods. Second, because the ghost position plays a critical role in judging aromaticity, only involving HF method satisfy the results through comparing NICS(1) with the aromaticity of benzene, pyridine and other heterobenzenes in normal temperature and pressure. Furthermore, according to the calculation of natural localized molecular orbitals (NLMO), we can get a conclusion that the π bonds are main contributions to the zz tensor of NICS(max), and the order is benzene>pyridine>phosphabenzene>arsabenzene>stibabenzene>bimabenzene. σ bonds all show σ aromaticity. However, other bonds' anti-aromaticity is revealed. In order to be further studied for aromaticity and chemical shifts of 1H NMR about the heterobenzenes, the magnitudes induced are depicted by the outer magnetic field. For pyridine, the magnitudes of red area coincide with the proton chemical shifts (α-H>γ-H>β-H); others are in accord with the order (α-H>β-H>γ-H). Finally, the induced magnitudes by the outer magnetic field show the same global aromaticity characteristics as NICS(max)zz and π bonds contributing to NICS(max)zz. These results all represent that the order of global aromaticity is benzene>pyridine>phosphabenzene>arsabenzene>stibabenzene>bimabenzene. Especially, the π molecular orbital excluding the X atom presents a surprising high π aromaticity. It is very useful for us to design new materials in the magnetic theory.
Oxidative coupling as a highly efficient and economic strategy for carbon-carbon bond formation has been applied in the total syntheses of natural products. Recently, Ma’s group achieved the total syntheses of four complex indole alkaloids by developing a highly versatile LiHMDS/I2 oxidative coupling condition, which merits an important progress in this filed. In this highlight, recent progress of Ma’s group is reviewed.
Due to the steric hindrance effects in combination with stability of the tertiary benzylic α-methylstyryl radical, there is a dynamic equilibrium between the monomer α-methylstyrene (AMS) and its polymer (PAMS) when the temperature is greater than 61℃ (the ceiling polymerization temperature). Based on this unique feature, a novel strategy to prepare copolymers of AMS having liable bonds as potential macromolecular free radical initiators for synthesizing block and graft copolymers has been successfully developed in our laboratory. By conventional free radical polymerization, a series of AMS copolymers, including copolymers with (meth)acrylate, acrylic acid, styrene and maleic anhydride were synthesized. Typically, with the increasing of AMS fraction in monomer feed, the rate of copolymerization was significantly retarded and the molecular weight of the copolymers was reduced. However, the copolymer yield could be as high as 90% (w) with the increased addition of initiator, up to 4% (w), and the molar fraction of AMS structural unit in AMS copolymers could be up to 25% (mol%). It has been demonstrated that the copolymers containing AMS structural units are efficient free radical initiators when the temperature is greater than 80℃ (much better higher than 90℃). These copolymers could be exploited as macroinitiator in preparing block copolymers and core-shell polymer particles by bulk, solution and emulsion polymerization processes. In addition, the experimental results demonstrated that the molecular weight of copolymer products prepared with AMS copolymers as macromolecular initiators increased steadily with the monomer conversion. Though the polymerization initiated by AMS copolymers was not a well-controlled living system yet, it showed some characteristics of living polymerization. The ESR spectrum presented direct evidence of the generation of carbon centered radicals in the products of copolymer of AMS with glycidyl methacrylate (PAG) heated with N-t-butyl-α-phenylnitrone at 90℃ in toluene. Besides initiating the polymerization of vinyl monomer to prepare diblock copolymer, the AMS copolymers offered a practical pathway to synthesize grafting polymers in melting state. For example, with the addition of PAG in the PP/Nylon melten blending, it has been demonstrated a significant in situ compatibilization effect and the formation of graft polymer of PAG and PP. Furthermore, the AMS copolymers could also be used to modify MWCNT by free radical grafting onto mechanism. Instead of competing with the other existing controlled free radical polymerization technologies, the AMS copolymer method, with competitive cost and no small molecular residues, offers an alternative tool for polymer chemists to develop block copolymers on an industrial scale for some applications, such as dispersant and compatibilizer.
The main thrust of this contribution is to review applications of numerical simulations to biological systems over the past 35 years-specifically classical molecular-dynamics simulations and related preferential sampling approaches aimed at exploring selected degrees of freedom of the molecular assembly. Arguably enough, structural biology and biophysics represent one of the greatest challenges for molecular dynamics, owing to the size of the biological objects of interest and the time scales spanned by the molecular processes of the cell machinery in which these objects are prominent actors. The reader is assumed to be fully familiarized with the basic theoretical underpinnings of molecular-dynamics simulations, which will be discussed here from a biological standpoint, emphasizing how the enterprise of modeling increasingly larger molecular assemblies over physiologically relevant times has shaped the field. This review article will further show how the unbridled race to dilate both the spatial and the temporal scales, in an effort to bridge the gap between the latter, has greatly benefitted from groundbreaking advances on the hardware, computational front-notably through the development of massively parallel and dedicated architectures, as well as on the methodological, algorithmic front. The current trends in this research field, boosted by recent, cutting-edge achievements, wherein molecular dynamics has reached new frontiers, provide the basis for an introspective reflection and a prospective outlook into the future of biologically-oriented, high-performance numerical simulations. Furthermore, alternatives to brute-force molecular dynamics towards connecting time and size scales will be discussed, in particular a class of approaches relying upon the preferential sampling of judiciously chosen, important degrees of freedom of the biological object at hand. These methods, targeted primarily at providing a detailed thermodynamic picture of the molecular process at hand, can be viewed as computational tweezers designed to dissect the latter by means of a reduced set of collective variables.
Here we present the magnetic field dependence of the solid-state Photo-CIDNP effect observed in phototropin LOV1-C57S using 13C magic-angle spinning (MAS) NMR spectroscopy. Both dark and light spectra were measured at 4.7 T (i.e., 200 MHz 1H frequency) using a spinning frequency of 8 kHz. An Avance 200 MHz spectrometer equipped with 4-mm MAS probe (Bruker, Karlsruhe, Germany) was used for the 13C MAS NMR experiments. The sample was packed into a 4-mm sapphire rotor and inserted into the MAS probe. For a homogeneous sample distribution against the rotor wall, the sample was frozen at a very low spinning frequency of 500 Hz. Freezing was monitored on the proton tuning channel as a shift of ca. 0.1 MHz. The variable temperature unit on the spectrometer was set to 235 K. The spinning frequency was increased to 8 kHz after the sample is completely frozen. This frequency and set temperature were used for all 13C MAS NMR measurements. A simple Hahn-echo pulse sequence with two-pulse phase modulation proton-decoupling was used. Continuous illumination was supplied by a 1 kW xenon lamp. The cycle delay was 2 s, and the measurement time was about 12 h. In the spectrum obtained in the dark, standard broad protein responses appear. Under illumination, several strong additional light-induced signals appeared. In contrast to the entirely emissive (negative) peaks in the photo-CIDNP MAS NMR spectra observed at 2.3 T (i.e., 100 MHz 1H frequency), the first observation of this effect in a nonphotosynthetic system, the light induced 13C NMR peaks at 4.7 T show mixed absorptive/emissive enhancement pattern. This pattern is reminiscent of the spectra observed by liquid state photo-CIDNP of a LOV2 sample. The observed solid-state photo-CIDNP effect is strongly magnetic field dependent, and this field-dependence is well distinguished for the various nuclei. This large difference in magnetic field dependence reflects the large variety of hyperfine factors found in this comparable small-sized and asymmetric radical pair.
Two novel [Dy4(μ4-O)] based dysprosium(III) clusters, namely, [Dy8(bpt)8(μ4-O)2(μ-OMe)8(μ1,1,3,3-N3)(μ1,3-N3)- (N3)2]·11H2O·9MeOH (1) and [Dy10(bpt)6(μ4-O)4(μ3-OMe)4(μ-OMe)8(μ-OAc)2(OAc)2]·40H2O (2) (Hbpt=3,5-bis(pyridin- 2-yl)-1,2,4-trizole), are synthesized successfully. To obtain complex 1, a mixture of DyCl3 (0.1 mmol), 2,2'-Hbpt (0.1 mmol) and NaN3 (0.15 mmol) was sealed in a 25 mL vessel and then heated at 160℃ in methanol condition (8 mL) for 72 h. The reaction of Dy(OAc)3 (0.17 mmol) and 2,2'-Hbpt (0.1 mmol) under the same condition as complex 1 yielded complex 2. Single-crystal X-ray diffraction reveals that complex 1 consists of a pair of [Dy4(μ4-O)] tetrahedral units bridged by two azido groups in μ1,1,3,3 and μ1,3 modes as well as two bpt ligands, while complex 2 possesses four edge-sharing [Dy4(μ4-O)] tetrahedral units. Magnetic susceptibility of polycrystalline samples were carried out using a SQUID magnetometer in the temperature range 2~300 K at 500 Oe dc field. The χMT value are 107.8 cm3·K·mol-1 for complex 1 and 133.6 cm3·K·mol-1 for complex 2 at 300 K, which are close to the expected values. The maximum values of magnetization at 1.8 K are 40.81 Nb and 51.62 Nb for 1 and 2, slightly smaller than the expected saturation values. For further investigation of the dynamic behaviour, ac susceptibility measurements were undertaken under zero-dc field between 1~1500 Hz, they both show temperature dependence and have maximum values in the χM″ vs v plots above 1.8 K, indicating the presence of slow relaxation of the magnetization. After linear fitting the first four points of ln(τ/s) vs 1/T plot, we get energy barrier Ueff=9.83(9) K, pre-exponential factor τ0=1.63(2)×10-5 s for 1, and Ueff=12.05(2) K, τ0=6.75(8)×10-7 s for 2 respectively. The bridging mode of azido in complex 1 is novel and complex 2 holds the record for highest nuclearity among the reported pure lanthanide single-molecule magnets (SMMs) under zero dc field.
Polyoxometalates (POMs) are discrete metal-oxygen clusters with different shapes, sizes, and compositions, which provides a variety of structural building units (SBUs) for making novel and robust POM-based cluster-organic frameworks. Therefore, the combination of POM clusters and metal-organic frameworks will open up a new avenue for the creation of a variety of novel functional materials. Recent years, the hydrothermal technique proved to be a particularly powerful synthetic means of making crystals of numerous organic-inorganic hybrids. In this paper, three organic-inorganic hybrid open- frameworks constructed from different types of polyoxoanion cluster units and Cu-(2-ptz) (2-ptz=5-(2-pyridyl)-tetrazole) complexes, Cu4(2-ptz)4(H2O)7SiW12O40·4H2O (1), Cu5(2-ptz)6(OH)(H2O)3PW12O40·H2O (2), Cu9(μ-O)6(2-ptz)6(H2O)9-(H6P2W18O62)·3H2O (3) have been hydrothermally made and structurally characterized by elemental analyses, infrared spectrum (IR) spectroscopy, thermogravimetric (TG) analyses, ultraviolet-visable diffuse reflectance spectrum (UV-DSR), powder X-ray diffractions (PXRD), and single-crystal X-ray structural analyses, respectively. Structure analyses reveal that compounds 1~3 are three-dimensional (3-D) frameworks. The structure of 1 is built up of the isolated zigzag Cu-(2-ptz) complex segments and SiW12O404- clusters; 2 is constructed from the 2-D Cu-(2-ptz) networks and PW12O403- cluster pillars; while 3 is made of the linear Cu-(2-ptz) chains and PW18O626- clusters. Magnetic measurements indicated that compounds 1 and 2 exhibit antiferromagnetic interactions between Cu ions, while compound 3 display ferrimagnetic coupling behavior. UV-DSR spectra indicate that compounds 1~3 are potential semiconductor materials. The successfully syntheses of compounds 1~3 not only testify that the shapes and the number of negative charges of POM anions have an important influence on the self-assembly of organic-inorganic hybrid POM-based materials, but also may open up possibilities for the design and construction of new POM-based frameworks with particular functions in the near future.
The dissipative particle dynamics (DPD) simulation method was used to simulate the self-assembly behavior of three triblock copolymers, EO106PO70EO106, EO80PO30EO80 and EO13PO30EO13, at the oil/water interface. Gaussian chain is used to represent the three triblock copolymers. The effects of molecular weight, PO/EO ratio and oil/water volume ratio on the aggregation behavior of the copolymer were discussed in our simulation. The simulation results indicate that the triblock copolymer aggregate at the oil/water interface at lower concentration. The PEO groups of copolymer chains are immersed in the water phase while the PPO groups are located close to the oil phase. With the concentration of copolymer increasing, some copolymer chains begin stretch into the bulk. Copolymers can self-assemble into micelles in the water phase when the surface is saturated. The PEO groups are in the surface of micelles and some oil beads in the core, and this is in good agreement with the experimental results concerning their structures. In addition, molecular weight, and the ratio of PO/EO and oil/water have great effect on the interfacial properties (interfacial density, interfacial thickness and interfacial tension) and structural properties of the triblock copolymers. We found that the oil/water/copolymer system has lower interfacial tension and higher interfacial thickness when the copolymer has higher PO/EO ratio and larger molecular weight. If the value of PO/EO ratio is similar, the interfacial tension and interfacial thickness increases with molecular weight. Though the PO/EO ratio of F68 is lower than F127, the arrangement of F68 chains at the interface is more compact because of its lower molecular weight. With oil/water ratio increasing, O/W type emulsion is gradually transformed to a W/O type emulsion for the oil/water/copolymer systems. Furthermore, the effect of oil/water ratio on the self-assembly behavior of block copolymer is related to its molecular weight. Significant effect is observed for larger molecular weight of triblock copolymers (F127 and F68), but little effect on L64. Our simulation results show that DPD simulation is a valuable tool to supplement the experimental study on the micro-structural properties of Pluronic copolymers.
Photovoltaic conversion performances of dye-sensitized solar cells (DSCs) are significantly influenced by the interface charge recombination in DSCs. Lots of factors affecting the charge recombination, such as surface states of TiO2 and components of electrolytes, have been studied and dyes have been always ignored for the charge recombination in DSCs. Although the charge recombination occurring between the injection electrons and triiodide in electrolyte is calculated to take priority kinetically to the one between the injection electrons and oxidized dye molecules, dyes are not independent from the electrolyte related electron recombination. Instead by dye molecules themselves, the chance of injection electrons recaptured by triiodide in electrolyte could rise due to the increase of the adsorbed concentration of dye, which leads to the local concentration of triiodide increasing. In this paper, an effect of low charge recombination in DSCs with low adsorbed concentration of dye is observed. The adsorbed concentration of dye is defined as the adsorbed amount of dye in unit specific surface area of TiO2 films and adjusted by adsorbing similar amount of dye on the surface of TiO2 films with different film thickness. The influence of the adsorbed concentration of dye on the charge recombination in DSC is investigated by the electrochemical impedance spectroscopy (EIS) technology. It turns out that with the adsorbed concentration of dye decreasing, the electron lift time within TiO2 film and the interface resistance of TiO2/electrolyte increase significantly, which indicates the charge recombination in DSC decrease. Owing to this effect, with the TiO2 film thickness increasing from about 2 μm to 18 μm, the cells keep the fill factor (ff) as high as 0.72~0.80. And the energy conversion efficiency loss, which resulted from the increase of the active area of TiO2 photoanode from 0.25 cm2 to 1 cm2, decreased from 34.7% to 19.6%.
The molecular dynamics (MD) simulation is employed to investigate a certain enzymatic family of Sirtuin, which is related to the human silent information regulator 2. The interactive mechanism between Sirt1, Sirt2 (two members of the family of Sirtuin) and an active molecule (named INA in the present article) is studied in detail. The initial geometry of INA comes from the reference and is optimized at the B3LYP/6-311G** level. The homology modeling method is used to construct the conformation of Sirt1. Orderly, the NAD+ and INA are combined with the Sirt1 and Sirt2 (the initial Sirt2 conformation comes from the X-ray crystal diffraction) by using the molecular docking. In either system, the docking complex which has the lowest energy is set as the initial conformation in the next step. The MD simulations of 50 ns are carried out to optimize the two complexes of Sirt1(NAD+)-INA and Sirt2(NAD+)-INA, respectively. The MM-GBSA calculation is carried out to obtain the binding free energies between some key residues and INA. The decomposition values of binding free energies can indicate the binding sites of INA with the Sirt1(NAD+) and Sirt2(NAD+) complexes, respectively. It is located at Val72, Ser73 and Arg272 in the former and Phe235, Leu264 and Gly305 in the latter. The result of MD simulation can also indicate that the distance between INA and enzymatic substrate of NAD+ is longer in the Sirt2(NAD+)-INA than that in the Sirt1(NAD+)-INA complex, which leads to a weaker interaction between INA and NAD+in the former. Thus, the reactive activity of INA is weaker in Sirt2 than in Sirt1. The result is corresponding with that in experiment. And it is very significance to search some novel medicines which are mainly aimed at the histone acetylase of Sirt1 and Sirt2.
The Ba-doped ZrO2 materials were prepared by three methods and used as support for Ru catalysts for ammonia synthesis, i.e., citric acid sol-gel method (SG), modified co-precipitation (CP) and impregnation method (IP). The certain amount of analytical-grade Zr(NO3)4·5H2O and Ba(NO3)2 were dissolved in deionized water to form a transparent mixed nitrate solution. The citric acid was slowly added into the mixture to form a transparent solution and then heated to 80℃ under vigorous stirring until all the water evaporated and a viscous material was obtained. After calcination at 750℃ for 5 h and a puffy white powder was obtained. This was BZ-SG. The solution of NH3·H2O and K2C2O4·H2O was added dropwise to the mixture solution of Zr(NO3)4·5H2O and Ba(NO3)2 with vigorous stirring, and the obtained white suspension was aged at 60℃ for 60 min. The resulting precipitate was centrifuged and washed with distilled water for several times, and then calcined at 750℃ for 5 h. The obtained white solid was named as BZ-CP. The Zr(OH)4 was prepared by adding the KOH into the Zr(NO3)4·5H2O solution. Then the obtained Zr(OH)4 was baked at 300℃ for 3 h and impregnated with aqueous solution of Ba(NO3)2. After dried at 85℃ for 12 h, the sample was heated at 750℃ for 5 h and obtained the BZ-IP sample. Ruthenium catalysts were prepared by impregnating the supports directly with K2RuO4 solution. After reduction with ethyl alcohol, then was dried at 120℃ for 12 h. The samples with 4 wt% Ru were labeled as RBZ-X (X=SG, CP and IP). The molar ratio of Ba to Zr in all the samples is 1:9. The composites materials and catalysts were characterized by X-ray diffraction (XRD), temperature programmed reduction of H2 (H2-TPR), temperature programmed desorption of CO2 (CO2-TPD), N2 adsorption- desorption isotherms, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and CO chemisorption. The results displayed that the RBZ-SG catalyst showed the highest activity for ammonia synthesis compared to those of RBZ-CP and RBZ-IP. The optimum ammonia concentration over RBZ-SG catalyst is 5.72% under the conditions of 3 MPa, 10000 h-1 and 425℃. This activity is 3.8 and 14.3 times of that of RBZ-CP and RBZ-IP, respectively. Such high activity is mainly resulted from the presence of BaZrO3, which has high electron-donating ability. Mobile electrons would be transferred from BaZrO3 to the Ru metal surface by means of the strong metal-support interaction existed between Ru and reduction BaZrO3, which can facilitate the cleavage of N≡N and enhance the activity for ammonia synthesis sufficiently.
A well-aligned ZnFe2O4/TiO2 nanotube array electrode with visible-light activity was successfully prepared using a two-step electrochemical process of anodization and a novel cathodic electrodeposition method. Its morphology and chemical composition was characterized by environmental scanning electron microscope, transmission electron microscope and X-ray diffraction. The ZnFe2O4 nanoparticles were highly dispersed inside the TiO2 nanotube but minimized at the tube entrances. The composites displayed a strong photo response in the visible region and low recombination rate of the electron- hole pairs. The synthesized ZnFe2O4/TiO2 nanotube electrode showed much higher photocurrent density in the visible region than pure TiO2 nanotube electrode. In addition, we discussed the influence on the electrode properties of ZnFe2O4/TiO2 nanotube array from mass concentration sedimentary time, cycle times and sedimentary voltage. The optimal experimental condition was 0.05 mol/L Zn(NO3)3+0.1 mol/L Fe(NO3)3, 20 min 5 times and 1 V. The photocatalytic activity of the composite electrode was evaluated in the decomposition of phenol under visible light irradiation. It was found that the degradation rate increased with voltages and an increase in the activity by a factor of 1.5~2 relative to pure TiO2 nanotube was obtained under the optimal conditions. The improved photoelectrocatalytic activity is derived from the synergetic effect between ZnFe2O4 and TiO2, which promoted the migration efficiency of photogenerated carriers at the interface of the composite and enhanced the efficiency of photon harvesting. Under the visible region, the ZnFe2O4/TiO2 nanotube electrode was operated under the same experimental conditions. The results clearly show a good recycle with the degradation rate of 95% even after five repeated experiments. These results demonstrate that the ZnFe2O4/TiO2 nanotube electrode was an ef?cient material in utilizing solar energy for the photodecomposition of pollutants.
The objective of this study was to investigate the feasibility of applying surface-enhanced Raman spectroscopy (SERS) coupled with partial least squares regression (PLSR) to detect and determine prohibited or restricted residual fish drugs including malachite green, crystal violet, chloramphenicol and sulfamerazine. Standard solutions of malachite green (0.5~50 μg/L), crystal violet (5~100 μg/L), chloramphenicol (50~5.0×103 μg/L) and sulfamerazine (500~5.0×103 μg/L) were used to determine the sensibility of the SERS method as well as the accuracy of the PLSR models for quantitative analyses of the fish drugs. In addition, fish muscles artificially contaminated with malachite green (0.5~50 μg/kg) or crystal violet (10~100 μg/kg) were used for the study. Two different types of commercial gold-coated SERS substrates were used to acquire SERS spectra (400~2000 cm-1) of standard solutions or fish extracts. Then, laser source (633 and 780 nm) and laser power (5 and 10 mW) were varied for optimum results to collect spectra of different drugs. PLSR was applied for quantitative analysis of the tested fish drugs. The results indicated that SERS technology is a sensitive method for analyzing industrial dyes, which could detect malachite green and crystal violet at concentration levels as low as 0.8 and 10 μg/L, respectively. For chloramphenicol and sulfamerazine, the lowest concentrations could be detected were 50 and 500 μg/L, respectively. The PLSR models for four standard solutions yielded R2 of 0.865 to 0.954. For malachite green and crystal violet extracts from fish, the lowest concentrations detected were 1.0 and 20 μg/kg, respectively, which indicated great potential of applying SERS in determination of residual prohibited or restricted fish drugs in food system.
Direct methanol fuel cells are excellent power sources due to their high energy density, low pollutant emission and easy handling. However, commercial applications are limited by the high cost related to noble metal catalysts. Recent findings have proved that appropriate catalyst support, which improves the utilization of the noble metals in great depth, may be one breakthrough. Graphene nanosheet (GNS), a new two-dimensional carbon material with a single (or a few) atomic thickness, as the combination of its high surface area, high conductivity and unique graphitized basal plane structure, has recently attracted an enormous amount of interest from both theoretical and experimental scientists. It has been proved that catalysts supported on GNSs show improved activity than those supported on carbon black. Furthermore, alloying Pt with other metal is widely approved as a practical method to relieve the CO-poisoning of the catalyst, which can be ascribed to both a bi-functional mechanism and a ligand (electronic) effect. In this experiment, PtCo/graphene (GN) composite catalysts were synthesized on an indium tin oxide (ITO) substrate by the potentiostatic method. Catalyst samples were characterized by scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDX) and electrochemical methods. SEM results showed that the addition of graphene could enhance the dispersion of the catalytic particles and reduce the particle size, especially when the molar ratio of Pt and Co is 1:2.93, the particles had the smallest size and the best dispersion. Electrochemical tests demonstrated that graphene as the catalytic support could improve the CO-tolerance of the catalysts, which was determined by the outstanding electric conductivity and rich oxygen-containing species of graphene, resulting in good performance for electrocatalytic methanol oxidation. Furthermore, owing to the special electronic effect of Co, its addition also influenced the catalytic activity. It was found that when the molar ratio of Pt and Co was 1:2.93, the composite catalyst exhibited the most excellent catalytic performance for electrocatalytic methanol oxidation with the forward anodic peak current density of 662 A·gpt-1and the If/Ib of 2.34 which was nearly 1.8 times that of the traditional PtCo/C catalyst (If/Ib=1.32).
Grape is very perishable in transportation and storage, so its early warning is particularly important to lower the risks of large-scale deterioration. In order to study grape deterioration process, we analyzed the volatile compounds from grapes using Fourier transform infrared (FTIR) spectroscopy. Several grapes were put in the sample compartment of the FTIR spectrometer for 2 h per day. Then, the volatile compounds vaporized from the grapes were measured directly using the spectrometer. A high energy ceramic IR-source was used to improve the signal-to-noise ratio. We collected the FTIR spectrum before sample was put in as a background to eliminate the influence of air. Spectral signatures of the volatiles from grapes were analyzed and used to classify the grape samples into deterioration or not. By spectral analysis, the volatile mainly includes ethyl acetate, ethanol and carbon dioxide. The above three volatile vaporized more and more from the grapes during deterioration process. We also found that the release rates of volatile compounds get its highest value when the grapes just started deteriorating, so, this value could be used to monitor the beginning of deterioration. The methods to classify grapes deterioration levels were also studied. Firstly, grape deterioration processes were divided into three stages, fresh, slight deterioration and severe deterioration, by appearance and sensory evaluation. Then, a principle compounds analysis (PCA) was used for unsupervised classification to FTIR spectra. Results showed that this method could distinguish grapes into fresh and deterioration by choosing proper data pre-processing algorithms. This paper provides a new way to study the fruit deterioration mechanism, and premise a foundation for developing early-warning equipment for evaluation and monitoring fruit deterioration during its storage and transportation. Furthermore, because of the step change of release rates of volatile compounds at the beginning of deterioration, this kind of classifying method and monitoring system may not influenced by grapes quantity and store patterns.
Three-dimensional structure gold nanoparticle clusters (3D Au) were electrodeposited onto multiwalled carbon nanotubes (MWCNTs) through improved three-step method, which involves: (1) potential cycling (CV, 200 mV·s-1) from +1.8 to -0.4 V was performed in 0.5 mol/L K2SO4 solutions for 10 min in order to produce oxide functional groups (carbonyl, hydroxyl, and carboxyl) at the defect sites located at the ends and/or the sidewalls of MWCNTs, (2) electrochemical oxidation of the Au(III) complex to the Au(V) complex from 2 mol/L K2PtCl4+0.1 mol/L K2SO4 aqueous solutions by using potential-step method (PS). The potential was jumped from 0.3 V to 1.1 V with different pulse width and this was repeated until a steady pulse current was reached. and (3) electrochemical transformation of the Au(V) complex to Au nanoparticle clusters on the surface of MWCNTs through cycling from +1.0 to -0.26 V in 0.1 mol/L H2SO4 solutions to the steady state. For comparison, however, experiments were also carried out with CV in the second step (2 mol/L K2PtCl4+0.1 mol/L K2SO4 aqueous solution with 190 cycles: these proved to be the optimal conditions). The morphology of 3D Au/MWCNTs electrode was characterized by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The voltammetric behavior of hemoglobin (Hb) on 3D Au/MWCNTs-Nafion has been investigated in 10 nmol/L Hb solution (pH=6 PBS) by cyclic voltammetry (CV) and current-time method (CT). Compared with Au+MWCNTs-Nafion (+means mix together), Au/MWCNTs-Nafion (uniform Au nanoparticle dispersion of MWCNTs, which was obtained when the second step adopts cyclic voltammetry instead of potential-step method), 3D Au/MWCNTs-Nafion gave a higher peak current and better reversibility. The higher sensitivity and lower detection limit show that 3D Au/MWCNTs-Nafion can offer a conductive microenvironment for the immobilized Hb to achieve direct electrochemistry. The average coverage (Γ) of Hb immobilized on 3D Au/MWCNTs-Nafion was calculated to be 7.65×10-9 mol·cm-2, testifies a high surface-to-volume ratio. Electron transfer rate constant (kS) was calculated to be 1.8 s-1, which was proved 3D Au/MWCNTs-Nafion is more conducive to direct electron transfer between Hb and the electrode. Hb/Au/MWCNTs-Nafion potential application towards the electrocatalytic reduction of H2O2 was also conducted to show immobilized Hb exhibits excellent biocompatibility and stability. Our work points to a new path for the preparation of 3D Au/MWCNTs nanocomposites, which are promising as electrocatalysts in direct electrochemistry of Hb.
Methotrexate (MTX) was intercalated into the layered double hydroxides (LDHs) by the coprecipitation method to form MTX/LDHs nanocompounds, the effect of different solvents, i.e. water, mixture of ethanol and water, mixture of polyethylene glycol-400/4000 (PEG-400/4000) and water, on the properties of MTX/LDHs nanocompounds has been examined carefully. The nanocompounds were then characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron/micrograph (TEM), atomic force microscopy (AFM), thermogravimetry/differential scanning calorimetry (TG-DSC) and UV-visible diffuse spectroscopy (UV-vis). XRD and FTIR investigations demonstrated the successful intercalation of MTX anions as a declining monolayer into the interlayer of LDHs and the interlayer spacing changed accordingly with the variation in the kind of solvents. We thought that the addition of ethanol and PEG just changed the growth environment, especially the property of interlayer water in MTX/LDHs compounds and the hypothesis has been proved by the analysis of TG-DSC. There is no intercalation of PEG molecular into the LDHs interlayers from all the characterization. Compared with the product prepared in other solvents, the particles obtained in the mixture of PEG-400 and water exhibited round plates with the best monodispersity and the most regular morphology. The mechanism how PEG-400 molecules influence the formation of MTX/LDHs nanocompounds is described emphatically: non-ionized PEG-400 molecules will form chain-like structures due to the assembly in water, and the growth of nanocompounds is strictly limited in these structures. Due to the inhibition effect of PEG-400, further agglomeration will be forbidden; as a result the monodispersity will be improved. But when the molecular chain of PEG is too long (i.e. PEG-4000), it goes against the growth of nanocompounds on the contrary. The in vitro release experiment has been carried out in phosphate buffer solution at the pH value of 7.4, and the result revealed that the release property of MTX/LDHs can be well described by parabolic diffusion equation, or the release mechanism is mainly belongs to drug diffusion. The work reported here will help to establish a general method for the synthesis of drug/LDH nanocompounds with regular morphology and perfect dispersion properties.
A facile and scalable fabrication method of highly periodic array of nano-sized voids with large area (182 cm2) has been achieved by means of a template related 3-step procedure. A non-close packed (NCP) colloidal SiO2 array was fabricated by programmed spin-coating and in situ polymerization. The colloidal SiO2 arrays are embedded in a polymer matrix, and the spheres of the top layer protrude out of the film, forming a periodic surface. After being etched by HF aqueous solution, the first layer of SiO2 microspheres in the template were etched off and left behind a highly periodic hexagonal array of polymer nanovoids. The periodicity of the resulting polymer nanovoids array is the same as that of colloidal SiO2 arrays. The volume of nanovoid is as small as about 4.72 attoliter per void, and the density of voids can be as high as about 4.9×108 voids/cm2. The metallic nanovoids array could be fabricated by subsequent deposition of Cr and Au layers. The resulting array of metallic nanovoids could be used as surface-enhanced Raman scattering (SERS) active substrates with ultra-sensitivity and excellent reproducibility. The SERS performance of our nanovoids array was probed by benzenethoil. The SERS enhancement factor (EF) can be as high as in the order of 108~109 on average over 182 cm2. The mean relative standard deviation (RSD) of EF is in the range of 5.5% to 8.6% over 182 cm2 which indicates the reproducibility of the substrates is quite good. The methodology leverages the high uniformity of the spin-coated colloidal arrays and well-established physical vapor deposition techniques. The formation of nanovoids array with high periodicity over large areas could lead to important technological applications in nanoelectronics and sensors.
We study mechanism for combinet graphdiyne and graphene on TiO2 which can improve the photocatalytic performance of TiO2 by density functional theory with dispersion corrections (DFT-D) methods. Because of the different lattice parameters of graphdiyne, graphene and TiO2(101), we used (1×1) graphdiyne supercell with (1×4) TiO2(101) supercell to built the graphdiyne-TiO2(101) composite, and (2×6) graphdiyne supercell with (1×5) TiO2(101) supercell to built the graphene-TiO2(101) composite. In detail, as the strong adsorption between carbon atom and the TiO2 support, numbers of new high electron delocalization C—O covalent bonds were formed by O atom in TiO2 surface and atop C atom in graphdiyne. While for the graphene-TiO2(101) composite, the equilibrium distances between graphene and TiO2 are so large that even the nearest C atoms were far as 2.869 ? to the TiO2 planes, indicating the weak interaction between graphene and TiO2 surface. The electron density, electron density difference were analyzed, the result shown that the graphdiyne combined with TiO2(101) surface is beneficial to the charge transfer. The Mulliken charge population shows that the graphdiyne or graphene surface has a positive Mulliken charge, forming large opposite interface dipole at the interface, leading to a strong built-in electric field throughout the superlattice, which can resist the possibility of electron-hole recombination. Since the magnitude of charge accumulation in graphdiyne is larger than graphene surface, stronger electrons capture ability of graphdiyne- TiO2(001) composite could be expected compared to graphene-TiO2(001) composite. The electronic band structure shown that in the graphdiyne-TiO2(101) composite, numbers of isolated energy levels were localized in the band gap which can reduce the electronic excitation energy from the isolated energy levels to the conductive band. The graphene-TiO2(101) composite had no isolated energy level appeared in the band gap. The graphdiyne-TiO2(101) composite has a lower valence band position than the graphene-TiO2(101) composite ones, means compared with graphene composite, graphdiyne composite always shows higher oxidation ability, which induce a higher photocatalytic performance.
Using hydroxyethylcellulose (HEC) solution as polymer matrix, this work systematically studied the separation performance of 100 base pairs (bp) DNA ladder (100~1500 bp) by direct current electric field capillary electrophoresis (CE). In the present paper, we systematically investigated the influence of polymer concentration and molecular weight of HEC, electric field strength (E), the effective length (le) and the shape of the capillary, the temperature of the background electrolyte (BGE) on the separation performance of DNA. Furthermore, we compared the migration of DNA in polymer with the non-gel sieving model. Results show that: (1) When the concentration of HEC is above the entangled threshold c*, the mobility difference increases with the growth of molecular weight, whereas the mobility of DNA decreases with the rise of concentration of HEC. (2) The resolution of adjacent DNA fragments linearly increases with the effective length (le) of the capillary when le ranges from 4 to 12 cm. (3) The mobility of DNA increases with the growth of area ratio R (Slateral/Ssection), and thus the separation performance improves. (4) The increase of BGE temperature strengthens the diffusion effect of DNA, thus increases the mobility, and deteriorates the resolution. Based on the results above, we separated the φ×174-Hirc II digest by CE in an optimal electrophoretic condition. Experiment shows that rapid separation of φ×174-Hirc II digest was realized with high resolution. In our experiment, the fused-silica capillary is coated by acrylamide, and the background electrolyte (BGE) used for the sieving matrix contains 0.5×Tris-borate-EDTA (TBE) and 1×SYBR Green I. The DNA sample was injected for 2.0 s at an E of 100 V/cm. The self-build CE device involved is reliable and showed some remarkable achievements previously. Such a study is beneficial to the realization of rapid and effective separation of DNA, and allows deep insight into DNA migration in the polymer matrix under constant electric field.
In order to well understand the halogen (F2, Cl2, Br2, I2, ICl) doping effect on electronic structure of poly(methylphenyl)silane (PMPSi), a theoretical investigation on halogen doped models has been performed using density functional theory (DFT). The optimized structures of PMPSi are obtained at the BH&HLYP/6-31G* level, and the stagger conformation is the most stable conformation among three isomers. Halogen doped PMPSi were optimized at the BH&HLYP level based on the stagger conformation, and the changes of geometry parameters are compared for PMPSi and halogen doped PMPSi. Furthermore, frontier molecular orbital energies and electronic absorption spectra of halogen doped PMPSi are investigated. The results show that energy of the highest occupied molecular orbital (HOMO) almost keeps the same when PMPSi is doped by halogen, but energy of the lowest unoccupied molecular orbital (LUMO) becomes lower, the energy gap is therefore decreased according to the order Cl2>F2>ICl>Br2>I2. When PMPSi is doped by halogen, electron transition is assigned to the HOMO-1→LUMO, it leads to red shift of the absorption spectrum of complex, and presents relative strong absorption peak in visible region. Natural bond orbital (NBO) analyses were performed to study the charge distribution of halogen doped PMPSi, it is found that charge transfer from backbone to halogen in the complex. The interaction energies of all the complexes which were corrected for basis set superposition error (BSSE) are from -0.61 to -3.20 kcal/mol. The result what arouse most interest is, the higher polarity of dopant, the larger interaction energy of complex. In addition, the influence of position of dopant on energy gaps and interaction energies of all complexes is discussed in our present work. This study is expected to provide theoretical clues and foundation for future research on improving the photoelectric property of PMPSi.