The Effect of Cations on Uranyl Transport and Fluorescence in Mesoporous Silica Gel

The fluorescence intensity and transport kinetics of uranyl into mesoporous silica gel was measured in the presence of six naturally occurring cations. It was shown that the presence of the cations can reduce the fluorescence intensity of the uranyl through collision quenching and through competition for the silica gel surface sites. Stern-Volmer quenching coefficients were obtained by measuring the uranyl fluorescence as a function of cation concentration. The cations compete with uranyl to occupy silica gel surface sites and cause a decrease in uranyl fluorescence intensity and a reduction in the uranyl saturation time constant. Energy-dispersive x-ray spectroscopy (EDS) was used to measure the weight percentage of uranium and the cations in the silica gel samples and these results correlated well with the results of the saturation time constant measurements. The results of this study show that, at high concentrations, the presence of cations in water can influence the fluorescence intensity and transport kinetics of uranyl into mesoporous silica gel.     

Structure and phase transitions of DMPC multilamellar vesicles in the presence of Ca<Superscript>2+</Superscript> ions

Results obtained via small-angle neutron scattering studies of the influence of calcium ions on the structure and phase transitions of phospholipid membranes are presented. The main phase transition temperature of 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (1 wt %) multilamellar vesicles is demonstrated to increase by more than 1°C even when the calcium-ion content of the solution is low (0.1 mM). Detailed analysis of the multilamellar vesicles transition between “bound” and “unbound” state indicates the continuous character of the investigated process in both liquid and gel phases. The critical Ca²⁺ ion concentrations which initiate the destruction of the multilamellar structures and the formation of unilamellar vesicles are found to be ~0.3 mM in the gel and ~0.4–0.5 mM in the liquid-crystal phases during heating and ~0.5 mM in the phases under study upon cooling.     

Reduced Fluoresceinamine for Peroxynitrite Quantification in the Presence of Nitric Oxide

A new fluorescent analytical methodology for the quantification of peroxynitrite (ONOO(-)) in the presence of nitric oxide (NO) was developed. The quantification of ONOO(-) is based in the oxidation of the non-fluorescent reduced fluoresceinamine to a high fluorescent oxidized fluoresceinamine in reaction conditions where the interference of NO is minimized. Screening factorial experimental designs and optimization Box-Behnken experimental design methodologies were used in order to optimize the detection of ONOO(-) in the presence of NO. The factors analysed were: reduced fluoresceinamine concentration (C( Fl)); cobalt chloride concentration (C(CoCl2)); presence of oxygen (O(2)); and, the pH (pH). The concentration of sodium hydroxide (C(NaOH)) needed to diluted the initially solution of ONOO(-) was also evaluated. An optimum region for ONOO(-) quantification where the influence of NO is minimal was identified - C(Fl) from 0.50 to 1.56 mM, C(CoCl2) from 0 to 1.252?×?10(-2) M, pH from 6 to 8 and C(NaOH) 0.10 M. Better results were found in the presence of NO at pH 7.4, C(Fl) 0.5 mM, without oxygen, without cobalt chloride and with a previous dilution of peroxynitrite solution with C(NaOH) 0.1 M. This methodology shows a linear range from 0.25 to 40 μM with a limit of detection of 0.08 μM. The bioanalytical methodology was successfully applied in the ONOO(-) quantification of fortified serum and macrophage samples.     

Microscopic study of a pressure-induced ferromagnetic-spin-glass transition in the geometrically frustrated pyrochlore (Tb1-xLax)2Mo2O7

We have studied (Tb1-xLax)2Mo2O7 pyrochlores by neutron diffraction and muSR at ambient and under applied pressure. (Tb,La) substitution expands the lattice and induces a change from a spin-glass-like state (x=0) to a noncollinear ferromagnet (x=0.2). In the ferromagnetic structure, the Tb moments orient close to their local anisotropy axes as for an ordered spin ice, while the Mo ones orient close to the net moment. The temperature dependence of the muSR relaxation rates and static local fields suggests a second transition of dynamical nature below the Curie transition. Under pressure, the long range order breaks down and a spin-glass-like state is recovered. The whole set of data provides a microscopic picture of the spin correlations and fluctuations in the region of the ferromagnetic-spin-glass threshold.     

Role of weighting in the dynamics of front propagation

Non-equilibrium front propagation in a two-dimensional network modelling wildfire propagation was studied. The model includes deterministic long-range interactions due to radiation and a time weighting procedure. Three weight-dependent propagation regimes were found: dynamical, static, and non-propagative. The dynamical regime shows saturation for small weight values and a percolation transition area depending on the weight and size of the interaction domain. From the scaling interface exponents, the model seems to belong to the dynamical percolation universality class. In the limit of static regime it belongs to the random deposition class.     

Controlled hydrothermal growth of ZnO nanostructures by sequestering the Zn metal ions with the chelating agent EDTA

In the present work, a controlled growth of ZnO nanostructures by manipulating Zn metal ion concentration by the chelating action of ethylene diaminetetra acetic acid in hydrothermal method is studied. EDTA produces metal–chelate complex by the formation of bidentate ligand with Zn²⁺ in the solution and diminishes the reactivity of Zn metal cations. Concentration of EDTA in the mother solution was varied in different ranges like 3, 5 and 10 mM while retaining the zinc metal salt and the NaOH concentration the same. Three different morphologies of wurtzite structured ZnO nanostructures such as nanorods-bunch, separate/discrete uniformly sized hexagonal nanorods and tapered flower petals like shapes are achieved by 3, 5 and 10 mM strengths of EDTA, respectively. The medium concentration 5 mM of EDTA is found to have moderate control over producing ZnO nanostructures of uniform diameter and a high aspect (length to diameter) ratio. An array of vertically aligned free standing ZnO nanorods with uniform spacing is successfully achieved by the addition of 5 mM of EDTA in the mother solution and the same is studied for its fluorescence property at an excitation of 325 nm and it has exhibited a characteristic UV emission of ZnO around 383 nm.     

酒石酸钠调控草酸钙晶体生长的SEM,XRD和FTIR研究

采用扫描电镜(SEM)、X射线衍射(XRD)和傅里叶红外光谱(FTIR)研究了凝胶体系中尿抑制剂酒石酸钠(Na₂tart)的浓度和结晶温度对草酸钙(CaOxa)晶体生长的影响。当Na₂tart浓度为0.01 mol·L-1时,体系中主要生成棱角尖锐的蔷薇花状一水草酸钙(COM)聚集体,二水草酸钙(COD)含量小于5％,此时XRD图谱上主要为归属于COM的(101),(020)和(202)晶面的衍射峰,FTIR光谱中COM晶体的羧基不对称伸缩振动ν_as(COO-)和对称伸缩振动ν_s(COO-)分别为1 618和1 317 cm-1。当Na₂tart浓度增加到0.10和0.50 mol·L-1时,COD百分含量分别增加至10％和50％,COM晶体的比表面积减小。COD含量增加后,XRD图谱上归属于COD的(200),(211),(411)和(213)晶面的衍射峰增强。环境温度的影响比浓度的影响更为显著。高温(＞47 ℃)有利于COM生成,而低温(＜27 ℃)有利于Na₂tart诱导COD。FTIR光谱中COD的ν_as(COO-)和ν_s(COO-)分别为1 647.6和1 327.7 cm-1。     

青蒿素与氯化血红素作用的荧光研究及分析应用

介绍了吡罗红为指示剂通过荧光降低法研究青蒿素与氯化血红素之间的相互作用。实验发现两者为酶和底物作用模型,作用位点为药物的过氧基团和氯化血红素活性中心的金属离子,其动力学催化常数K_m, V_max和K_cat分别为8.4×10-5 mol·L-1, 7.4×10-6 mol·L-1·s-1及50.23 s-1,催化活性分别受去激活剂和高温影响。在最佳条件下, 荧光降低值ΔF(F₀-F)与青蒿素浓度在0.0～1.27×10-6 mol·L-1范围内成线性关系, 检测限为2.3×10-8 mol·L-1, 该方法已用于测定血浆和尿液介质中的微量青蒿素。     

Explosive synchronization through dynamical environment

We report the emergence of an explosive synchronization transition in the identical oscillators interacting indirectly through a network of dynamical agents. The transition from incoherent state to coherent state and vice–versa in these coupled oscillator exhibits an abrupt as well as irreversible. Such transition depends on the network topology as well as the interaction between the oscillators and dynamical agents rather than degree-frequency correlation in the network of oscillators. The occurrence of explosive synchronization is studied in details by using an appropriate order parameter for limit-cycle oscillators with respect to the different parameters like rewiring probability, average degree, and diffusion rate in dynamical agents.     

Wetting on nanorough surfaces

We present in this Letter a free-energy approach to the dynamics of a fluid near a nanostructured surface. The model accounts both for the static phase equilibrium in the vicinity of the surface (wetting angles, Cassie-Wenzel transition) and the dynamical properties like liquid slippage at the boundary. This method bridges the gap between phenomenological phase-field approaches and more macroscopic lattice-Boltzmann models.     

Encapsulation of a proteasome inhibitor with gold-polysaccharide nanocarriers

Groundwater remediation using iron oxide and zero-valent iron nanoparticles (NPs) can be effective, but is limited in many applications due to the NP strong retention in groundwater-saturated porous media after injection, the passivation of the porous surface, and the high cost of nanomaterials versus macro scale iron. In this study, we investigated transport of bare and polymer-coated 2-line ferrihydrite NPs (30–300 nm) in saturated aquifer sediments. The influence of poly(acrylic acid) (PAA) polymer coatings was studied on the colloidal stability and transport in sediments packed column tests simulating groundwater flow in saturated sediments. In addition, the influence of calcium cations was investigated by transport measurements using sediments with calcium concentrations in the aqueous phase ranging from 0.5 (typical for most sediments) to 2 mM. Measurements were also made of zeta potential, hydrodynamic diameter, polymer adsorption and desorption properties, and bio-availability of PAA-coated NPs. We found that NP transport through the saturated aquifer sediments was improved by PAA coating and that the transport properties could be tuned by adjusting the polymer concentration. We further discovered that PAA coatings enhanced NP transport, compared to bare NPs, in all calcium-containing experiments tested, however, the presence of calcium always exhibited a negative effect on NP transport. In tests of bioavailability, the iron reduction rate of the coated and bare NPs by Geobacter sulfurreducens was the same, which shows that the PAA coating does not significantly reduce NP Fe(III) bioavailability. Our results demonstrate that much improved transport of iron oxide NP can be achieved in saturated aquifer sediments by introducing negatively charged polyelectrolytes and optimizing polymer concentrations, and furthermore, these coated NPs retain their bioavailability that is needed for applications in bio-environmental remediation.     

氯盐溶液近红外光谱分析研究

氯盐近红外光谱分析在生物医学上有着十分重要的意义。在室温下对氯化钠,氯化钾,氯化钙水溶液的近红外光谱采集分析表明,氯盐溶液浓度的变化会影响水分子的氢键而使得水溶液的近红外光谱发生变化。通过选择合理波长区间以及温度变化影响为零的波长点(等吸光点),减小温度的干扰对溶液近红外光谱影响,采用偏最小二乘法建立了氯盐溶液的浓度模型用于预测氯盐的离子浓度。分析氯盐溶液中氯盐阳离子的离子半径大小、离子电荷数和离子在水中络合效应等因素对水的近红外光谱所造成的影响以及产生影响因素的原因。实验结果表明,温度和浓度都会影响溶液的近红外光谱,氯盐溶液浓度较低时,温度的影响占主导地位;氯盐浓度高时,浓度的影响占主导地位。氯盐在水溶液中形成络合物,并与氯盐阳离子共同作用对水的氢键产生影响,对于浓度相同种类不同的氯盐溶液, 形成的络合物和阳离子破坏效应对水的氢键的破坏作用为: CaCl₂>NaCl>KCl。最终建立的样品浓度模型校正集的决定系数(R2)=99.97%,交叉验证均方误差(RMSECV)=4.51,剩余预测偏差(RPD)=62.7,满足日常生化检测精度要求。     

pH-Shifting combined with ultrasound treatment of emulsion-filled β-conglycinin gels as β-carotene carriers: Effect of emulsion concentration on gel properties

In this work, emulsion-filled gels were prepared from natural and pH-shifting combined with ultrasound β-conglycinin (7S) as emulsifiers. The emulsifier modification and emulsion concentrations (5, 10, 15, 20 wt%) were evaluated on the structural and β-carotene release properties of the gels. Compared to the 7S hydrogel, the emulsion-filled gels exhibited better water-holding and textural properties. The 7S modification and the increase in emulsion concentration resulted in altered water distribution and improved microstructure and rheological properties of the emulsion-filled gels. The dense and homogeneous gel network was formed at an emulsion content of 15 wt%. The gels were regulated by different release kinetics in a simulated gastrointestinal environment. M−15 showed the highest bioaccessibility and chemical stability (72.25% and 89.87%) with good slow-release properties of β-carotene. These results will guide the development of encapsulated delivery systems for gel food products.     

Rapana thomasiana hemocyanin (RtH): dissociation and reassociation behavior of two isoforms, RtH1 and RtH2

Rapana thomasiana hemocyanin (RtH) is a mixture of two hemocyanin isoforms, termed RtH1 and RtH2. The two subunit types, purified by ion exchange chromatography, were used for macromolecular reassociation studies. In vitro reassociation was achieved with Tris-saline stabilizing buffer at pH 7.4, containing 100mM calcium and magnesium chloride at 4 degrees C. The relatively slow progress of reassociation was monitored, and the different oligomeric forms of RtH1 and RtH2 were studied by transmission electron microscopy, using samples negatively stained with 1% (w/v) uranyl acetate or 5% (w/v) ammonium molybdate containing 1% (w/v) trehalose at pH 7.0. The two subunits reassociate to produce characteristic didecamers, oligomeric and polymeric forms depending on the dissociated material and the reassociation conditions (i.e. divalent ion concentration, duration). In contrast to the didecamers of the freshly isolated RtH preparations, RtH1 and RtH2 show after 2 weeks' reassociation a clear tendency to generate multidecameric structures. The behavior of the native RtH1 and RtH2 during reassociation in the presence of 100mM calcium and magnesium chloride corresponds to the reported common oligomerization characteristics of KLH1/HtH1 and KLH2/HtH2, respectively. It is important to note that during the reassociation of the RtH isoforms: (I) no smaller diameter tubular polymers (ca. 25-27nm) were formed from the subunits as well as from the decamers; (II) multidecamers with one or more 'nucleating' didecamers were detected in addition to the multidecamers, composed of didecamers with associated decamers at one or both ends.     

Influence of different alcohols on the swelling behaviour of hydrogels

The swelling equilibrium of cross-linked poly(N-isopropylacrylamide) (PNIPAAm) hydrogels in alcohol solutions as a function of temperature, alcohol concentration, kind of alcohol (C₁OH–C₃OH) and gel properties was investigated experimentally. Additionally, the swelling degree as a function of the alcohol concentration was modelled with the UNIQUAC-Free Volume model in combination with the Phantom Network theory. The experiments show that, in pure water, the transition temperature is between 303.15 and 308.15?K depending on the properties of the gel and hence on the polymerization conditions. The transition from a swollen to a shrunken state is caused by the polymeric network and the change of polymer chain localization. In a system with hydrogel?+?water?+?alcohol, the swelling degree decreases with increasing alcohol concentration until the shrunken state is reached and increases again by further addition of alcohol at constant temperature. With increasing carbon number of the alcohols, the transition from a swollen to a shrunken state and vice versa shifts to lower concentrations at constant temperature. The use of the UNIQUAC-Free Volume model with Phantom Network theory leads to results in good agreement with the experimental data.     

EHPG-Tb(Ⅲ)体系荧光法测定稀土铽的研究

采用荧光光谱分析法,探索了N-N’-乙烯-二[2-(2羟基苯基)甘氨酸](EHPG)测定铽离子的最佳条件,建立了稀土铽的分析方法,在室温条件下,pH在7～9,最大激发和发射波长分别为296和547 nm,EHPG浓度为2.5×10-5 mol·L-1,反应3 min后在75 min内测定。结果表明：铽离子的测定范围为1.0×10-8～1.0×10-5 mol·L-1,检出限为1.18×10-9 mol·L-1,在稀土干扰离子存在下,回收率达98%以上,相对标准偏差为3.02％。供试稀土氧化物样品测试值与其含量吻合。     

Quasi-elastic laser light scattering study of polyacrylamide hydrogel immersed in water and salt solutions

Polyacrylamide (PAAm) hydrogels immersed in water and aqueous NaCl solutions were investigated for their structure and dynamics using static and quasi-elastic laser light scattering (QELS) techniques. Ensemble-averaged electric field correlation function f(q, t) obtained from the non-ergodic analysis of intensity-autocorrelation function for PAAm gel immersed in water and in 5 M NaCl showed an exponential decay to a plateau with an initial decay followed by saturation at long times. The value of the plateau was found to depend on NaCl concentration and was higher than that of water. Collective diffusion coefficient, D, of the polymer network of the hydrogel immersed in water and in different concentrations of NaCl was determined by analysing f(q, t). The measured diffusion coefficient showed linear decrease with increase in concentration of NaCl. The characteristic network parameters were obtained by analyzing f(q, t) with harmonically bound Brownian particle model and from static light scattering studies.     

Theory of XMCD spectra at the L2,3 absorption edges of mixed valence Ce and Yb compounds in high magnetic fields

We examine the structure of aggregates formed due to DNA interaction with dipalmitoylphosphatidylcholine (DPPC) in presence of Ca²⁺ and Zn²⁺ using small-angle synchrotron X-ray diffraction (SAXD) and neutron scattering (SANS). SAXD shows structural heterogeneity as a function of the cation concentration and temperature: At low cation concentration (∼1 mM), aggregates show two DPPC phases, one with a lateral segregation of DNA and cation, while higher cation concentration improves the DNA packing and the condensed lamellar phase is observed in DNA+DPPC+20mMion²⁺ aggregates. The SANS detected the dissolution of the condensed lamellar phase into unilamellar DPPC+Zn²⁺ vesicles due to gel ↦ liquid-crystal phase transition in DNA+DPPC+20mM Zn²⁺ aggregates with the short fragmented salmon sperm DNA.     

Direct imaging of dynamical heterogeneities near the colloid-gel transition

We observe the microscopic dynamics of a suspension of colloids with attractive interaction by confocal fluorescence microscopy to provide a deeper understanding of the relationship between local structure and dynamics near the gel transition. We study the distinct and self-parts of the van Hove density-density correlation function applied to our experimental data. Separable fast and slow populations emerge in the self-part, while the distinct part shows a pronounced signature of dynamic heterogeneities close to the gel transition, dominated by the fast particles. The slow population close to the gel transition shares features with an attraction-driven colloidal glass, including a plateau in the mean squared displacement that provides an estimate for the dynamical localization length.     

Conductivity and thermal stability of proton-conducting electrolytes at confined geometry of polymeric gel

The proton-conducting gel electrolytes based on poly(methyl methacrylate) (PMMA) doped by acid solutions in aprotic solvents were synthesized and discussed in this work. The gel conductivity as a function on concentrations of acid and polymer as well as of molecular mass of PMMA has been analyzed. The thermal stability of electrolytes was estimated and discussed. Extreme dependence of the conductivity on concentration is found to be for the gel (at a concentration of PMMA from 5 to 15 wt.%). The increase of electrical conductivity in the concentration range from 5 to 10 wt.% of PMMA with an increase in viscosity of the system is discussed as an indication of an involvement of the polymer matrix in increasing the mobility of the charge carriers in frame of Grotthuss mechanism.