甲氧基多溴联苯醚色谱相对保留时间的QSRR研究

基于有机化合物定量结构与色谱相对保留时间的关系,对26个甲氧基多溴联苯醚化合物进行了B3LYP/6-31G*水平上的结构优化,并在优化结构基础上进行了分子连接性指数和量子化学结构参数的提取。应用SPSS统计软件对甲氧基多溴联苯醚化合物的色谱相对保留时间与分子连接性指数进行了多元线性回归(MLR)。结果表明,三阶类分子连接性指数可以很好地表达甲氧基多溴联苯醚化合物色谱相对保留时间与结构描述符之间的定量关系。用外部测试集的方法对模型预测能力进行了验证,结果表明:所建立的QSRR模型具有较强的稳健性和预测能力。     

A novel method for time-resolved fluorimetric determination and imaging of the activity of peroxidase, and its application to an enzyme-linked immunosorbent assay

A new type of fluorescence assay for the determination of peroxidase (POx) activity is presented. The assay is based on the indication of the enzymatic consumption of H(2)O(2) (HP), using a fluorescent europium-tetracycline (Eu(3)TC) complex as indicator. On addition of HP, this complex forms a highly fluorescent adduct (Eu(3)TC-HP), which is decomposed in the presence of POx to form the weakly fluorescent europium-tetracycline (Eu(3)TC). Hence, the activity of the enzyme can be directly determined by means of the luminescent Eu(3)TC complex as indicator. The POx assay demonstrated herein was elaborated starting from a spectral characterization of the complex systems involved. Due to the long lifetime of lanthanide luminescence, both steady-state and time-resolved luminescence assays can easily be performed. The time-resolved assay can quantify POx in the range from 4.0 x 10(-5) to 5.9 x 10(-3) U mL(-1), with a limit of detection of 1.0 x 10(-5) U mL(-1). The effects of POx inhibitors such as cyanide, hydroxylamine, and azide have also been studied. In addition, a time-resolved fluorescent detection method for a POx-based enzyme-linked immunosorbent assay (ELISA) has been developed, which is demonstrated in a sandwich model assay with bovine IgG serving as analyte. Furthermore, a time-resolved fluorescent imaging method is demonstrated that makes use of a straightforward imaging set-up adjusted to the optical properties of the europium reagent.     

Preparation of the individual compact single-chain globular particulates of Poly(N-isopropylacrylamide)

The compact single-chain (SC) particulates of Poly(N-isopropylacrylamide) (PNIPAM), which have been formed above its lower critical solution temperature in an aqueous solution containing the surfactant of sodium n-dodecyl sulfate (SDS), were recovered from the solution by freeze-drying. Under scanning electron microscopy, the compact particulate appears as a spherical or elliptical particulate individually dispersed in SDS, which acts as a solid solvent to prevent agglomeration. The conformation of the compact SC particulates of PNIPAM dispersed in SDS had been studied by the solid-state high-resolution ¹³C NMR spectroscopy. The ¹³C spin-lattice relaxation time T ₁ of the SC sample was determined in comparison with that of the original one. It was found that the T ₁ of the methyl carbon in the isopropyl group of the SC sample was about 45% higher than that in the original multichain sample, which revealed the differences in the motion of the methyl group in the different condensed states and illuminated the characteristic conformation of the compact SC globular particulates of PNIPAM.     

Time‐dependent density functional calculations on the electronic spectra of the neutral nickel complex [Ni(LISQ)2] (LISQ = 3,5‐di‐tert‐butyl‐o‐diiminobenzosemiquinonate(1−)) and its monoanion and dication

The electronic spectrum of the neutral nickel complex [Ni(L^ISQ)₂] (L^ISQ = 3,5‐di‐tert‐butyl‐o‐diiminobenzosemiquinonate(1^?)) and the spectra of its anion and dication have been calculated by means of time‐dependent density functional theory. The electronic ground state of the neutral complex exhibits an open shell singlet diradical character. The mandatory multireference problem for this electronic ground state has been treated approximately by using the unrestricted and spin symmetry broken Kohn‐Sham Slater determinant as the wave function for the noninteracting reference system in the time‐dependent density functional calculations. A reasonable agreement with observed transition energies and band intensities has been achieved. This holds also for the long wavelength transitions that are shown to be of charge transfer type. The charge distributions in the electronic ground state and the corresponding low lying excited states, however, are rather similar. Thus, the known failure of standard time‐dependent density functional theory to describe improperly long range charge transfer transitions is absent in this work. The applied computational scheme might be adequate for calculating electronic spectra of transition metal complexes with noninnocent ligands. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Analysis of phenolic choline esters from seeds of Arabidopsis thaliana and Brassica napus by capillary liquid chromatography/electrospray‐ tandem mass spectrometry

Total phenolic choline ester fractions prepared from seeds of Arabidopsis thaliana and Brassica napus were analyzed by capillary LC/ESI‐QTOF‐MS and direct infusion ESI‐FTICR‐MS. In addition to the dominating sinapoylcholine, 30 phenolic choline esters could be identified based on accurate mass measurements, interpretation of collision‐induced dissociation (CID) mass spectra, and synthesis of selected representatives. The compounds identified so far include substituted hydroxycinnamoyl‐ and hydroxybenzoylcholines, respective monohexosides as well as oxidative coupling products of phenolic choline esters and monolignols. Phenolic choline esters are well separable by reversed‐phase liquid chromatography and sensitively detectable using electrospray ionization mass spectrometry in positive ion mode. CID mass spectra obtained from molecular ions facilitate the characterization of both the type and substitution pattern of such compounds. Therefore, LC/ESI‐MS/MS represents a valuable tool for comprehensive qualitative and quantitative analysis of this compound class. Copyright © 2008 John Wiley & Sons, Ltd.     

Mass defect filter technique and its applications to drug metabolite identification by high‐resolution mass spectrometry

Identification of drug metabolites by liquid chromatography/mass spectrometry (LC/MS) involves metabolite detection in biological matrixes and structural characterization based on product ion spectra. Traditionally, metabolite detection is accomplished primarily on the basis of predicted molecular masses or fragmentation patterns of metabolites using triple‐quadrupole and ion trap mass spectrometers. Recently, a novel mass defect filter (MDF) technique has been developed, which enables high‐resolution mass spectrometers to be utilized for detecting both predicted and unexpected drug metabolites based on narrow, well‐defined mass defect ranges for these metabolites. This is a new approach that is completely different from, but complementary to, traditional molecular mass‐ or MS/MS fragmentation‐based LC/MS approaches. This article reviews the mass defect patterns of various classes of drug metabolites and the basic principles of the MDF approach. Examples are given on the applications of the MDF technique to the detection of stable and chemically reactive metabolites in vitro and in vivo. Advantages, limitations, and future applications are also discussed on MDF and its combinations with other data mining techniques for the detection and identification of drug metabolites. Copyright © 2009 John Wiley & Sons, Ltd.     

Ultrafast Dynamics of o‐Bromofluorobenzene Studied by Time‐Resolved Photoelectron Imaging

Photodissociation dynamics and rotational wave packet coherences of o‐bromofluorobenzene are studied by femtosecond time‐resolved photoelectron imaging (see figure). The decay of different photoelectron rings shows the population decay of states from which the lifetimes of different states are determined. The variation of photoelectron angular distributions reflects the evolution of rotational coherences.

     

Headspace solid phase microextraction in the determination of pesticides in water samples from the Okavango Delta with gas chromatography-electron capture detection and time-of-flight mass spectrometry

Headspace solid phase microextraction (HS-SPME) was optimized for the analysis of pesticides with gas chromatography electron capture detection (GC-ECD) and high-resolution mass spectrometry. Factors influencing the extraction efficiency such as fiber type, extraction mode and temperature, effect of ionic strength, stirring and extraction time were evaluated. The lowest pesticide concentrations that could be detected in spiked aliquots after HS-SPME–GC-ECD ranged from 0.0005 to 0.0032 μg L^{− 1}. Consequently hexachlorobenzene, trans-chlordane, 4,4′-DDD and 4,4′-DDE were detected in water samples after HS-SPME at concentrations ranging from 2.4 to 61.4 μg L^{− 1} that are much higher than the 0.1 μg L^{− 1} maximum limit of individual organochlorine pesticides in drinking water set by the European Community Directive. The same samples were cleaned with ISOLUTE C₁₈ SPE sorbent with an optimal acetone/n-hexane (1:1 v/v) mixture for the elution of analytes. No pesticides were detected after SPE clean-up and pre-concentration. Precision for both methods was satisfactory with relative standard deviations less than 20%. This work demonstrated the superiority of HS-SPME as a sample clean-up and pre-concentration technique for pesticides in water samples as well as the need to identify and control point sources of pesticides.     

Alkali-hydroxide-doped matrices for structural characterization of neutral underivatized oligosaccharides by MALDI time-of-flight mass spectrometry

We report new approaches using alkali-hydroxide-doped matrices to facilitate structural characterization of neutral underivatized oligosaccharides by matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) MS. The approaches involved pretreatment of the analytes with NaOH or LiOH in aqueous solution, followed by mixing them with MALDI matrices prior to MS analysis. It was found that for open-ended neutral underivatized oligosaccharides partial alkaline degradation occurred upon laser desorption and ionization of the hydroxide-pretreated analytes in 2,5-dihydroxybenzoic acid (DHBA). The effect intensified when nonacidic compounds such as 2,4,6-trihydroxyacetophenone (THAP) and 5-amino-2-mercapto-1,3,4-thiadiazole (AMT) were used as matrix. The degradation allowed facile identification of the reducing end residue of the analyte and facilitated its structural characterization by postsource decay TOF-MS. Applying the same technique using matrices composed of LiOH and THAP or AMT led to the production of singly as well as multiple lithiated ions of oligosaccharides containing hexoses with free 3-OH groups. Extensive lithiation through multiple hydrogen-lithium exchanges up to 6 Li atoms was observed for maltoheptaose, beta-cyclodextrin, and dextran 1500. Such a 'lithium tagging' technique makes it possible to differentiate positional isomers of milk-neutral oligosaccharides, lacto-N-difucohexaose I and II (LNDFH-I and LNDFH-II), without the need of chemical derivatization or tandem MS analysis.