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Journal articles on the topic 'Positional isomers'

Author: Grafiati

Published: 4 June 2021

Last updated: 1 February 2022

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1

Poriel, Cyril, and Joëlle Rault-Berthelot. "Dihydroindenofluorene Positional Isomers." Accounts of Chemical Research 51, no. 8 (July 18, 2018): 1818–30. http://dx.doi.org/10.1021/acs.accounts.8b00210.

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2

Anderson, Derrick R., Pavlo V. Solntsev, Hannah M. Rhoda, and Victor N. Nemykin. "How big is big? Separation by conventional methods, X-ray and electronic structures of positional isomers of bis-tert-butylisocyano adduct of 2(3),9(10),16(17),23(24)-tetrachloro-3(2),10(9),17(16),24(23)-tetra(2,6-di-iso-propylphenoxy)-phthalocyaninato iron(II) complex." Journal of Porphyrins and Phthalocyanines 20, no. 01n04 (January 2016): 337–51. http://dx.doi.org/10.1142/s1088424616500164.

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A presence of bulky 2,6-di-iso-propylphenoxy groups in bis-tert-butylisocyano adduct of 2(3),9(10),16(17),23(24)-tetrachloro-3(2),10(9),17(16),24(23)-tetra(2,6-di-iso-propylphenoxy)-phthalocyaninato iron(II) complex allows separation of two individual positional isomers and a mixture of the remaining two isomers using conventional chromatography. X-ray structures of “[Formula: see text]” and “[Formula: see text]” isomers were confimed by X-ray crystallography. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations of each individual positional isomer allowed insight into their electronic structures and vertical excitation energies, which were correlated with the experimental UV-vis and MCD spectra.

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3

Cisterna, Jonathan, Catherine Araneda, Pilar Narea, Alejandro Cárdenas, Jaime Llanos, and Iván Brito. "The Positional Isomeric Effect on the Structural Diversity of Cd(II) Coordination Polymers, Using Flexible Positional Isomeric Ligands Containing Pyridyl, Triazole, and Carboxylate Fragments." Molecules 23, no. 10 (October 14, 2018): 2634. http://dx.doi.org/10.3390/molecules23102634.

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To systematically investigate the influence of the positional isomeric effect on the structures of polymer complexes, we prepared two new polymers containing the two positional isomers ethyl 5-methyl-1-(pyridin-3-yl)-1H-1,2,3-triazole-3-carboxylate (L1) and ethyl-5-methyl-1-(pyridin-3-yl)-1H-1,2,3-triazole-4-carboxylate (L2), as well as Cd(II) ions. The structures of the metal–organic frameworks were determined by a single crystal XRD analysis. The compound [Cd(L1)2·4H2O] (1), is a hydrogen bond-induced coordination polymer, whereas the compound [Cd(L2)4·5H2O]n (2) is a three-dimensional (3-D) coordination polymer. Their structures and properties are tuned by the variable N-donor positions of the ligand isomers. This work indicates that the isomeric effect of the ligand isomers plays an important role in the construction of the Cd(II) complexes. In addition, the thermal and luminescent properties are reported in detail.

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4

Vasilkova, N. O., M. Ju Borisova, N. A. Jurasov, and A. P. Krivenko. "Reaggregation Positional Isomers Tetrazologeksahidroquinazoline." Chemistry. Biology. Ecology 16, no. 1 (March 18, 2016): 5–8. http://dx.doi.org/10.18500/1816-9775-2016-16-1-5-8.

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5

Kucherenko, T. T., A. V. Zadorozhny, and V. A. Kovtunenko. "Positional isomers of thienopyrimidinones." Chemistry of Heterocyclic Compounds 44, no. 6 (June 2008): 750–58. http://dx.doi.org/10.1007/s10593-008-0100-y.

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6

Chen, Fengli, Dongjie Bai, Donghao Jiang, Yao Wang, and Yabing He. "A comparative study of C2H2 adsorption properties in five isomeric copper-based MOFs based on naphthalene-derived diisophthalates." Dalton Transactions 46, no. 34 (2017): 11469–78. http://dx.doi.org/10.1039/c7dt02290e.

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7

Bailey, T. R., G. D. Diana, T. L. Draper, and D. C. Pevear. "Acetylfurans as Bio-Isosteres for 3-Methylisoxazole. The Effect of Acetylfuran Positional Isomers on Antirhinoviral Activity." Antiviral Chemistry and Chemotherapy 7, no. 1 (February 1996): 46–52. http://dx.doi.org/10.1177/095632029600700108.

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A panel of four isomeric acetylfuran analogues of disoxaril were prepared. Using a 96-well tissue culture inhibitory dose assay (TCID), these acetylfuran isomers were screened against 15 rhinovirus serotypes. Comparison of the results obtained suggested that antiviral activity was related to hydrogen bond participation by the carbonyl oxygen within the viral pocket. Modelling acetylfuran conformations using an X-ray crystal structure template of 1 in HRV-14 demonstrates that three of the four isomers can adopt the desired conformation for this hydrogen bonding, and the fourth isomer 15 is prohibited by steric constraints from achieving the necessary conformation. These observations are consistent with the hypothesis that broad-spectrum antirhinoviral activity may require a hydrogen bond acceptor at that region of the inhibitor.

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8

Völker, Plum, Gindikin, and Breslauer. "Dynamic DNA Energy Landscapes and Substrate Complexity in Triplet Repeat Expansion and DNA Repair." Biomolecules 9, no. 11 (November 6, 2019): 709. http://dx.doi.org/10.3390/biom9110709.

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DNA repeat domains implicated in DNA expansion diseases exhibit complex conformational and energy landscapes that impact biological outcomes. These landscapes include ensembles of entropically driven positional interchanges between isoenergetic, isomeric looped states referred to as rollamers. Here, we present evidence for the position-dependent impact on repeat DNA energy landscapes of an oxidative lesion (8oxodG) and of an abasic site analogue (tetrahydrofuran, F), the universal intermediate in base excision repair (BER). We demonstrate that these lesions modulate repeat bulge loop distributions within the wider dynamic rollamer triplet repeat landscapes. We showed that the presence of a lesion disrupts the energy degeneracy of the rollameric positional isomers. This lesion-induced disruption leads to the redistribution of loop isomers within the repeat loop rollamer ensemble, favoring those rollameric isomers where the lesion is positioned to be energetically least disruptive. These dynamic ensembles create a highly complex energy/conformational landscape of potential BER enzyme substrates to select for processing or to inhibit processing. We discuss the implications of such lesion-induced alterations in repeat DNA energy landscapes in the context of potential BER repair outcomes, thereby providing a biophysical basis for the intriguing in vivo observation of a linkage between pathogenic triplet repeat expansion and DNA repair.

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9

Bałczewski, Piotr, Joanna Skalik, Paweł Uznański, Dariusz Guziejewski, and Witold Ciesielski. "Use of isomeric, aromatic dialdehydes in the synthesis of photoactive, positional isomers of higher analogs of o-bromo(hetero)acenaldehydes." RSC Advances 5, no. 31 (2015): 24700–24704. http://dx.doi.org/10.1039/c4ra14071k.

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A series of photoresistant, positional isomers of o-bromo(hetero)acenaldehydes containing RO-Ar and bifunctional ortho-CHO/Br structural motifs, is available in the peculiar Friedel–Crafts modification, using isomeric aromatic o,o-dibromodialdehydes.

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10

Delmonte, Pierluigi, Martin P. Yurawecz, Magdi M. Mossoba, Cristina Cruz-Hernandez, and John K. G. Kramer. "Improved Identification of Conjugated Linoleic Acid Isomers Using Silver-Ion HPLC Separations." Journal of AOAC INTERNATIONAL 87, no. 2 (March 1, 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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11

Ngubeni, Grace N., Jonathan Britton, John Mack, Edward New, Ian Hancox, Marc Walker, Tebello Nyokong, Tim S. Jones, and Samson Khene. "Spectroscopic and nonlinear optical properties of the four positional isomers of 4α-(4-tert-butylphenoxy)phthalocyanine." Journal of Materials Chemistry C 3, no. 41 (2015): 10705–14. http://dx.doi.org/10.1039/c5tc01601k.

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An enhanced NLO response in terms of both the β and γ values was observed for C_4h isomer compared to the other isomers, smallest NLO response were observed for the C_2v and C_s isomers, respectively.

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12

Nagai, Toshiharu, Tetsuaki Kinoshita, Erika Kasamatsu, Kazuaki Yoshinaga, Hoyo Mizobe, Akihiko Yoshida, Yutaka Itabashi, and Naohiro Gotoh. "Simultaneous Quantification of Mixed-Acid Triacylglycerol Positional Isomers and Enantiomers in Palm Oil and Lard by Chiral High-Performance Liquid Chromatography Coupled with Mass Spectrometry." Symmetry 12, no. 9 (August 19, 2020): 1385. http://dx.doi.org/10.3390/sym12091385.

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Palm oil and lard are edible fats which are rich in palmitic (P) and oleic acids (O). In this study, triacylglycerol (TAG) positional isomers (symmetric and asymmetric isomers) and enantiomers (asymmetric isomers) in palm oil and lard were quantified simultaneously by using liquid chromatography/mass spectrometry. The CHIRALPAK IF-3 column used in our previous study recognized the difference of TAG isomers consisting of P and O in palm oil and lard, separated sn-OPP/sn-PPO/sn-POP and sn-OPO/sn-OOP/sn-POO into each isomer peak, and enabled the quantification of these TAG isomers with good recovery (95–120%). Although sn-POP and sn-OPO were the major TAGs in palm oil and lard, a comparison of the abundance ratios of TAG enantiomers such as sn-PPO/sn-OPP and sn-OOP/sn-POO revealed that there were slightly more TAG enantiomers with O at the sn-1 position and P at the sn-3 position in palm oil and P at the sn-1 position and O at the sn-3 position in lard. These results were consistent with previous reports for the positional distribution of fatty acids of palm oil and lard. This is the first study that has enabled all TAG isomers consisting of P and O in natural oils and fats to be individually quantified by mass spectrometry.

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13

Kasperkowiak, Małgorzata, Monika Beszterda, Izabela Bańczyk, and Rafał Frański. "Differentiation of bisphenol F diglycidyl ether isomers and their derivatives by HPLC-MS and GC-MS—comment on the published data." Analytical and Bioanalytical Chemistry 413, no. 7 (January 20, 2021): 1893–903. http://dx.doi.org/10.1007/s00216-021-03157-2.

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AbstractPositional isomers of bisphenol F diglycidyl ether (BFDGE) have been analyzed by high-pressure liquid chromatography-mass spectrometry and by gas chromatography-mass spectrometry (HPLC-MS, GC-MS). Positional isomers of BFDGE derivatives (BFDGEx2H2O, BFDGExH2OxHCl) have been analyzed by HPLC-MS. On the basis of the obtained fragmentation patterns, the elution order of the isomers has been unequivocally determined, in standard solutions and in the sample of liquid obtained after rinsing an empty mackerel fish can with acetonitrile. Under HPLC condition, para,para isomers are eluted first, then ortho,para isomers’ elution follows, and ortho,ortho isomers are eluted last. Under GC condition, the reverse elution order has been obtained. For the first time, two ortho,para isomers of BFDGExH2OxHCl have been detected and their elution order has been determined. The obtained results are of key importance for determination of the isomer distribution of BFDGE and its derivatives in food samples.

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14

Cook, H. W., and E. A. Emken. "Geometric and positional fatty acid isomers interact differently with desaturation and elongation of linoleic and linolenic acids in cultured glioma cells." Biochemistry and Cell Biology 68, no. 3 (March 1, 1990): 653–60. http://dx.doi.org/10.1139/o90-094.

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A range of geometrical and positional isomers of 18-carbon acyl chains are potential components of diets containing fats from processed vegetable oils or ruminant animals. We have examined seventeen 18-carbon fatty acids, with cis or trans double bonds in positions 8–15, for their effects on desaturation and chain elongation of [1-14C]18:2(n − 6) or [1-14C]18:3(n − 3), primarily to 20:4(n − 6) or 20:5(n − 3) respectively, in cultured glioma cells. All trans monoenoic positional isomers inhibited Δ5 desaturation by approximately 60% when 18:2(n − 6) was the substrate, with no positional discrimination evident; with 18:3(n − 3) as substrate, only the 11- and 12-trans isomers were effective inhibitors of formation of 20:5(n − 3). All cis positional monoene isomers, except for 12-cis 18:1, produced 25–30% inhibition of conversion of 18:2(n − 6) to 20:4(n − 6), but had little effect on the conversion of 18:3(n − 3) to 20:5(n − 3). For dienoic isomers, the presence of a 12-trans bond inhibited formation of both 20:4(n − 6) and 20:5(n − 3) and this was enhanced markedly when the other bond in the dienoic acid was 9-trans. Presence of a 9-trans or 15-trans bond with 12-cis gave little effect except for a slight inhibition of 20:4(n − 6) formation by the 12-cis,15-trans 18:2 isomer. All-cis 20:3(n − 9) blocked Δ5 desaturation, increasing 20:3(n − 6) accumulation from 18:2(n − 6) and suggesting that formation of 20:3(n − 9) from 18:1(n − 9) during essential fatty acid deficiency may further exacerbate the already compromised formation of 20:4(n − 6). Further, the differential effects of various cis and trans isomers on the metabolism of 18:2(n − 6) and 18:3(n − 3) suggest that either Δ5 desaturation is not common in both pathways of conversion of 18:2(n − 6) or 18:3(n − 3) to their primary products or that selective interactions of trans and cis isomers occur when the essential fatty acid substrates are different.Key words: trans isomers, essential fatty acids, desaturation, glioma cells, fatty acid metabolism.

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15

Searle, Brian C., Robert T. Lawrence, Michael J. MacCoss, and Judit Villén. "Thesaurus: quantifying phosphopeptide positional isomers." Nature Methods 16, no. 8 (July 29, 2019): 703–6. http://dx.doi.org/10.1038/s41592-019-0498-4.

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16

Jadhav, Thaksen, Jeong Min Choi, Jivan Shinde, Jun Yeob Lee, and Rajneesh Misra. "Mechanochromism and electroluminescence in positional isomers of tetraphenylethylene substituted phenanthroimidazoles." Journal of Materials Chemistry C 5, no. 24 (2017): 6014–20. http://dx.doi.org/10.1039/c7tc00950j.

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17

Masike, Keabetswe, and 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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18

Ohnishi, Atsushi, Tohru Shibata, Tatsuya Imase, Satoshi Shinkura, and Kanji Nagai. "Achiral Molecular Recognition of Substituted Aniline Position Isomers by Crown Ether Type Chiral Stationary Phase." Molecules 26, no. 2 (January 18, 2021): 493. http://dx.doi.org/10.3390/molecules26020493.

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To understand the selectivity of the crown ether type chiral stationary phase (CSP), the retention selectivity for aniline and the positional isomers of substituted anilines were studied. In various substituted isomers, except nitroaniline, a remarkable decrease of retention due to steric hindrance was observed for the 2-substituted isomer. To determine the detailed molecular recognition mechanism, quantum chemical calculations were performed for the aggregates between the crown ether and the anilines. The results suggested that the 20-Crown-6, which includes a phenyl-substituted 1,1′-binaphthyl moiety, interacts with alkyl and aryl amines in an unconventional form different from the proposed one for 18-Crown-6.

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19

Zeng, Zhen, and Elliot R. Bernstein. "Anionic fructose-related conformational and positional isomers assigned through PES experiments and DFT calculations." Physical Chemistry Chemical Physics 19, no. 34 (2017): 23325–44. http://dx.doi.org/10.1039/c7cp03492j.

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20

Glemza, Amy Jo, Jeffrey A. Koehler, Brian J. Brune, and Gregory F. Payne. "Selective Adsorption of Methoxyphenol Positional Isomers." Industrial & Engineering Chemistry Research 37, no. 9 (September 1998): 3685–90. http://dx.doi.org/10.1021/ie9801554.

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21

van Outersterp, Rianne E., Jonathan Martens, Giel Berden, Valerie Koppen, Filip Cuyckens, and Jos Oomens. "Mass spectrometry-based identification of ortho-, meta- and para-isomers using infrared ion spectroscopy." Analyst 145, no. 18 (2020): 6162–70. http://dx.doi.org/10.1039/d0an01119c.

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Distinguishing positional isomers presents a significant challenge for mass spectrometric analyses, for instance in drug metabolism research. We show that IR ion spectroscopy readily identifies ortho-, meta- and para-isomers.

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22

Jayabharathi, Jayaraman, Shanmugam Thilagavathy, and Venugopal Thanikachalam. "Non-doped OLEDs based on tetraphenylethylene phenanthroimidazoles with negligible efficiency roll-off: effects of end group regulated stimulus responsive AIE luminogens." Materials Advances 2, no. 15 (2021): 5160–70. http://dx.doi.org/10.1039/d1ma00391g.

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The positional isomers of phenanthroimidazoles, TPE-NPPB and TPE-APPB, have been designed to understand the positional effects of triphenylamine (TPA) and tetraphenylethylene (TPE) units on the aggregation-induced emission and mechanochromism.

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23

Inoue, Satoru, Toshiki Higashino, Shunto Arai, Reiji Kumai, Hiroyuki Matsui, Seiji Tsuzuki, Sachio Horiuchi, and Tatsuo Hasegawa. "Regioisomeric control of layered crystallinity in solution-processable organic semiconductors." Chemical Science 11, no. 46 (2020): 12493–505. http://dx.doi.org/10.1039/d0sc04461j.

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An isomorphous bilayer-type layered herringbone crystal packing is reported for a series of four positional isomers of mono-C8-BTNTs, where the single-crystal devices with the isomers exhibit high-performance TFT characteristics.

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24

Witzgall, P., P. Trematerra, I. Liblikas, M. Bengtsson, and C. R. Unelius. "Pheromone communication channels in tortricid moths: lower specificity of alcohol vs. acetate geometric isomer blends." Bulletin of Entomological Research 100, no. 2 (July 9, 2009): 225–30. http://dx.doi.org/10.1017/s0007485309990186.

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AbstractDiscrimination of conspecific and heterospecific signals is a key element in the evolution of specific mate recognition systems. Lepidopteran pheromone signals are typically composed of several compounds that synergize attraction of conspecific and inhibit attraction of heterospecific males. Blends convey specificity, but not their single components, that are typically shared by several species. Many sex pheromones are blends of geometric or positional isomers of straight-chain acetates, while species-specific blends of analogous alcohols have not been described. We have, therefore, studied the attraction of tortricid moths to the geometric isomers (E,E)-, (E,Z)-, (Z,E)- and (Z,Z)-8,10-dodecadien-1-ol. Only one species responding to these alcohols seemed to be attracted to a blend of two isomers, while most species are attracted to only one alcohol isomer. Lack of a pronounced synergist or antagonist effect of the other geometric isomers explains the lack of specific attraction to isomer blends and reduces accordingly the number of specific communication signals composed of these alcohols. In comparison, many more species respond to the analogous (E,E)-, (E,Z)-, (Z,E)- and (Z,Z)-8,10-dodecadienyl acetates and their binary blends. The acetate isomers all play a behavioural role, either as attractants, attraction synergists or antagonists, and thus promote specific communication with acetate blends. Male moths seem to discriminate the acetate isomers with greater precision than the analogous alcohols. It is proposed that discrimination is facilitated by steric differences between the four acetate isomers, as compared to the more uniform steric properties of the alcohols.

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25

Ekbote, Anupama, Shaikh M. Mobin, and Rajneesh Misra. "Stimuli-responsive phenothiazine-based donor–acceptor isomers: AIE, mechanochromism and polymorphism." Journal of Materials Chemistry C 8, no. 10 (2020): 3589–602. http://dx.doi.org/10.1039/c9tc05192a.

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Stimuli responsive phenothiazine-based donor–acceptor (D–A) molecules were designed and synthesized as positional isomers p-PTZ, m-PTZ and o-PTZ. A comprehensive comparative study of the electronic and photophysical properties has been performed to study the effect of positional change.

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26

Schillmöller, Timo, Paul Niklas Ruth, Regine Herbst-Irmer, and Dietmar Stalke. "Three colour solid-state luminescence from positional isomers of facilely modified thiophosphoranyl anthracenes." Chemical Communications 56, no. 54 (2020): 7479–82. http://dx.doi.org/10.1039/d0cc02585b.

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27

Jakuš, Vladimír, Eva Matisová, and Stanislav Miertuš. "Application of Quantum Chemical Calculations to the Identification of Positional Isomers of Polysubstituted Alkylbenzenes." Collection of Czechoslovak Chemical Communications 57, no. 12 (1992): 2494–500. http://dx.doi.org/10.1135/cccc19922494.

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The problem of assignment of positional isomers of alkylbenzenes to chromatographic peaks is addressed. Probable structures are attributed based on the correlation of stabilities of the isomers, which are expressed as the total molecular energies calculated by the MINDO/3 semiempirical quantum chemical method, and the proportions of the isomers in the reaction mixture. Multicomponent alkylbenzene mixtures were prepared and separated by capillary gas chromatography, and the identity of the isomers was confirmed by the gas chromatography-mass spectrometry combination.

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28

Hindocha, Darsha, and Norman W. Smith. "Resolution of positional isomers by capillary electrochromatography." Journal of Chromatography A 904, no. 1 (December 2000): 99–106. http://dx.doi.org/10.1016/s0021-9673(00)00913-4.

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29

Gimarc, Benjamin M., and Anna R. Brant. "Bullvalene: Reaction Graphs Relating Polysubstituted Positional Isomers." Journal of Chemical Information and Modeling 34, no. 5 (September 1, 1994): 1167–73. http://dx.doi.org/10.1021/ci00021a025.

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30

Tague, Andrew J., Papanin Putsathit, Thomas V. Riley, Paul A. Keller, and Stephen G. Pyne. "Positional Isomers of Biphenyl Antimicrobial Peptidomimetic Amphiphiles." ACS Medicinal Chemistry Letters 12, no. 3 (February 3, 2021): 413–19. http://dx.doi.org/10.1021/acsmedchemlett.0c00611.

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31

Masike, Keabetswe, Ian Dubery, Paul Steenkamp, Elize Smit, and Edwin Madala. "Revising Reverse-Phase Chromatographic Behavior for Efficient Differentiation of Both Positional and Geometrical Isomers of Dicaffeoylquinic Acids." Journal of Analytical Methods in Chemistry 2018 (2018): 1–11. http://dx.doi.org/10.1155/2018/8694579.

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Dicaffeoylquinic acids (diCQAs) are plant metabolites and undergo trans-cis-isomerization when exposed to UV irradiation. As such, diCQAs exist in both trans- and cis-configurations and amplify the already complex plant metabolome. However, analytical differentiation of these geometrical isomers using mass spectrometry (MS) approaches has proven to be extremely challenging. Exploring the chromatographic space to develop possible conditions that would aid in differentially separating and determining the elution order of these isomers is therefore imperative. In this study, simple chromatographic parameters, such as column chemistry (phenyl versus alkyl), mobile phase composition (methanol or acetonitrile), and column temperature, were investigated to aid in the separation of diCQA geometrical isomers. The high-performance liquid chromatography photodiode array (HPLC-PDA) chromatograms revealed four isomers post UV irradiation of diCQA authentic standards. The elution profile/order was seen to vary on different reverse-phase column chemistries (phenyl versus alkyl) using different mobile phase composition. Here, the elution profile/order on the phenyl-derived column matrices (with methanol as the mobile phase composition) was observed to be relatively reproducible as compared to the alkyl (C18) columns. Chromatographic resolution of diCQA geometrical isomers can be enhanced with an increase in column temperature. Lastly, the study highlights that chromatographic elution order/profile cannot be relied upon to fathom the complexity of isomeric plant metabolites.

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Ekbote, Anupama, Si Hyun Han, Thaksen Jadhav, Shaikh M. Mobin, Jun Yeob Lee, and Rajneesh Misra. "Stimuli responsive AIE active positional isomers of phenanthroimidazole as non-doped emitters in OLEDs." Journal of Materials Chemistry C 6, no. 8 (2018): 2077–87. http://dx.doi.org/10.1039/c7tc05450e.

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Yang, Xiaohong, Changxia Li, Meiling Qi, and Liangti Qu. "A graphene-based porous carbon material as a stationary phase for gas chromatographic separations." RSC Advances 7, no. 51 (2017): 32126–32. http://dx.doi.org/10.1039/c7ra04774f.

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Wang, Kai, Hui Xiao, Li Qian, Mingxi Han, Xianfeng Wu, Zhiyong Guo, and Hongbing Zhan. "Diversified AIE and mechanochromic luminescence based on carbazole derivative decorated dicyanovinyl groups: effects of substitution sites and molecular packing." CrystEngComm 22, no. 12 (2020): 2166–72. http://dx.doi.org/10.1039/c9ce01958h.

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35

Rana, Anup, and Pradeepta K. Panda. "β-Tetrachlorotetramethoxyporphycenes: positional effect of substituents on structure and photophysical properties." Chemical Communications 51, no. 61 (2015): 12239–42. http://dx.doi.org/10.1039/c5cc03867g.

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Wang, Xiaojuan, Ting He, Lan Yang, Huiqiong Wu, Jiafu Yin, Rujuan Shen, Juan Xiang, Yi Zhang, and Chuanwan Wei. "Designing isometrical gel precursors to identify the gelation pathway for nickel-selective metallohydrogels." Dalton Transactions 45, no. 46 (2016): 18438–42. http://dx.doi.org/10.1039/c6dt03828j.

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Gayathri, Parthasarathy, Subramanian Karthikeyan, Mehboobali Pannipara, Abdullah G. Al-Sehemi, Dohyun Moon, and Savarimuthu Philip Anthony. "Aggregation-enhanced emissive mechanofluorochromic carbazole-halogen positional isomers: tunable fluorescence via conformational polymorphism and crystallization-induced fluorescence switching." CrystEngComm 21, no. 43 (2019): 6604–12. http://dx.doi.org/10.1039/c9ce01227c.

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Halder, Senjuti, Utsab Manna, and Gopal Das. "Tuning the aggregation performance by varying the substituent position: comparative study of neutral bis-urea derivatives in aqueous medium." New Journal of Chemistry 43, no. 35 (2019): 14112–19. http://dx.doi.org/10.1039/c9nj03297e.

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Scanferlato, Roberta, Massimo Bortolotti, Anna Sansone, Chryssostomos Chatgilialoglu, Letizia Polito, Marco De Spirito, Giuseppe Maulucci, Andrea Bolognesi, and Carla Ferreri. "Hexadecenoic Fatty Acid Positional Isomers and De Novo PUFA Synthesis in Colon Cancer Cells." International Journal of Molecular Sciences 20, no. 4 (February 15, 2019): 832. http://dx.doi.org/10.3390/ijms20040832.

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Palmitic acid metabolism involves delta-9 and delta-6 desaturase enzymes forming palmitoleic acid (9cis-16:1; n-7 series) and sapienic acid (6cis-16:1; n-10 series), respectively. The corresponding biological consequences and lipidomic research on these positional monounsaturated fatty acid (MUFA) isomers are under development. Furthermore, sapienic acid can bring to the de novo synthesis of the n-10 polyunsaturated fatty acid (PUFA) sebaleic acid (5cis,8cis-18:2), but such transformations in cancer cells are not known. The model of Caco-2 cell line was used to monitor sapienic acid supplementation (150 and 300 μM) and provide evidence of the formation of n-10 fatty acids as well as their incorporation at levels of membrane phospholipids and triglycerides. Comparison with palmitoleic and palmitic acids evidenced that lipid remodelling was influenced by the type of fatty acid and positional isomer, with an increase of 8cis-18:1, n-10 PUFA and a decrease of saturated fats in case of sapienic acid. Cholesteryl esters were formed only in cases with sapienic acid. Sapienic acid was the less toxic among the tested fatty acids, showing the highest EC50s and inducing death only in 75% of cells at the highest concentration tested. Two-photon fluorescent microscopy with Laurdan as a fluorescent dye provided information on membrane fluidity, highlighting that sapienic acid increases the distribution of fluid regions, probably connected with the formation of 8cis-18:1 and the n-10 PUFA in cell lipidome. Our results bring evidence for MUFA positional isomers and de novo PUFA synthesis for developing lipidomic analysis and cancer research.

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Sun, Tao, Xiaomin Shuai, Kaixin Ren, Xingxing Jiang, Yujie Chen, Xinyu Zhao, Qianqian Song, Shaoqiang Hu, and Zhiqiang Cai. "Amphiphilic Block Copolymer PCL-PEG-PCL as Stationary Phase for Capillary Gas Chromatographic Separations." Molecules 24, no. 17 (August 30, 2019): 3158. http://dx.doi.org/10.3390/molecules24173158.

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This work presents the first example of utilization of amphiphilic block copolymer PCL-PEG-PCL as a stationary phase for capillary gas chromatographic (GC) separations. The PCL-PEG-PCL capillary column fabricated by static coating provides a high column efficiency of 3951 plates/m for n-dodecane at 120 °C. McReynolds constants and Abraham system constants were also determined in order to evaluate the polarity and possible molecular interactions of the PCL-PEG-PCL stationary phase. Its selectivity and resolving capability were investigated by using a complex mixture covering analytes of diverse types and positional, structural, and cis-/trans-isomers. Impressively, it exhibits high resolution performance for aliphatic and aromatic isomers with diverse polarity, including those critical isomers such as butanol, dichlorobenzene, dimethylnaphthalene, xylenol, dichlorobenzaldehyde, and toluidine. Moreover, it was applied for the determination of isomer impurities in real samples, suggesting its potential for practical use. The superior separation performance demonstrates the potential of PCL-PEG-PCL and related block copolymers as stationary phases in GC and other separation technologies.

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Zhang, Jun-Hui, Mei Zhang, Sheng-Ming Xie, Pin-Gang He, and Li-Ming Yuan. "A novel inorganic mesoporous material with a nematic structure derived from nanocrystalline cellulose as the stationary phase for high-performance liquid chromatography." Analytical Methods 7, no. 8 (2015): 3448–53. http://dx.doi.org/10.1039/c5ay00551e.

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Luan, Jiabin, Shuquan Cui, Juntao Wang, Wenjia Shen, Lin Yu, and Jiandong Ding. "Positional isomeric effects of coupling agents on the temperature-induced gelation of triblock copolymer aqueous solutions." Polymer Chemistry 8, no. 17 (2017): 2586–97. http://dx.doi.org/10.1039/c7py00232g.

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Chen, Z. Y., W. M. N. Ratnayake, L. Fortier, R. Ross, and S. C. Cunnane. "Similar distribution of trans fatty acid isomers in partially hydrogenated vegetable oils and adipose tissue of Canadians." Canadian Journal of Physiology and Pharmacology 73, no. 6 (June 1, 1995): 718–23. http://dx.doi.org/10.1139/y95-093.

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The objective of this study was to evaluate the composition of trans fatty acids in the subcutaneous fat of Canadians relative to the composition of dietary sources of trans fatty acids. The fatty acid composition, total trans fatty acid content, and the geometric and positional isomer distribution of unsaturated fatty acids of subcutaneous adipose tissue of Canadians were determined using a combination of capillary gas–liquid chromatography and silver nitrate thin-layer chromatography. The mean total trans fatty acid content was 6.80% at the abdominal site and 5.80% at the lateral thigh site. Total trans isomers of linoleic acid (18:2n−6) were present at 1.17% in abdominal and 1.59% in thigh adipose tissue, with 9c,12t-18:2 being the most prevalent isomer followed by 9c-13t-18:2 and 9t,12c,-18:2. The oleic acid (18:1) trans isomer distribution in adipose tissue differed from that in butter fat, but it was similar to that in partially hydrogenated vegetable oils. The reverse was true for the 18:1 cis isomers. Total 18:1 trans isomers were inversely related to 18:2n−6 content in adipose tissue, suggesting the trans fatty acid intake is inversely related to the intake of linoleic acid. Partially hydrogenated vegetable oils appear to be the major source of trans fatty acids in adipose tissue of Canadians.Key words: trans fatty acids, adipose tissue, partially hydrogenated vegetable oil, linoleic acid.

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Ravat, Prince, and Martin Baumgarten. "Positional Isomers of Tetramethoxypyrene-based Mono- and Biradicals." Journal of Physical Chemistry B 119, no. 43 (July 9, 2015): 13649–55. http://dx.doi.org/10.1021/acs.jpcb.5b03056.

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Watanabe, Natsuko, Toshiharu Nagai, Hoyo Mizobe, Kazuaki Yoshinaga, Akihiko Yoshida, Yohei Kitamura, Takashi Shimizu, Fumiaki Beppu, and Naohiro Gotoh. "Quantification of Triacylglycerol Positional Isomers in Rat Milk." Journal of Oleo Science 65, no. 12 (2016): 977–83. http://dx.doi.org/10.5650/jos.ess16115.

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Hartshorn, Chris M., Kimberly A. Maxwell, Peter S. White, Joseph M. DeSimone, and Thomas J. Meyer. "Separation of Positional Isomers of Oxidation Catalyst Precursors." Inorganic Chemistry 40, no. 4 (February 2001): 601–6. http://dx.doi.org/10.1021/ic9911724.

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Ligon, Evelyn S., Jason Nawyn, Lonnie V. Jones, B. McKay Allred, Daniel V. Reinhardt, and Stefan France. "Synthesis of Flubromazepam Positional Isomers for Forensic Analysis." Journal of Organic Chemistry 84, no. 16 (July 20, 2019): 10280–91. http://dx.doi.org/10.1021/acs.joc.9b01433.

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48

Newton, Kelly A., Lili Zhou, Bruce D. Johnson, Richard Thompson, Dean Ellison, and Jean M. Wyvratt. "THE SEPARATION OF POSITIONAL ISOMERS BY CAPILLARY ELECTROCHROMATOGRAPHY." Journal of Liquid Chromatography & Related Technologies 24, no. 6 (March 31, 2001): 755–71. http://dx.doi.org/10.1081/jlc-100103408.

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TANIMOTO, Toshiko, Junko TSUJIKAWA, and Kyoko KOIZUMI. "Preparation of Three Positional Isomers of Diglucosyl-cyclomaltohexaose." CHEMICAL & PHARMACEUTICAL BULLETIN 40, no. 5 (1992): 1125–29. http://dx.doi.org/10.1248/cpb.40.1125.

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Pokrovskiy, O. I., K. B. Ustinovich, O. I. Usovich, O. O. Parenago, and V. V. Lunin. "Interaction of positional isomers of dimethylbenzene with graphite." Russian Journal of Physical Chemistry A 90, no. 8 (July 21, 2016): 1602–8. http://dx.doi.org/10.1134/s0036024416080215.

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