直链单烯烃保留指数与分子结构关系的研究

根据同系直链单烯烃保留指数与同碳数正构烷烃保留指数差值与分子碳数间关系曲线拟合,提出预测同系直链单烯烃保留指数的准确公式。在ＳＱ,ＰＦＥ,ＰＥＧ－４０００上,利用所提出的公式对检验集中化合物保留指数预测值与实测值差的标准偏差在±０．９ｉ．ｕ．～±１．５ｉ．ｕ．之间。并且研究发现,同碳数、同几何构型直链单烯烃各位置异构体分子中双键位置与化合物保留指数具有指数关系。首次提出依据分子中双键位置预测其保留指数的准确公式。公式适合各种不同极性固定相。     

Characterization of polymer monolithic stationary phases for capillary HPLC

Monolithic capillary columns have been prepared in fused‐silica capillaries by radical co‐polymerization of ethylene dimethacrylate and butyl methacrylate in the presence of porogen solvent mixtures containing various concentration ratios of 1‐propanol, 1,4‐butanediol, and water with azobisisobutyronitrile as the initiator of the polymerization reaction. The through pores in organic polymer monolithic columns can be characterized by “equivalent permeability particle size”, and the mesopores with stagnant mobile phase by “equivalent dispersion particle size”. Increasing the concentration of propanol in the polymerization mixture diminishes the pore volume and size in the monolithic media and improves the column efficiency, at a cost of decreasing permeability. Organic polymer monolithic capillary columns show similar retention behaviour to packed alkyl silica columns for compounds with different polarities characterized by interaction indices, I_x, but have different methylene selectivities. Higher concentrations of propanol in the polymerization mixture increase the lipophilic character of the monolithic stationary phases. Best efficiencies and separation selectivities were found for monolithic columns prepared using 62–64% propanol in the porogen solvent mixture. To allow accurate characterization of the properties of capillary monolithic columns, the experimental data should be corrected for extra‐column contributions.     

Limonene in Arizona liquid systems used in countercurrent chromatography. II Polarity and stationary-phase retention

The previous article in this series described the physico-chemical properties and chemical compositions of the two phases of the limonene–ethyl acetate–ethanol–water biphasic liquid system. This system was designed to be a “green” version of the so-called Arizona (AZ) scale of heptane–ethyl acetate–methanol compositions in which the heptane–ethyl acetate volume ratio is exactly the same as the methanol–water ratio. The first major difference between the standard and “green” AZ systems is the difference in upper and lower phase densities. The higher density of limonene compared with heptane greatly reduces the density difference of the “green” system: half the compositions have a density difference lower than 0.06 g mL^?1, precluding their use in hydrodynamic CCC columns. The other major difference is the phase polarity. The better distribution of ethanol between the upper organic and lower aqueous phases of the “green” AZ scale renders them more polar than their counterparts in standard heptane-based compositions. The test solutes aspirin and coumarin have higher distribution constants in the “green” AZ compositions. It is revealed that a hydrostatic column is suitable for use with all “green” compositions, with very good phase retention and limited driving pressure at high flow rates. A hydrodynamic column only functioned at limited flow rates with polar compositions of sufficient phase-density difference. The CCC chromatograms obtained with different compositions and columns are shown, and their peak position and sharpness discussed.     

Generalized Wiener indices in hexagonal chains

The Wiener index, or the Wiener number, also known as the “sum of distances” of a connected graph, is one of the quantities associated with a molecular graph that correlates nicely to physical and chemical properties, and has been studied in depth. An index proposed by Schultz is shown to be related to the Wiener index for trees, and Ivan Gutman proposed a modification of the Schultz index with similar properties. We deduce a similar relationship between these three indices for catacondensed benzenoid hydrocarbons (graphs formed of concatenated hexagons, or hexagonal chains, or sometimes acenes). Indeed, we may define three families of generalized Wiener indices, which include the Schultz and Modified Schultz indices as special cases, such that similar explicit formulae for all generalized Wiener indices hold on hexagonal chains. We accomplish this by first giving a more refined proof of the formula for the standard Wiener index of a hexagonal chain, then extending it to the generalized Wiener indices via the notion of partial Wiener indices. Finally, we discuss possible extensions of the result. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

基于分子结构预测气相色谱程序升温保留指数

从拓扑指数出发,研究了分子结构与气相色谱程序升温保留指数之间的关系。对所选择的部分分子结构,利用主成分回归(PCR)的相关系数R=0.9998,标准偏差S=9.987,交互检验(leave one out cross-valida-tion)所得标准偏差S=11.17。同时,对同一柱型不同升温速率条件下的保留指数之间的关系、同一升温速率不同柱型条件下保留指数之间的关系进行了初步探讨,建立的模型线性关系明显。     

Discrimination of isomeric structures using information theoretic topological indices

Three newly defined information theoretic topological indices, namely “degree complexity (I^d),” “graph vertex complexity (H^V),” and “graph distance complexity (H^D)” along with three other information indices have been used to study their discriminating power of 45 trees and 19 monocyclic graphs. It is found that the newly defined indices have satisfactory discriminating power while H^D has been found to be the only index to discriminate all the graphs studied.     

Butyl acrylate porous polymer monoliths in fused-silica capillaries for use in capillary electrochromatography

Capillary electrochromatography incorporates features of both capillary electrophoresis and liquid chromatography. Butyl acrylate polymers, cast in-situ with heat initiated polymerization and no retaining frits have been made. Van Deemter plots of chrysene have been examined at a variety of operating temperatures to examine column behavior. Hmin moves to faster flow-rates and increases slightly in magnitude as temperature is increased. The longevity and reproducibility of the columns have been examined with a homologous series. Performance is very reproducible between two different columns of different diameters, operated on different systems and prepared from the same polymeriation batch. The relative standard deviation of retention factors is a maximum of 3.1% with most values calculated at less than 1%. The uniformity of the polymers as a function of length has also been studied with a series of polycyclic aromatic hydrocarbons, and the columns have proved to be very uniform across their length as measured by the consistency of retention factors with a maximum relative standard deviation of 3.4% and most values calculated between 1 and 2%. Plate numbers of between 65000 and 80000 plates/m have been attained for compounds with retention factors of 3 to 12. These columns have proved easy to make, are quite reproducible, and long lived.     

Gas chromatographic retention indices for alkenes on OV-101 and squalane capillary columns

Summary Gas chromatographic retention indices for 47 C₅ to C₈ alkenes on OV-101 dimethylsilicone at 50 and 70 °C were determined within a standard deviation of 0.3i.u. Data obtained on OV-101 are compared with those measured on squalane. The comparison of the retention index and dl/dT values from both columns is presented as linear regression equations with correlation coefficients greater than 0.98.     

Capillary gas chromatography of aromatic bicyclic and tricyclic spiro ketones

Summary The separation of some aromatic bicyclic and tricyclic spiro ketones on fused silica capillary columns coated with polydimethylsiloxane, cyanopropylmethylsiloxane and poly(ethylene glycol) stationary phases was investigated. Retention indices were determined at two temperatures in order to enable understanding of the compounds’ chromatographic behaviour. The respective standard deviation values were 0.8, 0.5 and 0.3 index units. The influence of the polarity of the stationary phases on the chromatographic retention of these cyclic spiro ketones is discussed.     

Comparison of Retention Indices of Some Monosubstituted Benzenes Calculated by Different Mathematical Methods in RP-LC

In reversed phase liquid chromatography, the retention indices of benzene and nine mono substituted benzenes with different functionality based on the alkan-2-ones and alkyl aryl ketones retention index standards have been determined by the application of two new mathematical adaptation methods, viz. a multiparametric least-squares regression iterative method based on the determination of the adjusted retention times and a local cubic interpolation method directly using the total retention times. The two methods were applied to two types of columns. The first group includes four octadecyl-C₁₈ columns with different packing materials obtained from different manufacturers, while the second comprises an octyl-C₈ column. The retention indices have been extensively studied using either methanol–water or acetonitrile–water mobile phase systems. The influences of the concentration of the organic modifier in the mobile phase (methanol or acetonitrile), the column temperature, and the column packing material on retention indices of the set of the ten monoaromatics studied were also investigated. The calculated multiparametric retention indices values, those obtained by the local cubic interpolation and Kováts’ methods are compared. Good agreement was observed between the retention indices calculated by the three methods.     

Comparison of Retention Indices of Some Explosives and Related Compounds Calculated by Different Mathematical Methods in Reversed-Phase Liquid Chromatography

In reversed phase liquid chromatography, the retention indices of some neutral and acidic explosives and related compounds (nitramines, nitroaromatics, aminoaromatics, and nitrophenols) based on the alkan-2-one, alkyl aryl ketone, and 1-nitroalkane retention index standards have been determined by the application of a new mathematical adaptation method, viz. a multiparametric least-squares regression iterative method. This method was applied to two types of columns. The first group includes six octadecyl-C₁₈ columns with different packing materials and obtained from different manufacturers, while the second group comprises one octyl-C₈ column. The retention indices have been extensively studied using either methanol-water or methanol-phosphate buffer mobile phase systems. The calculated multiparametric retention indices values were compared with those obtained by Guardino's, Grobler's, and Kovàts' methods. The influences of the concentration of the organic modifier in the mobile phase, aqueous mobile phase pH, and the column packing material on the retention indices of the explosives were also investigated. Good agreement was observed between the retention indices calculated by the use of the four mathematical methods for both neutral and acidic explosives.     

Stability conditions for the solutions of the hartree-fock equations. VII. Stability of some closed-shell nonalternant systems

The instabilities of the solutions to the Hartree-Fock equations for the nonalternants in the pentalene, heptalene, etc., series and in the azulene, etc., series are examined. The systems are found to have symmetry-adapted solutions which are unstable for values of the core integral β close to the standard (spectroscopic) value; for example, the pentalene solution is unstable with β equal to 75% of its standard value. The “broken” symmetry solutions although exhibiting only a very slightly lower energy (0.01 eV) may exhibit dramatically different values for other properties, e.g., 30% changes in bond orders. The off-diagonal charge-density wave (CDW ) appearing in the “broken” symmetry solutions at the onset of instability is amplified as the cooperative phenomena dominate, until in the “fully correlated” limit, the linked-ethylenic (bond alternating) structure is obtained.     

Gas chromatographic separation of expoxystyrenes on carbowax 20 M capillary column

Summary The separation of some epoxystyrenes on fused silica capillary columns coated with poly(ethylene glycol) was investigated, Retention indices were determined at two temperatures to interpret chromatographic behaviour, The standard deviation was 0.3 index units.     

Estimation of Kováts retention indices using group contributions

We have constructed a group contribution method for estimating Kováts retention indices by using observed data from a set of diverse organic compounds. Our database contains observed retention indices for over 35,000 different molecules. These were measured on capillary or packed columns with polar and nonpolar (or slightly polar) stationary phases under isothermal or nonisothermal conditions. We neglected any dependence of index values on these factors by averaging observations. Using 84 groups, we determined two sets of increment values, one for nonpolar and the other for polar column data. For nonpolar column data, the median absolute prediction error was 46 (3.2%). For data on polar columns, the median absolute error was 65 (3.9%). While accuracy is insufficient for identification based solely on retention, it is suitable for the rejection of certain classes of false identifications made by gas chromatography/mass spectrometry.     

Reliability of the Assessment of Water Pollution by Petroleum Hydrocarbons and Phenols Using Some of Total Indices

The problems of the application of total indices “phenolic index” and “petroleum products” for water quality assessment are considered. It is demonstrated that these indices do not reflect the actual contamination of aquatic media by phenols and petroleum hydrocarbons. The effect of hydrocarbons of different classes on the error in determining petroleum products was revealed. The presence of phenols and other organic compounds was found to affect the results of the determination of the phenolic index. It is necessary to identify pollutants contained in wastewater to assess the applicability of total indices in the analysis of such waters. Marker components of wastewater must be included in the research program, in addition to total indices.     

Evaluation and comparison of n‐alkyl chain and polar ligand bonded stationary phases for protein separation in reversed‐phase liquid chromatography

Protein retention is very sensitive to the change of solvent composition in reversed‐phase liquid chromatography for so called “on–off” mechanism, leading to difficulty in mobile phase optimization. In this study, a novel 3‐chloropropyl trichlorosilane ligand bonded column was prepared for protein separation. The differences in retention characteristics between the 3‐chloropropyl trichlorosilane ligand bonded column and n‐alkyl chain modified (C₂, C₄, C₈) stationary phases were elucidated by the retention equation . Retention parameters (a and c) of nine standard proteins with different molecular weights were calculated by using homemade software. Results showed that retention times of nine proteins were similar on four columns, but the 3‐chloropropyl trichlorosilane ligand bonded column obtained the lowest retention parameter values of larger proteins. It meant that their retention behavior affected by acetonitrile concentration would be different due to lower |c| values. More specifically, protein elution windows were broader, and retentions were less sensitive to the change of acetonitrile concentration on the 3‐chloropropyl trichlorosilane ligand bonded column than that on other columns. Meanwhile, the 3‐chloropropyl trichlorosilane ligand bonded column displayed distinctive selectivity for some proteins. Our results indicated that stationary phase with polar ligand provided potential solutions to the “on–off” problem and optimization in protein separation.     

Effects of Permeation of Helium through the Walls of Fused Silica Capillary GC Columns

Hold-up times and peak widths have been measured in long fused silica GC capillary columns at high temperature with helium as the carrier gas. The results lead to the conclusion that the helium permeates through the column walls. The conventional Poiseuille theory of carrier gas flow has been extended to include this phenomenon. The resulting “loss modified Poiseuille” model, which uses literature values for the permeability of fused silica to helium, has been used to simulate the observed behavior. Good agreement between simulation and experiment validates the model. Simulations have been used to explore the effect of column permeability on hold-up times, peak widths, and velocity profiles over a broad range of column geometries.     

Optimizing data-acquisition schedules in physicochemical experiments : Part 2. Refinement of the Method and Principles of “Burst” (“Clustered-point”) Experimentation

A method was recently described for choosing the data-acquisition schedule in a physicochemical experiment so as to maximize the precisions obtained in evaluating the parameters that characterize the behavior of the system being studied. Separating the variables that control the spacing and distribution of the data points renders that method independent of the shape of the relative-influence curve. It also leads to substantial increases of the precision indices that express the degree of optimization attained, because it entails closer spacing than the original method and because the precision indices increase as the spacing becomes closer. The limit is reached in “burst” or “clustered-point” experimentation, in which the data are tightly bunched around the peak(s) of the relative-influence curve, and which provides the best precisions that can be secured from data corresponding to any particular values of the standard errors of measurement of the dependent and independent variables.