Kinetics of epidermal growth factor/receptor binding on cells measured by total internal reflection/fluorescence recovery after photobleaching

Total internal reflection fluorescence (TIRF) microscopy is used to measure the dissociation kinetic rate of fluorescein-labeled epidermal growth factor from its specific receptors on the surface of intact but mildly fixed A431 human epidermoid cells in culture. Prior applications of TIRF microscopy have been limited to nonreceptor binding or to model membrane systems. The evanescent field excites fluorescence selectively at the surface of the cell proximal to the coverslip. Prismless epiillumination TIR is employed to avoid space limitations and is achieved by passing the excitation laser beam through a high (1.4)-aperture objective so that the light is incident at the glass/water interface beyond the critical angle. Long-term focus is maintained by a special feedback system. Of the possible effects that can influence the time course of the postbleach fluorescence recoveries—the EGF/receptor dissociation ratek ₂, the bulk solution diffusion rate of EGF, and the cell surface motion of the receptors—we infer that the dissociation ratek ₂ dominates. Several fitting schemes are compared and indicate the presence of a multiplicity of values fork ₂, ranging from about 0.05 to 0.004 s^–1, with an average value of about 0.012 s^–1. These results compare well with values previously obtained by radiolabel/washing techniques. The significance of the results in terms of kinetic models and the advantages of the TIRF technique for these sorts of measurements are discussed.     

Element determination in medieval soil samples by total reflection X-ray fluorescence analysis

An aqua regia extraction procedure for heavy metals in soils optimised for total reflection X-ray fluorescence analysis is presented. The procedure is applied to 92 soil samples of medieval layers from the city area of Dortmund. Sixteen elements (P, S, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Sr, Ag, Sn, and Pb) were used to characterise 17 sample sites. The results are projected onto the medieval urban structure of Dortmund. Two sites loaded with non-ferrous heavy metal could be detected and correlated with archaeological data. The efficiency and repeatability of the proposed extraction procedure is discussed.     

Analysis of low Z elements on Si wafer surfaces with synchrotron radiation induced total reflection X-ray fluorescence at SSRL, Beamline 3-3: comparison of droplets with spin coated wafers

The unique properties of synchrotron radiation, such as high incident flux combined with low divergence, its linear polarization and energy tunability, make it an ideal excitation source for total reflection X-ray fluorescence (TXRF) spectroscopy in order to non-destructively detect trace impurities of transition metals on Si wafer surfaces. When used with a detector suitable for the determination of low energy radiation this technique can be extended to the detection of low-Z elements, such as Al, Na and Mg. Experiments have been performed at SSRL Beamline 3-3, a bending magnet beamline using monochromatic radiation from a double multilayer monochromator. The wafer was mounted vertically in front of the detector, which was aligned along the linear polarization vector of the incoming synchrotron radiation. This configuration allows the detector to accept a large solid angle as well as to take advantage of the reduced scattered X-ray intensity emitted in the direction of the linear polarization vector. A comparison between droplet samples and spin coated samples was done, in order to compare the capabilities of vapor phase decomposition (VPD-TXRF) with conventional SR-straight-TXRF. Detection limits in the range of 50 fg corresponding to 2E10 atoms/cm² have been obtained for Na. The spin coated samples, prepared from solutions containing an equal amount of Na, Mg and Al showed an unexpected result when performing a scan of the angle of incidence of the incoming X-rays suggesting a different adsorption behavior of the elements in a multielement solution on the wafer surface. The observation of this behavior is important because the spin coating technique is the standard method for the preparation of surface standards in semiconductor quality control. This effect could be characteristic of the Na, Mg, Al solution used, but the angle dependence of the fluorescence signal of a standard should always be investigated before using the standard for calibration of the apparatus and quantification.     

Benzolignanoid and Polyphenols from Origanum Vulgare

A new dihydrobenzodioxane derivative, origalignanol ( 10 ), together with nine polyphenolic compounds, salvianolic acid A ( 1 ), salvianolic acid C ( 2 ), lithospermic acid ( 3 ), apigenin 7‐O‐β‐D‐glucuronide ( 4 ), apigenin 7‐O‐β‐D‐(6″‐methyl)glucuronide ( 5 ), luteolin, ( 6 ), luteolin 7‐O‐β‐D‐glucopyranoside ( 7 ), luteolin 7‐O‐β‐D‐glucuronide ( 8 ), and luteolin 7‐O‐β‐D‐xylopyranoside ( 9 ), were isolated from the aqueous ethanolic extract of the aerial parts of Origanum vulgare for the first time. The structure of new compound 10 was determined on the basis of spectroscopic methods. Compound 5 is probably an artifact formed during the isolation. Compounds 1, 2 and 3 showed strong DPPH radical scavenging activity with an EC₅₀ of 7.2 ± 0.4, 9.6 ± 0.9, and 9.5 ± 0.7 μM, respectively, and protected rat hepatocytes from CCl₄‐damage at 100 μM.     

Immunosensor for estrone with an equal limit of detection as common analytical methods

Immunoanalytical methods at a very low limit of detection (LOD) and a low limit of quantification (LOQ) are becoming more and more important for environmental analysis and especially for monitoring drinking water quality. Biosensors have suitable characteristics such as efficiency in allowing very fast, sensitive, and cost-effective detection. Here we describe a fully automated immunoassay for estrone with a LOD below 0.20 ng L^–1 and a LOQ below 1.40 ng L^–1. In contrast to common analytical methods such as GC-MS or HPLC-MS, the biosensor used requires no sample pre-treatment and pre-concentration. The basis of our sensitive assay is the antibody with a high affinity constant towards estrone. The very low amount of antibody per sample results in low validation parameters (LOD, LOQ, and IC50), but this assay for estrone represents the current device-related limitation of the River Analyser (RIANA).     

泥炭中全氮的测定

采用连续流动化学分析仪（Continuous Flow Analyzer,CFA）,对泥炭中的全氮进行分析.方法有良好的线性关系（r=0.9999）,回收率为99％-105％,测试速度是比色法测试速度的15-20倍,操作简便、准确度好,对氮化学研究有一定意义.     

Total Synthesis of (±)-Isocembrene: A Tactic for Both Diene Construction and Macrocycle Formation

Abstract

The total synthesis of (±)-isocembrene 1, a naturally occurring cembrene diterpenoid, has been achieved via a unified, convergent and highly efficient strategy by imploying an intramolecular Stille sp²–sp² macrocyclization as the key step and it presents an ideal opportunity to extend the effectiveness of the tactic for both 1,3-diene construction and macrocycle formation.     

First total synthesis of isoquinolinone alkaloid marinamide and its methyl ester

The first total synthesis of isoquinolinone alkaloid marinamide 1 and its methyl ester 2 was described. The key steps involved a regioselective Frieclel-Crafts reaction of 1-benzyl-1H-pyrrole to form the intermediate 8.     

Conductivity as a Sensor for Monitoring Relative Magnesium Corrosion Rates in Real‐time,in Serum‐containing Media under Cell Culture Conditions

Because controlling the corrosion rate of magnesium metal will be crucial to the success of biomedical implants containing pure magnesium or magnesium alloys, many ways have been sought to improve in vitro tests to analyze corrosion rates, and also to identify new methods of preparing or post‐processing magnesium. In this work, for an in vitro assay, we explored the use of a commercially available conductivity sensor to study magnesium corrosion under cell culture conditions that duplicate many physiologically appropriate parameters. With this sensor, we studied the corrosion of two previously untested magnesium single crystal samples that differed in surface treatments that could alter corrosion rates. The results show that the relative conductivity changes in (mS/cm) over the total time of immersion were proportional to the corrosion rates in (mm/y) and also to the total magnesium released, as detected by inductively coupled plasma mass spectrometry (ICP‐MS).     

Sedimentary process inferences from Humic substances analysis and deposition rates (Western Ross Sea,Antarctica)

The first 40?cm of sediment of three basins in the Ross Sea were sampled using a box corer. Site Y1 was located close to the coast in Terra Nova Bay; the sediment of site Y3 was collected in a more distal basin in the central sector of the Ross Sea; finally site Y5 was sampled in the deepest zone of the Joides Basin.

Sediment cores were sliced and analysed with a depth resolution of 2–4.5?cm. The distribution of humic substances and their structural features along the cores were determined and related to the pattern of Total Organic Carbon (TOC) and sedimentological data. The grain size distribution and the ²¹⁰Pb inventories allow the sediment of the study sites to be characterised.

The humic substance content in the sediment decreases, with a change in slope between 23 and 26?cm at Y1, between 12 and 15?cm at Y3 and constant values with further depth. At Y5 the depth profile of humic substance content shows constant values in the upper 17?cm and values decrease with further depth. The pattern of humic substance yield is similar to that found for TOC. The analysis of the elemental composition of the humic acids extracted from different sediment depths shows an increasing C/N atomic ratio at sites Y1 and Y3 and constant values along the Y5 core. The depth profile of the C/N atomic ratio is confirmed by the changes observed in the structural characterisation and indicates a shift from the freshly deposited organic matter on the sediment surface to more humified material (humin). The results obtained highlight a different sedimentation rate at the three sites as deduced from sedimentological analysis.