Development of a capillary electrophoresis-based assay of sirtuin enzymes

Sirtuins are a family of nicotinamide adenine dinucleotide (NAD(+))-dependent enzymes catalyzing the deacetylation of acetyl-lysine residues of histones and other proteins. Three 9-fluorenylmethoxycarbonyl (Fmoc)-labeled peptide substrates derived from the amino acid sequence of p53, i.e. Fmoc-KK(Ac)-NH(2), Fmoc-KK(Ac)L-NH(2) and Fmoc-RHKK(Ac)-NH(2), were synthesized and evaluated as substrates of the human isoenzyme SIRT1. The acetylated and respective deacetylated peptides as well as nicotinamide as the reaction product of nicotinamide adenine dinucleotide were separated by capillary electrophoresis in a fused-silica capillary using 200 mM phosphate-Tris buffer, pH 2.7. Sodium hydroxide-mediated sample stacking was performed in order to overcome peak asymmetry due to the high salt and acid content of the sample as well as to enhance UV detection sensitivity. The assay was subsequently validated. Upon incubation of the acetylated peptides for 60 min in the presence of 2.5 U of SIRT1 at least 87% of the peptides was deacetylated, indicating that the new derivatives are efficient substrates of the enzyme.     

Natural gas pipeline leak detector based on NIR diode laser absorption spectroscopy

The paper reports on the development of an integrated natural gas pipeline leak detector based on diode laser absorption spectroscopy. The detector transmits a 1.653 microm DFB diode laser with 10 mW and detects a fraction of the backscatter reflected from the topographic targets. To eliminate the effect of topographic scatter targets, a ratio detection technique was used. Wavelength modulation and harmonic detection were used to improve the detection sensitivity. The experimental detection limit is 50 ppmm, remote detection for a distance up to 20 m away topographic scatter target is demonstrated. Using a known simulative leak pipe, minimum detectable pipe leak flux is less than 10 ml/min.     

On the low surface tension of lung surfactant

Natural lung surfactant contains less than 40% disaturated phospholipids, mainly dipalmitoylphosphatidylcholine (DPPC). The mechanism by which lung surfactant achieves very low near-zero surface tensions, well below its equilibrium value, is not fully understood. To date, the low surface tension of lung surfactant is usually explained by a squeeze-out model which predicts that upon film compression non-DPPC components are gradually excluded from the air-water interface into a surface-associated surfactant reservoir. However, detailed experimental evidence of the squeeze-out within the physiologically relevant high surface pressure range is still lacking. In the present work, we studied four animal-derived clinical surfactant preparations, including Survanta, Curosurf, Infasurf, and BLES. By comparing compression isotherms and lateral structures of these surfactant films obtained by atomic force microscopy within the physiologically relevant high surface pressure range, we have derived an updated squeeze-out model. Our model suggests that the squeeze-out originates from fluid phases of a phase-separated monolayer. The squeeze-out process follows a nucleation-growth model and only occurs within a narrow surface pressure range around the equilibrium spreading pressure of lung surfactant. After the squeeze-out, three-dimensional nuclei stop growing, thereby resulting in a DPPC-enriched interfacial monolayer to reduce the air-water surface tension to very low values.     

Electrochemical investigation of redox thermodynamics of immobilized myoglobin: ionic and ligation effects

In this study, we investigated redox thermodynamics of myoglobin as well as the ionic (phosphate ions) and ligation (imidazole) effects via a dynamic electrochemical approach. We employed a previously established system that features nonmediated, direct electrochemistry of myoglobin and myoglobin in an immobilized state (i.e., diffusionless electrochemistry). Thermodynamics parameters were obtained by measuring redox potential (E degrees ') of myoglobin at varied temperature (T), in the presence and in the absence of specific ions or axial ligands. As a step further, we evaluated contributions from allosteric effect and axial iron ligation by partitioning E degrees ' changes into entropic and enthalpic terms. Compensation phenomena between the entropic and enthalpic changes were observed in all these cases. On the basis of these studies, we also correlated these phenomena to possible structural variations.     

Aflatoxin plate kit. Performance Tested Method 081003

The level of total aflatoxin contamination was analyzed in naturally contaminated and spiked samples of corn and peanut using the Aflatoxin Plate Kit. This kit is an enzyme-linked immunosorbent assay (ELISA) suitable for rapid testing of grains and peanuts. The assay was evaluated for ruggedness and linearity of the standard curve. The test kit results were then statistically evaluated for accuracy, precision, and correlation to a validated HPLC method (AOAC 994.08). The results were verified by an independent laboratory.     

1,9-Bis(N,N-dimethylaminomethyl)dipyrromethanes in the synthesis of porphyrins bearing one or two meso substituents

A synthesis of 5,15-disubstituted zinc-porphyrins has been developed that employs condensation of a 1,9-bis(N,N-dimethylaminomethyl)dipyrromethane+a dipyrromethane in refluxing ethanol containing zinc acetate followed by oxidation with DDQ. The N,N-dimethylaminomethylation of the dipyrromethane was achieved via Eschenmoser's reagent (N,N-dimethylmethyleneammonium iodide) in CH₂Cl₂ at room temperature. The synthesis is compatible with diverse substituents (e.g., alkyl, aryl, ester, acetal) and enables rapid synthesis of trans-AB-, A₂-, and A-porphyrins. The synthesis of >40 zinc porphyrins has been surveyed; 13 zinc porphyrins were isolated in yields of 5-20% without detectable scrambling.     

Preparation and characterisation of ultrafine amorphous alloy particles

Received: 3 July 1998     

稀土对PVC热稳定机理的光谱研究

稀土ＰＶＣ热稳定剂量是最近才发展起来的一类高效、无毒的稳定体系。本文通过对稀土化合物作用下ＰＶＣ降解的光声光谱和ＰＶＣ傅里叶红外光谱的分析证明,稀土热稳定剂具有优越的稳定性能。稀土作用下ＰＶＣ降解的光声光谱研究显示了稀土热稳定剂比其他热稳定剂具有更好的初色性能;红外光谱研究表明,稀土化合物的稳定作用是由于改变了ＰＶＣ分子的构象,从而增加了ＰＶＣ的稳定性。     

关于“测量最有利条件”教学的探讨

加强“测量最有利条件”的教学在物理实验课中有重要意义。测量最有利条件问题可分为函数极值、仪器准确度及物理现象规律性等类型。     

Lyapunov exponents,dual Lyapunov exponents,and multifractal analysis

It is shown that the multifractal property is shared by both Lyapunov exponents and dual Lyapunov exponents related to scaling functions of one-dimensional expanding folding maps. This reveals in a quantitative way the complexity of the dynamics determined by such maps. (c) 1999 American Institute of Physics.