Colorimetric method for determination of bisphenol A based on aptamer-mediated aggregation of positively charged gold nanoparticles

A sensitive, specific and rapid colorimetric aptasensor for the determination of the plasticizer bisphenol A (BPA) was developed. It is based on the use of gold nanoparticles (AuNPs) that are positively charged due to the modification with cysteamine which is cationic at near-neutral pH values. If aptamers are added to such AuNPs, aggregation occurs due to electrostatic interactions between the negatively-charged aptamers and the positively-charged AuNPs. This results in a color change of the AuNPs from red to blue. If a sample containing BPA is added to the anti-BPA aptamers, the anti-BPA aptamers undergo folding via an induced-fit binding mechanism. This is accompanied by a conformational change, which prevents the aptamer-induced aggregation and color change of AuNPs. The effect was exploited to design a colorimetric assay for BPA. Under optimum conditions, the absorbance ratio of A ₅₂₇/A ₆₈₀ is linearly proportional to the BPA concentration in the range from 35 to 140 ng∙mL⁻¹, with a detection limit of 0.11 ng∙mL⁻¹. The method has been successfully applied to the determination of BPA in spiked tap water and gave recoveries between 91 and 106 %. Data were in full accordance with results obtained from HPLC. This assay is selective, easily performed, and in our perception represents a promising alternative to existing methods for rapid quantification of BPA.

The negatively-charged anti-BPA aptamers can absorb onto the positively-charged cysteamine-capped AuNPs (cysteamine-AuNPs) via electrostatic interactions, which can cause the aggregation of AuNPs accompanied by a red-to-blue color change. In the presence of BPA, the specific binding of BPA to the aptamers induces the conformation changes of anti-BPA aptamers, which can release the aptamers from cysteamine-AuNPs and thus prevent the aggregation and color change of cysteamine-AuNPs.

     

Cytotoxicity and inhibition of lipid peroxidation activity of resveratrol/cyclodextrin inclusion complexes

Resveratrol (Res) is a plant-based polyphenol compound and is known to inhibit the growth of a variety of cancer cells and protect lipoproteins against oxidative damage. However the poor solubility and labile property may constitute a serious problem for its bioavailability. The problem could be overcome by the formation of inclusion complexes with cyclodextrins (CDs). The aim of this work is to include Res by β-cyclodextrin (β-CD) and 2-hydroxypropyl-β-cyclodextrin (HP-CD) to form the Res/β-CD and Res/HP-CD inclusion complexes and evaluate their cytotoxicity on cancer cells and inhibition of lipid peroxidation activity. The complexes are characterized by powder X-ray diffraction, fourier transform infrared spectroscopy and scanning electron microscopy. The cytotoxicity of the two complexes has been evaluated by methylthiazoletetrazolium reduction assay on two cancer cell lines (cervical carcinoma cells HeLa and hepatocellular liver cancer cells Hep3B) and one normal cell line (umbililical vein endothelial cell HUVEC). The results showed that the two complexes exhibit high cytotoxicity on two cancer cells, especially for Hep3B, and show no significant effect on normal cells. The Res/HP-CD complex shows higher cytotoxicity on the two cancer cells than that of the Res/β-CD complex. The inhibition of lipid peroxidation induced by Fe²⁺/ascorbate of the two inclusion complexes has been determined by thiobarbituric acid assay. The inhibition rate shows a linear increase with the increase of CDs concentration, and the Res/HP-CD complex shows stronger inhibition activity than that of the Res/β-CD complex. The results of this work indicate a potential for using the Res/CD complexes to inhibit human cancer growth and lipoproteins peroxidation.     

铁磁/反铁磁/铁磁三层膜系统中反铁磁自旋结构及其交换各向异性

研究铁磁/反铁磁/铁磁三层膜中界面存在二次以及双二次交换耦合下反铁磁磁矩转动及其交换各向异性.结果表明,其反铁磁膜中的磁矩转动存在可逆"恢复行为"、不可逆"连续倒转行为"以及不可逆"中断倒转行为"三种情形,三种情形的出现强烈地依赖于两界面处的线性耦合和双二次耦合.钉扎界面的交换耦合与旋转界面的交换耦合相互竞争,当钉扎界面耦合占主导时,反铁磁磁矩发生可逆"恢复行为",系统出现交换偏置.在旋转界面耦合占主导情形下,其线性耦合与双二次耦合也相互竞争,分别导致反铁磁磁矩发生不可逆"连续倒转行为"和不可逆"中断倒转行为",系统都不出现交换偏置,但矫顽场都得以增强.相关结论为实验上观测的磁滞能耗以及界面垂直耦合提供了可能的解释.     

Synthesis and characterization of biodegradable network hydrogels having both hydrophobic and hydrophilic components with controlled swelling behavior

A new class of biodegradable hydrogels, consisting of hydrophobic poly(D ,L )lactic acid (PDLLA) and hydrophilic dextran segments with a polymer network structure, was synthesized with UV photopolymerization. Unsaturated vinyl groups first were introduced onto the PDLLA and dextran polymer backbones, then followed by a crosslinking reaction of diacrylate-terminated PDLLA and dextran acrylate. The chemical crosslinking forced the hydrophobic PDLLA and hydrophilic dextran segments to mix with each other in the network hydrogels. The new polymers were characterized by standard polymer characterization methods such as NMR, Fourier transform infrared spectroscopy, and gel permeation chromatography. The effects of reaction time, temperature, and molar ratio of the reactants on the incorporation of acrylate onto the polymer backbone were examined. A series of hydrogels with different dextran/PDLLA composition ratios was prepared, and their swelling behaviors were studied. These new bicomponent network hydrogels had a wide range of hydrophilicity to hydrophobicity that was difficult to achieve in totally hydrophilic hydrogels. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4554–4569, 1999     

Continuous and discontinuous precipitation in Fe-1 at.%Cr-1 at.%Mo alloy upon nitriding; crystal structure and composition of ternary nitrides

The internal nitriding response of a ternary Fe–1 at.%Cr–1 at.%Mo alloy, which serves as a model alloy for many CrMo-based steels, was investigated. The nitrides developing upon nitriding were characterised by X-ray diffraction, scanning electron microscopy, electron probe microanalysis, transmission electron microscopy and atom probe tomography. The developed nitrides were shown to be (metastable) ternary mixed nitrides, which exhibit complex morphological, compositional and structural transformations as a function of nitriding time. Analogous to nitrided binary Fe–Cr and Fe–Mo alloys, in ternary Fe–Cr–Mo alloys initially continuous precipitation of fine, coherent, cubic, NaCl-type nitride platelets, here with the composition (Cr_½,Mo_½)N_¾, occurs, with the broad faces of the platelets parallel to the {1?0?0}_α-Fe lattice planes. These nitrides undergo a discontinuous precipitation reaction upon prolonged nitriding leading to the development of lamellae of a novel, hexagonal CrMoN₂ nitride along {1?1?0}_α-Fe lattice planes, and of spherical cubic, NaCl-type (Cr,Mo)N _x nitride particles within the ferrite lamellae. The observed structural and compositional changes of the ternary nitrides have been attributed to the thermodynamic and kinetic constraints for the internal precipitation of (misfitting) nitrides in the ferrite matrix.     

Study of the complexation of resveratrol with cyclodextrins by spectroscopy and molecular modeling

In present work the complexation of Res with two kinds of cyclodextrins (CDs), native β-cyclodextrin (β-CD) and modified hydroxypropyl-β-cyclodextrin (HP-CD), have been investigated by fluorescence spectroscopy, ¹H-NMR spectroscopy and molecular modeling methods. The stoichiometric ratios, inclusion constants and thermodynamic parameters have been determined by the fluorescence data. In all cases 1:1 inclusion complexes are formed. The inclusion ability of HP-CD is larger than that of β-CD. Both inclusion processes have negative ?G, negative ?H and positive ?S. Thermodynamic analysis suggests that Van der Waals force of guest-host interactions and the release of high-enthalpy water molecules from the cavity of CDs play important roles in driving complex formation. The study of molecular modeling shows that part of the A-ring and the B-ring of Res are placed in the cavity of β-CD, and the hydroxyl groups are projected outside. As for Res in HP-CD, the B-ring of Res is included in the cavity of HP-CD, and part of the A-ring is pointed outside. ¹H-NMR spectroscopy results show that H_2, H₃, H₄ and H₅ protons of Res are more affected by the complexatin, indicating that they are located inside the torus of CDs, which are in agreement with the result of the molecular modeling.     

An analytical solution of rectangular laminated plates by higher-order theory

I.IntroductionSincecompositematerialshavesuperiormechanicalproperties,theyarewidelyconcernedbytechnicians.Fromtheclassicallaminatetheorytothefirst-ordersheardeformationtheoryandfromthehigher-ordertheorytotheelasticitytheory,thetheoriesoflaminatedplatesofcompositemeterialsgetfastdevelopment.TheNaviersolutionofsimplysupportedrectangularplateswasdevelopedbyWhitneyandLeissalllforclassicallaminatetheory.TheNaviersolutionwasdevelopedbyWhitneyandPaganol'1forthefirst-ordersheardeformationtheory.Th…     

Isolation and Identification of Pennogenin Tetraglycoside from Cestrum nocturnum (Solanaceae) and Its Antifungal Activity against Fusarium kuroshium,Causal Agent of Fusarium Dieback

Antifungal assay-guided fractionation of the methanolic crude extract of Cestrum nocturnum (Solanaceae), popular known as ‘lady of the night’, led the isolation and identification of the steroidal saponin named pennogenin tetraglycoside, which was identified for the first time in this plant species by spectroscopic means. The crude extract, fractions and pennogenin tetraglycoside exhibited mycelial growth inhibition of Fusarium solani and F. kuroshium. F. solani is a cosmopolitan fungal phytopathogen that affects several economically important crops. However, we highlight the antifungal activity displayed by pennogenin tetraglycoside against F. kuroshium, since it is the first plant natural product identified as active for this phytopathogen. This fungus along with its insect symbiont known as Kuroshio shot hole borer (Euwallacea kuroshio) are the causal agents of the plant disease Fusarium dieback that affects more than 300 plant species including avocado (Persea americana) among others of ecological relevance. Scanning electron microscopy showed morphological alterations of the fungal hyphae after exposure with the active fractions and 12 phenolic compounds were also identified by mass spectrometry dereplication as part of potential active molecules present in C. nocturnum leaves.     

Synthesis and characterization of biodegradable hydrophobic–hydrophilic hydrogel networks with a controlled swelling property

A biodegradable polymer network hydrogel system with both hydrophilic and hydrophobic components was synthesized and characterized. The hydrophilic and hydrophobic components were dextran and poly(D,L )lactic acid (PDLLA), respectively. These two polymers were chemically modified for incorporating unsaturated groups for subsequent UV crosslinking to generate a hydrogel with a three‐dimensional network structure. The effects of the reaction conditions on the synthesis of a dextran derivative of allyl isocyanate (dex‐AI) were studied. All newly synthesized materials were characterized by Fourier transform infrared and NMR. The swelling property of the hydrogels was studied in buffer solutions of different pHs. The results of this study showed that a wide‐range swelling property was obtained by changes in the dex‐AI/PDLLA composition ratio, the type and degree of unsaturated groups incorporated into dextran, and the UV photocrosslinking time. The solvent extraction effect on the swelling property of the hydrogels was also studied. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2392–2404, 2000