CEC and EKC of natural compounds

In this review, an overview of CEC and EKC methods with their developments are summarized for different natural compounds. It is divided into three main parts. The first part elaborates the separation of lipophilic compounds without any charged groups. The second part constitutes CEC and EKC of lipophilic compounds containing ionizable functional groups whereas the third part contains hydrophilic compounds. Packed, monolithic, coated, or raw fused-silica (FS) capillaries are among the choice for stationary phases. Applications of these phases on the above-mentioned three classes of compounds, coupled with different detection methods, e.g. MS or LIF, are explored and their advantages and disadvantages are discussed.     

Preparation approaches of the coated capillaries with liposomes in capillary electrophoresis

The use of liposomes as coating materials in capillary electrophoresis has recently emerged as an important and popular research area. There are three preparation methods that are commonly used for coating capillaries with liposomes, namely physical adsorption, avidin–biotin binding and covalent coupling. Herein, the three different coating methods were compared, and the liposome-coated capillaries prepared by these methods were evaluated by studying systematically their EOF characterization and performance (repeatability, reproducibility and lifetime). The amount of immobilized phospholipids and the interactions between liposome or phospholipid membrane and neutral compounds for the liposome-coated capillaries prepared by these methods were also investigated in detail. Finally, the merits and disadvantages for each coating method were reviewed.     

Comparison of different methods to measure contact angles of soil colloids

We compared five different methods, static sessile drop, dynamic sessile drop, Wilhelmy plate, thin-layer wicking, and column wicking, to determine the contact angle of colloids typical for soils and sediments. The colloids (smectite, kaolinite, illite, goethite, hematite) were chosen to represent 1:1 and 2:1 layered aluminosilicate clays and sesquioxides, and were either obtained in pure form or synthesized in our laboratory. Colloids were deposited as thin films on glass slides, and then used for contact angle measurements using three different test liquids (water, formamide, diiodomethane). The colloidal films could be categorized into three types: (1) films without pores and with polar-liquid interactions (smectite), (2) films with pores and with polar-liquid interactions (kaolinite, illite, goethite), and (3) films without pores and no polar-liquid interactions (hematite). The static and dynamic sessile drop methods yielded the most consistent contact angles. For porous films, the contact angles decreased with time, and we consider the initial contact angle to be the most accurate. The differences in contact angles among the different methods were large and varied considerably: the most consistent contact angles were obtained for kaolinite with water, and illite with diiodomethane (contact angles were within 3 degrees); but mostly the differences ranged from 10 degrees to 40 degrees among the different methods. The thin-layer and column wicking methods were the least consistent methods.     

Mass spectrometric study of randomly methylated beta-cyclodextrins using ionspray, atmospheric pressure chemical ionization and matrix-assisted laser desorption/ionization

Mixtures of methylated beta-cyclodextrins were characterized using three different methods of mass spectrometry: ionspray, atmospheric pressure chemical ionization (APCI) and matrix-assisted laser desorption/ionization (MALDI). Each of these methods allows a fast and simple determination of the degree of substitution, and can provide evidence for differences in the methylation of batches which have very similar global degrees of substitution. The three methods are in good qualitative agreement, but there are systematic differences in the quantitative results for the percentages of the various methylated molecules present in a batch. This is attributed to ionization yields which increase with the number of methyl groups, with different slopes for the different methods.     

Application of different polarimetric methods for the analysis of enzyme-catalyzed enantioselective reactions

Identification of model parameters in kinetic equations requires the determination of reactant concentrations in the course of time. In the case of enzyme catalyzed enantioselective reactions, three different polarimetric methods were used for concentration measurements obtained in both initial rate experiments and under dynamically changing conditions. Two on-line methods for the determination of different numbers of chiral species and a more universal off-line method were applied. For the investigated substrate 5-benzylhydantoin and the enzyme hydantoinase it is shown, that the obtained polarimetric data are most suitable for identification of kinetic parameters. Furthermore, it is demonstrated that on-line data of only one conversion allow for an assessment of an enzyme with regard to its enantioselectivity. Received: 20 October 1998 / Revised: 28 December 1998 / Accepted: 4 January 1999     

Chlorophyll-a determination: results of an interlaboratory comparison

A chlorophyll-a interlaboratory comparison was carried out to compare three different analytical chlorophyll-a determination methods: a German standard DIN 38412-16, a method of the HELCOM-Combine-Manual and the different “in-house” methods of participating laboratories. Eleven laboratories took part. They had to determinate the chlorophyll-a and phaeopigment content in two seawater samples taken from the Baltic Sea. Furthermore, for the assessment three different statistical evaluation methods were applied: the German standard DIN 38402-42, the Q-method combined with an estimator according to Huber and the Cofino-method. All analytical methods were appropriate to determine the chlorophyll-a content. The relative standard deviations of reproducibility for chlorophyll-a varied between 12 and 31%. None of the analytical methods was appropriate to determine the phaeopigment content quantitatively. The relative standard deviations of reproducibility for phaeopigments ranged between 87 and 158%. The applied statistical evaluation methods resulted in different assessments. The Q-method combined with an estimator according to Huber proved to be the best qualified method.Presented at the Eurachem PT Workshop September 2005, Portorož, Slovenia     

Considerations in the determination of orientational order parameters from X-ray scattering experiments

An assessment of the data processing and analysis methods used to obtain the second- and fourth-rank orientational order parameters of liquid crystals from X-ray scattering experiments has been carried out, using experimental data from four extensively studied alkyl-cyanobiphenyls and calculated data generated from two general types of theoretical orientational distribution function. The application of a background subtraction and two different baseline correction methods to the scattering profiles is assessed, along with three different methods to analyse the processed data. The choice of baseline correction method is shown to have a significant effect: an offset to zero overestimates the order parameters from the experimental and calculated data sets, particularly for lower order parameters arising from broad distributions, whereas an offset to a value estimated from regions of low scattering intensity provides experimental values close to those reported from other experimental techniques. By contrast, the three different analysis methods are shown generally to result in relatively small absolute differences between the order parameters. We outline a straightforward general approach to experimental X-ray scattering data processing and analysis for uniaxial phases that results in order parameters that match well with those reported using other experimental techniques.     

Encapsulation of living cells with polymeric systems

Microencapsulation of cells producing recombinant proteins or hormones leads to immunoprotection and immobilization in culture or in vivo. We are investigating three different strategies for the production of calcium cross-linked alginate beads of a small size with immobilized and immunoprotected mammalian cells: a) the AirJet technology (coaxial gas flow extrusion), b) the vibrating nozzle technology, and c) the JetCutter technology. A alginate/poly-L-lysine/alginate complexation was used as the polymeric system. All three methods may be used for production of homogeneous beads with a diameter of approximately 350 μm. While the vibrating nozzle technique was limited to an alginate viscosity of 0.2 Pa·s or less, the AirJet and JetCutter technology were less sensitive to higher viscosities. High frequency Scanning Acoustic Microscopy is used for mechanical characterization of the microspheres as well as for investigation of surface properties.     

Chemometrics in near-infrared spectroscopy

Spectroscopy methods of chemical analysis are excellent for the application of chemometric methods, because the measurements at many different wavelengths provide inherently multivariate data. The chemist generally requires three categories of information from specimens under investigation: quantitative data, qualitative data, and fundamental information on the properties of the material. Spectroscopy has long been used for all three purposes; the recent application of chemometric algorithms has assisted greatly in these endeavors. Although there is some overlap, three chemometric methods correspond to the three types of information: multiple regression, discriminant analysis, and principal components analysis. The basis of these chemometric methods and some of their strengths and limitations in application to near-infrared spectroscopy are discussed.     

Effect of ionizing radiation on polyaniline solutions

This communication presents the optical studies associated with transition doped (metallic)-neutral (semiconductor or insulator) state for conducting polymers. Special attention is focused on the electronic properties of polyaniline. The interconversion of different oxidation states of polyanilines has been studied by chemical and radiolytic methods. The polyaniline system is described by three sets of chromophores of three different oxidation states: fully reduced leucoemeraldine base (LB), partially oxidized emeraldine base (EB), and fully oxidized pernigraniline (PB). Each oxidation state can exist in its protonated form by treatment with an acid. All members of polyaniline family are spectroscopically distinguishable. The radiolytic study presents evidence that the polyaniline can exist in a continuum of oxidation states. The highly conducting form of polymer, i.e. emeraldine salt can be converted by using ionizing radiation into leucoemeraldine salt. The leucoemeraldine base is the final product of radiolysis of emeraldine base solution. The fully oxidized form of polyaniline can also be obtained by the irradiation of EB in the presence of CCl₄ or chlorobenzene.     

Free energy calculations using flexible-constrained, hard-constrained and non-constrained molecular dynamics simulations.

A comparison of different treatments of bond-stretching interactions in molecular dynamics simulation is presented. Relative free energies from simulations using rigid bonds maintained with the SHAKE algorithm, using partially rigid bonds maintained with a recently introduced flexible constraints algorithm, and using fully flexible bonds are compared in a multi-configurational thermodynamic integration calculation of changing liquid water into liquid methanol. The formula for the free energy change due to a changing flexible constraint in a flexible constraint simulation is derived. To allow for a more direct comparison between these three methods, three different pairs of models for water and methanol were used: a flexible model (simulated without constraints and with flexible constraints), a rigid model (simulated with standard hard constraints), and an alternative flexible model (simulated with flexible constraints and standard hard constraints) in which the ideal or constrained bond lengths correspond to the average bond lengths obtained from a short simulation of the unconstrained flexible model. The particular treatment of the bonds induces differences of up to 2 % in the liquid densities, whereas (excess) free energy differences of up to 5.7 (4.3) kJ mol(-1) are observed. These values are smaller than the differences observed between the three different pairs of methanol/water models: up to 5 % in density and up to 8.5 kJ mol(-1) in (excess) free energy.     

Multiple homo- and hetero-functionalizations of alpha-cyclodextrin through oriented deprotections

Introduction of one or more functions on a cyclodextrin in a regioselective manner is a complex task. The discovery of a blueprint strategy involving regioselective deprotection reactions of fully protected cyclodextrins, instead of functionalization of native cyclodextrins, allowed us to propose an efficient alternative to reach this goal. In this paper, we have applied previously delineated strategies, based on steric decompression, to duplicate our deprotection reaction, using a combination of mono- or di-deprotections to access cyclodextrins with two, three and five points of attachment for one, two or three different new functions. The patterns of multi-functionalization delineated here are not accessible by any other methods. Indeed, it is the first time ever a cyclodextrin bearing four different groups is synthesized in a completely controlled manner. This work paves the way to the use of cyclodextrins as multi-functional macrocyclic scaffolds, a use they have long been meant for, but lack of reliable functionalization methods hindered this development.     

Simulation of aggregate structure and SANS-spectra in filled elastomers

We report preliminary simulations of anisotropic scattering from aggregates of small hard spherical particles embedded in an elastic polymer matrix, using simple geometrical methods. First we build several types of aggregates in three dimensions: crystalline, amorphous compact, fractals, of different numbers of particles and varying polydispersity. We then turn to the spectra of deformed samples simulated in two dimensions. We impose an affine displacement inside the matrix to the fillers, which can be isolated particles or small aggregates, and account for the collisions which arise due to lateral shrinking of the material. The two-dimensional scattering spectra are shown and discussed. They reproduce experimentally observed isointensity curves: ellipses, banana-shaped maxima and splitting of these maxima in four spots. Finally, we explore the consequences of the reduction to two dimensions via statistics of the number of collisions. It is found that even if collisions are more important in 3 dimensions, the behavior is qualitatively similar in two and three dimensions.     

Temperature Calibration in Dielectric Measurements

Dielectric experiments are often performed in non-isothermal conditions. Thus, there is a difference between the temperature of the sample and the sensor temperature. In this work we propose and compare three temperature calibration methods based on the detection of transitions or relaxations: i) the melting of high-purity metallic standards (indium and tin), ii) the 2^nd order phase transition of a ferroelectric crystal (TGS); iii) the -relaxation of an amorphous polymer (poly(carbonate)). The results obtained from the three different methods were used to construct a calibration curve for a given heating rate.This revised version was published online in November 2005 with corrections to the Cover Date.     

Simultaneous separation and analysis of water- and fat-soluble vitamins on multi-modal reversed-phase weak anion exchange material by HPLC-UV

Several methods for the separation of vitamins on HPLC columns were already validated in the last 20 years. However, most of the techniques focus on separating either fat- or water-soluble vitamins and only few methods are intended to separate lipophilic and hydrophilic vitamins simultaneously. A mixed-mode reversed-phase weak anion exchange (RP-WAX) stationary phase was developed in our laboratory in order to address such mixture of analytes with different chemical characteristics, which are difficult to separate on standard columns. The high versatility in usage of the RP-WAX chromatographic material allowed a baseline separation of ten vitamins within a single run, seven water-soluble and three fat-soluble, using three different chromatographic modes: some positively charged vitamins are eluted in ion exclusion and ion repulsion modes whereas the negatively charged molecules are eluted in the ion exchange mechanism. The non-charged molecules are eluted in a classical reversed-phase mode, regarding their polarities. The method was validated for the vitamin analysis in tablets, evaluating selectivity, robustness, linearity, accuracy, and precision. The validated method was finally employed for the analysis of the vitamin content of some commercially available supplement tablets.     

Comparison of supervised pattern recognition methods with McNemar’s statistical test: Application to qualitative analysis of sugar beet by near-infrared spectroscopy

The application of supervised pattern recognition methodology is becoming important within chemistry. The aim of the study is to compare classification method accuracies by the use of a McNemar’s statistical test. Three qualitative parameters of sugar beet are studied: disease resistance (DR), geographical origins and crop periods. Samples are analyzed by near-infrared spectroscopy (NIRS) and by wet chemical analysis (WCA). Firstly, the performances of eight well-known classification methods on NIRS data are compared: Linear Discriminant Analysis (LDA), K-Nearest Neighbors (KNN) method, Soft Independent Modeling of Class Analogy (SIMCA), Discriminant Partial Least Squares (DPLS), Procrustes Discriminant Analysis (PDA), Classification And Regression Tree (CART), Probabilistic Neural Network (PNN) and Learning Vector Quantization (LVQ) neural network are computed. Among the three data sets, SIMCA, DPLS and PDA have the highest classification accuracies. LDA and KNN are not significantly different. The non-linear neural methods give the less accurate results. The three most accurate methods are linear, non-parametric and based on modeling methods. Secondly, we want to emphasize the power of near-infrared reflectance data for sample discrimination. McNemar’s tests compare classification developed with WCA or with NIRS data. For two of the three data sets, the classification results are significantly improved by the use of NIRS data.     

Determination of carbohydrates in juices by capillary electrophoresis, high-performance liquid chromatography, and matrix-assisted laser desorption/ionization-time of flight-mass spectrometry

The objective of this work was to develop a sample preparation procedure for determination of the carbohydrate profiles in commercial juice samples by three principally different analytical methods: capillary electrophoresis (CE) with indirect detection, high-performance liquid chromatography (HPLC), and matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS). The preparation and purification of juice samples prior to analysis is described. The method using Carrez reagents was found to be an efficient preparation tool for all three methods. The addition of Carrez reagents to the samples for mass analysis improved the quality of the mass spectra of oligosaccharides. The amounts of glucose, fructose, and sucrose as major carbohydrates in fruit juices measured by CE using a simple instrument are in good agreement with the HPLC values and the data declared by the producers of the juices. The results from both methods are critically evaluated and their impact for studies of authenticity is discussed. The decrease of sucrose amount during the storage of samples was explained by acid hydrolysis of this disaccharide.     

Comparison of different extraction and detection methods for sugars using amino-bonded phase HPLC

In this study, different methods are compared in order to quantitate individual sugars extracted from apple samples using methanol and water. Glucose, fructose, and sucrose are separated in 20 min using an amino-bonded carbohydrate column and a 75:25 acetonitrile-water mobile phase, followed by UV (190 nm) and refractive index detection. Variations in the sugar profiles are observed using different extraction or detection methods (or both) at a 1.4-mL/min flow rate. The data obtained show differences (p < 0.01) from both extraction or detection methods. The highest contents of free sugars studied occur in samples extracted with water.     

图案化TiO2薄膜的制备技术

本文综述了图案化TiO2薄膜的制备技术,按图案的生成方式可分为图案的直接生成,掩膜复制法,硬质模板复制法三大类。可以通过针尖写蚀法、电子书写蚀法、激光写蚀法、自组装法、光电化学法直接制备图案。掩膜复制法包括光刻胶法、自组装膜法、光敏凝胶膜法等。硬质模板法也称软刻蚀技术,分为复制微模塑、转移微模塑、毛细管微模塑、微接触印刷法、光-盖印印刷等技术。对每类方法的优缺点作了适当评述,对今后图案化TiO2薄膜制备的研究方向提出了一些建议。