Automation of Structure Analysis. Part II. Automation of the Evaluation

The extent to which it is possible to automate the determination of a structure from the data collected with automatic measuring equipment is discussed. The development of the automatic evaluation is synchronous with that of digital computer program.—Even the simple calculation of structure factors from the intensities (i.e. the analysis of the geometrical and physical intensity factors) takes several weeks when the many thousand reflections are processed “manually”, i.e. with a desk calculator. A large electronic computer, on the other hand, executes these calculations in a few seconds. Nevertheless, even the largest computers available at present are too small for many of the complex steps in the calculation and for the quantity of data involved. Evaluation methods which, owing to long computing times, can at present only be tested on relatively simple structures will become more attractive with the advent of machines with computing times in the nanosecond range. For corrigendum see DOI: 10.1002/anie.196605112     

Modeling the fractionation process in TREF systems. II. Numerical analysis

Temperature raising elution fractionation (TREF) allows qualitative short chain branching (SCB) analysis in copolymers. In order to make the analysis quantitative, information on how such fractionation occurs must be incorporated into the interpretation of TREF spectra. In a previous work a model of the fractionation was proposed and some preliminary results given. In this article a rigorous mathematical analysis of the solution of the fractionation model is presented by defining two problems. The direct problem, of little practical use, helps to understand the fractionation process. The inverse problem consists in obtaining the distribution of crystallizable lengths (DCL) (directly related to the SCB distribution) from the TREF spectrum. This last problem (i.e., the main interest of this work) is explained in detail. TREF experiments are simulated solving the so-called direct problem using DCLs of different shapes. The synthetic TREF spectra are then processed using the inverse algorithm. The synthetic experiments demonstrate the adequacy of the proposed algorithm as a tool of analysis. A linear ethylene polymer was used to test, experimentally, the numerical procedure. The results obtained are in agreement with those obtained in earlier studies on the same sample by Raman spectroscopy. © 1996 John Wiley & Sons, Inc.     

Stopped-flow injection analysis. The influence of diffusion on dispersion of normal and reverse flow injection

A relationship is derived to enable the comparison of the dispersion heights of normal and reverse flow injection analysis (FIA). A single channel flow system is employed in the absence of a chemical reaction. The stopped-flow injection method is used to probe the influence of molecular diffusion on the overall dispersion of normal and reverse FIA, which appeared to demonstrate fundamentally different diffusion behaviors. Small discrepancies are observed between the dispersion heights, which are enhanced by the stopped-flow period, especially when unmatched matrix ionic compositions of the indicator and counter solutions were involved. For these conditions, the diffusion flux rate is enhanced considerably, displaying a peak, in addition to the transient, for both methods. The influence of diffusion on the dispersion characteristics of normal and reverse FIA is discussed theoretically. Diffusion in the proposed model is postulated to oppose dispersion by convection. The latter initiates concentration gradients in the injection zone and propagates it with flow time over the dispersion zone profile. The diffusion flux then reacts in order to confine the indicator dispersion for normal FIA and to enhance it for reverse FIA. This model is consistent with the experimental results and accounts for most of the phenomena encountered. Probably owing to the influence of secondary flow phenomena, the use of coiled tubes has suppressed the effects of diffusion on the overall dispersion behavior.Part of the experimental work was performed at IMI Institute for Research and Development, Haifa, Israel.     

Physico-chemical characterization of nanofiltration membranes.

This study presents a methodology for an in-depth characterization of six representative commercial nanofiltration membranes. Laboratory-made polyethersulfone membranes are included for reference. Besides the physical characterization [molecular weight cut-off (MWCO), surface charge, roughness and hydrophobicity], the membranes are also studied for their chemical composition [attenuated total reflectance Fourier spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS)] and porosity [positron annihilation spectroscopy (PAS)]. The chemical characterization indicates that all membranes are composed of at least two different layers. The presence of an additional third layer is proved and studied for membranes with a polyamide top layer. PAS experiments, in combination with FIB (focused ion beam) images, show that these membranes also have a thinner and a less porous skin layer (upper part of the top layer). In the skin layer, two different pore sizes are observed for all commercial membranes: a pore size of 1.25-1.55 angstroms as well as a pore size of 3.20-3.95 angstroms (both depending on the membrane type). Thus, the pore size distribution in nanofiltration membranes is bimodal, in contrast to the generally accepted log-normal distribution. Although the pore sizes are rather similar for all commercial membranes, their pore volume fraction and hence their porosity differ significantly.     

The non-isothermal thermogravimetric tests of animal bones combustion. Part. I. Kinetic analysis

The non-isothermal combustion of animal bones was investigated by simultaneous thermogravimetric and differential thermal analysis (TG–DTA), in the temperature range ΔT = 20–650 °C. The full kinetic triplet (A, E_a and f(α)) for the investigated process was established, using different calculation procedures: isoconversional (model-free) and the Kissinger's methods. The non-isothermal process occured through three reaction stages (I, II and III). Stage I was described by a reaction model, which contains two competing reactions with different values of the apparent activation energy. The autocatalytic two-parameter Šesták–Berggren (SB) model (conversion function f(α) = α^0.62(1 − α)^3.22), best described the second (II) reaction stage of bone samples. This stage, which corresponds to the degradation process of organic components (mainly collagen), exhibited the autocatalytic branching effect, with increasing complexity. Stage III, attributed to the combustion process of organic components, was best described by an n-th reaction order model with parameter n = 1.5 (f(α) = (1 − α)^1.5). The appearance of compensation effect clearly showed the existence of three characteristic branches attributed to the dehydration, degradation and combustion processes, respectively, without noticable changes in mineral phase. The isothermal predictions of bone combustion process, at four different temperatures (T_iso = 200, 300, 400 and 450 °C) were established in this paper. It was concluded that the shapes of the isothermal conversion curves at lower temperatures (200–300 °C) were similar, whereas became more complex with further temperature increase due to organic phase degradation.     

用IR,NMR,HPLC研究煤超临界抽提油F2馏分

本文采用ＩＲ、ＮＭＲ、ＨＰＬＣ方法研究了我国峰峰矿瘦煤、焦煤、肥煤三种烟煤超临界抽出物Ｆ＿２馏分，这一馏分为抽出油已烷可溶物（ｏｉｌ）在硅胶色谱柱上用苯冲洗而得到￣［６］。由ＩＲ、ＮＭＲ、ＨＰＬＣ分析结果表明：三种烟煤Ｆ＿２馏分主要由芳烃化合物组成；以单取代苯和邻位双取代苯为主（包括缩合环体系）；芳环上取代基链不长，其中含有相当数量的申基取代的芳烃化合物，像甲苯、甲萘、二甲基萘等等。三种烟煤Ｆ＿２馏分中都含有较多的双环和三环芳烃，以三环芳烃含量最多。双环芳烃主要是萘系化合物；三环芳烃为蒽、菲类化合物；单环和三环以上芳烃含量较少。     

Synthesis of two new thioesters bearing ferrocene: Vibrational characterization and ab initio calculations. X-ray crystal structure of S-(2-methoxyphenyl)ferrocenecarbothioate

Structural and conformational properties of S-benzyl ferrocenecarbothioate (I) and S-(2-methoxyphenyl) ferrocenecarbothioate (II) are analyzed using data obtained from X-ray diffraction, vibrational data and theoretical calculations. According to chemical quantum calculations, the synperiplanar and antiperiplanar forms are found as the first and second more stable conformations, respectively, for the title compounds. The geometric parameters and normal modes of vibration were calculated using a density functional theory method (B3LYP) and the 6-31+G∗∗ basis set for all atoms except for iron. For this atom the calculations were carried out with the Lanl2dz basis set. The calculated parameters are in good agreement with the corresponding X-ray diffraction values. The combined experimental and theoretical approach allows a consistent assignment for most of the fundamental modes.     

Comparison of Integration Vs. Fixed-Time Methods For Kinetic Analyses

Abstract

Results for an integration method of enzymatic analysis are directly compared to concurrently-achieved fixed-time rate data. Two to fiftyfold enhancement of signal-to-noise ratios are obtained for the integration method vs. the fixed-time method for theoretically-calculated response vs. time data. the signal-to-noise ratio improves substantially as the number of increments increases for estimating the integral of changes in product concentration over time. Also, advantages of the integration method are enchanced as enzyme activities increase and as instrument noise decreases.     

Structure-activity relationships of pyrethroid insecticides. Part 2. The use of molecular dynamics for conformation searching and average parameter calculation

Summary Molecular dynamics simulations have been performed on a number of conformationally flexible pyrethroid insecticides. The results indicate that molecular dynamics is a suitable tool for conformational searching of small molecules given suitable simulation parameters. The structures derived from the simulations are compared with the static conformation used in a previous study. Various physicochemical parameters have been calculated for a set of conformations selected from the simulations using multivariate analysis. The averaged values of the parameters over the selected set (and the factors derived from them) are compared with the single conformation values used in the previous study.     

Solid phase extraction of organophosphorus,triazine, and triazole-derived pesticides from water samples. A critical study

A critical study using C18 SPE columns for the determination of organophosphorus, triazine, and triazole-derived pesticides, nap-ropamide, and amitraz is presented. The type of sorbent, sorbent mass, flow rate in the extraction process, sample concentration of the different compounds, sample volume, pH, and ionic strength were evaluated. Special emphasis was placed on the evaporation step of eluates prior to GC determinations and on prefiltration of sample waters. Pesticide recovery is linear over a wide range of concentrations for most of compounds under study. Under general extraction conditions losses can be expected for amitraz, pro-metryn, prometon, dimethoate, penconazole, and propiconazole. At 100 ng L^?1, enhanced responses are produced for mevinphos, simazine, malathion, triadimefon, methidathion, and phosmet, which can be attributed to matrix effects. At basic pH, recovery of prometon, prometryn, and penconazole are improved. Low flow rates and high ionic strength enhance the recovery of prometon and prometryn. For phosmet, the influence of sample volume was established. Likewise, the influence of sorbent quantity was established for phosmet and dimethoate. Losses during the evaporation step were observed for mevinphos, dimethoate (> 50%), penconazole, propiconazole, and prometon (30%). Prefiltration of sample waters did not cause significant variations in the whole process of extraction. Impurities arising from the sorbent materials were not detected.     

Chemometric study of liquid water simulations. I. The parameters of the TIP4P model potential

The multivariate chemometric techniques two level factorial design (TLFD) and principal component analysis (PCA) were used to investigate the TIP4P model potential behavior with respect to perturbations on all intermolecular interaction parameters. The effects of these perturbations were calculated for the enthalpy of vaporization, the density, the first maximum of the radial distribution functions of the O-H and O-O pairs, and the second maximum of the radial distribution function of the O-H pair obtained from Monte Carlo simulations of liquid water at 25 degrees C. The principal effects were quantified and rationalized in terms of the pair-wise interaction potential of the TIP4P model. They also corroborate previously published sensitivity analysis results using molecular dynamics and other model potentials. In addition, significant interaction effects between some parameters of the TIP4P model potential were observed and quantified, which hardly could be obtained without such a statistic approach. These interaction effects are very regular and systematic, and their behavior has not been encountered in other chemometric studies and cannot be rationalized in terms of the functional form of the pair-wise potential.     

Analysis of glass and glass melts during the vitrification of fly and bottom ashes by laser-induced plasma spectroscopy. Part II. Process analysis

Laser-induced plasma spectroscopy (LIPS) is employed for in situ and on-line process analysis of major glass constituents during a vitrification process for fly and bottom ashes from waste incineration. The system is based on an Nd:YAG laser for plasma ignition, while the elemental emissions from the plasma are detected time-resolved by an intensified multichannel analyzer. The perpendicular, single axis, imaging optics allow a remote sensing of the composition of the hot glass melt. Taking into account the plasma characteristics for calibration, good agreement between the LIPS analysis and the established reference analysis is achieved for the concentration ratios of SiO₂, Al₂O₃, and CaO. In addition, LIPS is applied to the analysis of aerosols generated by homogeneous nucleation during the heating-up of the investigated fly ashes. A distinctive temperature dependence of the heavy metal concentration of the aerosols is observed.     

P. M. R. Spectroscopic Analysis of Bacterial Polysaccharides Containing Pyruvic Acid

Abstract

The characteristic p.m.r. signal at τ 8.4–8.6 given by the CH₃-C group of a pyruvic acid ketal (1-carboxyethylidene derivative)may be used to demonstrate the presence of such a substituent in polysaccharides. Similar signals are given when the pyruvic acid ketal is methylated or reduced. The method is convenient for monitoring purification procedures and chemical transformations of polysaccharides such as are involved in structural studies. In certain cases the molar ratio of pyruvic acid may be estimated.     

Molecular dynamics simulations of conserved Hox protein hexapeptides. I. Folding behavior in water solution

Molecular dynamics simulations of hexapeptides TFDWMK and LFPWMR; the highly conserved regions of Hox proteins Hox B1 and Hox B8, respectively, are carried out starting from extended structures to investigate their conformational space in water solution. In addition, we have studied TADWMK and TADAMK, where the aromatic residues Phenylalanine and Tryptophan were successively substituted for Alanine to investigate effects from the presence/absence of aromatic amino acids and interactions between them to folding behavior. The backbone of the hexapeptides in all simulations folds to a similar conformation found in experimental studies in solution. Intramolecular, hydrophobically driven interactions between the aromatic residues and internal hydrogen bonds are found to stabilize the conformations.     

The absolute retention index in chromatography. Part 1

A definition for an absolute retention index is given. This index is independent of whether the process is isothermal or temperature programmed. The relation between this index and Kovats's index is discussed. General equations are derived for the retention times of homologous series, from which the position of the air peak or missing members can be determined. Methods used in the literature for air peak determination are improved and extended to other cases of interest. The retention index in temperature programmed chromatography is reexamined in the light of recent publications on temperature programming.     

The Fundamental Basis for Cyclopolymerization. III. A Spectroscopic Study of Dimethacrylamides

The purpose of this investigation was to prepare suitable solid 1,6-dienes and the corresponding monoenes and to compare their UV and NMR spectra. A comparison of their polymerization characteristics will be reported in the succeeding paper of this series. The compounds chosen for this study were dimethacrylamide, N-isobutyrylmethacrylamide, and their N-methyl and N-phenyl derivatives. Since the dimethacryl derivatives are solids at room temperature, they are suitable monomers for solid-state polymerization studies, the results of which could lead to significant conclusions regarding the fundamental basis for cyclopolymerization. A previously postulated electronic interaction between the neighboring double bonds of the dienes should be detectable when their UV spectra are compared with their monoene counterparts. The UV spectra of the N-isobutyrylmethacrylamides and dimethacrylamides were compared with the spectra of the related di-isobutyramides, methacrylamides, and isobutyramides. The spectra of the diacylamides were much more complicated than predicted, and it seems that interaction of the carbonyls through the nitrogen is the major factor affecting the observed spectral transitions. This is different from the corresponding anhydrides in which the carbonyl groups appear to behave as isolated chromophores. The NMR spectra of the compounds were determined since a comparison of chemical shifts and variations of chemical     

Qualitative and quantitative analysis of phenolic acid glycosides in Ginkgo biloba L. leaf,G. biloba leaf extract and its injection

Ginkgo biloba L. leaf (GBL) is one of the most commonly used medicinal plants in the world. Phenolic acids with biological activities have a relatively high content in G. biloba leaf extracts (GBE); therefore they are of great significance for the quality control of GBL, GBE and its preparations. However, there have been few studies focused on their analysis. In this work, 12 phenolic acids, including 11 phenolic acid glycosides, were identified by liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (LC–Q-TOF/MS). Then, a method combining enzymolysis with HPLC was established for quantification of phenolic acid glycosides. It was found that the aglycones of phenolic acid glycosides mainly comprised five phenolic acids: 2,4,6-trihydroxybenzoic acid, protocatechuic acid, p-hydroxybenzoic acid, vanillic acid and p-coumaric acid. The quantitative method was validated, and the correlation coefficient (0.9993–0.9999), recovery (≥88.4%), repeatability (≤0.8%), and inter-day precision (≤5.5%) were satisfactory. Finally, the contents of glycosides of five phenolic acids in GBL, GBE and GBE injection from different sources were determined by the developed method. The method was accurate, repeatable and practicable, which could be helpful for the quantification of phenolic acid glycosides in other products containing GBL or GBE.     

PCB separation by HRGC-MS. Fourier analysis for characterizing Aroclor chromatograms

Aroclor and Aroclor mixture chromatograms obtained using temperature programmed high resolution capillary GC coupled with mass spectrometric selective detection have been investigated by Fourier analysis developed for the study of multicomponent chromatograms. The experimental autocorrelation function (EACF), i.e. peak shape and position correlation, showed a retention - structure pattern which could be associated with both the type of Aroclor and the ion used for selective ion monitoring (m/z value). In particular, o-m and m-m isomerization effects were singled out by EACF analysis. By fitting EACF with previously developed theoretical models, it was possible to characterize a specific Aroclor in terms of the number of PCB congeners present in it. The results obtained agreed closely with the typical Aroclor content. For the Aroclor mixture, the distribution of inter-distance between successive peaks was derived. The two first distribution moments obtained agreed with those derived from retention data reported in the literature. The consequences on the separation performance, i.e. the number of singlets, doublets, etc. in the chromatogram, are discussed.     

High speed analysis in packed columns. Part II. Some guidelines and procedures for time optimisation

Summary The work described in Part I has been extended to show that the basic equation derived therein can be reduced to allow a direct analytical solution. For convenience, solution by this technique is termed DAMAT-X (Direct Approach Minimising Analysis time based on X) to distinguish it from solutions obtained by the technique in Part I, named here simply DAMAT. An additional advantage of the reduced equation is that some solutions are readily available by inspection and this feature is illustrated diagrammatically. Finally it is indicated how DAMAT-X can be used as the basis for assessing the accuracy of other techniques based on the (h/ū) group, but which require less data for approximating to minimising conditions.     

Metrics of separation performance in chromatography. Part 1. Definitions and application to static analyses

Earlier introduced metrics of separation performance are described in a systematic way. After providing the definitions of the metrics suitable for a broad variety of applications, the study focuses on static analyses (isothermal GC, isocratic LC, etc.) and their general separation performance. Statistically expected number of resolved (adequately separated) single-component peaks is treated as the ultimate metric of general separation performance of chromatographic analysis. That number depends on the peak capacity of the analysis and the number of components in a test mixture. The peak capacity, in turn, depends on the separation capacity of a column and the lowest separation required by the data-analysis system for resolving poorly separated peaks. The separation capacity is a special case of a broader metric of the separation measure which is a function of column efficiency, solute separability, and the level of the solute interaction with a column stationary phase. The formulae for theoretical prediction of all these metrics for arbitrary pairs of peaks in static analyses are derived. To provide a better insight into the basic metrics of the separation performance, additional metrics such as the solute discrimination (relative difference in solute velocities), utilization of separability (solute discrimination per unit of their separability), specific separation (the separation per unit of separability), and others are defined and found for static analyses.