Effect of sildenafil citrate on interleukin-1beta-induced nitric oxide synthesis and iNOS expression in SW982 cells

The purpose of this study was to identify the effect of sildenafil citrate on IL-1β-induced nitric oxide (NO) synthesis and iNOS expression in human synovial sarcoma SW982 cells. IL-1β stimulated the cells to generate NO in both dose- and time-dependent manners. The IL-1β-induced NO synthesis was inhibited by guanylate cyclase (GC) inhibitor, LY83583. When the cells were treated with 8-bromo-cGMP, a hydrolyzable analog of cGMP, NO synthesis was increased upto 5-fold without IL-1β treatment suggesting that cGMP is an essential component for increasing the NO synthesis. Synoviocytes and chondrocytes contain strong cGMP phosphodiesterase (PDE) activity, which has biochemical features of PDE5. When SW982 cells were pretreated with sildenafil citrate (Viagra), a PDE5 specific inhibitor, sildenafil citrate significantly inhibited IL-1β-induced NO synthesis and iNOS expressions. From this result, we noticed that PDE5 activity is required for IL-1β-induced NO synthesis and iNOS expressions in human synovial sarcoma cells, and sildenafil citrate may be able to suppress an inflammatory reaction of synovium through inhibition of NO synthesis and iNOS expression by cytokines.     

Spectrophotometric determination of tartrate in the presence of citrate

Methods are described for the determination of 5–30 μg of tartrate alone and of 15–60 μg in the presence of up to 6 mg of citrate, based on oxidation by 3 moles or 1 mole of periodate respectively. The iodate formed is determined spectrophotometrically at 350 nm as tri-iodide after reaction with iodide, the excess of periodate being masked with molybdate.     

Photocatalytic reaction by Fe(III)–citrate complex and its effect on the photodegradation of atrazine in aqueous solution

The photodegradation of atrazine in aqueous solutions containing citrate and Fe(III) was studied under Xe lamp irradiation on a time scale of hours. It was found that the presence of Fe(III)–citrate complex enhanced the photodegradation rate of atrazine as a result of OH attack. Atrazine photodegradation followed first-order reaction kinetics and the rate depended upon pH and light intensity. High citrate concentrations led to increased photodegradation of atrazine due to the fact that citrate not only acted as a carboxylate ligand but also a reductant of Fe(III). The interaction of Fe(III) with citrate was characterized using UV–visible absorption and Fourier-transform infrared (FTIR) spectroscopy, indicating that the hydrogen ions on the carboxyl groups were exchanged for Fe(III) ions. On the basis of these results, a reaction scheme was proposed in which the cycling of iron and carbon, the depletion of citrate and O₂, and the formation of reactive oxygen species (ROS) were involved.     

Complex citrates of metals in Inorganic Analysis : Some preliminary observations and the application of citrate complex formation in the qualitative analysis of the metallic ions of the Silver group

The use of sodium citrate as a reagent for the separation of silver group metals has been described. Silver, lead and mercurous ions are all capable of forming soluble citrate complexes, but they differ in their stability. The lead complex is not decomposed by soluble chlorides, whereas silver and mercurous complexes yield the insoluble chlorides. The fact that lead sulphate is soluble in a hot solution of sodium citrate has been utilized for the detection of lead, when present as insoluble sulphate, in a mixture.     

Insights into the early stages of metal nanoparticle formation via first-principle calculations: the roles of citrate and water

The early stages of silver nanoparticle formation in the presence of citrate and water have been investigated via first-principle theoretical calculations. Our study revealed that the charge density of the clusters is a key factor determining the selectivity among various growth pathways. An optimal charge density appears to control the selection between neutral and charged species in cluster growth; partially positively charged clusters are thermodynamically preferred and can serve as seeds for further growth. They interact favorably with both the solvent, leading to their solubility, and the citrate. The solvent (water) plays an important role in cluster growth both on the energetics of reactions including highly charged clusters and on the geometry of the resulting silver structures by preventing the formation of asymmetric ones (a structure directing action). Contrary to the common belief we found, from an energetic viewpoint, that growth of small clusters is not blocked by the citrate. Citrate, by acting as a reducing agent, opens up new channels for cluster growth involving highly charged species. By regulating the cluster charge, cluster-cluster associations may be promoted by the citrate, providing a new mechanistic interpretation for the effect of citrate concentration on nanoparticle size substantially different from the classic nucleation theory. From the citrate-silver and water-silver cluster interactions, linear free energy relationships have been retrieved that provide insights into metal nanoparticle growth mechanisms.     

Study of interaction of iron and lead during their uptake process in wheat roots by total-reflection X-ray fluorescence spectrometry

Microwave assisted acidic digestion and total-reflection X-ray fluorescence spectrometry (TXRF) was used for the determination of lead and iron in wheat roots cultured in CaSO₄ solution, and treated with Pb(NO₃)₂ and Fe(III)–citrate or Fe(III)–EDTA under controlled conditions, respectively. It was established that lead has a stimulation effect on the iron uptake in the presence of Fe(III)–citrate. The lead uptake, however, is hardly influenced by iron independently from the complex forming agents applied. To check the stability of the accumulated iron and lead constituents, some of the roots were washed with various solutions and the removable iron and lead were also measured by TXRF. These experiments indicate that the presence of lead results in higher stability of iron constituents in the root; however, iron does not have any effect on the lead constituents, the stabilities of which increase in the order Pb–citrate<Pb–(cell wall)<Pb–EDTA. © 1997 Elsevier Science B.V.     

Spectrophotometric determination of Cu(II) with sequential injection analysis

A sequential injection system, based on the reaction of Cu(II) with diethyldithiocarbamate (DDTC), was developed for the determination of Cu(II) in plant food and water samples. The extraction procedure, generally used to extract the Cu(II)–DDTC complex for subsequent analysis was eliminated in this procedure. The complex was detected spectrophotometrically in aqueous solutions at 460 nm. The physical and chemical parameters depicting the system were studied to obtain optimum conditions for sample analysis. The system developed is fully computerized and able to monitor Cu(II) in samples at seven samples per hour with a relative standard deviation of <4.50%. The calibration curve is linear from 0.5–5.0 mg/l with a detection limit of 0.2 mg/l. Interferences were reduced by introducing multiple flow reversals, to increase mixing between the reagent and sample zones, and subsequently enhance working of the masking agents (EDTA/citrate).     

Experimental study on effect of different parameters on size and shape of triangular silver nanoparticles prepared by a simple and rapid method in aqueous solution

This paper continues our previous work on preparation of truncated triangular silver nanoparticles. The method proceeds with reaction of silver nitrate with hydrazine in the presence of sodium citrate in aqueous solution, in which triangular nanoparticles are formed in a few minutes with some spherical ones. In particular range of reactants, especially high reductant concentration, only spherical nanoparticles are formed. In further investigation we observed that spherical nanoparticles shape could change to triangular by aging. This means that controlled growth of nanoparticles could lead to the formation of triangular ones. Therefore, a method was devised to slow down the rate of reduction by adding Fe³⁺ to the reaction solution. The results show that in this case more triangular nanoparticles are formed compared to the original one. This result also confirms that with the increasing hydrazine concentration, growth becomes less important compared to nucleation and smaller triangles are formed.     

Hydroxyapatite micro- and nanoparticles: nucleation and growth mechanisms in the presence of citrate species

Hydroxyapatite (HAP) particles with different morphologies were precipitated from homogeneous calcium/citrate/phosphate solutions at physiological temperature. Small variations of the starting solution pH in the range 7.4相似文献   

A selective voltammetric method for uric acid detection at Nafion(R)-coated carbon paste electrodes

A square-wave voltammetric method together with Nafion®-coated carbon paste electrodes were used for the selective determination of uric acid in the presence of a high concentration of ascorbic acid. Since the oxidation potential of uric acid is about 200 mV more positive than that of ascorbic acid at the Nafion®-coated carbon paste electrode, the selectivity can be greatly improved simply by applying an electrolysis potential of +0.4 V vs. Ag/AgCl where only ascorbic acid is oxidised. The acceptable tolerance of ascorbic acid concentration for the determination of uric acid is as high as 1.5 mM. With 30 s of electrolysis time, a linear calibration curve is obtained over the 0–50 μM range in 0.05 M citrate buffer solution, pH 4.0, with slope (μA/μM) and correlation coefficient of 0.34 and 0.9984, respectively. The detection limit (3σ) is 0.25 μM. The practical analytical utility is illustrated by selective measurements of uric acid in human urine without any preliminary treatment.     

Biomimetic arrays of oriented helical ZnO nanorods and columns

Extended helical or chiral nanostructures are usually associated with biomolecules but are mostly absent in synthetic materials. Here we report the first synthesis of unusual oriented and extended helical nanostructures in synthetic ceramics. Large arrays of oriented helical ZnO nanorods and columns are formed using simple citrate ions to control the growth habits of the ZnO crystal. This novel mechanism could lead to new approaches to control the orientation, the surface area, and the defect structure of synthetic materials that are critical for practical applications. The morphology generated in the helical ZnO nanostructure shows remarkable resemblance to the growth morphology of nacreous calcium carbonate and thus may shed new light on morphology and orientation control of biominerals.     

Ion-selective electrode measurements for the determination of formation constants of alkali and alkaline earth metals with low-molecular-weight ligands

Formation constants of acetate, hydrogencarbonate, malonate, citrate and 1,2,3-propanetricarboxylate complexes with Na⁺, K⁺ and Ca²⁺ were determined potentiometrically using sodium, potassium and calcium selective electrodes, at 25 °C and at different ionic strengths, in the range 0 < I ≤ 1 M. Formation constants obtained by ion-selective electrode (ISE) measurements were compared with those obtained by different techniques. It has been found that the use of ISEs gives reliable results in the study of weak complexes, also under non-constant ionic strength conditions.     

Cu2O微晶的可控制备及可见光催化亚甲基蓝降解性能

以醋酸铜为铜源, 柠檬酸钠为形貌导向剂, 乙二醇和水为溶剂, 采用溶剂热法制备了立方状形貌的Cu₂O微晶. 利用X射线衍射(XRD)、 X射线光电子能谱( XPS)、 扫描电子显微镜(SEM)、 透射电子显微镜(TEM)和紫外-可见漫反射光谱(UV-Vis DRS)等对Cu₂O微晶进行了表征. 结果表明, 在柠檬酸钠与醋酸铜摩尔比为1.0时, 于180 ℃反应5 h可以制备出尺寸分布在0.6~1.5 μm间的均一立方状形貌Cu₂O微晶. 研究了该微晶对亚甲基蓝(MB)在可见光下降解反应的光催化性能. 结果表明, 在H₂O₂存在下, Cu₂O微晶(0.3 g/L)在100 min内对30 mg/L MB溶液的降解率可以达到98%. 该催化剂经过8次循环使用对MB的降解率仍保持在96%以上, 展现了较高的催化活性及良好的稳定性. 通过活性物种的分析对催化体系的光催化机理进行了推测.     

Method development for the determination of lead in wine using electrothermal atomic absorption spectrometry comparing platform and filter furnace atomizers and different chemical modifiers

A method has been developed for the determination of lead in wine by electrothermal atomic absorption spectrometry without any sample preparation and calibration against aqueous standards, using 7.5 μg Pd as a chemical modifier. The results obtained for seven wines using the proposed method and an acid digestion procedure did not show any significant difference using a Student's t-test. Atomization in a transversally heated filter atomizer (THFA) was compared with atomization in a conventional transversally heated platform furnace. The former provided a 2.6-fold higher sensitivity, improving the characteristic mass from 34 to 12 pg and a 1.6-fold better limit of detection (0.3 μg L⁻¹ compared to 0.5 μg L⁻¹) for aqueous solutions using the same injection volume of 20 μL. However, the average precision, expressed as the relative standard deviation for the determination of lead in wine under routine conditions was improved from 4.6% with platform atomization to 0.6% in the THFA. The lead content found in seven arbitrarily chosen white and red wines, five from Brazil, one from Chile and one from Spain, ranged from 6 to 60 μg L⁻¹ Pb with an average content of 11.4 μg L⁻¹ Pb for the wines from South America.     

Indirect determination of cyclamate by an on-line continuous precipitation-dissolution flow system

A continuous-flow procedure is proposed for the indirect determination of sodium cyclamate by an atomic absorption spectrometric method in artificial sweeteners mixtures and soft drinks. Sulfamic group is oxidized to sulfate and it is continuously precipited with lead ion in a flow manifold. The lead sulfate formed is retained on a filter, washed with diluted ethanol and dissolved in ammonium acetate for on-line atomic absorption determination of lead, the amount of which in the precipitate is proportional to that of cyclamate in the sample. The proposed method allows the determination of sodium cyclamate in the range 1–90 μg ml⁻¹ with a relative standard deviation of 3.1% at a rate of ca. 35 samples per h. The 3σ detection limit is 0.25 μg ml⁻¹. The method is very selective, no compounds normally found in the analysed samples and other artificial sweeteners had any effect on the determination of cyclamate.     

Effects and structures of the O/Cu surfactant layer in O-mediated film growth of Cu on Ru(0 0 0 1)

The O-mediated Cu-film growth on O-precovered Ru(0 0 0 1) is investigated by means of scanning tunneling microscopy for growth temperatures between 300 and 600 K. Cu-films on clean Ru(0 0 0 1) grow in a multilayer mode. For O precoverages (Θ) between 0.2 ML (monolayer) and the saturation coverage (Θ=0.5 ML), a layer-by-layer growth is observed at growth temperatures between 350 and 450 K. On Cu-islands, an O/Cu surfactant layer is formed, which floats on-top of the growing film and induces the layerwise Cu-film growth. The surface coverage of the O/Cu surfactant layer linearly rises with the O precoverage up to Θ≈0.4 ML, where it completely covers the surface. Two different types of the surfactant layer are identified, inducing different surfactant mechanisms. For Θ=0.1–0.4 ML, the O/Cu surfactant structure (A-type) displays some local order and induces inhomogeneous nucleation at the misfit-induced relaxation structure of the Cu-film. The layer-wise growth is explained by the concept of two mobilities, implying a large attempt frequency for adatom jumps over the interlayer diffusion barrier at the steps. For Θ = 0.4–0.5 ML, a disordered O/Cu surfactant layer is established (B-type), inducing homogeneous nucleation. The layer-wise Cu-film growth is attributed to a reduction of the effective interlayer diffusion barrier. Cu-film growth at 400 K on the ordered (3×2√3)O/Cu structure formed at temperatures around 520 K yields the conclusion that the O/Cu surfactant structures are composed of randomly arranged O–Cu–O strings and disrupted “Cu₂O(1 1 1)” fragments.     

Interaction of citrate with Pt(100) surface investigated by cyclic voltammetry towards understanding the structure-tuning effect in nanomaterials synthesis

This study aims to understand the effects of functional agents such as capping agents, stabilizers, surfactants and additives in shape-controlled synthesis of nanomaterials. The well-defined Pt(100) single crystal surface was used as a model to investigate its interaction with citrate, a capping agent that is often used in shape-controlled synthesis of nanomaterials. It demonstrated that, through a systematic study of electrochemical cyclic voltammetry, the presence of citrate in solution could increase the current peak density of hydrogen adsorption at high potential (j p,L ), while decrease proportionally the current peak density of hydrogen adsorption at low potential (j p,S ). Furthermore, the increase of citrate concentration shifted negatively the peak potentials (E p,L and E p,S ) of both j p,L and j p,S . The results indicated that the interaction of citrate with Pt(100) surface could induce increasing the (100) surface domains of two-dimensional long range order (2D-(100)), and decreasing the (100) surface domains of one-dimensional short range order (1D-(100)). It also revealed that the interaction of citrate with Pt(100) surface could stabilize the 2D-(100) structure. The findings gained in this study implied that the citrate may lead to form stable 2D-(100) domains on Pt nanoparticles upon the shape-controlled synthesis of Pt nanomaterials.     

Use of silica gel chemically modified with zirconium phosphate for preconcentration and determination of lead and copper by flame atomic absorption spectrometry

An analytical method using silica gel chemically modified with zirconium (IV) phosphate for preconcentration of lead and copper, in a column system, and their sequential determination by flame atomic absorption spectrometry (FAAS), was developed. Sample solutions are passed through a glass column packed with 100 mg of the sorbent material, at pH 4.5, and lead and copper are eluted with 1.0 mol l⁻¹ HNO₃ at a flow rate of 2.0 ml min⁻¹. The extraction of copper is affected by Fe(II), Mn(II), Zn(II), Ni(II) and Co(II) while only Fe(II) interferes in the lead determination. These interferences may be overcome with an appropriate addition of a KI or NaF solution. An enrichment factor of 30 was obtained for both metals. While the limits of detection (3σ) were 6.1 and 1.1 μg l⁻¹, for Pb and Cu, respectively, the limits of determination were 16.7 and 3.3 μg l⁻¹. The precision expressed as relative standard deviation (R.S.D.) obtained for 3.3 μg l⁻¹ of Cu and 16.7 μg l⁻¹ of Pb were 4.3 and 4.7%, respectively, calculated from ten measurements. The proposed method was evaluated with reference material and was applied for the determination of lead and copper in industrial and river waters.     

Effect of hydrogen-ion concentration on the extraction of cobalt, nickel, cadmium and lead with APDC/MIBK: time stability of the extracts

The extraction of cobalt, nicke cadmium and lead ions by means of APDC/MIBK has been studied at various acidities of the aqueous phase (pH 0.2–6). Lead and nickel are extracted equally well over this pH-range, while cobalt and cadmium require pH> 1. The time stability of the extracted complexes in MIBK increases in the order cadmium < lead < nickel < cobalt. The decomposition of the complexing agent or the metal complexes is rapid in the two-phase system MIBK/water.     

Spectrophotometric determination of tin in copper-based alloys using pyrocatechol violet

In the present paper, a new procedure using Pyrocatechol Violet (PCV) for the determination of tin in copper-based alloys is proposed. The use of HEDTA as masking agent allowed tin to be determined in the presence of large amounts of copper, without any separation procedure. The method is more selective than previous methods. Cetyltrimethylammonium bromide (CTAB) and Tween-20 are used to increase the stability of the system.

The method can be applied directly to an acidic solution of Sn(IV) in the range 2.0–60.0 μg with a final volume of 50 ml. The pH is adjusted to 2.0 ± 0.2 with glycine buffer and, after 30 min, the absorbance is measured at 660 nm. Al(III), Cd(II), Co(II), Mg(II), Ca(II), Mn(II), Ni(II) and Pb(II) do not interfere at the 500 mg level; 20 000 μg of Cu(II) and 400 μg of NaCl can be present. The interference at 100 μg of Fe(III) can be masked with ascorbic acid. Bi(III), Sb(V), Ti(IV), Mo(VI), EDTA, tartrate, citrate and iodide interfere. The proposed method was used for tin determination in several copper-based alloys and a comparison of the analytical results with certified values indicates that the procedure provides accurate and precise results.