Artículos de revistas: "Isotopomer molecules"

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Hellerstein, M. K., C. Kletke, S. Kaempfer, K. Wu y C. H. Shackleton. "Use of mass isotopomer distributions in secreted lipids to sample lipogenic acetyl-CoA pool in vivo in humans". American Journal of Physiology-Endocrinology and Metabolism 261, n.º 4 (1 de octubre de 1991): E479—E486. http://dx.doi.org/10.1152/ajpendo.1991.261.4.e479.

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Measurement of hepatic fatty acid (FA) and cholesterol synthesis has been limited by lack of access to the precursor pool, cytosolic acetyl-CoA. We present a method for inferring the enrichment of the true hepatic lipogenic precursor pool in humans using the frequency distribution of mass isotopomers within enriched circulating polymers of acetyl-CoA [very low-density lipoprotein (VLDL)-palmitate, VLDL-stearate]. Human subjects were infused intravenously (n = 16) with [1-13C]- or [2-13C]acetate. Oral sulfamethoxazole (SMX) was administered concurrently, and the acetylated conjugate (SMX acetate) was used to estimate independently the hepatic cytosolic acetyl-CoA enrichment. Isotopomer frequencies in VLDL-FA were determined by gas chromatography-mass spectrometry, whereas high-performance liquid chromatography-mass spectrometry was used to measure enrichments in SMX acetate. Based on the excess M2/excess M1 ratio in VLDL-FA, calculated acetyl-CoA enrichments were 5.59 +/- 0.33 molar percent excess (MPE), whereas SMX acetate enrichments were 5.38 +/- 0.31 MPE (the 2 methods were not significantly different). Mass isotopomer-calculated and SMX acetate-measured estimates of acetyl-CoA enrichments correlated very closely in individual subjects (r2 = 0.93; P less than 0.0001). De novo hepatic lipogenesis can be measured using isotopomer-calculated precursor enrichments compared with measured incorporation in specific isotopomers of VLDL-FA. In summary, excess isotopomer frequencies in secreted lipids provide a non-invasive technique for estimating hepatic cytosolic acetyl-CoA enrichments in humans in vivo and correlate closely with enrichments observed using the xenobiotic probe technique. Isotopomeric distributions represent a new strategy for accurate measurement of macromolecule synthesis that may be applicable to other classes of molecules besides lipids.

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Rousu, Juho, Ari Rantanen, Raimo A. Ketola y Juha T. Kokkonen. "Isotopomer distribution computation from tandem mass spectrometric data with overlapping fragment spectra". Spectroscopy 19, n.º 1 (2005): 53–67. http://dx.doi.org/10.1155/2005/575686.

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We present a method for determination of the isotopomer distributions of metabolites from the data generated by a tandem mass spectrometer. The method is an improvement over existing method as it is able to deal with overlapping fragments in the spectra. Our experiments indicate that the new method surpasses its predecessors in separating isotopomers from each other. When using the daughter ion scanning (collision induced dissociation) mode, the method was shown to be able to constrain the isotopomer distribution of different amino acids better than two existing methods. In particular, the isotopomer distributions of three amino acids, glycine, alanine and serine, can be fully uncovered with the method. However, due to the imperfect fragmentation of molecules in the tandem mass spectrometer, isotopomer distributions of larger amino acids still cannot be fully uncovered. In tests with isotope-labelled alanine, most accurate results were obtained using multiple reaction monitoring and 15 eV collision energy. The meausured isotopomer frequecies were in the range 99?106% of the theoretical value and the deviation between repetitions was in the range 1?10%.

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Hellerstein, M. K. y R. A. Neese. "Mass isotopomer distribution analysis: a technique for measuring biosynthesis and turnover of polymers". American Journal of Physiology-Endocrinology and Metabolism 263, n.º 5 (1 de noviembre de 1992): E988–1001. http://dx.doi.org/10.1152/ajpendo.1992.263.5.e988.

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Mass isotopomer distribution analysis (MIDA) is a technique for measuring biosynthesis and turnover of polymers in vivo. A stable isotopically enriched precursor is administered, and the relative abundances of different mass isotopomers in the polymer of interest are measured by mass spectrometry (MS). By comparison of statistical distributions predicted from the binomial or multinomial expansion to the pattern of excess isotopomer frequencies observed in the polymer, the enrichment of the biosynthetic precursor subunits (p) for newly synthesized polymers is calculated. MIDA thereby provides a solution to the problem of determining the isotope content in the actual precursor molecules that entered a particular polymeric product (the “true” precursor). The fraction of polymer molecules in a mixture that were newly synthesized during an isotopic experiment (fractional synthesis) can then be calculated. We describe some mathematical characteristics of MIDA and point out certain advantageous features. For example, mathematical estimates of p remain valid even if there does not exist a single anatomic or functional precursor pool. The interpretation of decay curves of endogenously labeled polymers may be improved by the use of higher mass isotopomers, which better fulfill the assumption of flash labeling. By combining fractional synthesis values with rate constants of decay, absolute endogenous synthesis rates can be calculated. Thus, by using probability logic combined with MS analysis, MIDA allows dynamic measurements to be made through analyses on a polymer alone during both isotopic incorporation and decay phases. The method has been applied to fatty acids, cholesterol, and glucose and is potentially applicable to nucleic acids, porphyrins, perhaps proteins, and many other classes of polymers.

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Lee, Wai-Nang Paul, Laszlo G. Boros, Joaquim Puigjaner, Sara Bassilian, Shu Lim y Marta Cascante. "Mass isotopomer study of the nonoxidative pathways of the pentose cycle with [1,2-13C2]glucose". American Journal of Physiology-Endocrinology and Metabolism 274, n.º 5 (1 de mayo de 1998): E843—E851. http://dx.doi.org/10.1152/ajpendo.1998.274.5.e843.

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We present a single-tracer method for the study of the pentose phosphate pathway (PPP) using [1,2-13C2]glucose and mass isotopomer analysis. The metabolism of [1,2-13C2]glucose by the glucose-6-phosphate dehydrogenase, transketolase (TK), and transaldolase (TA) reactions results in unique pentose and lactate isotopomers with either one or two13C substitutions. The distribution of these isotopomers was used to estimate parameters of the PPP using the model of Katz and Rognstad (J. Katz and R. Rognstad. Biochemistry 6: 2227–2247, 1967). Mass and position isotopomers of ribose, and lactate and palmitate (products from triose phosphate) from human hepatoma cells (Hep G2) incubated with 30% enriched [1,2-13C2]glucose were determined using gas chromatography-mass spectrometry. After 24–72 h incubation, 1.9% of lactate molecules in the medium contained one 13C substitution ( m 1) and 10% contained two 13C substitutions ( m 2). A similar m 1-to- m 2ratio was found in palmitate as expected. Pentose cycle (PC) activity determined from incubation with [1,2-13C2]glucose was 5.73 ± 0.52% of the glucose flux, which was identical to the value of PC (5.55 ± 0.73%) determined by separate incubations with [1-13C] and [6-13C]glucose.13C was found to be distributed in four ribose isotopomers ([1-13C]-, [5-13C]-, [1,2-13C2]-, and [4,5-13C2]ribose). The observed ribose isotopomer distribution was best matched with that provided from simulation by substituting 0.032 for TK and 0.85 for TA activity relative to glucose uptake into the model of Katz and Rognstad. The use of [1,2-13C2]glucose not only permits the determination of PC but also allows estimation of relative rates through the TK and TA reactions.

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Kelleher, J. K. y T. M. Masterson. "Model equations for condensation biosynthesis using stable isotopes and radioisotopes". American Journal of Physiology-Endocrinology and Metabolism 262, n.º 1 (1 de enero de 1992): E118—E125. http://dx.doi.org/10.1152/ajpendo.1992.262.1.e118.

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Important syntheses in living systems occur by condensation reactions of the type nA----1B (where n is the number of A molecules needed to synthesize 1 molecule of B). Quantitative relationships for estimating the rate of synthesis of B from radioactive and stable isotope tracers are compared. With radioisotope tracers, only a single quantity is detected, the amount of radioactivity in B. In contrast, isotopes of varying mass produce multiple mass isotopomers B that are detected using mass spectrometry. The analysis demonstrates that the rate of synthesis of B is identifiable from stable isotope data but not from radioisotope data. This results because the isotopomer distribution of B at any time after tracer addition is a function of only the multinomial distribution representing the synthesis of B from n molecules of A and two parameters representing the fractional fluxes of isotopically enriched molecules to the sampled compartment of B. The model considers the possibility that the sampled compartment of B may not reach isotopic steady state during the experiment. A graphical method for obtaining initial estimates of the two parameters is presented.

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Des Rosiers, C., B. R. Landau y H. Brunengraber. "Interpretation of isotopomer patterns in tracing glycogen synthesis and glucose recycling using [13C6]glucose". American Journal of Physiology-Endocrinology and Metabolism 259, n.º 5 (1 de noviembre de 1990): E757—E762. http://dx.doi.org/10.1152/ajpendo.1990.259.5.e757.

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Tracing glycogen synthesis with [U-13C]glucose involves determination of isotopomer patterns in precursors and products. The contribution of the direct pathway to glycogen synthesis has been estimated from the ratio (R) of the number of glycogen glucose molecules having six 13C atoms to the total number of glucose molecules having one to six 13C atoms. Using theoretical examples, we show that the equation to calculate R underestimates the contribution of the direct pathway. We derive a correct stoichiometric expression for R. Also, we show how to correct these estimates for 1) recondensation of two M+3 three-carbon intermediates into M+6 glucose 6-phosphate, and 2) the increasing enrichment of arterial glucose in various isotopomers arising from the indirect pathway. Finally, using the developed formulas we recalculate data from the literature. Similar considerations apply to investigations of glucose recycling using [U-13C6]glucose.

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7

Kelleher, Joanne K. "Estimating gluconeogenesis with [U-13C]glucose: molecular condensation requires a molecular approach". American Journal of Physiology-Endocrinology and Metabolism 277, n.º 3 (1 de septiembre de 1999): E395—E400. http://dx.doi.org/10.1152/ajpendo.1999.277.3.e395.

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Recently three equations for estimating gluconeogenesis in vivo have been proposed, two by J. A. Tayek and J. Katz [ Am. J. Physiol. 270 ( Endocrinol. Metab. 33): E709–E717, 1996, and Am. J. Physiol. 272 ( Endocrinol. Metab. 35): E476–E484, 1997] and one by B. R. Landau, J. Wahren, K. Ekberg, S. F. Previs, D. Yang, and H. Brunengraber [ Am. J. Physiol.274 ( Endocrinol. Metab. 37): E954–E961, 1998]. Both groups estimate gluconeogenesis from cycling of [U-13C]glucose to lactate and back to glucose, detected by mass spectrometry. Landau’s approach is based on analysis of labeled molecules, whereas Tayek and Katz’s is based on labeling of carbon atoms by use of the concept of “molar enrichment,” which weights each mass isotopomer by the number of labeled carbons. We derived an equation very similar to Landau’s using binomial probability. Our analysis demonstrates that the molecular-based approach is correct. Additionally, equations appropriate for 14C studies are not appropriate for 13C studies, because the method used to detect14C, decay of atoms, differs from13C mass isotopomers detected as labeled molecules. We conclude that the molar enrichment carbon-based approach is not useful in the derivation of equations for the polymerization of molecules detected by mass spectrometry of molecules, and we confirm the findings of Landau et al.

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8

Ajie, H. O., M. J. Connor, W. N. Lee, S. Bassilian, E. A. Bergner y L. O. Byerley. "In vivo study of the biosynthesis of long-chain fatty acids using deuterated water". American Journal of Physiology-Endocrinology and Metabolism 269, n.º 2 (1 de agosto de 1995): E247—E252. http://dx.doi.org/10.1152/ajpendo.1995.269.2.e247.

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To determine the contributions of preexisting fatty acid, de novo synthesis, and chain elongation in long-chain fatty acid (LCFA) synthesis, the synthesis of LCFAs, palmitate (16:0), stearate (18:0), arachidate (20:0), behenate (22:0), and lignocerate (24:0), in the epidermis, liver, and spinal cord was determined using deuterated water and mass isotopomer distribution analysis in hairless mice and Sprague-Dawley rats. Animals were given 4% deuterated water for 5 days or 8 wk in their drinking water. Blood was withdrawn at the end of these times for the determination of deuterium enrichment, and the animals were killed to isolate the various tissues for lipid extraction for the determination of the mass isotopomer distributions. The mass isotopomer distributions in LCFA were incompatible with synthesis from a single pool of primer. The synthesis of palmitate, stearate, arachidate, behenate, and lignocerate followed the expected biochemical pathways for the synthesis of LCFAs. On average, three deuterium atoms were incorporated for every addition of an acetyl unit. The isotopomer distribution resulting from chain elongation and de novo synthesis can be described by the linear combination of two binomial distributions. The proportions of preexisting, chain elongation, and de novo-synthesized fatty acids as a percentage of the total fatty acids were determined using multiple linear regression analysis. Fractional synthesis was found to vary, depending on the tissue type and the fatty acid, from 47 to 87%. A substantial fraction (24-40%) of the newly synthesized molecules was derived from chain elongation of unlabeled (recycled) palmitate.

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9

Lee, W. N., S. Bassilian, Z. Guo, D. Schoeller, J. Edmond, E. A. Bergner y L. O. Byerley. "Measurement of fractional lipid synthesis using deuterated water (2H2O) and mass isotopomer analysis". American Journal of Physiology-Endocrinology and Metabolism 266, n.º 3 (1 de marzo de 1994): E372—E383. http://dx.doi.org/10.1152/ajpendo.1994.266.3.e372.

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Fractional biosynthesis of palmitate, stearate, and cholesterol was determined with deuterated water (2H2O) using mass isotopomer analysis in Hep G2 and MCA sarcoma cells in culture. The method employed differs from previous ones in that the number of deuterium atoms from 2H2O incorporated into newly synthesized molecules was determined and not assumed. After correction for background natural abundances, the isotopomer distribution due to deuterium incorporation in fatty acids and cholesterol was shown to follow a simple binomial distribution depending on the deuterium enrichment in water (p) and the maximum number of deuterium atoms incorporated per molecule (N). Under a wide range of 2H2O enrichments, N could be determined to be 17 for palmitate, 20 for stearate, and 20 for cholesterol by regression analysis or from a series of consecutive mass isotopomer ratios. The fraction derived from de novo synthesis was given by the ratio of the observed to the theoretical deuterium enrichment, which is the product (N x p). The new synthesized fraction of palmitate and stearate by Hep G2 cells for the length of the experiment was found to be 77 and 65%, respectively. These values were confirmed by experiments with [U-13C]glucose as the precursor. In MCA sarcoma cells grown in lipid-poor medium, the average values for fractional synthesis of palmitate, stearate, and cholesterol were 70, 35, and 70%, respectively. This approach should be generally applicable to the simultaneous determined of fractional synthesis of a number of compounds with either deuterium or 13C tracers. Its application is only limited by the accuracy of mass spectrometric analysis.

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Rosenblatt, J., D. Chinkes, M. Wolfe y R. R. Wolfe. "Stable isotope tracer analysis by GC-MS, including quantification of isotopomer effects". American Journal of Physiology-Endocrinology and Metabolism 263, n.º 3 (1 de septiembre de 1992): E584—E596. http://dx.doi.org/10.1152/ajpendo.1992.263.3.e584.

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In metabolic tracer studies it is frequently useful to infuse tracers that are differently labeled variants of the same molecule. These tracers are known as isotopomers. Analysis of the enrichment of each isotopic analogue can be accomplished by gas chromatography-mass spectrometry (GC-MS). However, the raw GC-MS data must be corrected to give the information required. This paper addresses how to transform the raw GC-MS data, consisting of relative abundance ratios at specific ion masses, into relative molar ratios of tracer and tracee molecules. Several correction factors are necessary. First, the background must be measured and corrected for, since it is always present in the sample. Second, the abundances in the spectrum of the labeled molecule are different from those in the unlabeled molecule, and this proportionality "skew" is corrected. A third correction factor accounts for the overlapping spectra of two or more isotopomers that cannot be measured independently. The final correction removes the "double vision" effect that may appear in some spectra due to the presence of (M - H)+ species.

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11

Murthy, Parvathi S. y Josef Michl. "Conformational analysis by infrared linear dichroism of solutes in stretched polyethylene: The twist angle in biphenyl and 4,4'-dibromobiphenyl". Collection of Czechoslovak Chemical Communications 53, n.º 10 (1988): 2366–76. http://dx.doi.org/10.1135/cccc19882366.

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A method is proposed for using the IR linear dichroism of molecules embedded in stretched polyethylene and containing two weakly coupled symmetry-related subunits for the determination of the spatial relationship of the subunits. The procedure requires an IR LD measurement on the parent and on an isotopomer in which the equivalence of the subunits has been removed by isotopic substitution, without affecting the molecular shape or the orientation factors. The method has been tested on biphenyl, found to be planar, and 4,4'-dibromobiphenyl, found to be nearly orthogonally twisted in stretched polyethylene. Possible implications for the orientation mechanism are discussed briefly.

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12

Böttcher, O., V. Meyer y D. H. Sutter. "On the Validity of Additivity Rules for the Molecular Magnetizability Tensor and the Molecular g-Tensor in van der Waals Complexes. A Rotational Zeeman Effect Study o f 1,1-Dideutero-Cyclopropane". Zeitschrift für Naturforschung A 49, n.º 4-5 (1 de mayo de 1994): 585–88. http://dx.doi.org/10.1515/zna-1994-4-510.

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AbstractThe molecular g-tensor and the magnetic susceptibility anisotropy of cyclopropane were deter mined by a microwave Fourier transform study of the rotational Zeeman effect of its 1,1-dideuterated isotopomer. The results g⊥ = 0.02675(23), g∥ = 0.06998(23), and ξ⊥ - ξ ∥ = 8.80(31) · 10-6 erg G-2 mol-2 are in agreement with values determinea indirectly from van der Waals complexes. This finding provides experimental evidence that in van der Waals molecules additivity rules might hold to a high degree of approximation for both types of tensors. Rotational Zeeman effect studies of van der Waals complexes may thus provide valuable extra information on their structures.

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13

Kisiel, Z. y L. Pszczółkowski. "The High-Frequency Rotational Spectrum of 1,1 -Dichloroethylene". Zeitschrift für Naturforschung A 50, n.º 4-5 (1 de mayo de 1995): 347–51. http://dx.doi.org/10.1515/zna-1995-4-505.

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Abstract The b-type rotational spectrum of 1,1-dichloroethylene was investigated up to 450 GHz and was found to be dominated by type-II R-type bands. All constants in the sextic Hamiltonian for the ground states of the common isotopic species and of the 37C1 isotopomer were determined from measurements on transitions with J up to 95. Quartic and sextic planarity defects were evaluated and are compared and discussed with those for several recently investigated planar molecules

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Dhamelincourt, P. y F. J. Ramirez. "Polarized Micro-Raman and FT-IR Spectra of L-Glutamine". Applied Spectroscopy 47, n.º 4 (abril de 1993): 446–51. http://dx.doi.org/10.1366/0003702934335083.

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The infrared, Raman, and polarized micro-Raman spectra of the amino acid L-glutamine and its N,N'-d5 derivative in the crystalline state have been recorded and measured. The data obtained were used to propose a general assignment of the vibrational fundamentals on the basis of the intensity changes observed from the polarized Raman spectra, the iso-topic shifts measured from the deuterated isotopomer, and the correlations with frequencies assigned for other amino acids and related molecules.

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15

García Alonso, J. Ignacio, P. Rodríguez-González, A. González-Gago y A. González-Antuña. "Determination of the uncertainties in the theoretical mass isotopomer distribution of molecules". Analytica Chimica Acta 664, n.º 1 (abril de 2010): 68–76. http://dx.doi.org/10.1016/j.aca.2010.01.063.

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16

Vazart, Fanny, Cecilia Ceccarelli, Nadia Balucani y Dimitrios Skouteris. "Quantum Chemical Computations of Gas-phase Glycolaldehyde Deuteration and Constraints on Its Formation Route". Astrophysical Journal 941, n.º 2 (1 de diciembre de 2022): 196. http://dx.doi.org/10.3847/1538-4357/aca3a3.

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Abstract Despite the detection of numerous interstellar complex organic molecules (iCOMs) for decades, it is still a matter of debate whether they are synthesized in the gas phase or on the icy surface of interstellar grains. In the past, molecular deuteration has been used to constrain the formation paths of small and abundant hydrogenated interstellar species. More recently, the deuteration degree of formamide, one of the most interesting iCOMs, has also been explained with the hypothesis that it is formed by the gas-phase reaction NH2 + H2CO. In this paper, we aim at using molecular deuteration to constrain the formation of another iCOM, glycolaldehyde, which is an important prebiotic species. More specifically, we have performed dedicated electronic structure and kinetic calculations to establish the glycolaldehyde deuteration degree in relation to that of ethanol, which is its possible parent species according to the suggestion of Skouteris et al. We found that the abundance ratio of the species containing one D atom over the all-protium counterpart depends on the produced D isotopomer and varies from 0.9 to 0.5. These theoretical predictions compare extremely well with the monodeuterated isotopomers of glycolaldehyde and that of ethanol measured toward the solar-like protostar IRAS 16293–2422, supporting the hypothesis that glycolaldehyde could be produced in the gas phase for this source. In addition, the present work confirms that the deuterium fractionation of iCOMs cannot be simply anticipated based on the deuterium fractionation of the parent species but necessitates a specific study, as already shown for the case of formamide.

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17

Sangeetha, R., P. Sriramachandran, S. P. Bagare, N. Rajamanickam y R. Shanmugavel. "On the effective temperature of sunspot umbrae using beryllium hydride isotopomer lines". Serbian Astronomical Journal, n.º 179 (2009): 95–99. http://dx.doi.org/10.2298/saj0979095s.

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A search for fourteen bands of the visible and infrared systems of the beryllium hydride isotopomers, in addition to the previously identified bands A - X(0, 0; 1, 1; 2, 2) for BeH, A - X(0, 0; 1, 1; 2, 2) for BeD and A - X(0, 0; 1, 1; 2, 2) for BeT molecules was conducted. The equivalent widths were measured for the well isolated identified lines of the strongest band and the effective temperatures were estimated for the systems for which the presence of hints is confirmed.

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18

Cohen, D. M. y R. N. Bergman. "Prediction of positional isotopomers of the citric acid cycle: the syntactic approach". American Journal of Physiology-Endocrinology and Metabolism 266, n.º 3 (1 de marzo de 1994): E341—E350. http://dx.doi.org/10.1152/ajpendo.1994.266.3.e341.

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We propose a syntactic approach to modeling of biochemical fluxes that combines a rule-based description of atomic transfer in chemical reactions with a structurally oriented, stochastic model of chemical reaction kinetics. This approach avoids the use of differential equations to describe the production and disappearance of each molecule. The computer simulation predicts the changes over time in the abundance of each positional isotopomer of every metabolic intermediate in the citric acid cycle of heart cells, subsequent to administration of [2-13C]acetate (including natural abundance of 13C). (Positional isotopomers are isomers that differ in the positions of isotopes within the molecule.) The 32 positional isotopomers of glutamate fell into four groups with similar intragroup dynamics but with very different amplitudes. From the relative abundance of each isotopomer of glutamate, we calculate the relative area of multiplets of the nuclear magnetic resonance spectrum.

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Lin, Penghui, Li Dai, Daniel R. Crooks, Leonard M. Neckers, Richard M. Higashi, Teresa W.-M. Fan y Andrew N. Lane. "NMR Methods for Determining Lipid Turnover via Stable Isotope Resolved Metabolomics". Metabolites 11, n.º 4 (29 de marzo de 2021): 202. http://dx.doi.org/10.3390/metabo11040202.

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Lipids comprise diverse classes of compounds that are important for the structure and properties of membranes, as high-energy fuel sources and as signaling molecules. Therefore, the turnover rates of these varied classes of lipids are fundamental to cellular function. However, their enormous chemical diversity and dynamic range in cells makes detailed analysis very complex. Furthermore, although stable isotope tracers enable the determination of synthesis and degradation of complex lipids, the numbers of distinguishable molecules increase enormously, which exacerbates the problem. Although LC-MS-MS (Liquid Chromatography-Tandem Mass Spectrometry) is the standard for lipidomics, NMR can add value in global lipid analysis and isotopomer distributions of intact lipids. Here, we describe new developments in NMR analysis for assessing global lipid content and isotopic enrichment of mixtures of complex lipids for two cell lines (PC3 and UMUC3) using both 13C6 glucose and 13C5 glutamine tracers.

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20

Hovhannisyan, Astghik A., Tigran S. Kurtikyan, Robert K. Kazaryan y John A. Goodwin. "Interaction of NO2 gas with sublimed microporous layers of iron(II)-meso-mono-4-pyridyl-tri-aryl-porphyrins: Two different reaction pathways". Journal of Porphyrins and Phthalocyanines 12, n.º 01 (enero de 2008): 65–72. http://dx.doi.org/10.1142/s1088424608000091.

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Sublimed layers of Fe II MPyTPP and Fe II MPyTTP ( MPyTPP and MPyTTP are meso-mono-4-pyridyl-triphenyl- and meso-mono-4-pyridyl-tri-p-tolyl-porphyrin dianions, respectively) consist of coordination oligomers that are formed by binding of pyridyl nitrogen atoms with the iron centers of the adjacent molecules in the film. Fourier transform infrared (FT-IR) spectroscopy including experiments with the 15 NO 2 isotopomer demonstrates that the reaction of low pressure NO 2 gas with these layers leads to the formation of two types of complexes: six-coordinate nitro-complexes, in which the fifth site is occupied by the pyridyl group of the neighboring molecule in the layer and five-coordinate nitrito-complexes that terminate the oligomers. Further addition of NO 2 increments leads to the preferential oxidation of these nitrito ligands to bidentate nitrato ligands. These layers conserve their porosity upon standing and allow study of the oxo-transfer reactivity from coordinated nitro-groups to appropriate oxygen acceptors.

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Ehlers, Ina, Tatiana R. Betson, Walter Vetter y Jürgen Schleucher. "Elucidating Turnover Pathways of Bioactive Small Molecules by Isotopomer Analysis: The Persistent Organic Pollutant DDT". PLoS ONE 9, n.º 10 (28 de octubre de 2014): e110648. http://dx.doi.org/10.1371/journal.pone.0110648.

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22

Sheridan, P. M. y L. M. Ziurys. "Trends in the alkaline-earth amide series: The millimetre-wave spectrum of MgNH2 and MgND2 (2A1)". Canadian Journal of Physics 79, n.º 2-3 (1 de febrero de 2001): 409–21. http://dx.doi.org/10.1139/p00-087.

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The pure rotational spectra of MgNH2 ([Formula: see text]2A1) and its deuterium isotopomer have been recorded using millimetre/sub-millimetre wave direct absorption techniques. Both species were synthesized by the reaction of magnesium vapor and either NH3 or ND3 in a dc discharge. Twelve rotational transitions were measured for MgNH2, and eight transitions were observed for MgND2, both in the range 120530 GHz. Asymmetry components with Ka= 05,7, and sometimes 6, were measured for nearly every transition. Rotational, centrifugal distortion, and spinrotation parameters have been accurately determined for both molecules, as well as an r0 structure for magnesium amide. The data indicate that MgNH2is a planar molecule with C2v symmetry, similar to CaNH2 and SrNH2, and does not undergo inversion. However, there appears to be subtle differences between MgNH2 and its calcium and strontium analogs. Magnesium amide, for example, has a significantly larger HNH bond angle than CaNH2and SrNH2. In addition, the spinrotation constants indicate slightly more in-plane p character for the unpaired electron in this molecule relative to that in calcium or strontium amide. Such differences may result from more covalent character in the bonding of MgNH2 in comparison to the heavier alkaline-earth amide species. PACS No.: 32.20Bx

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23

Antolinez, S., J. L. Alonso, H. Dreizler y D. H. Sutter. "Trifluoroacetic Acid; r0 -Structure, Partial Substitution Structure and Deuterium Nuclear Quadrupole Coupling Studied by Molecular Beam Microwave Fourier Transform Spectroscopy and by ab initio Calculations". Zeitschrift für Naturforschung A 54, n.º 8-9 (1 de septiembre de 1999): 524–38. http://dx.doi.org/10.1515/zna-1999-8-915.

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We report the assignment and analysis of all stable monosubstituted isotopomers of trifluoroacetic acid. The 13C and 18O isotopomers were observed in natural abundance. The rotational constants and quartic centrifugal constants are presented. The rotational constants are used to derive a partial substitution structure and a complete ro structure for future comparison with the corresponding values in hydrogen bridged bimolecules containing trifluoroacetic acid as a subunit. The deuterium nuclear quadrupole coupling constants are derived from the hfs-splittings of low-J rotational transitions of the CF3COOD isotopomer. The results of ab initio quantum chemical calculations are presented, which were carried out to assist in the assignment of the rotational spectra of the isotopomers and for comparison with the experimental molecular parameters.

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24

Špirko, Vladimír, Ota Bludský y Wolfgang P. Kraemer. "Energies and Electric Dipole Moments of the Bound Vibrational States of HN2+ and DN2+". Collection of Czechoslovak Chemical Communications 73, n.º 6-7 (2008): 873–97. http://dx.doi.org/10.1135/cccc20080873.

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The adiabatic three-dimensional potential energy surface and the corresponding dipole moment surface describing the ground electronic state of HN2+ (Χ1Σ+) are calculated at different levels of ab initio theory. The calculations cover the entire bound part of the potential up to its lowest dissociation channel including the isomerization barrier. Energies of all bound vibrational and low-lying ro-vibrational levels are determined in a fully variational procedure using the Suttcliffe-Tennyson Hamiltonian for triatomic molecules. They are in close agreement with the available experimental numbers. From the dipole moment function effective dipoles and transition moments are obtained for all the calculated vibrational and ro-vibrational states. Statistical tools such as the density of states or the nearest-neighbor level spacing distribution (NNSD) are applied to describe and analyse general patterns and characteristics of the energy and dipole results calculated for the massively large number of states of the strongly bound HN2+ ion and its deuterated isotopomer.

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25

Babikov, Dmitri, Elizaveta Grushnikova, Igor Gayday y Alexander Teplukhin. "Four Isotope-Labeled Recombination Pathways of Ozone Formation". Molecules 26, n.º 5 (27 de febrero de 2021): 1289. http://dx.doi.org/10.3390/molecules26051289.

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A theoretical approach is developed for the description of all possible recombination pathways in the ozone forming reaction, without neglecting any process a priori, and without decoupling the individual pathways one from another. These pathways become physically distinct when a rare isotope of oxygen is introduced, such as 18O, which represents a sensitive probe of the ozone forming reaction. Each isotopologue of O3 contains two types of physically distinct entrance channels and two types of physically distinct product wells, creating four recombination pathways. Calculations are done for singly and doubly substituted isotopologues of ozone, eight rate coefficients total. Two pathways for the formation of asymmetric ozone isotopomer exhibit rather different rate coefficients, indicating large isotope effect driven by ΔZPE-difference. Rate coefficient for the formation of symmetric isotopomer of ozone (third pathway) is found to be in between of those two, while the rate of insertion pathway is smaller by two orders of magnitude. These trends are in good agreement with experiments, for both singly and doubly substituted ozone. The total formation rates for asymmetric isotopomers are found to be somewhat larger than those for symmetric isotopomers, but not as much as in the experiment. Overall, the distribution of lifetimes is found to be very similar for the metastable states in symmetric and asymmetric ozone isotopomers.

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26

Radziuk, Jerry y W. N. Paul Lee. "Measurement of gluconeogenesis and mass isotopomer analysis based on [U-13C]glucose". American Journal of Physiology-Endocrinology and Metabolism 277, n.º 2 (1 de agosto de 1999): E199—E207. http://dx.doi.org/10.1152/ajpendo.1999.277.2.e199.

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Two methods of measuring rates of gluconeogenesis based on label redistribution after the introduction of [U-13C]glucose into the whole body are examined. These methods are compared with methods previously derived for carbon-14 tracers. It is shown that the three approaches (stoichiometric, dilution, and combinatorial) are equivalent, provided the same set of assumptions are used. Barring a factor of two [see Am. J. Physiol. 270 ( Endocrinol. Metab. 33): E709–E717, 1996], the differences (∼10–15%) in the carbon-based dilutional and the molecule-based estimates of the rate of gluconeogenesis from published isotopomer data likely arise from small differences in the assumptions that concern the relative rate of label loss from the different isotopomers. The production of unlabeled substrate for glucose synthesis (phospho enolpyruvate) from the different isotopomers of lactate is shown to be a potential source of error in these methods. This error is estimated using models of the interaction of the gluconeogenetic pathway and the tricarboxylic acid (TCA) cycle and is shown to vary from negligible to 30% depending on the relative flux of the two pathways through the oxaloacetate pool. Because the estimates obtained by both methods considered are lower than is physiologically expected, some of the assumptions made may not hold. Future work will exploit the rich information content of isotopomer data to yield improved estimates.

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27

Wolschendorf, Ulrich, Uwe Kretschmer y Dieter H. Sutter. "Distortion of the Benzene Ring in 1,2,3-Trifluorobenzene; A High-Resolution Molecular Beam Fourier Transform Microwave Study". Zeitschrift für Naturforschung A 51, n.º 1-2 (1 de febrero de 1996): 46–52. http://dx.doi.org/10.1515/zna-1996-1-208.

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Abstract The results of a molecular beam microwave Fourier transform study of 1,2,3-trifluorobenzene and its monosubstituted 13C-isotopomers, all observed in natural abundance, are presented. Typically 30 transitions were observed for each isotopomer. Centrifugal perturbation theory up to fourth order was used to analyse the observed rotational spectra. Due to the high sensitivity and resolution of the spectrometer, very accurate vibronic ground state rotational constants can be reported:They are used to derive a partial r0-structure. which shows the distortions of the benzene ring caused by fluorine substitution.

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28

Alparone, Andrea. "Infrared and Raman Spectra of and Isotopomers: A DFT-PT2 Anharmonic Study". Journal of Chemistry 2013 (2013): 1–8. http://dx.doi.org/10.1155/2013/741472.

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IR and Raman spectra of selenophene and of its perdeuterated isotopomer have been obtained in gas phase through density-functional theory (DFT) computations. Vibrational wavenumbers have been calculated using harmonic and anharmonic second-order perturbation theory (PT2) procedures with the B3LYP method and the 6-311 basis set. Anharmonic overtones have been determined by means of the PT2 method. The introduction of anharmonic terms decreases the harmonic wavenumbers, giving a significantly better agreement with the experimental data. The most significant anharmonic effects occur for the C–H and C–D stretching modes, the observed H/D isotopic wavenumber redshifts being satisfactorily reproduced by the PT2 computations within 6–20 cm−1(1–3%). In the spectral region between 500 cm−1and 1500 cm−1, the IR spectra are dominated by the out-of-plane C–H (C–D) bending transition, whereas the Raman spectra are mainly characterized by a strong peak mainly attributed to the C=C + C–C bonds stretching vibration with the contribution of the in-plane C–H (C–D) bending deformation. The current results confirm that the PT2 approach combined with the B3LYP/6-311 level of calculation is a satisfactory choice for predicting vibrational spectra of cyclic molecules.

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29

Haymond, Morey W. y Agneta L. Sunehag. "The reciprocal pool model for the measurement of gluconeogenesis by use of [U-13C]glucose". American Journal of Physiology-Endocrinology and Metabolism 278, n.º 1 (1 de enero de 2000): E140—E145. http://dx.doi.org/10.1152/ajpendo.2000.278.1.e140.

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To improve upon the [U-13C]glucose method to estimate “gluconeogenesis” as described by J. Katz and J. A. Tayek ( Am. J. Physiol. Endocrinol. Metab. 272: E476–E484, 1997, and 275: E537–E542, 1998), we describe the reciprocal pool model by using only the isotopomer data of plasma glucose during infusion of [U-13C]glucose. The glucose pool serves as both precursor and product for the calculation of the fraction of molecules generated by gluconeogenesis and to correct for exchange and loss of labeled carbon at the level of the tricarboxylic acid cycle. We have applied this model to both our own data and those of other investigators using [U-13C]glucose and have demonstrated excellent agreement between the Katz and Tayek model and our reciprocal pool model. When we compare the results of the reciprocal pool model with those of Hellerstein ([2-13C]glycerol) and Landau (2H2O-glucose-C-5), the results are similar in short- and long-term fasted adult humans. Finally, when we apply the reciprocal pool model to our data from premature infants, it is clear that we account for the inflow of unlabeled glycerol and presumably amino acids. This is not surprising, because the vast majority of gluconeogenesis is the result of recycling of glucose and pyruvate carbon.

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30

Hellerstein, Marc K. y Richard A. Neese. "Mass isotopomer distribution analysis at eight years: theoretical, analytic, and experimental considerations". American Journal of Physiology-Endocrinology and Metabolism 276, n.º 6 (1 de junio de 1999): E1146—E1170. http://dx.doi.org/10.1152/ajpendo.1999.276.6.e1146.

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Mass isotopomer distribution analysis (MIDA) is a technique for measuring the synthesis of biological polymers. First developed approximately eight years ago, MIDA has been used for measuring the synthesis of lipids, carbohydrates, and proteins. The technique involves quantifying by mass spectrometry the relative abundances of molecular species of a polymer differing only in mass (mass isotopomers), after introduction of a stable isotope-labeled precursor. The mass isotopomer pattern, or distribution, is analyzed according to a combinatorial probability model by comparing measured abundances to theoretical distributions predicted from the binomial or multinomial expansion. For combinatorial probabilities to be applicable, a labeled precursor must therefore combine with itself in the form of two or more repeating subunits. MIDA allows dilution in the monomeric (precursor) and polymeric (product) pools to be determined. Kinetic parameters can then be calculated (e.g., replacement rate of the polymer, fractional contribution from the endogenous biosynthetic pathway, absolute rate of biosynthesis). Several issues remain unresolved, however. We consider here the impact of various deviations from the simple combinatorial probability model of biosynthesis and describe the analytic requirements for successful use of MIDA. A formal mathematical algorithm is presented for generating tables and equations ( ), on the basis of which effects of various confounding factors are simulated. These include variations in natural isotope abundances, isotopic disequilibrium in the precursor pool, more than one biosynthetic precursor pool, incorrect values for number of subunits present, and concurrent measurement of turnover from exogenously labeled polymers. We describe a strategy for testing whether isotopic inhomogeneity (e.g., an isotopic gradient or separate biosynthetic sites) is present in the precursor pool by comparing higher-mass (multiply labeled) to lower-mass (single- and double-labeled) isotopomer patterns. Also, an algebraic correction is presented for calculating fractional synthesis when an incomplete ion spectrum is monitored, and an approach for assessing the sensitivity of biosynthetic parameters to measurement error is described. The different calculation algorithms published for MIDA are compared; all share a common model, use overlapping solutions to computational problems, and generate identical results. Finally, we discuss the major practical issue for using MIDA at present: quantitative inaccuracy of instruments. The nature and causes of analytic inaccuracy, strategies for evaluating instrument performance, and guidelines for optimizing accuracy and reducing impact on biosynthetic parameters are suggested. Adherence to certain analytic guidelines, particularly attention to concentration effects on mass isotopomer ratios and maximizing enrichments in the isotopomers of interest, reduces error. Improving instrument accuracy for quantification of isotopomer ratios is perhaps the highest priority for this field. In conclusion, MIDA remains the “equation for biosynthesis,” but attention to potentially confounding factors and analytic performance is required for optimal application.

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31

Lattanzi, Valerio, Silvia Spezzano, Jacob C. Laas, Johanna Chantzos, Luca Bizzocchi, Kin Long Kelvin Lee, Michael C. McCarthy y Paola Caselli. "HSCO+ and DSCO+: a multi-technique approach in the laboratory for the spectroscopy of interstellar ions". Astronomy & Astrophysics 620 (diciembre de 2018): A184. http://dx.doi.org/10.1051/0004-6361/201834340.

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Context. Protonated molecular species have been proven to be abundant in the interstellar gas. This class of molecules is also pivotal for the determination of important physical parameters for the evolution of the interstellar medium (e.g. gas ionisation fraction) or as tracers of non-polar species which are not directly observable. The identification of these molecular species through radioastronomical observations is directly linked to precise laboratory spectral characterisation. Aims. The goal of the present work is to extend the laboratory measurements of the pure rotational spectrum of the ground electronic state of protonated carbonyl sulfide (HSCO+) and its deuterium substituted isotopomer (DSCO+). At the same time, we show how implementing different laboratory techniques allows for the determination of different spectroscopical properties of asymmetric-top protonated species. Methods. Three different high-resolution experiments were used in conjunction to detect for the first time the b-type rotational spectrum of HSCO+, and to extend, well into the sub-millimetre region, the a-type spectrum of the same molecular species and DSCO+. The electronic ground-state of both ions was investigated in the 273–405 GHz frequency range, allowing for the detection of 60 and 50 new rotational transitions for HSCO+ and DSCO+, respectively. Results. The combination of our new measurements with the three rotational transitions previously observed in the microwave region permits the rest frequencies of the most astronomically relevant transitions to be predicted to better than 100 kHz for both HSCO+ and DSCO+ up to 500 GHz, equivalent to better than 60 m s−1 in terms of equivalent radial velocity. Conclusions. The present work illustrates the importance of using different laboratory techniques to spectroscopically characterise a protonated species at high frequency. Each instrument addressed a complementary part of the same spectroscopic challenge, demonstrating the potential of such an approach for future studies of similar reactive species.

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32

Calucci, Lucia, Claudia Forte, Marco Geppi y Carlo Alberto Veracini. "Dynamics of Liquid Crystals by Means of 2 H-NMR: a Comparison between 4,4'-bis(hexyloxy)azoxybenzene and the Derivative Pd(II) Complex AZPAC". Zeitschrift für Naturforschung A 53, n.º 6-7 (1 de julio de 1998): 427–35. http://dx.doi.org/10.1515/zna-1998-6-724.

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Abstract In the present work we report a molecular dynamics investigation of the two mesogens 4,4'-bis(hexyloxy)azoxybenzene (HL) and its Pd(II) acetylacetonate derivative Azpac in their nematic phases. Deuterium Zeeman and quadrupolar spin-lattice relaxation times have been measured at 46.04 MHz on two isotopomers of Azpac (Azpac-d4 and Azpac-d26 , deuteriated on the aromatic core and on the alkoxy chains, respectively) and on HL-d4 , an isotopomer of HL partially deuteriated on the aromatic core, by means of the Wimperis pulse sequence. The spectral densities obtained from the measured relaxation times are discussed in terms of internal and overall molecular motions. A small step rotational diffusion model for the overall molecular motions, superimposed on a free rotational model for internal motions, allowed diffusion coefficients for molecular spinning and tumbling and for phenyl ring rotations to be derived for HL; the same models were used in describing the dynamics of Azpac.

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33

Yang, Nan, Chinh H. Duong, Patrick J. Kelleher, Mark A. Johnson y Anne B. McCoy. "Isolation of site-specific anharmonicities of individual water molecules in the I−·(H2O)2 complex using tag-free, isotopomer selective IR-IR double resonance". Chemical Physics Letters 690 (diciembre de 2017): 159–71. http://dx.doi.org/10.1016/j.cplett.2017.09.042.

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34

Coxon, John A. y Photos G. Hajigeorgiou. "Born–Oppenheimer breakdown in the ground state of carbon monoxide: A direct reduction of spectroscopic line positions to analytical radial Hamiltonian operators". Canadian Journal of Physics 70, n.º 1 (1 de enero de 1992): 40–54. http://dx.doi.org/10.1139/p92-004.

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A collection of 10 866 of the most precise ground-state (X1Σ+) vibration–rotational and pure rotational line positions of four carbon monoxide isptopomers (12C16O, 12C18O, 13C16O, and 13C18O) is employed simultaneously in a direct determination of the radial Hamiltonian operator in compact analytical form. The 22-parameter isotopically self-consistent operator takes full account of the Born–Oppenheimer breakdown and its quantum-mechanical eigenvalues represent all the available spectroscopic line positions of CO isotopomers to within the experimental uncertainties. Rayleigh–Schrödinger perturbation theory is employed to calculate quantum-mechanical molecular constants of rotation (Bν – Mν) for nine common isotopomeric forms of CO. Together with the quantum-mechanical vibrational eigenvalues these are fully consistent with the exact eigenvalues obtained by direct solution of the radial wave equation. The set of constants is expected to provide an accurate prediction of line positions of CO isotopomers that have not yet been experimentally observed.

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35

BANDSMA, Robert H. J., Frans STELLAARD, J. Roel VONK, T. Gijs NAGEL, A. Richard NEESE, K. Marc HELLERSTEIN y Folkert KUIPERS. "Contribution of newly synthesized cholesterol to rat plasma and bile determined by mass isotopomer distribution analysis: bile-salt flux promotes secretion of newly synthesized cholesterol into bile". Biochemical Journal 329, n.º 3 (1 de febrero de 1998): 699–703. http://dx.doi.org/10.1042/bj3290699.

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To quantify the contribution of newly synthesized cholesterol to total plasma and biliary cholesterol under physiological conditions, unrestrained rats were infused intravenously with [1-13C]acetate (0.6 mmol/h per kg) from 12:00 to 24:00 h, and fractional and absolute cholesterol-synthesis rates were determined by mass isotopomer distribution analysis (MIDA). As bile diversion leads to changes in cholesterol metabolism, rats were equipped with permanent catheters in the bile duct and duodenum, allowing sampling of small amounts of bile from an intact enterohepatic circulation. For comparison, rats with chronic bile diversion were also studied. Fractional synthesis of plasma cholesterol was 10.8±1.7% (mean±S.D.) after 12 h in rats with intact circulation. Fractional synthesis of biliary cholesterol was significantly higher than that of plasma cholesterol, i.e. 16.5±2.0% (P < 0.05) after 12 h. In contrast, no differences between fractional synthesis of cholesterol in plasma and bile were found in bile-diverted animals (31.8±2.1 and 33.1±3.3% respectively after 12 h). The calculated absolute rate of cholesterol biosynthesis increased from 53±10 to 221±19 μmol/day per kg after bile diversion. A comparison of MIDA results with those obtained from balance studies indicated that MIDA does not assess total body synthesis in rats, presumably because of incomplete equilibration of newly synthesized molecules with cholesterol in the plasma compartment. These studies demonstrate that the contribution of newly synthesized cholesterol to biliary cholesterol is higher than to plasma cholesterol under physiological conditions, probably reflecting bile-salt-induced secretion of newly formed cholesterol by the periportal hepatocytes.

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36

Cohen, David M. y Richard N. Bergman. "Improved estimation of anaplerosis in heart using 13C NMR". American Journal of Physiology-Endocrinology and Metabolism 273, n.º 6 (1 de diciembre de 1997): E1228—E1242. http://dx.doi.org/10.1152/ajpendo.1997.273.6.e1228.

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Anaplerotic enzymes, such as pyruvate carboxylase or malic enzyme, catalyze reactions that fill up the pools of the citric acid cycle (CAC), thereby increasing the total mass of CAC intermediates. Relative anaplerosis ( y) denotes the ratio of anaplerotic flux to the flux catalyzed by citrate synthase. We examine conventional methods [C. R. Malloy, A. D. Sherry, and F. M. H. Jeffrey. J. Biol. Chem. 263:6964–6971, 1988; C. R. Malloy, A. D. Sherry, and F. M. H. Jeffrey. Am. J. Physiol. 259 ( Heart Circ. Physiol. 28): H987–H995, 1990] of measurement of y using13C-labeled precursors and analysis of [13C]glutamate labeling by nuclear magnetic resonance (NMR) spectroscopy. Through mathematical analysis and computer simulation, we show that isotopic enrichment of the pool of pyruvate that is substrate for anaplerosis will severely decrease the accuracy of estimates of y made with conventional methods no matter how small the mass of the pool of pyruvate. Suppose that the recycling parameter R denotes the fraction of molecules of pyruvate that contain carbons derived from intermediates of the CAC. Each means of estimation of relative anaplerosis in the peer-reviewed literature assumes that R = 0, although this assumption has not been confirmed by experiment. We show that conventional formulas, using either fractional enrichments of carbons or isotopomer analysis, actually estimate at most y ⋅ (1 − R) instead of y during administration of [2-13C]acetate and unlabeled pyruvate. Using a new formula for estimation of y, we recalculate values of y from the literature and find them ∼50% too low. We assume that all anaplerosis is via pyruvate and that the difference in isotopic enrichment between cytosolic and mitochondrial malate is negligible.

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37

Katz, Joseph y John A. Tayek. "Gluconeogenesis and the Cori cycle in 12-, 20-, and 40-h-fasted humans". American Journal of Physiology-Endocrinology and Metabolism 275, n.º 3 (1 de septiembre de 1998): E537—E542. http://dx.doi.org/10.1152/ajpendo.1998.275.3.e537.

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Six subjects were infused with [U-13C]glucose (0.03–0.05 mg ⋅ kg−1 ⋅ min−1) starting 8–9 h after a meal, and the production of glucose, the recycling of glucose (the Cori cycle), the dilution of glucose by unlabeled carbon into the hepatic lactate-pyruvate pool, and gluconeogenesis were determined in these fasted volunteers by use of mass isotopomer analysis and equations previously described [J. A. Tayek and J. Katz. Am. J. Physiol.272 ( Endocrinol. Metab. 35): E476–E484, 1997]. A primed continuous 11-h infusion was started at 6:00 AM, and the above parameters were calculated after 3 h (for the 12-h fast) and at the end of the infusion (for the 20-h fast). Another group of five subjects was fasted for 40 h, and the above parameters were calculated as before. At 12, 20, and 40 h of fasting, respectively, blood glucose was 93 ± 2, 83 ± 2, and 71 ± 2 (SE) mg/dl; glucose production was 2.3, 1.8, and 1.77 mg ⋅ kg−1 ⋅ min−1; the recycling of labeled carbon was 8, 15, and 15%, and that of glucose molecules (Cori cycle) was 18, 35, and 36%; the contribution of gluconeogenesis to glucose production was 41, 71, and 92% or 0.96, 1.29, and 1.64 mg ⋅ kg−1 ⋅ min−1; and the contribution of other sources to glucose production was 1.37, 0.53, and 0.15 mg ⋅ kg−1 ⋅ min−1. The recycling of glucose is important in prolonged fasting for the maintenance of plasma glucose concentration. We demonstrate here that gluconeogenesis can be easily measured and that it accounts for ∼90% of glucose production after a 40-h fast.

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38

Kassi, S. y H. Dreizler. "On the Ambiguity of Molecular Complexes Formed by Two Molecules". Zeitschrift für Naturforschung A 54, n.º 3-4 (1 de abril de 1999): 213–17. http://dx.doi.org/10.1515/zna-1999-3-409.

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We present a general consideration how many structural conformers are compatible with one set of rotational constants if one rotational spectrum of a dimer is investigated. A selection of a certain con-former should be guided by the investigation of isotopomers, quantum chemical calculations or other arguments.

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39

Bodenmüller, W., M. Pfeffer, R. Ruber, B. Macht y A. Ruoff. "High Resolution FTIR Spectroscopy of 1,3,5-Triazine*: The Parallel Bands v11 and v12 of 12C314N3H3, 13C314N3H3 , 12C315N3H3 , 13C315N3H3 and 12C314N3D3". Zeitschrift für Naturforschung A 53, n.º 1-2 (1 de febrero de 1998): 1–9. http://dx.doi.org/10.1515/zna-1998-1-202.

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Abstract The present contribution reports on the analysis of the high resolution FTIR spectra of the only two IR-active parallel fundamentals ν11 and ν12 of the isotopomers 12C314N3H3 , 13C314N3H3 , 12C315N3H3 , C315N3H3 and 12C314N3D3 , respectively, of 1,3,5-triazine. The molecular constants of the ground state and the upper states ν11 = 1 and ν12 = 1, respectively, for all molecules under consideration are listed. The enhancement of the P-and the depletion of the R-banches, observed in the v11 bands of all non-deuterated isotopomers, is discussed, and the Herman-Wallis constants obtained are given.

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40

Tayek, J. A. y J. Katz. "Glucose production, recycling, Cori cycle, and gluconeogenesis in humans: relationship to serum cortisol". American Journal of Physiology-Endocrinology and Metabolism 272, n.º 3 (1 de marzo de 1997): E476—E484. http://dx.doi.org/10.1152/ajpendo.1997.272.3.e476.

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Six normal subjects (NL group) and 13 cancer patients (CAI and CAII groups) were fasted overnight and infused with [U-(13)C]glucose (0.016-0.058 mg x min(-1) x kg(-1)). Plasma glucose and lactate were isolated, and mass isotopomer distributions were determined by gas chromatography-mass spectroscopy. Applying equations modified from those previously described [J. A. Tayek and J. Katz. Am. J. Physiol. 270 (Endocrinol. Metab. 33): E709-E717, 1996], we determined glucose production (GP), recycling of glucose carbons, fraction of recycled molecules in blood glucose (Cori cycle), formation of pyruvate from unlabeled carbons, dilution of pyruvate via the tricarboxylic acid cycle and other reactions, and rate of gluconeogenesis. Glucose production was similar in all groups: 2.4 +/- 0.2 mg x min(-1) x kg (-1). The fraction of recycled carbon and of the Cori cycle were elevated in the CAI group vs. the CAII and NL groups: 15 and 33% vs. 7.8 and 19%, respectively (P = 0.01). Gluconeogenesis was 1.9 +/- 0.1, 1.0 +/- 0.1, and 0.83 +/- 0.11 mg x min(-1) x kg(-1) in the CAI, CAII, and NL groups, respectively. In the NL and CAII groups, 20% of GP is via recycling, 20% from unlabeled carbon sources (muscle glycogen, amino acids), and 60% from hepatic glycogenolysis; in the CAI group, 30% is from recycling, 50% from unlabeled carbon, and 20% from glycogen and other sources. Serum cortisol was elevated in the CAI group vs. the CAII group: 11.2 +/- 1.2 vs. 7.7 +/- 1.2 microg/dl (P < 0.05). There was a strong correlation between plasma cortisol and Cori cycle in the NL (r = 0.963) and CAI and CAII groups (r = 0.771). Serum cortisol was directly, and insulin was inversely, correlated with gluconeogenesis in the NL (r2 = 0.967) and CAI and CAII groups (r2 = 0.727). We conclude that whereas the cancer population is heterogeneous with respect to gluconeogenesis, many cancer patients derive their GP predominantly from gluconeogenesis compared with healthy controls, who derive less than one-half of their GP from gluconeogenesis.

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41

Fedorovsky, M. "Exploring Vibrational Optical Activity with PyVib2". Computing Letters 2, n.º 4 (6 de marzo de 2006): 233–36. http://dx.doi.org/10.1163/157404006779194132.

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In this work we present a practical example of the automatic correlation of the vibrations of two molecules based on an approach which introduces a new formalism for comparing force fields in cartesian coordinates via the normal modes they entail. We consider two partially deuterated isotopomers of (+)-(R)-1-methylindane, a molecule the absolute configuration of which was successfully verified with vibrational optical activity. The isotopomers are obtained by substituting four hydrogen atoms either in the aromatic or in the aliphatic ring by deuterium atoms. This substitution gives rise to the mixing of the normal modes of the parent system. The automatic correlation of the vibrations will be demostrated with the PyVib2 program.

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42

Murata, Yasujiro, Shih-Ching Chuang, Fumiyuki Tanabe, Michihisa Murata y Koichi Komatsu. "Recognition of hydrogen isotopomers by an open-cage fullerene". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 371, n.º 1998 (13 de septiembre de 2013): 20110629. http://dx.doi.org/10.1098/rsta.2011.0629.

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We present our study on the recognition of hydrogen isotopes by an open-cage fullerene through determination of binding affinity of isotopes H 2 /HD/D 2 with the open-cage fullerene and comparison of their relative molecular sizes through kinetic-isotope-release experiments. We took advantage of isotope H 2 /D 2 exchange that generated an equilibrium mixture of H 2 /HD/D 2 in a stainless steel autoclave to conduct high-pressure hydrogen insertion into an open-cage fullerene. The equilibrium constants of three isotopes with the open-cage fullerene were determined at various pressures and temperatures. Our results show a higher equilibrium constant for HD into open-cage fullerene than the other two isotopomers, which is consistent with its dipolar nature. D 2 molecule generally binds stronger than H 2 because of its heavier mass; however, the affinity for H 2 becomes larger than D 2 at lower temperature, when size effect becomes dominant. We further investigated the kinetics of H 2 /HD/D 2 release from open-cage fullerene, proving their relative escaping rates. D 2 was found to be the smallest and H 2 the largest molecule. This notion has not only supported the observed inversion of relative binding affinities between H 2 and D 2 , but also demonstrated that comparison of size difference of single molecules through non-convalent kinetic-isotope effect was applicable.

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43

Carvalho, Filipa, Joao Duarte, Ana Rita Simoes, Pedro F. Cruz y John G. Jones. "Noninvasive Measurement of Murine Hepatic Acetyl-CoA13C-Enrichment Following Overnight Feeding with13C-Enriched Fructose and Glucose". BioMed Research International 2013 (2013): 1–7. http://dx.doi.org/10.1155/2013/638085.

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The13C-isotopomer enrichment of hepatic cytosolic acetyl-CoA of overnight-fed mice whose drinking water was supplemented with [U-13C]fructose, and [1-13C]glucose andp-amino benzoic acid (PABA) was quantified by13C NMR analysis of urinaryN-acetyl-PABA. Four mice were given normal chow plus drinking water supplemented with 5% [1-13C]glucose, 2.5% [U-13C]fructose, and 2.5% fructose (Solution 1) overnight. Four were given chow and water containing 17.5% [1-13C]glucose, 8.75% [U-13C]fructose and 8.75% fructose (Solution 2). PABA (0.25%) was present in both studies. UrinaryN-acetyl-PABA was analyzed by13C NMR. In addition to [2-13C]- and [1,2-13C]acetyl isotopomers from catabolism of [U-13C]fructose and [1-13C]glucose to acetyl-CoA, [1-13C]acetyl was also found indicating pyruvate recycling activity. This precluded precise estimates of [1-13C]glucose contribution to acetyl-CoA while that of [U-13C]fructose was unaffected. The fructose contribution to acetyl-CoA from Solutions 1 and 2 was 4.0 ± 0.4% and 10.6 ± 0.6%, respectively, indicating that it contributed to a minor fraction of lipogenic acetyl-CoA under these conditions.

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44

Winther, Malte, David Balslev-Harder, Søren Christensen, Anders Priemé, Bo Elberling, Eric Crosson y Thomas Blunier. "Continuous measurements of nitrous oxide isotopomers during incubation experiments". Biogeosciences 15, n.º 3 (8 de febrero de 2018): 767–80. http://dx.doi.org/10.5194/bg-15-767-2018.

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Abstract. Nitrous oxide (N2O) is an important and strong greenhouse gas in the atmosphere. It is produced by microbes during nitrification and denitrification in terrestrial and aquatic ecosystems. The main sinks for N2O are turnover by denitrification and photolysis and photo-oxidation in the stratosphere. In the linear N = N = O molecule 15N substitution is possible in two distinct positions: central and terminal. The respective molecules, 14N15N16O and 15N14N16O, are called isotopomers. It has been demonstrated that N2O produced by nitrifying or denitrifying microbes exhibits a different relative abundance of the isotopomers. Therefore, measurements of the site preference (difference in the abundance of the two isotopomers) in N2O can be used to determine the source of N2O, i.e., nitrification or denitrification. Recent instrument development allows for continuous position-dependent δ15N measurements at N2O concentrations relevant for studies of atmospheric chemistry. We present results from continuous incubation experiments with denitrifying bacteria, Pseudomonas fluorescens (producing and reducing N2O) and Pseudomonas chlororaphis (only producing N2O). The continuous measurements of N2O isotopomers reveals the transient isotope exchange among KNO3, N2O, and N2. We find bulk isotopic fractionation of −5.01 ‰ ± 1.20 for P. chlororaphis, in line with previous results for production from denitrification. For P. fluorescens, the bulk isotopic fractionation during production of N2O is −52.21 ‰ ± 9.28 and 8.77 ‰ ± 4.49 during N2O reduction.The site preference (SP) isotopic fractionation for P. chlororaphis is −3.42 ‰ ± 1.69. For P. fluorescens, the calculations result in SP isotopic fractionation values of 5.73 ‰ ± 5.26 during production of N2O and 2.41 ‰ ± 3.04 during reduction of N2O. In summary, we implemented continuous measurements of N2O isotopomers during incubation of denitrifying bacteria and believe that similar experiments will lead to a better understanding of denitrifying bacteria and N2O turnover in soils and sediments and ultimately hands-on knowledge on the biotic mechanisms behind greenhouse gas exchange of the globe.

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45

Gronenberg, Wulfila, Ajay Raikhelkar, Eric Abshire, Jennifer Stevens, Eric Epstein, Karin Loyola, Michael Rauscher y Stephen Buchmann. "Honeybees ( Apis mellifera ) learn to discriminate the smell of organic compounds from their respective deuterated isotopomers". Proceedings of the Royal Society B: Biological Sciences 281, n.º 1778 (7 de marzo de 2014): 20133089. http://dx.doi.org/10.1098/rspb.2013.3089.

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The understanding of physiological and molecular processes underlying the sense of smell has made considerable progress during the past three decades, revealing the cascade of molecular steps that lead to the activation of olfactory receptor (OR) neurons. However, the mode of primary interaction of odorant molecules with the OR proteins within the sensory cells is still enigmatic. Two different concepts try to explain these interactions: the ‘odotope hypothesis’ suggests that OR proteins recognize structural aspects of the odorant molecule, whereas the ‘vibration hypothesis’ proposes that intra-molecular vibrations are the basis for the recognition of the odorant by the receptor protein. The vibration hypothesis predicts that OR proteins should be able to discriminate compounds containing deuterium from their common counterparts which contain hydrogen instead of deuterium. This study tests this prediction in honeybees ( Apis mellifera ) using the proboscis extension reflex learning in a differential conditioning paradigm. Rewarding one odour (e.g. a deuterated compound) with sucrose and not rewarding the respective analogue (e.g. hydrogen-based odorant) shows that honeybees readily learn to discriminate hydrogen-based odorants from their deuterated counterparts and supports the idea that intra-molecular vibrations may contribute to odour discrimination.

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46

Raabe, Gerhard, Wolfgang Schleker, Eberhard Heyne y Jörg Fleischhauer. "Borinine (Borabenzene): Its Structure and Vibrational Spectrum. A Quantumchemical Study". Zeitschrift für Naturforschung A 42, n.º 4 (1 de abril de 1987): 352–60. http://dx.doi.org/10.1515/zna-1987-0403.

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Recently we reported the results of some semiempirical and ab initio studies in which we compared the electronic structure of the hitherto unknown borinine with those of benzene and pyridine. The results of our calculations led us to the conclusion that the elusive nature of borabenzene is caused by its high reactivity, which might at least in part be due to the pronounced σ acceptor properties of a low-lying σ* molecular orbital.We now present the results of further ab initio and semiempirical (MNDO) investigations in which we performed full geometry optimizations for the molecule using two different basis sets (STO-3G, 4-31G) and also calculated the vibrational spectra of the 10B and 11B isotopomeric borabenzene molecules at the 4-31 G level of ab initio theory and with the semiempirical MNDO method.The calculated vibrational spectrum might be helpful to the experimentalist in identifying the molecule, for example trapped in a rare gas matrix among the side products.The calculated orbital energies can be useful in identifying the molecule by means of its photoelectron spectrum.

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47

Pfeffer, M., W. Bodenmüller y A. Ruoff. "FT-IR Study of the Perpendicular Bands of 1,3,5-Triazine I:* The v7 and v9 Bands of 12C314N3H3 , 13C314N3H3, 12C315N3H3 and the Difference Band v9-v14 of 12C314N3H3". Zeitschrift für Naturforschung A 53, n.º 8 (1 de agosto de 1998): 670–78. http://dx.doi.org/10.1515/zna-1998-0805.

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Abstract The analysis of the high resolution FT-IR spectra of the perpendicular bands v7 (E') at about 1550 cm -1 and V9 (E') at about 1170 cm -1 of the isotopomers 12C314N3H3 , 13C3 14N3H3 , and l2C3I5N3H3 is given. Both bands proved to be free from accidental resonances. The molecular constants of the state v7 = 1 and v9 = 1 of the isotopomers under consideration are listed. The weak difference band v9-vl4 (E" → E') of 12C314N3H3 was recorded and analyzed, using the molecular constants of v9 = 1 [this work] and V14 = 1 [of 1995], This analysis proves the quality of the molecular constants of the fundamental v14 which is IR-inactive.

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48

Slanina, Zdenek. "A Comparative Study of the BJH- and MCYL-Type Potentials Applied to the Gaseous Water Dimer". Zeitschrift für Naturforschung A 46, n.º 5 (1 de mayo de 1991): 426–32. http://dx.doi.org/10.1515/zna-1991-0509.

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AbstractVarious refined potentials describing the intra- and inter-molecular force fields of water molecules arc used to calculate the properties of the gas-phase water dimer. The intra-molecular parts have been taken from spectroscopic or quantum-chemical sources. The minimum energy structure was found iteratively using the first derivatives of the potential; the force-constant matrix was constructed by numerical difierentation. A quite close agreement between the Bopp-Jancso-Heinzinger and the Matsuoka-Clementi-Yoshimine-Lie potentials is found. The treatment is applied to seven observed water-dimer isotopomeric isomerizations

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49

Merke, I., J. U. Grabow, N. Heineking y W. Stahl. "The Microwave Spectrum of 1,1-Dichloro-2,2,2-Trifluoroethane". Zeitschrift für Naturforschung A 46, n.º 9 (1 de septiembre de 1991): 799–802. http://dx.doi.org/10.1515/zna-1991-0908.

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Abstract We assigned the microwave spectrum of 1,1-dichloro-2,2,2-trifluoroethane in its vibrational ground state using a pulsed molecular beam microwave Fourier transform (MB-MWFT) spectrometer. For the 35Cl, Cl-isotopomer the rotational constants were found to be A = 2105.7098(38) MHz, B = 1689.8304 (35) MHz, and C = 1135.6955 (23) MHz, the quadrupole coupling constants of the 35Cl-nuclei are χaa = 12.385 (35) MHz and χbb= -42.284(31) MHz. The rotational constants of the 35Cl,37Cl-isotopomer are A = 2071.5469 (33) MHz, B = 1670.7648 (36) MHz, and C = 1117.1755 (24) MHz, the corresponding quadrupole coupling constants are χaa = 17.639 (51) MHz and χbb= -47.670(67) MHz for the 35Cl-nucleus and χaa = 4.701 (54) MHz and χbb= -28.331 (83) MHz for the 37Cl-nucleus

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50

Klein, H., S. P. Belov y G. Winnewisser. "Terahertz Spectrum of Trioxane". Zeitschrift für Naturforschung A 51, n.º 1-2 (1 de febrero de 1996): 123–28. http://dx.doi.org/10.1515/zna-1996-1-218.

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Abstract The pure rotational spectrum of trioxane, (H2CO)3 the trimer of formaldehyde, has been recorded with high resolution in the frequency range between 326 and 947 GHz for the main isotopomer, the 13 C, and the 18O isotopic species in the vibrational ground state. These new high J and K data reveal that the molecule is fairly rigid. For the constants determinable from the recorded high J and K spectra (J = 90 and K = 75) the rotational constant B = 5273.257 180(33) MHz,the two quartic centrifugal distortion constants DJ, and DJK, and the three sextic constants HJ, HJK, and HKJ are needed in the fit to reproduce the measured spectra within experimental accuracy. In addition, for the 13C isotopomer the sextic constants HJK and HKJ are determined as well as the off-diagonal parameters d1 and d2.

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