Artículos de revistas: "Isomer identification"

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Zhang, Bolong, Jegadesan Subbiah, David J. Jones y Wallace Wing Ho Wong. "Separation and identification of indene–C70 bisadduct isomers". Beilstein Journal of Organic Chemistry 12 (6 de mayo de 2016): 903–11. http://dx.doi.org/10.3762/bjoc.12.88.

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Following an initial work on the isolation of a single geometric isomer from an indene–C70 bisadduct (IC70BA) mixture, we report the full fractionation and identification of the bisadduct species in the material. Eleven fractions of IC70BA isomers were separated by high-performance liquid chromatography. A number of fractions contained relatively pure isomer species and their configuration were deduced using a variety of analytical techniques including 1H and 13C NMR and UV–vis spectroscopy. The electrochemical properties and the organic solar cell device performance were investigated for fractions where a reasonable quantity of sample could be isolated.

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2

Yeston, J. S. "CHEMISTRY: Isomer Identification". Science 309, n.º 5743 (23 de septiembre de 2005): 1969a. http://dx.doi.org/10.1126/science.309.5743.1969a.

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3

Gosar, Amit, Tabrez Shaikh y Atharva Sindwani. "Fourier Transform Infrared (FTIR) Spectroscopic Analysis of Amino Acid Serine for its Chiral Identification". Journal of Pharmaceutical Quality Assurance and Quality Control 4, n.º 1 (14 de abril de 2022): 1–4. http://dx.doi.org/10.46610/jqaqc.2022.v04i01.001.

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Synthesis of chiral drugs required chiral starting materials organic compounds. DL serine is an amino acid that is used as a key starting material in the synthesis of many drug substances. D or L isomer of Serine will lead to the chiral drug substances whereas DL mixture will lead to racemic drug substances. FTIR can be used as the primary analytical tool for the identification of Serine isomers and its racemic mixture. Many absorption bands in FTIR spectra identify whether a molecule is a specific isomer or racemic mixture. A systematic comparison of FTIR spectroscopic data is carried out revealing that the compound is the specific isomer and the racemic mixture shows different spectra with different bands.

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4

Delmonte, Pierluigi, Martin P. Yurawecz, Magdi M. Mossoba, Cristina Cruz-Hernandez y John K. G. Kramer. "Improved Identification of Conjugated Linoleic Acid Isomers Using Silver-Ion HPLC Separations". Journal of AOAC INTERNATIONAL 87, n.º 2 (1 de marzo de 2004): 563–68. http://dx.doi.org/10.1093/jaoac/87.2.563.

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Abstract Silver-ion high-performance liquid chromatography (Ag+-HPLC) has been shown to be effective in the resolution of most of the isomers of conjugated octadecadienoic acids (18:2), also known as conjugated linoleic acid (CLA). The CLA isomers identified in natural fats from ruminants are a mixture of numerous positional and geometric isomers from 7,9- to 12,14–18:2. Ag+-HPLC separates both geometric (trans,trans < cis/trans < cis,cis) and positional CLA isomers using the mobile phase hexane/acetonitrile (99.9:0.1). The elution volumes for the CLA isomers were not only affected by the concentration of acetonitrile (in the prepared mobile phase) but also with successive runs during the day using a prepared mobile phase batch, due to the partial solubility of acetonitrile in hexane. However, this drift does not affect the relative resolution of the CLA isomers. The addition of diethyl ether to the mobile phase partly stabilizes the solvent mixture. In order to facilitate the interpretation of Ag-+HPLC chromatograms, the relative retention volumes (RRV) were calculated for each CLA isomer. Toluene was added to all the test portions and served as an estimator of dead volume, whereas the elution of the ubiquitous 9c,11t-CLA isomer was chosen as unity (1.00). Expressing the elution of all the CLA isomers as their RRV greatly helped to standardize each CLA isomer, resulting in relatively small coefficients of variation (% CV) for the trans,trans (<1.5%) and cis/trans (<0.5%) CLA isomers. The identification of the CLA isomers was further facilitated by synthesis of authentic CLA isomers. All the geometric CLA fatty acid methyl esters (FAME) from positions 6,8- to 13,15-CLA were commercially available or synthesized by a combination of partial hydrazine reduction of known polyunsaturated fatty acids followed by alkali isomerization, isolation of products, and further iodine-catalyzed geometric isomerization. Based on expressing the elution volume as RRV and the availability of the synthetic CLA isomers, a unique reversal of the elution order of the c/t CLA isomers was found. It is also proposed that the retention times of CLA isomers by gas chromatography (GC) should be expressed as their relative retention times (RRT) relative to methyl γ-linoleneate. The availability of CLA reference materials and the application of RRV and RRT to Ag+-HPLC and GC separations, respectively, will greatly improve in the identifications of CLA isomers.

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5

Yurawecz, Martin P., Jo-Yun T. Chen y Bartholomew J. Puma. "Identification of cis- and trans-1,1,2,3,4-PentachIoro-4-[1-methylethoxy]-l,3-butadiene Residues in Mississippi River Fish". Journal of AOAC INTERNATIONAL 69, n.º 4 (1 de julio de 1986): 586–91. http://dx.doi.org/10.1093/jaoac/69.4.586.

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Abstract The cis- and trans-isomers of 1,1,2,3,4-pentachloro-4-[1-methylethoxy]-1,3-butadiene have been identified as contaminants in fish caught from the Mississippi River at St. Louis, MO, and as far as 150 miles south of that location. Up to 0.1 ppm of the cis-isomer and 0.8 ppm of the trans-isomer were determined by using a method based on the AOAC multiresidue method for detecting organochlorine and organophosphorus pesticides. In tests of the modified AOAC method on spiked fish, both isomers were quantitatively recovered (95-106%). A mixture of the cis- and trans-isomers was synthesized by reacting hexachlorobutadiene with sodium isopropoxide. Separation of the reaction products by Florisil column chromatography provided reference standards of the individual isomers for identification and quantitation of the residues. The stereospecificity of the synthesis reaction and the infrared and mass spectral data used to verify the structures of the products are discussed.

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6

Sobhi, Hany F., Xinjie Zhao, Peter Plomgaard, Miriam Hoene, Jakob S. Hansen, Benedikt Karus, Andreas M. Niess et al. "Identification and regulation of the xenometabolite derivatives cis- and trans-3,4-methylene-heptanoylcarnitine in plasma and skeletal muscle of exercising humans". American Journal of Physiology-Endocrinology and Metabolism 318, n.º 5 (1 de mayo de 2020): E701—E709. http://dx.doi.org/10.1152/ajpendo.00510.2019.

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Little is known about xenometabolites in human metabolism, particularly under exercising conditions. Previously, an exercise-modifiable, likely xenometabolite derivative, cis-3,4-methylene-heptanoylcarnitine, was reported in human plasma. Here, we identified trans-3,4-methylene-heptanoylcarnitine, and its cis-isomer, in plasma and skeletal muscle by liquid chromatography-mass spectrometry. We analyzed the regulation by exercise and the arterial-to-venous differences of these cyclopropane ring-containing carnitine esters over the hepatosplanchnic bed and the exercising leg in plasma samples obtained in three separate studies from young, lean and healthy males. Compared with other medium-chain acylcarnitines, the plasma concentrations of the 3,4-methylene-heptanoylcarnitine isomers only marginally increased with exercise. Both isomers showed a more than twofold increase in the skeletal muscle tissue of the exercising leg; this may have been due to the net effect of fatty acid oxidation in the exercising muscle and uptake from blood. The latter idea is supported by a more than twofold increased net uptake in the exercising leg only. Both isomers showed a constant release from the hepatosplanchnic bed, with an increased release of the trans-isomer after exercise. The isomers differ in their plasma concentration, with a four times higher concentration of the cis-isomer regardless of the exercise state. This is the first approach studying kinetics and fluxes of xenolipid isomers from tissues under exercise conditions, supporting the hypothesis that hepatic metabolism of cyclopropane ring-containing fatty acids is one source of these acylcarnitines in plasma. The data also provide clear evidence for an exercise-dependent regulation of xenometabolites, opening perspectives for future studies about the physiological role of this largely unknown class of metabolites.

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7

Gal, Joseph. "New Single-Isomer Compounds on the Horizon". CNS Spectrums 7, S1 (abril de 2002): 45–54. http://dx.doi.org/10.1017/s1092852900028601.

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ABSTRACTIn 1992, the Food and Drug Administration (FDA) issued new guidelines governing stereoisomerism in new-drug development. The guidelines strongly encourage the development of single isomers and discourage stereoisomeric (eg, racemic) mixtures. As a result, most new chiral drugs are being developed as single enantiomers (ie, single isomers). There are three mechanisms for the identification and development of new single-isomer drugs: chiral switches (CS), chiral metashifts (CM), and new single-isomer chemical entities (NSICEs). In a CS, one of the two enantiomers of an established racemate is developed as a new drug, with the expectation that the single-isomer form has advantages over the racemic parent in terms of efficacy and/or adverse effects. Many new CS drugs are in development, eg, (S)-oxybutynin for urinary incontinence and escitalopram for depression. In a CM, a chiral metabolite of a drug is developed, in single-isomer form, as an agent with advantages over the parent. Among the current CM drugs in development are (+)-norcisapride (safer GI prokinetic agent than the racemic parent cisapride) and (S)-desmethylzopiclone (antianxiety agent, metabolite of the sedative-hypnotic zopi-clone). Many NSICEs are in development, eg, rosuvastatin as an antihypercholesterolemic, posaconazole as an antifungal, sitafloxacin as a fluoroquinolone antibacterial, pregabalin as an anticonvulsant, abarelix as an antineoplastic, etc. As in the development of any new drug, not every single-isomer candidate will reach the clinic, but there is no doubt that the move to single-isomer agents is an important step forward in the search for better and safer drugs.

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8

Baumgard, Lance H., Benjamin A. Corl, Debra A. Dwyer, A. Saebø y Dale E. Bauman. "Identification of the conjugated linoleic acid isomer that inhibits milk fat synthesis". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 278, n.º 1 (1 de enero de 2000): R179—R184. http://dx.doi.org/10.1152/ajpregu.2000.278.1.r179.

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Conjugated linoleic acids (CLA) are octadecadienoic fatty acids that have profound effects on lipid metabolism. Our previous work showed that CLA (mixture of isomers) markedly reduced milk fat synthesis. In this study, our objective was to evaluate the effects of specific CLA isomers. Multiparous Holstein cows were used in a 3 × 3 Latin square design, and treatments were 4-day abomasal infusions of 1) skim milk (control), 2) 9,11 CLA supplement, and 3) 10,12 CLA supplement. CLA supplements provided 10 g/day of the specific CLA isomer ( cis-9, trans-11 or trans-10, cis-12). Treatments had no effect on intake, milk yield, or milk protein yield. Only the 10,12 CLA supplement affected milk fat, causing a 42 and 44% reduction in milk fat percentage and yield, respectively. Milk fat composition revealed that de novo synthesized fatty acids were extensively reduced. Increases in ratios of C14:0 to C14:1 and C18:0to C18:1 indicated the 10,12 CLA supplement also altered Δ9-desaturase. Treatments had minimal effects on plasma concentrations of glucose, nonesterified fatty acids, insulin, or insulin-like growth factor-I. Overall, results demonstrate that trans-10, cis-12 CLA is the isomer responsible for inhibition of milk fat synthesis.

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9

Corvini, P. F. X., R. Vinken, G. Hommes, M. Mundt, J. Hollender, R. Meesters, H. Fr Schröder y B. Schmidt. "Microbial degradation of a single branched isomer of nonylphenol by Sphingomonas TTNP3". Water Science and Technology 50, n.º 5 (1 de septiembre de 2004): 189–94. http://dx.doi.org/10.2166/wst.2004.0327.

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The endocrine disrupting chemical nonylphenol (NP) is a technical product which consists of a complex mixture of nonylphenols with different alkyl side-chain isomers. Since the bio-degradation of each NP isomer may lead to its own range of metabolites, the isolation and identification of transformation products is very difficult. In order to overcome this difficulty, the nonylphenol isomer 4(3′,5′-dimethyl-3′-heptyl)-phenol (p353NP) was synthesized, and its degradation by an axenic culture of Sphingomonas TTNP3 was investigated with [ring-U-14C]-labelled and non-labelled p353NP including a time-course study. Radioactive mass balancing resulted in different polar soluble fractions, in insoluble radioactivity associated with biomass, and volatile radioactivity in the form of the mineralization product 14CO2. In the extracellular media, the presence of nonanol corresponding to the nonyl chain of the NP isomer was confirmed and its concentration was determined during the course of fermentation. No other radioactive compounds were detected beside the parent isomer. Radioactive metabolites were only found in the intracellular fraction of S. TTNP3.

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10

O'Neil, Constance A., Steven J. Schwartz y George L. Catignani. "Comparison of Liquid Chromatographic Methods for Determination of Cis-Trans Isomers of β-Carotene". Journal of AOAC INTERNATIONAL 74, n.º 1 (1 de enero de 1991): 36–42. http://dx.doi.org/10.1093/jaoac/74.1.36.

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Abstract Four liquid chromatographic columns and various solvent systems were evaluated for their ability to resolve and quantitate cls-trans Isomers of β-carotene. The Vydac C18 201 TP and Ca(OH)2 columns were most effective in resolving alltrans-, 13-cls-, and 9-cls-β-carotenes. Additionally, the 15- c18 Isomer was separated using the method employing a Ca(OH)2 column. Peak Identification was based on absorption spectra (obtained from photodlode array data), retention times, and coelutlon in comparison to authentic standards. A quantitative analysis of vegetable extracts using both the Vydac and Ca(OH)2 columns showed comparable results. However, both procedures lacked complete resolution of 2 minor clsβ-carotenes, tentatively identified as dl-cis Isomers. High selectivity for carotene Isomers as well as fewer interferences were observed with the Ca(OH)2 procedure for analysis of plant tissue extracts and thus, It is preferred for determination of β-carotene cis-isomer content In these samples.

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11

Alessandrini, Silvia, Mattia Melosso, Víctor M. Rivilla, Luca Bizzocchi y Cristina Puzzarini. "Computational Protocol for the Identification of Candidates for Radioastronomical Detection and Its Application to the C3H3NO Family of Isomers". Molecules 28, n.º 7 (4 de abril de 2023): 3226. http://dx.doi.org/10.3390/molecules28073226.

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The C3H3NO family of isomers is relevant in astrochemistry, even though its members are still elusive in the interstellar medium. To identify the best candidate for astronomical detection within this family, we developed a new computational protocol based on the minimum-energy principle. This approach aims to identify the most stable isomer of the family and consists of three steps. The first step is an extensive investigation that characterizes the vast number of compounds having the C3H3NO chemical formula, employing density functional theory for this purpose. The second step is an energy refinement, which is used to select isomers and relies on coupled cluster theory. The last step is a structural improvement with a final energy refinement that provides improved energies and a large set of accurate spectroscopic parameters for all isomers lying within 30 kJ mol−1 above the most stable one. According to this protocol, vinylisocyanate is the most stable isomer, followed by oxazole, which is about 5 kJ mol−1 higher in energy. The other stable species are pyruvonitrile, cyanoacetaldehyde, and cyanovinylalcohol. For all of these species, new computed rotational and vibrational spectroscopic data are reported, which complement those already available in the literature or fill current gaps.

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12

Alam, Mohammed S., Soheil Zeraati-Rezaei, Zhirong Liang, Christopher Stark, Hongming Xu, A. Rob MacKenzie y Roy M. Harrison. "Mapping and quantifying isomer sets of hydrocarbons ( ≥ C<sub>12</sub>) in diesel exhaust, lubricating oil and diesel fuel samples using GC × GC-ToF-MS". Atmospheric Measurement Techniques 11, n.º 5 (29 de mayo de 2018): 3047–58. http://dx.doi.org/10.5194/amt-11-3047-2018.

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Abstract. Airborne particles and vapours, like many other environmental samples including water, soils and sediments, contain complex mixtures of hydrocarbons, often deriving from crude oil either before or after fractionation into fuels, lubricants and feedstocks. Comprehensive 2D gas chromatography time-of-flight mass spectrometry (GC × GC-ToF-MS), offers a very powerful technique that separates and identifies many compounds in complicated hydrocarbon mixtures. However, quantification and identification of individual constituents at high ionization energies would require hundreds of expensive (when available) standards for calibration. Although the precise chemical structure of hydrocarbons does matter for their environmental impact and fate, strong similarities can be expected for compounds having very similar chemical structures and carbon numbers. There is, therefore, a clear benefit in an analytical technique which is specific enough to separate different classes of compounds and to distinguish homologous series while avoiding the need to handle each isomer individually. Varying EI (electron impact) ionization mass spectrometry significantly enhances the identification of individual isomers and homologous compound groups, which we refer to as “isomer sets”. Advances are reported in mapping and quantifying isomer sets of hydrocarbons (≥ C12) in diesel fuel, lubricating oil and diesel exhaust emissions. By using this analysis we report mass closures of ca. 90 and 75 % for diesel fuel and lubricating oil, and identify 85 and 75 % of the total ion current for gas- and particulate-phase diesel exhaust emissions.

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13

Cieri, Ugo R. "Identification and Estimation of the Levo Isomer in Raw Materials and Finished Products Containing Atropine and/or Hyoscyamine". Journal of AOAC INTERNATIONAL 88, n.º 1 (1 de enero de 2005): 1–4. http://dx.doi.org/10.1093/jaoac/88.1.1.

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Abstract The belladonna alkaloids atropine sulfate and hyoscyamine sulfate, occasionally used as anticholinergic and antimuscarinic agents, have identical molecular formulas but different stereo configurations. Hyoscyamine sulfate contains almost 100% of the levo isomer, whereas atropine sulfate is composed of equal parts of dextro and levo isomers. It is believed that the therapeutic properties of these alkaloids are due exclusively or primarily to the levo isomer. Currently available methods determine only the total amount of atropine (hyoscyamine) sulfate. A method has been developed and is reported for the identification and estimation of the levo and dextro isomers of atropine and hyoscyamine. Reference solutions are prepared in methanol at the following weights per 100 mL: 8.0 mg atropine sulfate; 4.0 mg hyoscyamine sulfate; 7.0 mg scopolamine hydrobromide; and 10.0 mg homatropine methylbromide. Samples of raw materials are similarly prepared in methanol, commercial products are also extracted or diluted with methanol, and solutions are filtered. Liquid chromatography is used for separations on a 25 cm Chirobiotic T2 column. The mobile phase is prepared by mixing 3.0 mL acetic acid and 2.0 mL triethylamine with 1000 mL methanol. The injection volume is 100 or 200 μL; the flow rate is about 0.35 mL/min. Fluorescence detection is at 255 nm excitation and 285 nm emission. Scopolamine hydrobromide and hyoscyamine eluted after 20 and 60 min, respectively. Atropine sulfate generated 2 peaks after 60 and 65 min. Homatropine methylbromide also produced 2 peaks after 70 and 85 min. Samples tested in this study included raw materials and commercial tablets or injections containing belladonna alkaloids. In all cases, the percentage calculated was that of the levo isomer relative to the total amount of atropine (hyoscyamine) present.

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14

Beihoffer, Jon, Ed Bour, Joe H. Lowry, John J. Reschl, Jivbmy L. Seidel y Charles P. Gibson. "Identification and Determination of the Isomeric Bromo- and/or Chloro-Substituted l,3-Dihalo-5,5- Dimethylhydantoins Used in Disinfectants and Molluscicides". Journal of AOAC INTERNATIONAL 79, n.º 4 (1 de julio de 1996): 823–28. http://dx.doi.org/10.1093/jaoac/79.4.823.

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Abstract Proton nuclear magnetic resonance spectrometry (1H NMR) was used to identify and quantitate the 4 isomeric bromo- and/or chloro-substituted 1,3-dihalo-5,5-dimethylhydantoins in technical-grade materials used to prepare commercial disinfectants and molluscicides. We found that the technical grades of bromo/chloro-substituted 1,3-dihalo-5,5-dimethylhydantoins are mixtures of the 4 possible isomers, that interconversion among isomers occurs in solution and can be detected by 1H NMR, and that isomer interconversion occurs over times greater than those of the NMR timescale.

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15

Lim, C. K., F. Li y T. J. Peters. "High-performance liquid chromatography of type-III heptocarboxylic porphyrinogen isomers". Biochemical Journal 247, n.º 1 (1 de octubre de 1987): 229–32. http://dx.doi.org/10.1042/bj2470229.

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A reversed-phase h.p.l.c. system is described for the separation of the four type-III heptacarboxylic porphyrinogen isomers. The effects of buffer concentration, pH and type and proportion of organic modifier in the mobile phase on retention and resolution of isomers were studied. Optimum separation on an ODS-Hypersil column was by elution with a ternary mobile phase of acetonitrile, methanol and 1 M-ammonium acetate, pH 5.16 (7:3:90, by vol.). Isomer identification was based on a comparison of their retention times with those of authentic standards, and was further confirmed by h.p.l.c. analysis of the characteristic mixture of three pentacarboxylic porphyrins formed after partial decarboxylation of individual isomers in 0.3 M-HCl at 160 degrees C.

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16

Sulignano, B., S. Heinz, F. P. Heßberger, S. Hofmann, D. Ackermann, S. Antalic, B. Kindler et al. "Identification of a K isomer in 252No". European Physical Journal A 33, n.º 4 (septiembre de 2007): 327–31. http://dx.doi.org/10.1140/epja/i2007-10469-3.

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17

Bingham, C. R., J. C. Batchelder, K. Rykaczewski, K. S. Toth, C. H. Yu, T. N. Ginter, C. J. Gross et al. "Identification of a proton-emitting isomer in151Lu". Physical Review C 59, n.º 6 (1 de junio de 1999): R2984—R2988. http://dx.doi.org/10.1103/physrevc.59.r2984.

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18

Hofmann, S., I. Zychor, F. P. Hessberger y G. M�nzenberg. "Identification of a 3.2?s isomer in76Rb". Zeitschrift f�r Physik A Atomic Nuclei 325, n.º 1 (marzo de 1986): 37–43. http://dx.doi.org/10.1007/bf01294240.

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19

Bauer, R. W., J. A. Becker, E. A. Henry y K. E. Sale. "Spectrometry for spin and shape isomer identification". Journal of Quantitative Spectroscopy and Radiative Transfer 40, n.º 6 (diciembre de 1988): 637–50. http://dx.doi.org/10.1016/0022-4073(88)90060-x.

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20

Nagy, Gabe y Nicola L. B. Pohl. "Complete Hexose Isomer Identification with Mass Spectrometry". Journal of The American Society for Mass Spectrometry 26, n.º 4 (5 de febrero de 2015): 677–85. http://dx.doi.org/10.1007/s13361-014-1072-z.

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21

Ma, Xiaoxiao, Leelyn Chong, Ran Tian, Riyi Shi, Tony Y. Hu, Zheng Ouyang y Yu Xia. "Identification and quantitation of lipid C=C location isomers: A shotgun lipidomics approach enabled by photochemical reaction". Proceedings of the National Academy of Sciences 113, n.º 10 (22 de febrero de 2016): 2573–78. http://dx.doi.org/10.1073/pnas.1523356113.

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The field of lipidomics has been significantly advanced by mass spectrometric analysis. The distinction and quantitation of the unsaturated lipid isomers, however, remain a long-standing challenge. In this study, we have developed an analytical tool for both identification and quantitation of lipid C=C location isomers from complex mixtures using online Paternò–Büchi reaction coupled with tandem mass spectrometry (MS/MS). The potential of this method has been demonstrated with an implementation into shotgun lipid analysis of animal tissues. Among 96 of the unsaturated fatty acids and glycerophospholipids identified from rat brain tissue, 50% of them were found as mixtures of C=C location isomers; for the first time, to our knowledge, the quantitative information of lipid C=C isomers from a broad range of classes was obtained. This method also enabled facile cross-tissue examinations, which revealed significant changes in C=C location isomer compositions of a series of fatty acids and glycerophospholipid (GP) species between the normal and cancerous tissues.

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22

Steinert, Roland, Hans Bettermann y Karl Kleinermanns. "Identification of Xylene Isomers in High-Pressure Liquid Chromatography Eluates by Raman Spectroscopy". Applied Spectroscopy 51, n.º 11 (noviembre de 1997): 1644–47. http://dx.doi.org/10.1366/0003702971939307.

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This contribution presents a combination of high-pressure liquid chromatography (HPLC) with a Raman spectrometer. With this approach, we have identified both isomer m-xylene and isomer p-xylene in solution at concentrations down to 10−5 mol/L. The setup was developed to analyze compounds that cannot be separated by using standard HPLC techniques.

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23

GRAHAM, P., K. W. D. LEDINGHAM, R. P. SINGHAL, S. M. HANKIN, T. MCCANNY, X. FANG, P. F. TADAY, A. J. LANGLEY y C. KOSMIDIS. "Angular distributions of fragment ions arising from tetrahedral CH3I and isomer identification using intense laser fields". Laser and Particle Beams 19, n.º 2 (abril de 2001): 187–93. http://dx.doi.org/10.1017/s0263034601192037.

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Utilizing an ultraintense (1016 W cm−2) fs laser, the laser/matter interaction of the tetrahedral CH3I molecule is investigated. A mass spectrum and the angular distributions of fragment ions arising from Coulomb explosion of molecular ions, obtained with linearly polarized light, are presented. The distributions for In+ (n ≤ 7), CHm+ (m ≤ 3), Cp+ (p ≤ 4) and H+ ions are all anisotropic and maximal when the polarization lies along the spectrometer axis. The molecule hence seems to behave as a diatomic, with the fragment ions being ejected along the field direction. Also presented are mass spectra of the isomers 1- and 2-nitropropane, which are explosive species, taken for horizontal and vertical polarizations at both 375 and 750 nm. It is shown that femtosecond laser mass spectrometry (FLMS) can be used to distinguish between these two isomers through their differing dissociation patterns. Isomer identification is important for many different applications and FLMS may provide a means of achieving this for a wide range of molecules.

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24

Huang, Wei, Rhitankar Pal, Lei-Ming Wang, Xiao Cheng Zeng y Lai-Sheng Wang. "Isomer identification and resolution in small gold clusters". Journal of Chemical Physics 132, n.º 5 (7 de febrero de 2010): 054305. http://dx.doi.org/10.1063/1.3299292.

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25

Lach, M., P. Bednarczyk, P. T. Greenlees, K. Helariutta, P. Jones, R. Julin, S. Juutinen et al. "Identification of the 13/2+ isomer in 199At". European Physical Journal A 9, n.º 3 (diciembre de 2000): 307–8. http://dx.doi.org/10.1007/s100500070014.

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26

Xin, Jing-fan y Yi-hong Ding. "Unprecedented Cyclic Isomer of Triazenes: A Computational Identification". ChemistrySelect 2, n.º 18 (21 de junio de 2017): 5100–5104. http://dx.doi.org/10.1002/slct.201700875.

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27

Hu, Huabin y Jürgen Bajorath. "Increasing the public activity cliff knowledge base with new categories of activity cliffs". Future Science OA 6, n.º 5 (1 de junio de 2020): FSO472. http://dx.doi.org/10.2144/fsoa-2020-0020.

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Aim: Extending the public knowledge base of activity cliffs (ACs) with new categories of ACs having special structural characteristics. Methodology: Dual-site ACs, isomer ACs and ACs with privileged substructures are described and their systematic identification is detailed. Exemplary results & data: More than 7400 new ACs belonging to different categories with activity against more than 200 targets were identified and are made publicly available. Limitations & next steps: For dual-site ACs, limited numbers of isomers are available as structural analogs for rationalizing contributions to AC formation. The search for such analogs will continue. In addition, the target distribution of ACs containing privileged substructures will be further analyzed.

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Finewax, Zachary, Aparajeo Chattopadhyay, J. Andrew Neuman, James M. Roberts y James B. Burkholder. "Calibration of hydroxyacetonitrile (HOCH₂CN) and methyl isocyanate (CH₃NCO) isomers using I⁻ chemical ionization mass spectrometry (CIMS)". Atmospheric Measurement Techniques 17, n.º 23 (5 de diciembre de 2024): 6865–73. https://doi.org/10.5194/amt-17-6865-2024.

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Abstract. The toxic reduced nitrogen compound methyl isocyanate (CH3NCO, MIC) has been reported as present in wildfire and biomass burning emissions, agricultural fumigation plumes, and indoor air. Its isomer, hydroxyacetonitrile (HOCH2CN, glycolonitrile, or HAN) has not been observed in the Earth's atmosphere to date. In this study, absolute sensitivity calibrations for these isomers using two I− chemical ionization mass spectrometry (I-CIMS) instruments, the time-of-flight (ToF) and quadrupole (Quad) instruments, commonly used in laboratory and field measurements, were performed, for the first time, over a range of ion-molecule reactor temperatures (10–40 °C) and I(H2O)− / I− ratio (0.01–1). This study demonstrates that I-CIMS, under typical operating conditions, is not sensitive to MIC with limits of detection (LOD) of > 860 and > 570 ppb for the ToF and Quad I-CIMS instruments, respectively. Both I-CIMS instruments are, however, highly sensitive to the HAN isomer with 0.3 and 3 ppt LODs for the ToF-CIMS and Quad-CIMS instruments, respectively. The present results show that several recent field studies using I-CIMS instrument detection have misattributed the C2H3NO signal to MIC. This study proposes that HAN rather than MIC was most likely the C2H3NO isomer observed in those field studies, although the source chemistry for HAN remains uncharacterized. This study demonstrates the importance of applying absolute calibration standards in the identification and quantification of isomeric compounds.

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Schlauer, Jan, Siegfried R. H. Hartmeyer y Irmgard Hartmeyer. "Quinone patterns and identification of Japanese Spider Leg Sundews (Drosera Sect. Arachnopus)". Carnivorous Plant Newsletter 48, n.º 4 (1 de diciembre de 2019): 161–63. http://dx.doi.org/10.55360/cpn484.js448.

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The Japanese sundews that have previously been collectively called D. indica L. (especially after the influential Flora of Japan, Ohwi 1965:492) are being split up. Various authors (e.g., Watanabe 2013) are trying to re-establish or create one or two additional species assumed endemic to Japan, following the contemporary trend to recognize a number of segregate taxa in Drosera sect. Arachnopus (Greek for “spider leg”), the group that contains D. indica. Previous research (Schlauer et al. 2017, 2018, 2019) has demonstrated a rather unexpected diversity in the naphthoquinones that are characteristic for the different species now recognized in this group. While a few Australian species contain ramentaceone (7-methyljuglone), most contain the regio-isomer plumbagin (2-methyljuglone). So far, only D. indica s.str. (accessions from Asia and Africa have been investigated) contains both isomers in the same plant. The morphological diversity found in Japan thus prompted a chemical investigation, the results of which are reported here.

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30

Bennett, J. F., F. Collin y D. R. Hastie. "A laboratory flow reactor with gas particle separation and on-line MS/MS for product identification in atmospherically important reactions". Atmospheric Measurement Techniques Discussions 2, n.º 3 (3 de junio de 2009): 1351–82. http://dx.doi.org/10.5194/amtd-2-1351-2009.

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Abstract. A system to study the gas and particle phase products from gas phase hydrocarbon oxidation is described. It consists of a gas phase photochemical flow reactor followed by a diffusion membrane denuder to remove gases from the reacted products, or a filter to remove the particles. Chemical analysis is performed by an atmospheric pressure chemical ionization (APCI) triple quadrupole mass spectrometer. A diffusion membrane denuder is shown to remove trace gases to below detectable limits so the particle phase can be studied. The system was tested by examining the products of the oxidation of m-xylene initiated by HO radicals. Dimethylphenol was observed in both the gas and particle phases although individual isomers could not be identified. Two furanone isomers, 5-methyl-2(3H)furanone and 3-methyl-2(5H)furanone were identified in the particulate phase, but the isobaric product 2,5 furandione was not observed. One isomer of dimethyl-nitrophenol was identified in the particle phase but not in the gas phase.

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31

Bennett, J. F., F. Collin y D. R. Hastie. "A laboratory flow reactor with gas particle separation and on-line MS/MS for product identification in atmospherically important reactions". Atmospheric Measurement Techniques 2, n.º 2 (14 de diciembre de 2009): 813–23. http://dx.doi.org/10.5194/amt-2-813-2009.

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Abstract. A system to study the gas and particle phase products from gas phase hydrocarbon oxidation is described. It consists of a gas phase photochemical flow reactor followed by a diffusion membrane denuder to remove gases from the reacted products, or a filter to remove the particles. Chemical analysis is performed by an atmospheric pressure chemical ionization (APCI) triple quadrupole mass spectrometer. A diffusion membrane denuder is shown to remove trace gases to below detectable limits so the particle phase can be studied. The system was tested by examining the products of the oxidation of m-xylene initiated by HO radicals. Dimethylphenol was observed in both the gas and particle phases although individual isomers could not be identified. Two furanone isomers, 5-methyl-2(3H)furanone and 3-methyl-2(5H)furanone were identified in the particulate phase, but the isobaric product 2,5 furandione was not observed. One isomer of dimethyl-nitrophenol was identified in the particle phase but not in the gas phase.

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32

Zhang, Qi y Qingxin Cui. "Target protein identification of andrographolide based on isomer approach". Journal of Pharmaceutical and Biomedical Analysis 222 (enero de 2023): 115111. http://dx.doi.org/10.1016/j.jpba.2022.115111.

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Riggs, Dylan L., Johanna Hofmann, Heung S. Hahm, Peter H. Seeberger, Kevin Pagel y Ryan R. Julian. "Glycan Isomer Identification Using Ultraviolet Photodissociation Initiated Radical Chemistry". Analytical Chemistry 90, n.º 19 (4 de septiembre de 2018): 11581–88. http://dx.doi.org/10.1021/acs.analchem.8b02958.

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34

Lindegårdh, N., F. Giorgi, B. Galletti, M. Di Mattia, M. Quaglia, D. Carnevale, N. J. White, A. Mazzanti y N. P. J. Day. "Identification of an isomer impurity in piperaquine drug substance". Journal of Chromatography A 1135, n.º 2 (diciembre de 2006): 166–69. http://dx.doi.org/10.1016/j.chroma.2006.09.066.

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35

Masike, Keabetswe y Ntakadzeni Madala. "Synchronized Survey Scan Approach Allows for Efficient Discrimination of Isomeric and Isobaric Compounds during LC-MS/MS Analyses". Journal of Analytical Methods in Chemistry 2018 (2018): 1–8. http://dx.doi.org/10.1155/2018/2046709.

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Liquid chromatography-mass spectrometry- (LC-MS-) based multiple reaction monitoring (MRM) methods have been used to detect and quantify metabolites for years. These approaches rely on the monitoring of various fragmentation pathways of multiple precursors and the subsequent corresponding product ions. However, MRM methods are incapable of confidently discriminating between isomeric and isobaric molecules and, as such, the development of methods capable of overcoming this challenge has become imperative. Due to increasing scanning rates of recent MS instruments, it is now possible to operate MS instruments both in the static and dynamic modes. One such method is known as synchronized survey scan (SSS), which is capable of acquiring a product ion scan (PIS) during MRM analysis. The current study shows, for the first time, the use of SSS-based PIS approach as a feasible identification feature of MRM. To achieve the above, five positional isomers of dicaffeoylquinic acids (diCQAs) were studied with the aid of SSS-based PIS method. Here, the MRM transitions were automatically optimized using a 3,5-diCQA isomer by monitoring fragmentation transitions common to all five isomers. Using the mixture of these isomers, fragmentation spectra of the five isomers achieved with SSS-based PIS were used to identify each isomer based on previously published hierarchical fragmentation keys. The optimized method was also used to detect and distinguish between diCQA components found in Bidens pilosa and their isobaric counterparts found in Moringa oleifera plants. Thus, the method was shown to distinguish (by differences in fragmentation patterns) between diCQA and their isobars, caffeoylquinic acid (CQA) glycosides. In conclusion, SSS allowed the detection and discrimination of isomeric and isobaric compounds in a single chromatographic run by producing a PIS spectrum, triggered in the automatic MS/MS synchronized survey scan mode.

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36

Qiu, Yan-Ling, Yuji Sekiguchi, Hiroyuki Imachi, Yoichi Kamagata, I.-Cheng Tseng, Sheng-Shung Cheng, Akiyoshi Ohashi y Hideki Harada. "Identification and Isolation of Anaerobic, Syntrophic Phthalate Isomer-Degrading Microbes from Methanogenic Sludges Treating Wastewater from Terephthalate Manufacturing". Applied and Environmental Microbiology 70, n.º 3 (marzo de 2004): 1617–26. http://dx.doi.org/10.1128/aem.70.3.1617-1626.2004.

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ABSTRACT The microbial populations responsible for anaerobic degradation of phthalate isomers were investigated by enrichment and isolation of those microbes from anaerobic sludge treating wastewater from the manufacturing of terephthalic acid. Primary enrichments were made with each of three phthalate isomers (ortho-, iso-, and terephthalate) as the sole energy source at 37Ã¯Â¿Â½C with two sources of anaerobic sludge (both had been used to treat wastewater containing high concentrations of phthalate isomers) as the inoculum. Six methanogenic enrichment cultures were obtained which not only degraded the isomer used for the enrichment but also had the potential to degrade part of other phthalate isomers as well as benzoate with concomitant production of methane, presumably involving strictly syntrophic substrate degradation. Our 16S rRNA gene-cloning analysis combined with fluorescence in situ hybridization revealed that the predominant bacteria in the enrichment cultures were affiliated with a recently recognized non-sulfate-reducing subcluster (subcluster Ih) in the group ‘Desulfotomaculum lineage I' or a clone cluster (group TA) in the class delta-Proteobacteria. Several attempts were made to isolate these microbes, resulting in the isolation of a terephthalate-degrading bacterium, designated strain JT, in pure culture. A coculture of the strain with the hydrogenotrophic methanogen Methanospirillum hungatei converted terephthalate to acetate and methane within 3 months of incubation, whereas strain JT could not degrade terephthalate in pure culture. During the degradation of terephthalate, a small amount of benzoate was transiently accumulated as an intermediate, indicative of decarboxylation of terephthalate to benzoate as the initial step of the degradation. 16S rRNA gene sequence analysis revealed that the strain was a member of subcluster Ih of the group ‘Desulfotomaculum lineage I', but it was only distantly related to other known species.

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37

Wang, Yali, Eskander Alhajji, Bernard Rieul, Francis Berthias y Philippe Maître. "Infrared isomer-specific fragmentation for the identification of aminobutyric acid isomers separated by differential mobility spectrometry". International Journal of Mass Spectrometry 443 (septiembre de 2019): 16–21. http://dx.doi.org/10.1016/j.ijms.2019.05.014.

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38

BATINIĆ-HABERLE, INES, ROBERT D. STEVENS y IRWIN FRIDOVICH. "Electrospray mass spectrometry of isomeric tetrakis(N-alkylpyridyl)porphyrins and their manganese(III) and iron(III) complexes". Journal of Porphyrins and Phthalocyanines 04, n.º 03 (abril de 2000): 217–27. http://dx.doi.org/10.1002/(sici)1099-1409(200004/05)4:3<217::aid-jpp198>3.0.co;2-e.

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Manganese(III) complexes of isomeric tetrakis(N-alkylpyridyl)porphyrins (N- alkyl = N- methyl , M or N- ethyl , E ), MnTM ( E )-2(3,4)- PyP 5+, are being developed as superoxide dismutase (SOD) mimics. Simultaneously, techniques for their purification, identification and characterization are being pursued. Electrospray mass spectrometry ( ESMS ) proved to be an excellent method for identification and characterization of this group of water-soluble cationic porphyrins. The multiply charged parent ion is observed for both the metal-free ligands and their corresponding manganese complexes. The other major peaks in the mass spectra result from loss of N-alkyl groups, reduction of the metal center, axial coordination of chloride or hydroxo ion in the case of the Fe porphyrin, loss of metal and deprotonation of pyrrolic nitrogens. As a result of inductive and resonance effects, which stabilize the ortho isomer, almost no loss of N-alkyl groups from the manganese complex or from its parent ligand was observed. The relative intensity of the multiply charged molecular ion Mn III TM -3(4)- PyP 5+/5 was 100% in the case of the meta and para isomers. Although manganese porphyrins display a low preference toward axial ligation, favorable electrostatics at the metal center of the ortho isomer gives rise to 100% relative intensity of the species that has chloride axially ligated at the manganese site, Mn III TM ( E )-2- PyPCl 4+/4. When the stronger preference of iron porphyrins toward axial ligation combines with the ortho effect, the monohydroxo iron porphyrin Fe III TM -2- PyP ( OH )4+/4 dominates the ESMS of an aqueous acetonitrile solution at pH 7.8.

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39

Kinsel, Gary R. y Murray V. Johnston. "Isomer identification by metastable decay rates of laser-produced ions". Analytical Chemistry 60, n.º 19 (octubre de 1988): 2084–89. http://dx.doi.org/10.1021/ac00170a020.

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40

Wheldon, C., P. M. Walker, R. D'Alarcao, P. Chowdhury, C. J. Pearson, E. H. Seabury, I. Ahmad et al. "Identification of a high-K isomer in neutron-rich 185Ta". European Physical Journal A 5, n.º 4 (agosto de 1999): 353–55. http://dx.doi.org/10.1007/s100500050296.

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41

Bento-Silva, Andreia, Letice Gonçalves, Elsa Mecha, Filipe Pereira, Maria Carlota Vaz Patto y Maria do Rosário Bronze. "An Improved HILIC HPLC-MS/MS Method for the Determination of β-ODAP and Its α Isomer in Lathyrus sativus". Molecules 24, n.º 17 (22 de agosto de 2019): 3043. http://dx.doi.org/10.3390/molecules24173043.

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β-N-Oxalyl-l-α,β-diaminopropionic acid (β-ODAP) is a non-protein amino acid present in Lathyrus sativus (grass pea) and other Lathyrus species, in parallel with its nontoxic isomer, α-ODAP. When consuming grass pea for several months as staple food, β-ODAP may cause neurolathyrism, a motor neuron degeneration syndrome. Therefore, the independent quantification of both ODAP isomers instead of only the total amount in grass pea allows the identification of less toxic varieties and the development of tools to support breeding for improving grass pea quality. In this work, a simple and fast HPLC-MS/MS method was developed without sample derivatization, using a hydrophilic interaction chromatography (HILIC) column and an isocratic gradient of eluents for 18 min, which allowed the determination of both α- and β-ODAP. The proposed method was fully validated and applied to the determination of α- and β-ODAP contents in a diverse collection of 107 grass pea accessions representative of the main grass pea-growing geographical regions in the world, with the prompt identification of contrasting accessions. β-ODAP content in the analyzed grass pea samples ranged from 0.45 ± 0.02 to 6.04 ± 0.45 mg g−1. The moderate correlation found between α- and β-ODAP contents (0.65) in this collection reinforces the importance of the independent quantification of both ODAP isomers.

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42

Li, Hai-Fang, Jing Zhao, Wenbo Cao, Wenpeng Zhang, Yu Xia y Zheng Ouyang. "Site-Specific Photochemical Reaction for Improved C=C Location Analysis of Unsaturated Lipids by Ultraviolet Photodissociation". Research 2022 (12 de febrero de 2022): 1–12. http://dx.doi.org/10.34133/2022/9783602.

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Unraveling the complexity of the lipidome requires the development of novel approaches to facilitate structural identification and characterization of lipid species with isomer-level discrimination. Ultraviolet photodissociation tandem mass spectrometry (UVPD MS/MS) is a promising tool for structure determination of lipids. The sensitivity of UVPD for lipid analysis however is limited mainly due to weak absorption of UV photons by a C=C. Herein, a C=C site-specific derivatization, the Paternò-Büchi (PB) reaction, was used to incorporate a chromophore to the C=C moiety in fatty acyls, leading to significantly improved UVPD efficiency and sensitivity for pinpointing C=C locations. The wavelength-dependent photodissociation of the PB products demonstrated 4-CF3-benzophenone as the best reagent for UVPD in terms of the efficiency of generating C=C diagnostic fragments and simplicity for C=C location assignments. We demonstrated the effectiveness of this approach for the shotgun profiling of C=C location isomers in different lipid classes from complex lipid extracts, highlighting its potential to advancing the identification of the C=C bond locations in unsaturated lipids.

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43

Aslam, Ali, Shengjie Zhao, Xuqiang Lu, Nan He, Hongju Zhu, Aman Ullah Malik, Muhammad Azam y Wenge Liu. "High-Throughput LC-ESI-MS/MS Metabolomics Approach Reveals Regulation of Metabolites Related to Diverse Functions in Mature Fruit of Grafted Watermelon". Biomolecules 11, n.º 5 (23 de abril de 2021): 628. http://dx.doi.org/10.3390/biom11050628.

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Grafting has been reported as a factor regulating the metabolome of a plant. Therefore, a comprehensive metabolic profile and comparative analysis of metabolites were conducted from fully mature fruit of pumpkin-grafted watermelon (PGW) and a self-rooted watermelon (SRW). Widely targeted LC-ESI-MS/MS metabolomics approach facilitated the simultaneous identification and quantification of 339 metabolites across PGW and SRW. Regardless of grafting, delta-aminolevulinic acid hydrochloride, sucrose, mannose-6-phosphate (carbohydrates), homocystine, 2-phenylglycine, s-adenosyl-L-homocysteine (amino acids and derivatives), malic, azelaic, H-butanoic acid ethyl ester-hexoside isomer 1, (organic acids), MAG (18:3) isomer1, LysoPC 16:0, LysoPC 18:2 2n isomer (lipids) p-coumaric acid, piperidine, and salicylic acid-o-glycoside (secondary metabolites) were among the dominant metabolite. Dulcitol, mono-, and disaccharide sugars were higher in PGW, while polysaccharides showed complex behavior. In PGW, most aromatic and nitrogen-rich amino acids accumulated greater than 1.5- and 1-fold, respectively. Intermediates of the tricarboxylic acid cycle (TCA), stress-related metabolites, vitamin B5, and several flavonoids were significantly more abundant in PGW. Most lipids were also significantly higher in grafted watermelon. This is the first report providing a comprehensive picture of watermelon metabolic profile and changes induced by grafting. Hence, the untargeted high-throughput LC-ESI-MS/MS metabolomics approach could be suitable to provide significant differences in metabolite contents between grafted and ungrafted plants.

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44

Galea, Anne M. y Vincent Murray. "The Anti-tumour Agent, Cisplatin, and its Clinically Ineffective Isomer, Transplatin, Produce Unique Gene Expression Profiles in Human Cells". Cancer Informatics 6 (enero de 2008): CIN.S802. http://dx.doi.org/10.4137/cin.s802.

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Cisplatin is a DNA-damaging anti-cancer agent that is widely used to treat a range of tumour types. Despite its clinical success, cisplatin treatment is still associated with a number of dose-limiting toxic side effects. The purpose of this study was to clarify the molecular events that are important in the anti-tumour activity of cisplatin, using gene expression profiling techniques. Currently, our incomplete understanding of this drug's mechanism of action hinders the development of more efficient and less harmful cisplatin-based chemotherapeutics. In this study the effect of cisplatin on gene expression in human foreskin fibroblasts has been investigated using human 19K oligonucleotide microarrays. In addition its clinically inactive isomer, transplatin, was also tested. Dual-fluor microarray experiments comparing treated and untreated cells were performed in quadruplicate. Cisplatin treatment was shown to significantly up- or down-regulate a consistent subset of genes. Many of these genes responded similarly to treatment with transplatin, the therapeutically inactive isomer of cisplatin. However, a smaller proportion of these transcripts underwent differential expression changes in response to the two isomers. Some of these genes may constitute part of the DNA damage response induced by cisplatin that is critical for its anti-tumour activity. Ultimately, the identification of gene expression responses unique to clinically active compounds, like cisplatin, could thus greatly benefit the design and development of improved chemotherapeutics.

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45

Quilliam, Michael A., Brian E. McCarry, Ken H. Hoo, Dennis R. McCalla y Susan Vaitekunas. "Identification of the photolysis products of nitrofurazone irradiated with laboratory illumination". Canadian Journal of Chemistry 65, n.º 5 (1 de mayo de 1987): 1128–32. http://dx.doi.org/10.1139/v87-188.

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Illumination of aqueous or organic solutions of nitrofurazone, 1, with fluorescent or tungsten light caused the appearance of two new compounds, 2 and 3. Compound 2, which eluted just before nitrofurazone on a reverse phase hplc column, had a mass spectrum identical to that of 1 and converted back to 1 at a rate proportional to the temperature and the polarity of the solvent when allowed to sit in the dark. High resolution proton nmr spectroscopy provided conclusive evidence that compound 2 is the syn isomer of 1. Compound 3 had a retention time, ultraviolet spectrum, and mass spectrum that were indistinguishable from those of synthetic 5-nitrofuraldehyde azine. The toxicity of 3 to E. coli was determined to be the same as 1 while its mutagenicity was over 10-fold lower. No detectable cross-links were formed in the DNA of E. coli in the presence of compound 3. Thus, it is unlikely that the relatively small amounts of the azine 3 formed have much influence on the antibacterial potency or mutagenicity of nitrofurazone solutions. However, these results do confirm the desirability of conducting experiments with these agents in the dark or under yellow light. Photochemical formation of syn isomers was also observed with two other Schiff 's base nitrofuran derivatives, nitrofurantoin and furazolidone.

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46

Ohi, Hiroshi y Masanori Kishino. "Acid hydrolysis kinetics and identification of erythro and threo α-ethyl ether derivatives of non-phenolic arylglycerol-β-syringyl ether lignin model compounds". Holzforschung 59, n.º 5 (1 de septiembre de 2005): 497–502. http://dx.doi.org/10.1515/hf.2005.082.

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Abstract Based on their hydrolysis behavior, NMR spectra of the erythro and threo forms of 3-(3,4-dimethoxy-phenyl)-2-(2,6-dimethoxyphenoxy)-3-ethoxypropan-1-ol (named VSE, i.e., α-ethyl ether derivative of veratrylglycerol-β-syringylether) were successfully assigned. A mixture of erythro and threo VSEs was treated at 90°C in pH 1.2 nitric acid solution. In order to assign them, the molar ratios of erythro and threo forms of 1-(3,4-dimethoxyphenyl)-2-(2,6-dimethoxy-phenoxy)propane-1,3-diol (named VS, i.e., veratrylglycerol-β-syringyl) ether given by each VSE were kinetically determined during the treatment. It was found that the inversion ratio at which the first VSE isomer gave erythro-VS was 0.73. Therefore, this isomer was identified as threo-VSE. In addition, from calculations using the least-squares method, the inversion ratio at which the other VSE isomer gave threo-VS was found to be >0.73. These values mean that threo-VSE yields 73% erythro- and 27% threo-VS, while erythro-VSE yields mainly threo-VS.

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47

NEGOIȚĂ, Mioara, Adriana Laura MIHAI, Alina Cristina ADASCĂLULUI y Enuța IORGA. "Development of a Performance Method for Determination of Cis/Trans Isomers of Oleic, Linoleic and Linolenic Acids from Potato Chips by GC-MS". Bulletin of University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca. Food Science and Technology 76, n.º 2 (23 de noviembre de 2019): 114. http://dx.doi.org/10.15835/buasvmcn-fst:2019.0021.

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The aim of this study was to develop and evaluate some validation parameters of a GC-MS sensitive method for the separation, identification, and simultaneous quantification of 18 cis/trans isomers of oleic (FAME C18:1), linoleic (FAME C18:2), and linolenic acid (FAME C18:3) methyl esters. Linearity, sensitivity, and recovery of the developed method were evaluated on calibration solutions. Correlation coefficients (R) were higher than 0.99 in the linear domain for each isomer, the sensitivity of the method was characterized by LOD = 0.03 - 0.05 g/100 g of fat, and LOQ = 0.09 - 0.17 g/100 g of fat, and the recovery ranged between 101.32 - 102.59%. Samples of potato chips were used to demonstrate the applicability of the method and the trans fatty acids (TFA) levels in analyzed sample were below 0.60 g/100 g fat, complying with international recommendations of less than 2 g/100 g of total fat. The proposed GC-MS method allows simultaneous determination of 18 cis/trans isomers (13 trans and 5 cis) of FAME C18 from potato chips.

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48

Espinosa, Marcela, Ubaldo S. Pacheco, Florentino Leyte y Ruben Ocampo. "Separation and identification of porphyrin biomarkers from a heavy crude oil Zaap-1 offshore well, Sonda de Campeche, México". Journal of Porphyrins and Phthalocyanines 18, n.º 07 (julio de 2014): 542–51. http://dx.doi.org/10.1142/s108842461450028x.

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The task to isolate metalloporphyrin compounds from crude oils is difficult, especially from reservoirs; the existence of well-known complexes homologous series type etioporphyrin (E), deoxophyloerythroetioporphyrin (DPEP), tetrahydrobenzodeoxoerythroetioporpyrin (THBD), benzoetio- porphyrin(BE) and benzodeoxoerythroetioporphyrin (BD) of vanadyl and nickel porphyrins, compounds found in crude oils around the world makes it hard. This includes natural porphyrins found in Mexican crude oils such as Ixtal-101, Zaap-1 and Ceh-1 from Sonda de Campeche, México, were the vanadyl porphyrins mixtures of the main series Etio and DPEP have also been reported elsewhere [14]. The objective of this investigation was to isolate porphyrins isomers from a single heavy crude oil from the Sonda de Campeche area, in México, and is based on the modified reversed-phase high-performance liquid chromatography method (RP-HPLC) [9, 11, 12]. Forty vanadyl porphyrin isomers, such as nickel porphyrin complexes were successfully isolated for the first time from heavy crude oil Zaap-1, through an exhaustive work which included a process of demetallization of vanadyl porphyrins to transmetallization to nickel porphyrins, in agreement with other methods [9, 11, 12, 14]. Further purification was achieved by thin-layer chromatography (TLC) with small glass chromatographic columns, packed with silica gel; then the purified isomers were analyzed and identified by electron impact mass spectrometry (EI-MS), providing the following results: from the Etio series seven isomers C 27 E , C 28 E , C 29 E , C 30 E , C 31 E , C 32 E , C 33 E were identified. From DPEP series six isomers C 29 D , C 30 D , C 31 D , C 32 D , C 33 D , C 34 D were identified; from the BD series it was identified only 1 isomer of vanadyl from BD.

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McKenna, Kristin R., Li Li, Andrew G. Baker, Jakub Ujma, Ramanarayanan Krishnamurthy, Charles L. Liotta y Facundo M. Fernández. "Carbohydrate isomer resolution via multi-site derivatization cyclic ion mobility-mass spectrometry". Analyst 144, n.º 24 (2019): 7220–26. http://dx.doi.org/10.1039/c9an01584a.

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Zhu, Mengle, Kegui Lu, Yiting Jin, Xiaowei Xu, Chengyu Chu, Haiping Hao y Qiuling Zheng. "Boronic derivatization-based strategy for monoacylglycerol identification, isomer annotation and quantification". Analytica Chimica Acta 1190 (enero de 2022): 339233. http://dx.doi.org/10.1016/j.aca.2021.339233.

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