Discrimination Of Isomers Research Articles

Branched alkanes from ancient and modern sediments: Isomer discrimination by GC/MS with multiple reaction monitoring

Linked scanning of a tandem sector mass spectrometer has been used to identify abundant, first field free region (FFR1) unimolecular fragmentations in branched and isoprenoid hydrocarbons. The most intense, structure-specific reactions were selected to establish multiple reaction monitoring (MRM) parameters for GC/MS analysis. This methodology has been used to study the identity of co-eluting and closely eluting hydrocarbon biomarkers from modern and ancient sediments anand from extant micro-organisms. Some sediments of Cambrian and Proterozoic age have been found to contain suites of monomethylalkanes with all possible isomers present and with little apparent preference for the site of branching.

Rotational isomers of several aromatic molecules studied by supersonic jet spectroscopy

The electronic spectra of m—substituted phenols and β-naphthol in supersonic free jets have been investigated. All the molecules studies exhibit two strong features in the fluorescence excitation spectra, which are due to two rotational isomers in which the hydrogen atom of the OH group is in cis and trans configurations with respect to the m—substituent. The difference between the S 1 — S 0 excitation energies of the two isomers is in the range from 100 to 300 cm −1. This large difference indicates the potentiality of electronic spectroscopy in the discrimination of the rotational isomers. The dispersed fluorescence spectra of the molecules as well as the electronic spectra of the hydrogen—bonded complexes provide definite evidences for the existence of the two isomers

Cell-free ethylene-forming systems lack stereochemical fidelity

In-vitro systems for the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene have been reported using pea supernatants, carnation petal microsomes, olive leaf protein and, most recently, pea mitochondria. It has also been shown, in intact tissues of apple, mung bean and pea, that the system responsible for conversion of ACC to ethylene can produce 1-butene from isomers of 1-amino-2-ethylcyclopropane-1-carboxylic acid (AEC). This conversion shows a high degree of steroselectivity, and isomer discrimination is therefore a valuable criterion by which to judge the validity of subcellular systems. It is shown here that all in-vitro ethylene-forming systems so far described fail by a wide margin to match the AEC-isomer preference of the corresponding intact tissues with respect to 1-butene generation. This work supports and extends recent reports by McKeon and Yang (1984, Planta 160, 84-87) and by Guy and Kende (1984, Planta 160, 281-287) on the characteristics of ethylene formation by pea homogenates. The vacuolar conversion described by the latter authors is the simplest system yet described that retains appropriate sterochemical fidelity.

Use of resonant two-photon ionization with supersonic beam mass spectrometry in the discrimination of cresol isomers

L'utilisation d'un faisceau moleculaire supersonique conduit a la formation de molecules ultrafroides qui sont ensuite soumises a une ionisation biphotonique pour la spectrometrie de masse

A search for site-filling ligands in the Mcg bence-jones dimer: Crystal binding studies of fluorescent compounds

In trigonal crystals grown in 1.9 M ammonium sulfate buffered at pH 6.2, the Mcg light-chain (Bence-Jones) dimer has a highly aromatic binding cavity accessible to a wide range of hydrophobic and aromatic ligands. A search was made for site-filling ligands by diffusing compounds into the crystals and determining their locations, orientations and relative occupancies by difference Fourier analysis at 2.7-Å resolution. 1-Anilinonaphthalene-8-sulfonate, a small ligand in comparison with the rest of the series, initially occupied a site in the main binding cavity. With time, however, this ligand changed its position to the deep binding pocket beyond the floor of the main cavity. The original binding site remained vacant, despite the presence of a large excess of ligand in the soaking solution. Ligands increasing in size from fluorescein to bis( N-methyl)acridine (lucigenin) to dimers of carboxytetramethylrhodamine were found to bind with stringent stereospecificity in the main cavity, but the mode of binding was different in each case. The dimer of the 6-isomer of carboxytetramethylrhodamine, in which the two carboxyl groups are in para positions on the phenyl moiety, proved to be an effective site-filling ligand. The differences in the binding properties of dimers of 5- and 6-carboxytetramethylrhodamine led to an explanation for isomeric discrimination in the binding site. There were extensive conformational changes in the binding cavity to accommodate the ligands, particularly 6-carboxytetramethylrhodamine. The second and third hyper-variable loops proved very flexible, and moved in ways to expand the binding site. The side chains of key tyrosine and phenylalanine residues in the site were also highly mobile. Their orientations adjusted to optimize complementarity with the ligands. These conformational adjustments are consistent with the tenets of a limited neo-instructive theory of ligand binding.

Discrimination of isomers of xylene by resonance-enhanced two-photon ionization

Discrimination of isomers of xylene by resonance-enhanced two-photon ionization

Isomer discrimination by topological information approach

AbstractA comparative analysis of ten topological indices is made. No index is found to discriminate isomers uniquely. A combined topological index, named the superindex, consisting of a number of topological indices is proposed. Information theory is applied to express all components of the superindex on a common quantitative scale. The superindex is tested on the sample of 427 graphs consisting of all acyclic, monocyclic, and bicyclic graphs with 4–8 vertices.

ChemInform Abstract: DISCRIMINATION OF THE GEOMETRICAL ISOMERS OF 2,3‐, 2,5‐, AND 2,6‐DIMETHYLPIPERAZINES BASED ON PROTON NMR SPECTRAL DATA

Chemischer InformationsdienstVolume 11, Issue 49 Physical Organic Chemistry ChemInform Abstract: DISCRIMINATION OF THE GEOMETRICAL ISOMERS OF 2,3-, 2,5-, AND 2,6-DIMETHYLPIPERAZINES BASED ON PROTON NMR SPECTRAL DATA M. TSUTSUI, M. TSUTSUISearch for more papers by this authorT. WATANABE, T. WATANABESearch for more papers by this authorA. OHTA, A. OHTASearch for more papers by this authorK. TAKIZAWA, K. TAKIZAWASearch for more papers by this author M. TSUTSUI, M. TSUTSUISearch for more papers by this authorT. WATANABE, T. WATANABESearch for more papers by this authorA. OHTA, A. OHTASearch for more papers by this authorK. TAKIZAWA, K. TAKIZAWASearch for more papers by this author First published: December 9, 1980 https://doi.org/10.1002/chin.198049079Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume11, Issue49December 9, 1980 RelatedInformation

Discrimination of the geometrical isomers of 2,3‐, 2,5‐, and 2,6‐dimethylpiperazines based on 1 HNmr spectral data

Abstract1 H‐Nmr spectra of cis and trans isomers of 2,3‐, 2,5‐, and 2,6‐dimethylpiperazines were taken at various temperatures. The spectra of geometrical isomers bearing the ae or ea dimethyl groups showed broadening at lower temperatures. It was clarified that the measurement of the spectra at lower temperatures is useful for the discrimination of the geometrical isomers of dimethylpiperazines.

The Crystal Structures of (+)589- and (−)589-trans(O)-Ethylenediaminebis(glycinato)cobalt(III) Hydrogen-d-tartrates and Their Thermal Behavior

Abstract The crystal structures of two diastereoisomeric salts, (+)589-trans(O)-[Co(gly)2en]H-d-tart·3H2O (1) and (−)589-trans(O)-[Co(gly)2en]H-d-tart·H2O (2), have been determined by three-dimensional X-ray analysis. The less-soluble salt (1) is monoclinic; space group, P21; Z=2, a=12.351(5), b=7.671(3), c=10.189(5) Å, and β=110.71(4)° (R=0.043, 2241 reflections). The more-soluble salt (2) is monoclinic; space group, P21; Z=2, a=11.135(4), b=10.037(3), c=7.716(3) Å, and β=98.61(3)° (R=0.064, 2076 reflections). A comparison of the (unit cell volume)/Z values of the two crystals shows that the crystal 1 is more tightly packed than the crystal 2. In both salts, adjacent complex cations form quite similar chain structures linked by (N–H…O) hydrogen bonds. The H-d-tart anions in 1 take a characteristic “head-to-tail” arrangement of an infinite chain of {H-d-tart}∞ along the b-axis. In contrast, this arrangement is not found in the more-soluble salt (2). From these findings, it can be considered that the discrimination of optical isomers in the H-d-tart system originates from the spiral chain structure of {H-d-tart}∞. The absolute configurations of (+)589- and (−)589-trans(O)-[Co(gly)2en]+ are determined to be Λ-δ and Λ-λ respectively. TG and DSC measurements were carried out for both salts, and the ΔH values of the dehydration step were estimated to be 64.4 kJ mol−1 for 1 and 73.0 kJ mol−1 for 2.

Diesters of alkane diols and 2-hydroxy fatty acids: Identification and discrimination of isomers with the aid of NMR spectroscopy

High resolution nuclear magnetic resonance spectroscopy has been shown to be extremely useful for the identification and discrimination of naturally occurring diesters of 1,2- and 2,3-alkanediols as well as for fatty alkyl esters of acylated 2-hydroxy fatty acids. A comparison of 220 MHz spectra of 1,2 and erythro- 2,3-alkanediol diesters exhibits the following distinguishing features: (1) two non-equivalent methylene protons from the glycol group of 1,2-alkanediol diesters resonate at 3.87 ppm and 4.17 ppm respectively while these resonances are completely absent in the spectrum of 2,3-isomer; (2) methylene protons adjacent to ester carbonyl groups appear as two overlapping triplets at 2.22 ppm in 1,2-alkanediol diesters while the corresponding protons in the 2,3-isomer are displayed as two partially overlapping triplets centered at 2.15 ppm and 2.2 ppm respectively; and (3) methyl protons adjacent to glycol group in 2,3-isomer appear as downfield doublet at 1.13 ppm; this downfield doublet is not shown by 1,2-alkanediol diesters. Erythro- and threo-2,3-alkanediol diesters have also been distinguished from each other; two α-methylenes in erythro isomers appear as partially overlapping triplets while these protons in threo isomer display an apparent quartet centered at 2.22 ppm. Fatty alkyl esters of acylated 2-hydroxy fatty acids display a triplet at 4.79 for 2-position methylene proton, a distinguishing feature not shown by diacyl alkanediols. A distinction between diester lipids and other classes of neutral lipids has also been achieved by the study of nuclear magnetic resonance spectra, particularly in the region of 3–6 ppm.

Doubly Charged Ion Mass Spectra(IV)

The 2E doubly charged ion mass spectra of several chlorobenzene derivatives(R-C6H4-Cl) were recorded. For most compounds, the[M-HCl]peak was observed together with CmH-R and CnH2 peaks. It is shown that the 2E spectrum can be used for the discrimination of isomers, which was exemplified by the case of chlorobenzaldehyde.

Miscellaneous : Ultrasonic method for metal-metal bond quality determination in alpher-treated cylinders Deputat, J., Pawlowski, Z., Archiwum Akustyki6 (1971) 317

Universal acquisition of reliable information regarding the qualitative and quantitative properties of complicated matrices is the premise for the success of metabolomics study. Liquid chromatography-mass spectrometry (LC-MS) is now serving as a workhorse for metabolomics; however, LC-MS-based non-targeted metabolomics is suffering from some shortcomings, even some cutting-edge techniques have been introduced. Aiming to tackle, to some extent, the drawbacks of the conventional approaches, such as redundant information, detector saturation, low sensitivity, and inconstant signal number among different runs, herein, a novel and flexible work-flow consisting of three progressive steps was proposed to profile in depth the quantitative metabolome of plants. The roots of Peucedanum praeruptorum Dunn (Peucedani Radix, PR) that are rich in various coumarin isomers, were employed as a case study to verify the applicability. First, offline two dimensional LC-MS was utilized for in-depth detection of metabolites in a pooled PR extract namely universal metabolome standard (UMS). Second, mass fragmentation rules, notably concerning angular-type pyranocoumarins that are the primary chemical homologues in PR, and available databases were integrated for signal assignment and structural annotation. Third, optimum collision energy (OCE) as well as ion transition for multiple monitoring reaction measurement was online optimized with a reference compound-free strategy for each annotated component and large-scale relative quantification of all annotated components was accomplished by plotting calibration curves via serially diluting UMS. It is worthwhile to highlight that the potential of OCE for isomer discrimination was described and the linearity ranges of those primary ingredients were extended by suppressing their responses. The integrated workflow is expected to be qualified as a promising pipeline to clarify the quantitative metabolome of plants because it could not only holistically provide qualitative information, but also straightforwardly generate accurate quantitative dataset.

Miscellaneous : Surface waveguide for a wave medium: Accurate solution Kaliski, S., Solarz, L., Proceedings of Vibration Problems13 (1972) 37

Universal acquisition of reliable information regarding the qualitative and quantitative properties of complicated matrices is the premise for the success of metabolomics study. Liquid chromatography-mass spectrometry (LC-MS) is now serving as a workhorse for metabolomics; however, LC-MS-based non-targeted metabolomics is suffering from some shortcomings, even some cutting-edge techniques have been introduced. Aiming to tackle, to some extent, the drawbacks of the conventional approaches, such as redundant information, detector saturation, low sensitivity, and inconstant signal number among different runs, herein, a novel and flexible work-flow consisting of three progressive steps was proposed to profile in depth the quantitative metabolome of plants. The roots of Peucedanum praeruptorum Dunn (Peucedani Radix, PR) that are rich in various coumarin isomers, were employed as a case study to verify the applicability. First, offline two dimensional LC-MS was utilized for in-depth detection of metabolites in a pooled PR extract namely universal metabolome standard (UMS). Second, mass fragmentation rules, notably concerning angular-type pyranocoumarins that are the primary chemical homologues in PR, and available databases were integrated for signal assignment and structural annotation. Third, optimum collision energy (OCE) as well as ion transition for multiple monitoring reaction measurement was online optimized with a reference compound-free strategy for each annotated component and large-scale relative quantification of all annotated components was accomplished by plotting calibration curves via serially diluting UMS. It is worthwhile to highlight that the potential of OCE for isomer discrimination was described and the linearity ranges of those primary ingredients were extended by suppressing their responses. The integrated workflow is expected to be qualified as a promising pipeline to clarify the quantitative metabolome of plants because it could not only holistically provide qualitative information, but also straightforwardly generate accurate quantitative dataset.

Miscellaneous : Non-invasive cardiac output measurement Mackay, R.S., Microvascular Research4 (1972) 438

Universal acquisition of reliable information regarding the qualitative and quantitative properties of complicated matrices is the premise for the success of metabolomics study. Liquid chromatography-mass spectrometry (LC-MS) is now serving as a workhorse for metabolomics; however, LC-MS-based non-targeted metabolomics is suffering from some shortcomings, even some cutting-edge techniques have been introduced. Aiming to tackle, to some extent, the drawbacks of the conventional approaches, such as redundant information, detector saturation, low sensitivity, and inconstant signal number among different runs, herein, a novel and flexible work-flow consisting of three progressive steps was proposed to profile in depth the quantitative metabolome of plants. The roots of Peucedanum praeruptorum Dunn (Peucedani Radix, PR) that are rich in various coumarin isomers, were employed as a case study to verify the applicability. First, offline two dimensional LC-MS was utilized for in-depth detection of metabolites in a pooled PR extract namely universal metabolome standard (UMS). Second, mass fragmentation rules, notably concerning angular-type pyranocoumarins that are the primary chemical homologues in PR, and available databases were integrated for signal assignment and structural annotation. Third, optimum collision energy (OCE) as well as ion transition for multiple monitoring reaction measurement was online optimized with a reference compound-free strategy for each annotated component and large-scale relative quantification of all annotated components was accomplished by plotting calibration curves via serially diluting UMS. It is worthwhile to highlight that the potential of OCE for isomer discrimination was described and the linearity ranges of those primary ingredients were extended by suppressing their responses. The integrated workflow is expected to be qualified as a promising pipeline to clarify the quantitative metabolome of plants because it could not only holistically provide qualitative information, but also straightforwardly generate accurate quantitative dataset.

PMR spectra of triglycerides: discrimination of isomers with the aid of a chemical shift reagent

PMR spectra of triglycerides: discrimination of isomers with the aid of a chemical shift reagent

Structural Isomer Discrimination between Cyanamides and Carbodiimides by Nitrogen Nuclear Magnetic Resonance

The structural isomers diethylcyanamide and N,N′-dicyclohexylcarbodiimide were studied by both proton and nitrogen NMR techniques. The structures R2N–C≡N and R–N=C=N–R have been shown to apply to cyanamides and carbodiimides, respectively.