GPC analysis of model compounds. I. Phenyl- and benzo-substituted aromatic compounds

A series of 36 compounds of known structure was used in a study to elucidate the mechanism of separation of gel-permeation chromatography (GPC). The various molecular dimensions were defined and measured for these compounds. The elution volume for these compounds was determined by GPC under specified and controlled conditions. The relationships between elution volume and molecular dimension were investigated using computer-based statistical analysis for the entire set of compounds and manual simultaneous equations for smaller sets of compounds. It was found that, as increasingly more molecular dimensions are considered, (1) the importance of the maximum molecular dimension A_p′ (the only dimension considered by many investigators) significantly decreases and (2) a significantly better prediction of the elution volume of these compounds could be made.     

Differences in retention of dioxin-like compounds and organochlorinated insecticides on an immunochromatographic column. Interpretation and applicability

The retention of organochlorinated compounds on an immunochromatographic column is studied. The compounds considered are usually found together in real samples of environmental concern, and include chlorinated biphenyls, chlorinated dibenzo-p-dioxins, chlorinated dibenzofurans, and organochlorinated insecticides. The different retention observed for different compounds is interpreted in light of the structural similarities of the compound studied with that used as a hapten to raise the antibodies employed as ligands in the immunochromatographic column. Differences in retention of the organochlorinated compounds on the immunocolumn make it possible to fractionate them. Mixtures of phosphate buffer solution and ACN in different ratios were used as desorption agents. Depending on the percentage of ACN employed, different fractionations of the organochlorinated compounds are obtained. The use of 20% ACN allows fractionation of most insecticides from chlorinated biphenyls, dioxins, and furans. Besides, chlorinated biphenyls of different chlorination degree can be separated. Moreover, pentachlorinated dioxins and pentachlorinated furans are separated from hexachlorinated biphenyls. Fractionation is of critical importance from a practical point of view, as it avoids some of the interferences that otherwise take place during the subsequent gas chromatography/mass spectrometry (GC/MS) analysis of these compounds. In this way, immunochromatography makes it possible to perform in a single step all the processes (extraction, clean-up, concentration, and fractionation) that are needed prior to the GC/MS analysis of these analytes in aqueous samples. An additional advantage of this method is the reusability of the immunoaffinity chromatography column for more than 500 times.     

Dereplication of Streptomyces sp. AMC 23 polyether ionophore antibiotics by accurate‐mass electrospray tandem mass spectrometry

Actinomycetes, especially those belonging to the genus Streptomyces, are economically important from a biotechnological standpoint: they produce antibiotics, anticancer compounds and a variety of bioactive substances that are potentially applicable in the agrochemical and pharmaceutical industries. This paper combined accurate‐mass electrospray tandem mass spectrometry in the full scan and product ion scan modes with compounds library data to identify the major compounds in the crude extract produced by Streptomyces sp. AMC 23; it also investigated how sodiated nonactin ([M + Na]⁺) fragmented. Most product ions resulted from elimination of 184 mass units due to consecutive McLafferty‐type rearrangements. The data allowed identification of four macrotetrolides homologous to nonactin (monactin, isodinactin, isotrinactin/trinactin and tetranactin) as well as three related linear dimer compounds (nonactyl nonactoate, nonactyl homononactoate and homononactyl homononactoate). The major product ions of the sodiated molecules of these compounds also originated from elimination of 184 and 198 mass units. UPLC‐MS/MS in the neutral loss scan mode helped to identify these compounds on the basis of the elimination of 184 and 198 mass units. This method aided monitoring of the relative production of these compounds for 32 days and revealed that the biosynthetic process began with increased production of linear dimers as compared with macrotetrolides. These data could facilitate dereplication and identification of these compounds in other microbial crude extracts. Copyright © 2014 John Wiley & Sons, Ltd.     

Spectral (u.v.-vis,i.r.MS), electrochemical and metallochromic properties of 2-hydroxy-benzoylhydrazones of acetylpyridines

The synthesis, electronic, infra-red and mass spectra of salicyloylhydrazones of 2-, 3-, and 4-acetylpyridine are reported. Ultraviolet absorption spectra have been applied to determine the dissociation constants which are ranged between 4.0–4.5 (pyridine nitrogen) and 6.2–6.3 (OH group). Infrared spectra show that strong intramolecular H-bonding exists in the solid compounds. Fragmentation of these compounds were found to undergo skeletal rearrangement in addition to either CON or NN simple bond cleavage; pyridine nitrogen position contributes in the paths leading to ions. These aroylhydrazones exhibit polarograms that show several reduction waves, the positions of which change with the pH value. Of the three compounds, 3-pyridyl derivative was the most difficult to reduce. The chelating properties of the compounds towards metal ions were investigated. The 2-acetylpyridine derivative results to be the most adequate ligand, as well as a good preconcentrating agent for metal ions.     

Understanding of rifamycin S. Reactions of the ansa-rings. Modifications of antibiotics. 8

The reactivity of rifamycin-S with respect to acids, bases, and oxydizing or reducing agents has been studied. A number of compounds resulting from these experiments as well as derivatives of rifamycin-S resulting from acylation and ketalisation reactions are described.     

Measurements of the order parameter by proton N.M.R. on N-(4-alkoxybenzylidene)4'-toluidines

N-(4-alkoxybenzylidene)4'-toluidines are a family of organic compounds which present a nematic and (depending on the chain length) a smectic mesophase. We have performed proton spin echo measurements on some members of the family in these mesophases. N.M.R. spectra present well-defined structures that can be assigned to one of the two end methyl groups on the basis of phenomenological as well as analytical discussion, despite the large number of protons contributing to the total line shape. The order parameter derived from this analysis is compared with optical data on the same compounds.     

Chromatographic methods for tetracycline analysis in foods.

The tetracyclines have served for decades as an important class of antibiotics in food animal health and production. As such, they have also been a source of concern for residue monitoring authorities around the world. In response to this concern a number of microbial inhibition, immunoassay and bacterial receptor methods have evolved for the detection of this class of compounds in various foods of animal origin. However, these methods often lack specificity and are subject to false positive and false negative results. For these reasons a number of chromatographic methods for the separation and determination of the tetracyclines isolated from foods have been developed that are capable of identifying and quantifying individual tetracycline drugs. We present here an overview of tetracycline analytical methods, including microbial inhibition, immunoassay and receptor technologies for detection, techniques for isolation from food matrices, and thin-layer chromatographic, high-performance liquid chromatographic, gas chromatographic and mass spectrometric procedures for determination of this class of compounds. A discussion of the variables involved in such methodology and a review of method criteria are offered.     

Regioregular head-to-tail oligothiophene-functionalized 9,9'-spirobifluorene derivatives. 2. NMR characterization,thermal behaviors,and electrochemical properties

Oligothiophene-functionalized 9,9'-spirobifluorene derivatives exhibit good solubility in polar organic solvents, especially compounds 5a-d to 7a-d due to the introduction of the flexible n-hexyl chain. The structures of all compounds studied are characterized and verified by (1)H and (13)C NMR spectra. The results not only show that these organic conjugated materials with no substituents or n-hexyl substituents are successfully synthesized through the corresponding synthetic methodologies, but also prove that chemical shifts of protons and carbons in the aromatic range change with the attachment and the increase of the thiophene ring at the 9,9'-spirobifluorene fragment. The thermal analysis results demonstrate that these compounds are quite stable, and evaporate from 300 to 700 degrees C. Most of these compounds exhibit a stable amorphous state in the solid state. The electrochemical properties of all compounds studied are also investigated. The results indicate that radical cation behaviors of oligothiophene-modified 9,9'-spirobifluorene derivatives are more stable than those of normal oligothiophenes, that oxidative and reductive peak potentials shift cathodically or anodically, and that the HOMO and LUMO energy levels are also tuned with the increase of the thiophene ring owing to the enhanced pi-electron delocalization and the increasing conjugation length. Oxidative potentials of nonsubstituted oligothiophene-functionalized 9,9'-spirobifluorene derivatives are more sensitive to the increase of thiophene rings than those of 9,9'-spirobifluorene derivatives with n-hexyl groups. The energy levels and band gaps of all compounds studied are also calculated from the onset potentials of n-doping and p-doping and are adjusted by varying thiophene oligomers and their attachment patterns to the 9,9'-spirobifluorene ring to make them suitable for the work functions of the electrodes.     

X-ray structural investigation of gossypol and its derivatives. IX. Semiclathrates of gossypol with esters of acetic acid

Inclusion compounds of gossypol with a number of acetic acid esters have been obtained and have been identified by derivatography and NMR spectroscopy. An x-ray structural investigation of the structures of crystalline complexes of gossypol with ethyl acetate and butyl acetate has shown that these complexes are isostructural semiclathrates. On the basis of the structures of these two semiclathrates of gossypol, it has been concluded that esters and ketone with chain lengths of from five to seven atoms form inclusion compounds isomorphous with the semiclathrates of ethyl and butyl acetates. If the chain length is shorter or longer than that given, inclusion compounds with a different crystal structure are formed.A. S. Sadykov Institute of Bioorganic Chemistry, Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 669–675, September–October, 1988.     

Repeatability and reproducibility of retention data and band profiles on reversed-phase liquid chromatography columns. III. Results obtained with Kromasil C18 columns.

The reproducibility of the retention data and the band profiles was investigated with Kromasil C18 columns (silica-based monomeric type reversed-phase packing material). High precision data were obtained and statistically compared among five columns from the same batch (column-to-column reproducibility) and six columns, one from each of six different batches (batch-to-batch reproducibility). These data were acquired under five different sets of chromatographic conditions, for a group of 30 neutral, acidic and basic compounds selected as probes following an experimental protocol previously described. Data characterizing the retention time, the retention factor, the separation factor, the column efficiency and the peak asymmetry for the different probe compounds are reported. Factors describing the silica surface interaction with the selected probe compounds, such as the hydrophobic interaction selectivity, the steric selectivity, and the separation factors of basic compounds at different pH values were also determined. The influence of the underlying silica on these data and correlations between the chromatographic and physico-chemical properties of the different batches are discussed.     

Fluorescence of tryptophan-containing peptides on paper or silica gel after treatment with formaldehyde, formaldehyde-ozone or formaldehyde-hydrochloric acid.

Sensitive and specific procedures for the chromatographic detection of tryptophan and tryptophan-containing peptides are described. Formaldehyde gas induces strong and characteristic fluorescence from tryptophan and peptides with NH2-terminal tryptophan residues on silica gel. On filter-paper, the detection of small amounts of these compounds requires the additional use of an oxidant, such as ozone. Treatment with formaldehyde-hydrochloric acid was used as a method for inducing fluorescence from tryptophan-containing peptides regardless of the position of the tryptophan residue in the peptide molecule. This reaction is useful for the chromatographic demonstration of small amounts of such peptides on both paper and silica gel. The spectral properties of the fluorophores of such tryptophan-containing peptides are distinctive and serve to distinguish them from all other known biogenic compounds that are capable of giving fluorescence with formaldehyde.     

秦岭龙胆的化学成分

从秦岭龙胆(Gentiana apiata N.E.Br.)全草的乙醇提取物中分离得到4个化合物,通过波谱分析分别鉴定为异荭草甙(isoorientin),龙胆苦甙(gentiopicroside),asystasioside A和蔗糖(D-sucrose).采用二维NMR分析,确定了asystasioside A的立体结构.以上化合物均为首次从该植物中发现.     

Trace analysis of carbonyl compounds by liquid chromatography-mass spectrometry after collection as 2,4-dinitrophenylhydrazine derivatives.

This study describes the utilization of carbonyl- 2,4-dinitrophenylhydrazine (DNPH) derivatives for the determination of a micro amount of carbonyl compounds in air by liquid chromatography-mass spectrometry (LC-MS). After the carbonyl compounds are collected using a Waters Sep-Pak C18 cartridge column with-impregnated DNPH on octadecylsilica, they are eluted by acetonitrile as carbonyl-DNPH derivatives. A 20-mm3 aliquot of eluent is injected into the LC-MS system. The four derivatives (formaldehyde-, acetaldehyde-, acrolein- and acetone-DNPH) were eluted within 7 min with acetonitrile-water (60:40, v/v) as the mobile phase. The proposed method offers sub-ppb sensitivity and good reproducibility and was applied to the determination of these carbonyl compounds in actual air samples from store rooms, laboratories and offices. The relative standard deviations for these samples (n = 6) were 1 to 3%.     

The mutagenic constituents of Rubia tinctorum.

Twenty compounds were isolated from the roots of Rubia tinctorum which are used as a commercial source of madder color. Among these compounds, mollugin (1), 1-hydroxy-2-methylanthraquinone (2), 2-ethoxymethylanthraquinone(11), rubiadin (13), 1,3-dihydroxyanthraqunone (14), 7-hydroxy-2-methylanthraquinone (16), lucidin (17), 1-methoxymethylanthraquinone (18) and lucidin-3-O-primeveroside (19) showed mutagenicity with Salmonella typhimurium TA 100 and/or TA 98. Since the mutagenic compounds isolated are anthraquinone derivatives with the exception of compound 1, structure-mutagenicity relationships of the anthraquinones were also studied. The results suggested that the greatest activity is exhibited by 1,3-dihydroxyanthraquinones possessing methyl or hydroxylmethyl group on carbon 2.     

Calculation of entropy and heat capacity of organic compounds in the gas phase. Evaluation of a consistent method without adjustable parameters. Applications to hydrocarbons

The purpose of this study has been to determine how well a consistent ab initio thermostatistical method reproduces experimental values of heat capacity and entropy. The method has been applied to calculation of heat capacity and entropy of a representative set of hydrocarbons that includes compounds consisting of multiple conformers. All Cp and S values are for the gaseous state at 1 atm; units are cal K-1 mol-1. A detailed sensitivity (error) analysis has been performed to determine the root mean square (rms) values of errors expected of the calculated values: these are 0.27 cal for Cp and 0.36 cal for entropy. In comparing calculated values with experimental values, it is necessary to consider also the uncertainties of the experimental data. When these are included, the expected rms values of Cp(experimental) - Cp(calculated) values at 298.15 K range from 0.21 to 0.73. For S(experimental) - S(calculated), they range from 0.36 to 0.72. Calculations with frequencies derived with the 6-31G(d,p) basis set and scaled by 0.91 yielded rms values for Cp(experimental) - Cp(calculated) of individual compounds from 0.14 to 0.84 cal and rms values for S(experimental) - S(calculated) of individual compounds from 0.07 to 1.11 cal. Calculated Cp values for 7 out of 16 compounds agree with experimental values within the rms uncertainty estimated for the compound, and 11 fall within twice that estimate. For entropy, the calculated values for 13 of 18 compounds agree with the very limited available experimental data within the rms estimated uncertainty for the compound, and 16 of 18 fall within twice the uncertainty.     

Prediction of retention indexes. II. Structure-retention index relationship on polar columns.

A method is described for the prediction of the retention index (I) from chemical structure, using the number of atoms in the molecule (Z), the I increment for atom addition (A) and the group retention factors (GRFs) of the functional groups and substituents. This method can predict the retention indexes of a wide range of compounds, such as acids, alcohols, amines, acid esters, aldehydes, ketones, ethers, aromatic hydrocarbons, alicyclics, heterocyclics, etc. on polar as well as non-polar columns to within 3% error. Accurate A and GRF values are essential to the prediction. These values can be obtained from homologous series, but a system of arbitrarily assigned A value and adjusted GRFs are also used. The GRFs of the substituents and functional groups depend on the polarity and polarizability of the analyte and the stationary phase and also on the molecular connectivity of the atoms, namely, primary, secondary and tertiary carbon atoms or hydrogen atoms, to which these groups are attached. Highly polar and polarizable groups can alter the A value. When the functionality of a group is masked by substitution, the analyte molecule will tend to behave chromatographically like hydrocarbons. The difficulty in predicting the I values of compounds of multi-functionality by the rule of additivity is the unknown intramolecular interaction that can alter both A and GRF values.     

Isoskeletomerism as an intermediate concept for mediating between stereoisomerism and isomerism. A remedy for conceptual defects of organic chemistry

After isoskeletomerism is introduced as an intermediate concept for mediating between stereoisomerism and isomerism, so-called ‘constitutional isomerism’ is critically discussed as one of the roots of confusion in organic chemistry. The convention that isomerism is subdivided into stereoisomerism and ‘constitutional isomerism’ is concluded to be misleading, because these concepts are conceptually distinct from a viewpoint of the concepts of equivalence relationships and equivalence classes. The indifference toward these concepts is one of the conceptual defects of organic chemistry. A new flowchart for judging enantiomerism, RS-stereoisomerism, stereoisomerism, isoskeletomerism, and isomerism is discussed to generate an isomer-classification diagram, where RS-stereoisomerism and isoskeletomerism are contained as new matters for remedying the conceptual defects. Skeletons are derived from basic skeletons by three operations (the bond operation, the replacement operation, and the substitutive operation), and they are used to examine the action of isoskeletomeric relationships. Equivalent molecular entities under an isoskeletomeric relationship are collected to give a set of isoskeletomers, which is concluded to be an equivalence class. The confusion caused by so-called ‘constitutional isomerism’ and its subcategories (‘skeletal isomerism’, ‘positional isomerism’, and so on) is critically discussed from the viewpoint of isoskeletomerism as a missing link. The double-entendre of the term constitution is examined when applied to both a 3D entity (a set of stereoisomers) and a 2D entity (a graph). Taxonomy of organic compounds and rational formulas, nomenclature of organic compounds, and combinatorial enumeration of chemical compounds are discussed from the viewpoint of isoskeletomerism.     

Synthesis of (+)-8-deoxyvernolepin and its 11,13-dihydroderivative. A novel reaction initiated by sulfene elimination leads to the 2-Oxa-cis-decalin skeleton

The title compounds are interesting candidates for antifungal screening. This paper describes the enantiospecific synthesis of these compounds starting from (+)-costunolide isolated from a commercially available extract. We used two novel reactions as key synthetic steps in this work: the acid-induced cyclization of an delta,epsilon-epoxy ester, which stereoselectively gave a hydroxymethyl-substituted delta-lactone, with the hydroxyalkyl group in the desired beta-equatorial disposition, and a reaction cascade, initiated by a base-promoted sulfene elimination, which led to a 10-oxiranyl-2-oxa-cis-decalin from the mesylate of a trans-fused delta-lactone. We also found that the reaction between selenium dioxide and the 1,5-diene system of elemanolides gave selenadecalins analogous to natural eudesmanolides. Our results prove that the synthetic strategy employed, on the basis of biomimetic concepts, is a useful procedure for the enantiospecific preparation of (+)-vernolepin-related compounds from accessible germacrolides.     

Quantitative thin-layer chromatography of pyrimethamine and related diaminopyrimidines in body fluids and tissues.

Several 2,4-diaminopyrimidines which inhibit the enzyme dihydrofolate reductase are quantitated following extraction and separation on silica gel thin-layer chromatographic plates. These compounds are candidates for the treatment of brain tumors and meningeal leukemia, because they have the ability to cross the blood-brain barrier. The ultraviolet absorption of the pyrimidine ring at 275 nm is utilized to quantitate these compounds on thin-layer chromatographic plates with a scanning instrument. This method offers the advantages of speed, specificity, versatility and sensitivity, and has proven to be satisfactory for the measurement of as little as 10 ng/ml of these compounds in biological fluids.