Chromatographic investigation of the hydrophobic properties of selected cis-trans geometrical isomers

Summary Selected cis-trans isomers were semiquantitatively compared in respect to their hydrophobic properties. Investigations were carried out by thin-layer adsorption and partition chromatography; the solubilities of the individual substances in water were also determined. The results were evaluated to explain the comparatively weaker hydrophobic properties of the cis-isomers as compared to their trans-counterparts.     

High-performance liquid chromatographic analysis of dinitrobenzene isomers

Summary An efficient, reproducible and rapid high-performance liquid chromatographic method, in normal phase mode, for the analysis of the three dinitrobenzene isomers is described. The method affords good linearity for each isomer in the range 10–160 g ml^–1. The total analysis time is only 10 minutes, and the method shows an accuracy of ±1.25% with a coefficient of variation from 0.30% to 2.85% for different levels of the dinitrobenzene isomers.     

~1H-NMR法鉴定白芷中天然呋喃香豆素衍生物的研究

本文对从川白芷[Angelica dahurca(Fisch ex Hoffm)Benth et oohk cv hangbaizhl Hort]根中获得的12种呋喃香豆素衍生物进行了~1H-NMR法的鉴定比较研究,得到一些规律和谱线归属,为判断呋喃香豆素衍生物的结构、取代基的位置提供了数据。     

Separation of xylidine isomers on heteroaromatic compounds by gas-liquid chromatography

Summary Nicotinic acid and 1H-benzotriazole appreciably resolved all the xylidine (dimethylaniline) isomers, while benzimidazole, nicotinamide and phthalimide can also separate all the isomers except 2,4- and 2,3-xylidines. The analyses were carried out on supports which were not treated with an alkali.     

Nifuroxazide Photodecomposition: Identification of the (Z)-isomer by 1H-NMR Study

 The objective of this work was to identify the transformation product of nifuroxazide which appeared during stability studies of the drug in hard-capsules using high-performance liquid chromatography. The impurity appears on exposure to light, and test samples contained 21.5% of the impurity after two hours of exposure to light at room temperature. Mass spectrometry, infrared and nuclear magnetic resonance spectroscopy indicated the occurrence of a geometric isomer of nifuroxazide. In general, ¹H-¹H NOE difference experiments after irradiation were in agreement with a photochemical Z/E isomerisation of nifuroxazide following exposure to ambient light. Correspondence: Dr. M. J. Galmier, Faculté de Pharmacie, Place Henri Dunant, B.P. 38, F-63001 Clermont-Ferrand Cédex, France. e-mail: galmier@inserm484.u-clermont1.fr Received August 8, 2002; accepted November 9, 2002     

High-performance liquid chromatographic determination of urocanic acid isomers in cosmetic products

Summary A method has been developed for the determination of trans and cis urocanic acid in oil-in-water cosmetic emulsions. It involves an extraction of the sample in 1:3 methanol-aqueous NaOH (10⁻³ M), by ultrasonication, which leads to quantitative recoveries, and a reversed-phase HPLC isocratic elution for the analysis of the extract. Chromatography is performed on a C18 column using 0.1 M sodium perchlorate (pH 3.0)-acetonitrile 98:2 (v/v), as the mobile phase, and UV detection at 263 nm. The separation of the isomers is good. Linearity and precision of the method have been assessed.     

高分辨1H-NMR研究溶聚丁苯橡胶链化学结构

With a high-resolution 1H-NMR the features of solution-SBRs chain structures have been analyzed and made quantitative calculations of the chemical composites, inparticular, the contents of butadiene isomers have been made. It is reveal that the Bayer solution-SBR, whose performance is highly recognized inthe tire industry, has a high content of cis-1,4 butadiene isomers, allow content of trans-1,4 butadiene isomers, and a medium contents of 1,2add butadiene isomers and styrene units, as well as that the butadiene isomers display orderly characteristics in the sequence. The above structural features determine that Bayer solution-SBR can play good role in the balance of the low heat building up, antiwetskip and antiwear properties of green tire.     

Gas chromatographic analysis of xylidine isomers on heteroaromatic compounds

Summary Nicotinic acid, picolinic acid, isonicotinic acid, histidine and other amphoteric heteroaromatic compounds, uracil, thymine, isatin and other heteroaromatic compounds having imino and carbonyl groups as well as IH-benzotriazole, benzoguanamine and guanidine phosphate effectively resolved all the xylidine (dimethylaniline) isomers. Furthermore, the mixed phases of nicotinamide + p-amino-benzoic acid and melamine+barbituric acid also provided an appreciable resolution. These analyses were carried out using a support which were not treated with an alkali.     

Nucleosides as stationary phases for the separation of xylenol isomers by gas-liquid chromatography

Summary Adenosine, guanosine and inosine used as liquid phases in gas chromatography permits the separation of all six xylenol isomers.     

Retention behavior of dipeptide isomers in reversed-phase high-performance liquid chromatography

Summary The effects of eluent pH and organic modifier concentration on the capacity factor (k) and selectivity of dipeptide isomers were investigated. It has been observed that the variation in the logarithm of the capacity factor of the dipeptide isomers is linearly dependent on the organic modifier concentration (C_b), however, the selectivity is almost independent of it. Both capacity factor and selectivity were seriously affected by the pH of the eluent. Both the capacity factor and the intercept of the ln k vs. C_b plot increased with increasing van der Waals volume of the non-polar amino acid subunit of the dipeptides.     

Effect of subambient temperature on RP-HPLC of β-carotene isomers

Summary (E)-β-carotene and three mono-(Z)-isomers (9(Z)-, 13(Z)-, 15(Z)-) were eluted isocratically on a VYDAC 201TP54 column, using column temperatures between +30°C and −7°C. In this temperature range, their elution order changed dramatically with decreasing temperature. Nearly baseline separation of the four isomers within one hour was achieved at −7°C. For laboratory routine, temperatures of 9±2°C can be recommended. Thus, a good resolution of β-carotene- and lycopene-isomers (e.g. in tomato products) within 30 minutes is possible.     

1H-NMR spectra of some ditriazolyls and ditriazolyalkanes

Summary The proton magnetic resonance spectra of 12 azoles were measured in neutral and acidic solvents. The protonation shifts observed by comparison of the spectra inDMSO-d ₆ andTFA were attributed to an amidinium type resonance of the resulting cations. The synthesis and characterization of the azoles are also discussed.

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¹H-NMR-Spektren einiger Ditriazolyle und Ditriazolylalkane

Zusammenfassung Es wurden die¹H-NMR-Spektren von 12 Azol-Verbindungen in neutralem (DMSO-d ₆) und azidischem (TFA) Lösungsmittel gemessen und die chemischen Verschiebungswerte verglichen. Der Unterschied beider Werte beruht höchstwahrscheinlich auf einer Amidinium-Typ Resonanz der im azidischen Bereich entstandenen Kationen. Im Rahmen dieser Arbeit wurden 12 Azol-Verbindungen synthetisiert und beschrieben.

     

Liquid chromatography of isomers of aromatic acids on microbore column packed with anion-exchange resin

Summary A low-capacity, anion-exchange, porous-polymer resin was used as the packing material in a microbore column. Using a phosphate buffer containing various organic modifiers, retention behavior of substituted benzoic acid isomers with amino, chloro, methyl, nitro and carboxylic groups was investigated. The effect of ethanol, acetonitrile and sodium dodecylsulfate used as organic modifiers on the retention behavior at various eluent pH values was studies and optimum separations of the positional isomers reported.     

Gas-liquid chromatographic resolution of free dichlorophenol isomers on new stationary liquid phases

Summary It is difficult to separate all the dichlorophenol isomers as free phenols by gas-liquid chromatography. However they were effectively separated on 4,4-dimethoxyazoxybenzene (liquid crystal), and all the isomers were separated appreciably well on sodium 1-naphthalenesulfonate, 2-naphthalenesulfonate and dodecylbenzenesulfonate.     

Optimization of mobile phases for HPLC of cis-trans carotene isomers

Summary Various methanol-based, binary and ternary solvent systems were compared with respect to resolution of cis isomers of and -carotene by reversed-phase HPLC. A ternary system: acetonitrile-methanol-methylene chloride (751510), or a binary system: acetonitrilemethanol (9010 or 595) provided the best separation of -carotene and its four cis isomers, 9-cis, 13-cis, 15-cis and 13,15-di-cis--carotene. The elution order of 9-cis and 13-cis--carotene was dependent on the methanol concentration. Methanol-methylene chloride (991) resolved -carotene and its three cis isomers, 9-cis, 13-cis, and 15-cis--carotene. It also proved the best for simultaneous separation of cis isomers of and -carotene. Sample solvent can affect the separation efficiency of each isomer. The presence of cis isomers of and -carotene in fresh and cooked carrots was also determined.     

氢核磁共振谱自旋耦合裂分现象的量子力学解释

Hydrogen nuclear magnetic resonance spectroscopy (¹H-NMR) is an important content in the university course of instrumental analysis and organic structure analysis. The splitting law of spin coupling between hydrogen nuclei is the focus of teaching and learning. Most textbooks explain that the cause of spin coupling splitting is due to the local magnetic field produced by the different spin orientation of other adjacent nuclei (nuclei magnetic dipole-dipole interaction, direct nuclear spin coupling), and a few monograph on Nuclear Magnetic Resonance refers to electron spin polarization mediated nuclear spin coupling (indirect nuclear spin coupling). Here we introduce quantum mechanics for explanation of the splitting law of spin coupling between hydrogen nuclei.     

Solvent Effects on the 1H-NMR Chemical Shifts of Imidazolium-Based Ionic Liquids

The ¹H nuclear magnetic resonance (¹H-NMR) spectrum is a useful tool for characterizing the hydrogen bonding (H-bonding) interactions in ionic liquids (ILs). As the main hydrogen bond (H-bond) donor of imidazolium-based ILs, the chemical shift (δ_H2) of the proton in the 2-position of the imidazolium ring (H2) exhibits significant and complex solvents, concentrations and anions dependence. In the present work, based on the dielectric constants (ϵ) and Kamlet-Taft (KT) parameters of solvents, we identified that the δ_H2 are dominated by the solvents polarity and the competitive H-bonding interactions between cations and anions or solvents. Besides, the solvents effects on δ_H2 are understood by the structure of ILs in solvents: 1) In diluted solutions of inoizable solvents, ILs exist as free ions and the cations will form H-bond with solvents, resulting in δ_H2 being independent with anions but positively correlated with β_S. 2) In diluted solutions of non-ionzable solvents, ILs exist as contact ion-pairs (CIPs) and H2 will form H-bond with anions. Since non-ionizable solvents hardly influence the H-bonding interactions between H2 and anions, the δ_H2 are not related to β_S but positively correlated with β_IL.     

Semi-preparative high-performance liquid chromatographic separation of trimedlure isomers

Summary Semi-preparative high-performance liquid chromatographic procedures on 5 m silica were developed for the isolation of gram quantities of eight trimedlure isomers (trans: A, B₁, B₂, and C;cis: V, W, X, and Y) for comparative biological evaluation and NMR studies. Isolations were made from an eight-component 21cis: trans-trimedlure mixture, a four-componentcis-trimedlure mixture, trimedlure-B₂:X and trimedlure-C:W epimerization merization mixtures, a trimedlure-B₁:Y:B₂ mixture, and a trimedlure-A concentrate.     

2,7,16,21-四氧[8.8]对环吩-1,8,15,22-四酮的~1H-NMR研究

2,7,16,21-四氧[8.8]对环吩-1,8,15,22-四酮是一个新的大环化合物。由于它的苯环不能自由转动,而苯环上的质子是化学位移不等价的。这给研究羰基的屏蔽和去屏蔽区域提供了一个很好的例证。