Fluorescence Energy Transfer Study of Interstrand DNA Cross-linking Caused by Rigid Bisintercalator

The intermolecular cross-linking of DNA with a rigid bisintercalator, 1,4-bis(( N -methylquinolinium-4-yl)vinyl)benzene (pMQVB) has been studied using fluorescence resonance energy transfer (FRET), fluorescence anisotropy measurements, and dynamic fluorescence microscopy. Short DNA duplexes, single-labeled with fluorescein (donor) and x-rhodamine (acceptor), were used as energy transfer partners. Due to the quenching effect of pMQVB on the emission of both fluorescein and x-rhodamine, the energy transfer was monitored using the corrected Stern-Volmer plots. The cross-linking ability of pMQVB depended on the ligand structure; the planar E , E isomer cross-linked DNA contrary to the non-planar E , Z isomer. Dynamic fluorescence microscopy observation also demonstrated the ability of pMQVB to cross-link large T4 DNA molecules.     

利用卵壳膜固定化葡萄糖氧化酶制备酶电极

报道了以卵壳膜为载体，用戊二醛将葡萄糖氧化酶固定于膜上，并探讨了酶膜制备过程的各种影响因素。在固定过程中，当戊二醛浓度为０．１％，酶用量为２０ＵＩ时，酶回收率为１７％。渗透性是影响酶膜重现的主因。以此酶膜制备的葡萄糖电极，线性范围为１．０×１０５～１．６×１０－３ｍｏｌ／Ｌ检测限为５×１０－６ｍｏ１／Ｌ，寿命两个月。     

Surface modification study of low energy electron beam irradiated polycarbonate film

The effect of low energy electron beam irradiation on polycarbonate (PC) film has been studied here. The PC film of thickness 20 μm was exposed by 10 keV electron beam with 100 nA/cm² current density. The irradiated film was characterized by mean of X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and residual gas analyzer (RGA). Formation of unsaturated bonds and partial graphitization of the surface layer are measured by XPS. Results of the AFM imaging shows electron implantation induce changes in surface morphology of the polymer film. The residual gas analyzer (RGA) spectrum of PC is recorded in situ during irradiation. The results show the change in cross-linking density of the polymer at the top surface.     

Synthesis of novel perfluorosulfonamide monomers and their application

The novel perfluorosulfonamide monomers and their preparation methods have been developed. The ternary-copolymer membranes, utilizing the perfluorosulfonamide monomers as the cross-linking site, can be efficiently converted to the cross-linked membranes with the strictly controlled structure. The novel cross-linking method has proved to be effective for the improvement of the mechanical properties at high temperature, while keeping its high proton conductivity.     

Structure and mobility in ferroelectric liquid crystalline elastomers

Time-resolved Fourier transform infrared (FTIR) spectroscopy with polarized light was employed to study the structure and mobility of a homologous series of ferroelectric liquid crystalline polymers (FLCPs) and ferroelectric liquid crystalline elastomers (FLCEs) in response to an external electric field. The chemical composition of the samples, besides the cross-linking units, is similar. For the elastomers, two different cross-linking architectures are realized: “intralayer” cross-linking leads to the formation of two-dimensional networks, whereas “interlayer” cross-linking forms three-dimensional networks. Due to its specificity, FTIR spectroscopy enables analysis of the reorientational dynamics for the different molecular moieties in detail, thus revealing information about reorientation times, angular excursion, and the phase relationship in the rearrangement of the various molecular groups. In comparison to the un-cross-linked FLCP, both elastomeric samples exhibited smaller reorientation angles and an increase of the reorientation times. In the case of the interlayer cross-linked FLCE, an elastic memory effect was observed: For the reversal from negative to positive field polarity, the reorientation times were longer than for those in the opposite direction. For the intralayer cross-linked sample, it was shown that the backbone molecules reorient slower than the other molecular units (“locomotive effect”). For the un-cross-linked FLCP and the two FLCE samples, different coupling mechanisms between the network and the mesogenic parts are derived from the measurements.     

Structural micromechanics of oriented polymers

To clarify whether the interfibrillar slippage occurs on plastic deformation of oriented polymers, flow creep of ultrahigh molecular weight polyethylene (UHMW PE) samples with various connectedness of microfibrils has been studied in a dead load mode at room temperature. The flow creep rate of melt-crystallized and gel-cast UHMW PE films drawn to various draw ratios, as well as of modified gel-crystallized samples (cross-linked/grafted or washed free of low molecular weight fraction) has been measured with the help of a unique laser interferometric technique (Doppler creep rate meter). The technique allows one to measure creep rates for deformation increments as small as 0.3 μ within an accuracy 1%. The interferometric technique enabled us to observe an extremely high variability of flow creep rate. It was recognized that the creep process accelerates or slows from time to time. A length of a loaded sample increased by multiple consecutive deformation jumps (or steps). The size distribution of the steps appeared to be controlled by the structure of interfibrillar regions. The influence of the latter on the variability of creep rate confirms a hypothesis that suggests a contribution of interfibrillar slippage to plastic deformation of oriented polymers. The observed phenomenon has been attributed to stick-slip motion of microfibrils and their aggregates sliding on each other under the action of applied stress. It was found that the creep rate decreases with increasing interfibrillar interaction.     

Strengthened graphene oxide/diazoresin multilayer composites from layer-by-layer assembly and cross-linking

The layer-by-layer assembly of graphene oxide and diazoresin is carried out via the electrostatic and hydrogen bond interactions on planar substrates and colloidal templates. The successful planar and spherical growth of multilayer could be investigated by UV-vis spectrophotometry and scanning electron microscopy, respectively. Subsequent UV irradiation or heating would convert the ionic bonds and hydrogen bonds to covalent bands, which significantly improves the stability of the multilayer composite against solvent etching. For the cross-linked core-shell composites, the template cores could be removed by dissolution and hollow microspheres are obtained.     

PERVAPORATION PROPERTIES OF PDMS MEMBRANES CURED WITH DIFFERENT CROSS-LINKING REAGENTS FOR ETHANOL CONCENTRATION FROM AQUEOUS SOLUTIONS

Ethanol perm-selective PDMS/PVDF composite membranes were prepared by curing polydimethylsiloxane (PDMS) with various cross-linking reagents,such as tetraethoxylsilane(TEOS),γ-aminopropyltriethoxylsilane(APTEOS), phenyltrimethoxylsilane(PTMOS) and octyltrimethoxylsilane(OTMOS) as well.The cross-linking density and surface properties of the PDMS active layer were adjusted by varying cross-linking reagents.The pervaporation performance of PDMS membranes cured with different cross-linking reagents was inves...     

Preparation and characterization of cross-linked hyaluronan nanoparticles

The present investigation describes the synthesis and characterization of novel biodegradable nanoparticles based on hyaluronic acid (HA). The diamine, 2,2′(ethylenedioxy)bis(ethylamine) was used for cross-linking of the HA linear chains. The condensation reaction of amino groups and pendant carboxyl groups of HA was performed in aqueous media at room temperature using water-soluble carbodiimide. The prepared nanosystems, aqueous solutions, or dispersions of nanoparticles were stable, transparent, or mildly opalescent systems depending on the ratio of cross-linking, findings consistent with values of transmittance above 77%. The structure of products was determined by nuclear magnetic resonance spectroscopy, and the particle size was identified by laser light scattering (DLS) and transmission electron microscopy (TEM) measurements. Particle size measured by TEM varied less than 130 nm; in the swollen state, the average size of the particles measured by DLS was in the range of 30–140 nm depending on the ratio of cross-linking and the molecular weight of HA. Formation of cross-linked nanoparticles results in a viscosity drop compared to the viscosity of the corresponding solution of the HA, and this trend becomes decreasingly appreciable as the molecular weight of HA decreases.     

Diffusion of the dicumyl peroxide in molten polymer probed by rheology

The mutual coefficient of diffusion of the dicumyl peroxide (DCP), which diffuses into an ethylene–octene copolymer above its T _g was measured from an innovative rheological experiment. The experiments were carried out on a parallel plate geometry rheometer. The method is based on the cross-linking of a two-layer sample; the upper layer contains 2 wt% of DCP, and the lower layer is free of DCP. Actually, this experiment is based on the competition between the reaction of cross-linking and the diffusion of DCP in the lower layer. Comparing this rheological behavior with the rheological kinetic of cross-linking of an homogeneous sample with 1 wt% DCP, we are able, from an inverse fitting procedure, to calculate the mutual coefficient of diffusion. Our hypothesis is that the diffusion of DCP in the copolymer above T _g, can be described by Fick’s classical law. Using Fick’s law, the concentration of the DCP was established for any given point of the thickness of the two-layer sample at any time. Using a one-dimensional grid to solve continuous equations that describe the different rheological contributions of each abscissa, we determined the linear viscoelastic response of the whole sample. Comparing the experimental storage modulus of the two layer sample to the values measured from an homogeneous sample, we found the values of the mutual coefficient of diffusion. Finally, a simple relation, which describes the mutual coefficient of diffusion of DCP into melt ethylene–octene copolymer was established according to an Arrhenius law as: