Carbon quantum dots(CQDs) with a quantum yield of 11% were synthesized via a simple, low-cost and green hydrothermal treatment using dried lemon peel as carbon source. The obtained CQDs showed a strong emission at the wavelength of 505 nm with an optimum excitation of 425 nm. Carmine with maximum absorption wavelength at 508 nm could selectively quench the fluorescence of CQDs. Based on this principle, a fluorescence probe was developed for carmine determination. The quenching mechanism of CQDs was elucidated. A linear relationship was found in the carmine concentration range of 0.20—30.00 mg/L with the detection limit(3σ/k) of 0.16 mg/L. Satisfactory results were achieved when the method was applied for the determination of carmine in soft drinks.
Chiral organocatalysts of 4-adamantane amide based on L-proline with double hydrogen potential were synthesized and used in asymmetric aldol reactions. The reactions were evaluated in toluene under‒20 °C. A series of aldol products was obtained from moderate to good yields(up to 98%) with excellent diastereoselectivities(up to >99:1) and enantioselectivities(up to >99%). The aldol products in the system were separated by α-cyclodextrin via host-guest interaction and determined by chiral HPLC. The catalyst could be reused up to five times. The 4-substitution position played an important role in diastereoselectivity and enantioselectivity.
The gene(ABK51908) from Acidothermus cellulolyticus encodes a mature protein of 484 residues with a calculated molecular mass of 53.0 kDa. Sequence analysis revealed that the protein had 59% identity to the β-glucosidases CAA82733, which belongs to glycoside hydrolase family 1(GH1). We cloned and expressed the gene in Escherichia coli BL21-Gold(DE3). The recombinant protein(AcBg) had an optimal pH and temperature of 7.0 and 70 °C, respectively. The specific activities of AcBg under optimal conditions were 290 and 33 U/mg for p-nitrophenyl-β-D-glucopyranoside(pNPG) and cellobiose, respectively. AcBg hydrolyzed the oligosaccharide sequentially from the non-reducing end to produce glucose units according to the results of HPLC analysis. AcBg showed high salt tolerance and monosaccharide-stimulation properties. Its activity rose more than 2-fold when 5 mol/L NaCl/KCl were added. The activity of the β-glucosidase was remarkably enhanced in the presence of 0.2 mol/L D-glucose(increased more than 1.9-fold), 0.1 mol/L α-methyl-D-glucose(increased more than 1.4-fold) and 1.0 mol/L D-xylose(increased more than 1.9-fold). The catalysis kinetics and structural changes in various concentrations of glucose were determined. The results indicate that glucose reduces substrate affinity and causes conformational changes.
An oligo-fluoropolymer(PFM) with functional cycloaliphatic epoxy and fluorinated groups was obtained via free radical polymerization and applied to the modification of cycloaliphatic epoxy resins(CE). The chemical structure of PFM was characterized by Fourier transform infrared(FTIR) spectroscopy, gel permeation chromatogra-phy(GPC) and nuclear magnetic resonance(NMR) spectroscopy, and the effects of different PFM concentra-tions(0.5%—6%, mass fraction) on the thermal resistance, mechanical properties, surface dewettability, light trans-mission, refractive index and various cured polymer properties were studied in detail. The DSC and TGA results demonstrate that the modified epoxy resins possess a higher thermal resistance than the neat epoxy resin. The im-provements in the surface dewettability and water resistance are caused by the high crosslinking density and the enrichment of the oligo-fluorinated random copolymers dispersed in the matrix. The fracture surface morphologies of the thermosets were investigated by scanning electron microscopy(SEM) and transmission electron microsco-py(TEM). It was observed that the optical transmittance of the composites was maintained even though microphase separation occurred during the curing process. With respect to the corresponding properties of the neat epoxy resins, the 2 phr(parts per hundreds of resin) PFM thermoset exhibited relatively better comprehensive properties, making the cured material a good candidate for light-emitting diode(LED) encapsulation.
Two novel energetic alkalic metal salts of 3,6-bis(1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine (BTATz), Li2(BTATz)·6H2O(compound 1) and Na2(BTATz)·2H2O(compound 2), have been synthesized by the reac-tion of BTATz with lithium hydroxide or sodium hydroxide in dimethylsulfoxide(DMSO) solution, respectively, and their structures were characterized by means of elemental analysis and Fourier transform infrared spectrometry(FTIR). Moreover, the single-crystal structure of compound 1 was determined by single crystal X-ray diffraction. It crystal-lizes in the monoclinic space group P1/c. Furthermore, their thermal decomposition behaviors were investigated by means of differential scanning calorimetry(DSC) and thermogravimetry-differential thermal gravimetry(TG-DTG). The results show that the exothermic decomposition peak temperatures for compounds 1 and 2 were 642.65 and 644.46 K, respectively, and the kinetic equations of the main exothermic decomposition were also derived from non-isothermal method. Additionally, the thermal safety of the two compounds was evaluated by calculating self-accelerating decomposition temperature(T SADT) and critical temperature of thermal explosion(T b). The results(the TSADT and T b values are 605.43 and 635.69 K for compound 1; 607.38 and 638.96 K for compound 2) reveal that the two compounds exhibit better thermal safety than BTATz.
A series of fluorine modified TAPO-5 molecular sieves was synthesized by one-pot method using ammo-nium hexafluorotitanate as titanium and fluorine sources. The XPS and DRS UV-Vis results indicated that the exis-tence of F could promote the formation of tetrahedrally coordinated framework Ti and Al, meanwhile, inhibit the formation of anatase TiO2 in TAPO-5 sieves due to the unique role of F in the sol-gel process of metal ions. Further-more, TG, contact angle test, Py-FTIR and 27Al MAS NMR results revealed that fluorine modification increased the surface hydrophobicity and the Lewis acidity of Ti active sites through forming Al xF y units in the neighborhood. All these factors make these fluorine modified TAPO-5 sieves exhibit good catalytic performance in the ammoximation of cyclohexanone.
Various imidazolium and choline-based functional ionic liquids(ILs) comprising different cations and anions were grafted onto Burkholderiacepacia lipase(BCL) through surface amino acids coupling. The catalytic ac-tivity, thermostability, organic solvent tolerance and adaptability to temperature and pH changes of the modified BCL were then evaluated in olive oil hydrolysis reaction. The results showed that different combinations of cations and anions in ILs had important influence on the catalytic performance of the modified lipases. BCL modified with IL [Choline][H2PO4] was the most improved lipase, in which increases by 1.2 folds in relative activity, 2.5 folds in typi-cal proton solvent(10% methanol, volume fraction), and 1.4 folds in thermostability(after incubation at 70 °C for 2 h) were achieved in relative toits native form. BCL modified with [HOOCEPEG350IM][BF4] had higher optimal tempe- rature and pH, and better thermosability compared with the native and other modified BCLs. The conformational changes of BCLs were also confirmed by fluorescence spectroscopy and circular dichroism spectroscopy.
The C3N4/Ag composite nanosheets were facilely prepared via an in situ reduction process and Ag nanoparticles were well dispersed on the surface of C3N4 nanosheets. The unique two-dimensional structure and strong interactions between C3N4 nanosheets and Ag nanoparticles contributed the good surface-enhanced Raman scattering(SERS) property due to the electromagnetic field enhancement. In addition, the as-prepared C3N4/Ag composite nanosheets could be used as catalysts or photocatalyst for the degradation of methylene blue(MB) in the presence of NaBH4 or under visible light. Therefore, a facile SERS monitoring of the catalytic and photocatalytic degradation process of MB and the determination of the reaction kinetics were developed.
In the paper, folic acid(FA)-mediated and β-cyclodextrin(β-CD) derivatives functionalized magnetic Fe3O4 nanoparticles(MNPs) were successfully prepared as drug carriers for the targeted delivery and controlled release of water-insoluble anticancer drug. FA-sulfobutyl ether-β-CD-MNPs(FA-SBE-β-CD-MNPs), FA-hydroxypropyl-β-CD-MNPs(FA-HP-β-CD-MNPs) and FA-carboxymethyl-β-CD-MNPs(FA-CM-β-CD-MNPs) were fabricated, and the loading efficiency and relative entrapment rate of curcumin are 12.04 mg/g, 95.56% for FA-SBE-β-CD-MNPs, 9.6 mg/g, 81.63% for FA-HP-β-CD-MNPs and 7.88 mg/g, 85.28% for FA-CM-β-CD-MNPs, respectively. Meanwhile, at pH=5.0, the optimal release rate of curcumin is about 46.07% for FA-SBE-β-CD-MNPs in 5 h. Cellular uptake indicates that curcumin can be selectively transported to targeting site and released from the internalized carriers. The in vitro cytotoxicity reveals that non-toxic FA-SBE-β-CD-MNPs have excellent biocompatibility on HepG2 cells in the tested concentrations. Therefore, FA-SBE-β-CD-MNPs could provide a promising platform for the targeting delivery of water insoluble anti-cancer drugs for different treatment needs of cancer therapy.
The equilibrium structures, formation energy, mechanical properties and electronic properties of Co-Sn intermetallics have been systemically studied by first-principles study. The results show that the CoSn phase is more thermodynamically stable than any other stoichiometry of Co-Sn intermetallics. With the increasing of Co content in Co-Sn intermetallics, the mechanical properties change into brittle behavior from ductility character. Adding proper amount of Co to Co-Sn intermetallics can improve the cycle performance for lithium ion battery anode. However, high Co content will lead to a poor cycle performance for Co-Sn intermetallics.
The removal of cadmium(Cd) from synthetic solutions by batch adsorption process was performed using eggshell powder, which is mainly composed of calcite(CaCO3). In order to optimize the adsorption process, a re-sponse surface methodology(RSM) based on Central Composite Design(CCD) was applied. Developed model for Cd remo- val yields(R, %) response was statistically validated by variance analysis(ANOVA) which showed a high de-termination coefficient value(R 2=0.9889). According to Minitab software, the optimal conditions were found at tem-perature of 44 °C, eggshell adsorbent dose of 2.98 g, initial Cd concentration of 36.74 mg/L and initial pH of 7. Un-der these conditions, the Cd removal yield was 98.76%. The deviation value of 1.24% confirms the validity of the model for the adsorption process optimization. The adsorption isotherm has been described by a Freundlich model. In addition, the predominant sorption mechanisms are the chemisorptions or precipitation(non-reversible) and ion ex-change(reversible).
A simple and efficient colorimetric biosensing for hydrogen peroxide and glucose with peroxidase-like vitamin C(Vc) functionalized Fe3O4 magnetic nanoparticles(VcFe3O4 MNPs) as a catalyst is reported. Compared with Fe3O4 MNPs and other catalysts, VcFe3O4 MNPs exhibited superior catalytic properties. Kinetic studies indicated that vitamin C incorporated on Fe3O4 MNPs improved the affinity toward H2O2. As low as 0.29 μmol/L H2O2 can be detected with a wide linear range of 0.5―100 μmol/L H2O2; moreover, as low as 0.288 μmol/L glucose can be detected with a linear range of 0.5―25 μmol/L glucose. The detection method was highly sensitive in sensing H2O2 and glucose. The robustness of VcFe3O4 MNPs rendered them suitable for wide ranging applications.