~(13)C代谢通量分析

代谢通量分析(metabolic flux analysis,MFA)是通过确定代谢网络中代谢流分布来表征细胞代谢状态的强有力的工具。鉴于计量学代谢通量分析在处理复杂代谢网络时表现出的局限性,发展了以13C标记实验为基础的13C MFA。本文介绍了13C MFA的原理与方法,总结和评述了13C MFA在实验与数据分析方面的最新进展以及MFA在功能基因组研究中的重要地位,同时对代谢通量分析的发展前景进行了展望。     

Improving the efficiency and convergence of geometry optimization with the polarizable continuum model: new energy gradients and molecular surface tessellation

New equations are derived and implemented for efficient and accurate computation of solvation energy derivatives for the conductor-like polarizable continuum model (C-PCM) and the isotropic integral equation formalism polarizable continuum model (IEF-PCM). Two new molecular surface tessellation procedures GEPOL-RT and GEPOL-AS that generate near continuous potential energy surfaces are proposed for PCM geometry optimization. The combined use of these new techniques leads to efficient and convergent geometry optimizations with the PCMs.     

Error estimation in peak‐shape analysis of XPS core‐level spectra using UNIFIT 2003: how significant are the results of peak fits?

An error analysis for numerically evaluating random uncertainties in x‐ray photoelectron spectroscopy has been implemented in version 2003 of the spectra treatment and analysis software UNIFIT in order to improve the understanding of the statistical basis and the reliability of the model parameters for photoelectron spectra. The theoretical basis as well as two approaches to obtain error limits of the fit parameters have been considered. Several test spectra have been analysed and discussed. A representative example has been chosen to demonstrate the relevance of the error estimation for practical surface analysis. Suggestions for the minimization of errors in the peak‐fitting procedures are presented. Copyright © 2004 John Wiley & Sons, Ltd.     

Performance of the diffusive gradients in thin films technique for measuring Ca and Mg in freshwater

Measurements of the major cations Ca and Mg by the technique of diffusive gradients in thin films (DGTs) were systematically evaluated. The concentration in solution was calculated using Fick’s first law of diffusion from the directly measured flux to the DGT device. A selective cation exchange resin (Bio-Rad Chelex^®100), which has been used extensively with DGT for trace metals, such as Cd²⁺, Cu²⁺ and Ni²⁺, was used for this work.

Elution of Ca and Mg from the resin with 1 M HNO₃ was very reproducible. Measurements of Ca and Mg concentrations in synthetic solutions agreed well with the theoretical predictions. The negative response on uptake caused by lowered pH was investigated. Uptake was found to decline below pH 5. The capacity of the DGT device for Ca and Mg was also investigated to establish maximum deployment times for given concentrations.

Experiments with filtered and modified lake water show that DGT can be used to measure Ca and Mg when trace metals are present in the solution. An in situ deployment of DGT combined with an ultrafiltration study suggest that the Mg concentration measured by DGT is similar to the concentration found in the fraction <1 kDa.     

基于差示扫描量热技术的生物质热解两步连续反应模型研究

采用差示扫描量热分析仪对我国的一种生物质试样在空气气氛中进行了实验, 发现试样从常温到923 K高温的低速升温过程中, 经历了两步明显的放热过程. 对放热机理的分析表明, 第一步主要是由半纤维素和纤维素的有氧热解过程控制, 第二步放热过程则受木质素热解和炭的氧化反应的共同作用. 采用等转化率方法和优化计算方法, 对热解过程的动力学模型进行了研究, 结果表明, 两步连续反应机理可用于描述生物质在空气气氛中热解的放热动力学.     

Combined use of high resolution TGA with the isoconversion method: Kinetic analysis of the thermal dehydration of KNbWO6·H2O

In the present study was combined the use of high resolution TGA with the isoconversion method, giving us a suitable methodology for determining the stages that occur during a reaction, and providing further insights about the kinetics of the processes involved. As a model reaction was used the thermal dehydration of KNbWO₆·H₂O. The results shown that the dehydration process is controlled by internal water diffusion (intra-crystallite); with activation energy values between 43 and 36 kJ/mol. This value is consistent with a diffusion mechanism dominated by van der Waals attractions. The estimated kinetic parameters are supported with a structural analysis, that suggest lower dimensionality character for water diffusion due to the specific orientations of 〈1 1 0〉 open channels in the pyrochlore framework. This would explain why the two-dimensional (D2) mechanism appears to be the most probable.     

The molecular and crystal structures of two diastereomeric 3,4-dihydropyrromethenones

The molecular and crystal structures of the two racemic diastereomeric 3,4-dihydropyrromethenone derivatives1 and2 of configurations (Z) and (E) were determined at 93 K (1, 2) and at room temperature (1). From an analysis of the crystallographically observed temperature coefficients a pseudorotation flexibility of the pyrrolidinone ring in the crystal is deduced. In both compounds a nearly orthogonal arrangement between the two heterocyclic ring systems is observed, which is ascribed to the steric bulk of the substituents in positions 1 and 3 of the pyrrolidinone ring.Herrn Prof.Josef Schurz zum 60. Geburtstag gewidmet.     

High-performance liquid chromatography with continuous gradient elution in screening for unknown metabolites of butoprozine directly in dog bile

This paper describes the screening for metabolites of butoprozine, a new anti-anginal drug, in dog bile by means of reverse-phase HPLC. Although it does involve a simple clean-up step to remove a substantial amount of endogenous bile compounds, this screening method nevertheless avoids extraction of metabolites and thus allows all metabolites to be introduced into the chromatographic system. A single run of 100 minutes from 100% water to 100% methanol in a linear gradient effects adequate separation of the great majority of metabolites without interference from remaining endogenous compounds. Two methods of differentiating between metabolite peaks and endogenous peaks have been worked out. The first one makes use of ¹⁴C-labeled butoprozine by measuring the amount of radioactivity in the column effluent while simultaneously recording the UV absorbance. The second method compares continuous gradient chromatograms of bile recorded before and after butoprozine administration under very similar conditions. The latter method can be applied to both radioactive and non-radioactive materials.