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Understanding the mechanisms of soil carbon (C) formation and loss is essential for predicting the C storage capacity of soils under ongoing global change scenarios. Climatic variables, vegetation structure, microbial activity, soil mineralogy, and tissue C chemistry each have the potential to affect the fate of C in soils, and the interactions among these controls vary in different environments. Our mechanistic understanding of how these factors interact with each other to determine soil C storage is still rudimentary. This dissertation used a series of field and laboratory studies to assess the interacting roles of vegetation, soil mineralogy, microbial activity, C chemistry, and temperature in regulating the fate of C in soils. In the first experiment, we sought to understand how soil mineralogy, soil nutrient and C status, and C chemistry interact to determine warming effects on the fate of newly added soil C using a 13C isotopic tracing approach. By tracking the added 13C label in soil pools at 4 days and 255 days in tropical forest soils with differing weathering and mineralogical conditions, we found that initial microbial uptake of 13C and average carbon use efficiency (CUE) by microbes were strongly correlated with longer-term C retention in mineral soils. Overall, warming had a negative effect on 13C retention in soil in the youngest, least-weathered soil only, with no warming effect on moderately to strongly weathered soils. Thus, soil C stocks in less weathered soils, and with lower microbial CUE, may be most vulnerable to C loss with a warming climate.Our second study assessed the fate of newly added organic 13C-labeled compounds in soils of differing fertility along weathering gradients. Comparing additions of two low molecular weight compounds, 2.9x greater retention occurred for 13C-labeled glucose versus 13C-labeled glycine after two years, suggesting that glucose may be a better precursor for soil organic matter formation. Soil mineralogy and nutrient availability were not significant factors in 13C retention in soil. Soil spectra from 13C NMR revealed an increase in the proportion of alkyl C in glucose and glycine amended soil relative to control soils, and alkyl C are commonly associated with relatively stable organic C. Thus, our results indicate that microbial incorporation of labile organic compounds like glucose into biomass may be associated with greater C retention in stable soil components. Our third study estimated the long-term effect of grass cover loss on soil organic C (SOC) and total nitrogen (TN) storage, and the spatial heterogeneity of SOC and TN in two arid grasslands. The nine years of experimental grass removal resulted in soil deflation and 30% and 35% declines in SOC and TN respectively in 100% grass removal plots (TU100). Grass removal also led to soil deposition in downwind areas of the plot (TD100). Soil organic C and TN concentrations in the deposition plot (TD100) was variable, and likely depended on the structure of the vegetation community trapping wind-blown particulates. Geostatistical analysis showed that weaker and smaller fertile islands, compared to the control, developed in TD100 plots over nine years of aeolian transport. The outcomes of this dissertation will add to the current body of knowledge about mechanisms of soil C stabilization across environmental conditions and with warming.

Aiming to reveal the humification process of organic waste and its contribution to the heavy metal behaviour affected by earthworm activity, it was studied about the variation of humic acid (HA) and heavy metal behaviour during vermicomposting of the mixed pig manure and 13C-labelled rice straw. The results showed that earthworms could well adapt to the culturing environment and feed organic matter for its growth and reproduction, the vermicomposting process increased the content of humic substances (HS), HA, and fulvic acid (FA) in substrate residues, but led to less transformation of HA into FA. The elemental, ultraviolet absorption spectroscopy, Fourier transform infrared (FTIR) and fluorescence excitation–emission matrix (EEM) analysis indicated that vermicomposting led to more aromatic structures and much higher humification degree in HA, whereas less protein, FA-like substances and plastein in HA. Vermicomposting could enhance the total Cu content and decrease Cu/Zn bioavailability in the substrate residues, and vermicomposting especially can help stabilize Cu in the substrate residues by forming more complexed HA–Cu.

14C-labeled saxagliptin, 13CD2-labeled saxagliptin, and its 13CD2-labeled 5-hydroxy metabolite were synthesized to further support development of the compound for biological studies. This paper describes new syntheses leading to the desired compounds. A total of 3.0 mCi of 14C-labeled saxagliptin was obtained with a specific activity of 53.98 μCi/mg (17.13 mCi/mmol). The radiochemical purity determined by HPLC was 99.29%, and the overall radiochemical yield was 3.0% based upon 100 mCi of [14C]CH2I2 starting material. By following similar synthetic routes, 580.0 mg of 13CD2-labeled saxagliptin and 153.1 mg of 13CD2-labeled 5-hydroxysaxagliptin metabolite were prepared. Copyright © 2014 John Wiley & Sons, Ltd.

Isodesmosine is a pyridinium amino acid that contributes to elastin’s crosslinking structure. It is known to form by condensation and aromatization of 3 allysines and 1 lysine, preceded by previous...

Boronic acid-substituted shapeshifting bullvalenes bearing a (13)C label are employed as sensor arrays for polyhydroxylated compounds, such as carbohydrates, flavanols, and sialic acids. The dynamic nature of the bullvalene core allows for covalent binding to a wide variety of analytes, allowing for specific analyte detection by a single NMR measurement. The resulting (13)C NMR patterns permit an inference to the identity of a particular analyte bound. Conversion of the (13)C NMR to an easy-to-read barcode provides a convenient method to catalog polyol analytes. The synthesis and study of a structurally related static sensor, which is not suitable for analyte recognition, underscores the advantages of the shapeshifting nature of the sensor.

13C labeled (>M + 4) metabolites of nitrogen and sulfur-based chemical warfare agent metabolites were prepared from readily available and 13C labeled commercial starting materials. The new chemical routes are efficient in the number of chemical steps, can be scaled to afford gram quantities, and occur in good yields on the basis of the 13C label. These labeled compounds are useful as internal standards in mass spectrometry for monitoring chemical warfare agents and their metabolites. Published 2012. This article is a US Government work and is in the public domain in the USA.

A [13C]-breath test is a promising method for measuring gastric emptying. The methodological relevance is based on a close correspondence between gastric emptying of [13C]-acetate/octanoate (input) and pulmonary excretion of [13CO2] (output). Despite the close input-output correspondence, the pulmonary output is quite remote from the gastric input: the pulmonary output is delayed compared to the gastric input, and the total recovery of [13CO2] in the breath is incomplete. This review focuses on the kinetics of [13C]-acetate/octanoate in the body and suggests that (1) the delayed pulmonary output results from temporal retention of [13CO2] in the well-perfused tissues (heart, brain, etc.), (2) the incomplete recovery results from incorporation of the label into metabolic products (ketone bodies, amino acids, etc.) or from fixation of [13CO2] in the low-perfused tissues (bone, skeletal muscle, etc.), and (3) knowledge on the retention is the key to appropriate interpretations of breath test results. Recognition of these kinetic aspects is essential for appropriate interpretations of these breath test results.

The additional mass associated with 13C in metabolic tracers may interfere with their metabolism. The comparative isomerization and biohydrogenation of oleic, [1-(13)C]oleic, and [U-13C]oleic acids by mixed ruminal microbes was used to evaluate this effect. The percent of stearic, cis-14 and -15, and trans-9 to -16 18:1 originating from oleic acid was decreased for [U-(13)C]oleic acid compared with [1-(13)C]oleic acid. Conversely, microbial utilization of [U-(13)C]oleic acid resulted in more of the 13C label in cis-9 18:1 compared with [1-(13)C]oleic acid (53.7 vs. 40.1%). The isomerization and biohydrogenation of oleic acid by ruminal microbes is affected by the mass of the labeled tracer.

A simple, rapid and cost-effective laboratory method was developed for labelling soil-feeding earthworms simultaneously with 15N and 13C. The method circumvents the production of labelled plant material and can be adapted to devise pulse-labelling or long-term labelling protocols. Soil was amended with 15NH4+ and incubated for 7 days. Then, U-13C-glucose was added and endogeic earthworms, Aporrectodea caliginosa (Oligochaeta: Lumbricidae), were provided individually with 4 g of this pre-incubated soil. The labelling period was 4 days. The labelling efficiency (percentage of tracer retained in earthworm tissues) was estimated to be 15.8% for 15N and 10.3% for 13C. The loss of 15N and 13C label from tissue and mucus was traced for 21 days post-labelling. Label loss from mucus was best described by a two-term exponential function, whereas the label loss in body tissue followed a single-term exponential function. Half-life estimates for the 15N and 13C tracers in body tissue were 16 and 37 days, respectively.

The degradation pathways of Amadori compounds in vivo have not been fully understood because of the lack of suitable techniques although the compounds are considered to be key intermediates in glycation, which contributes to the development of pathologies associated with various chronic and age-related diseases. A new approach using 13C labeling and NMR spectroscopy has thus been described to obtain more insight into the degradation pathways. A 13C-labeled model Amadori compound, [1-13C]Nepsilon-(1-deoxy-D-fructos-1-yl)hippuryl-lysine, was synthesized to investigate the degradation pathways of the sugar moiety. The labeled compound was then incubated under aerobic and physiologic conditions, followed by analysis using 13C-NMR spectroscopy to obtain the degradation profile. Consequently, after 28-d incubation at least nine 13C signals due to 13C-labeled products were observed with those due to unlabeled hippuryl-lysine. These labeled products included not only carboxymethylated hippuryl-lysine as the major product and alpha- and beta-glucose but also acetate and formate. These experiments demonstrate the potential of using a 13C label and NMR spectroscopy in that the technique provides the comprehensive profiling of the degradation products containing the labeled position in spite of their chemical structures.

A synthetic scheme has been developed to prepare methyl methacrylate specifically 13C-labelled at all different positions and in any combination of positions, from simple, commercially available starting materials. According to this scheme methyl (1-13C)- and methyl (2-13C)methacrylate (1a and 1b) have been prepared with high label incorporation (99%).

Partitioning patterns of 13C‐labelled assimilate were studied in mature field‐grown plants of three asparagus (Asparagus officinalis L.) cultivars. Plants were labelled in January and destructively harvested at different stages of the summer fern growth phase and in early spring. There was very little new fern establishment after January, so the majority of the assimilated label was translocated from the labelled fern to the storage roots, and in smaller amounts to buds on the rhizome, from where it was later remobilised into new spear growth in the spring. The label was confined to a physiological unit composed of the labelled fern, the rhizome from which it grew, and buds, roots, and new shoot material associated with that rhizome. Similar patterns of 13C distribution within the physiological unit were observed in three cultivars differing in spear yield.

13C-2 labeled phenyl ethynyl triflone undergoes regiospecific CH alkynylation upon reaction with cyclohexane. The 13C label is found to be exclusively adjacent to the phenyl group in the product phenyl cyclohexyl acetylene, consistent with cyclohexyl radical addition at the α-position. Control studies show preferential phenyl migration from a vinylidine carbene, thus excluding the presence of such an intermediate.

This study shows foraminiferal dynamics after experimentally induced hypoxia within the wider context of ecosystem recovery. 13C-labeled bicarbonate and glucose were added to the sediments to examine foraminiferal diet shifts during ecosystem recovery and test-size measurements were used to deduce population dynamics. Hypoxia-treated and undisturbed patches were compared to distinguish natural (seasonal) fluctuations from hypoxia-induced responses. The effect of timing of disturbance and duration of recovery were investigated. The foraminiferal diets and population dynamics showed higher fluctuations in the recovering patches compared to the controls. The foraminiferal diet and population structure of Haynesina germanica and Ammonia beccarii responded differentially and generally inversely to progressive stages of ecosystem recovery. Tracer inferred diet estimates in April and June and the two distinctly visible cohorts in the test-size distribution, discussed to reflect reproduction in June, strongly suggest that the ample availability of diatoms during the first month of ecosystem recovery after the winter hypoxia was likely profitable to A. beccarii. Enhanced reproduction itself was strongly linked to the subsequent dietary shift to bacteria. The distribution of the test dimensions of H. germanica indicated that this species had less fluctuation in population structure during ecosystem recovery but possibly reproduced in response to the induced winter hypoxia. Bacteria seemed to consistently contribute more to the diet of H. germanica than diatoms. For the diet and test-size distribution of both species, the timing of disturbance seemed to have a higher impact than the duration of the subsequent recovery period.

The biosynthesis of 5-hydroxy-4-oxo-L-norvaline (HON) in Streptomyces akiyoshiensis has been investigated using 13C-labelled substrates. Incorporations of 13C label from sodium [1-13C]-, [2-13C]-, and [1,2-13C2]acetate indicated that HON was formed from a four-carbon compound derived from the citric acid cycle and the methyl carbon of acetate. Feeding experiments using DL-[4-13C]- and DL-[2-13C,15N]aspartate demonstrated that aspartate served as the four-carbon precursor to HON. Both enantiomers of aspartate were metabolized by S. akiyoshiensis, but the D isomer was consumed at a slower rate. The distribution of 13C label in the intracellular L-glutamic acid isolated in these feeding experiments is consistent with the operation of the citric acid cycle in S. akiyoshiensis. A biosynthetic hypothesis that involves a condensation reaction between acetyl or malonyl CoA and the β-carboxyl group of aspartate, and subsequent oxidative decarboxylation, is proposed to account for the incorporation results. An analogous condensation step has been proposed for the biosynthesis of other natural products, including the carbapenem antibiotics. DL-[2-13C,15N]Aspartate was synthesized from [2-13C]diethylmalonate and potassium [15N]phthalimide via diethyl [2-13C,15N]phthalimidomalonate.

Treatment of Cp(CO) 2 Fe-CO 2 - K + with R 3 SnCl (R=Me, Ph) in THF (-78 o C) gave Cp(CO) 2 Fe-SnR 3 , which was attributed to preferred dissociation of the starting metallocarboxylate to Cp(CO) 2 Fe - K + . (Abbreviations: Cp=η 5 -C 5 H 5 ; Cp * =C 5 Me 5 ). The more nucleophilic Cp(CO) 2 Fe-CO 2 - K + was trapped by Ph 3 SnCl as the thermally stable iron-tin carboxylate Cp * (CO) 2 Fe-CO 2 SnPh 3 (8). 13 C-labeled product Cp * (CO) 2 Fe- 13 CO 2 SnPh 3 also was obtained in excess of 90% yield

The biosynthesis of 5-hydroxy-4-oxo-L-norvaline (HON) in Streptomyces akiyoshiensis has been investigated using 13C-labelled substrates. Incorporations of 13C label from sodium [1-13C]-, [2-13C]-, ...

Metabolic networks possess redundant functionalities and thus they can behave as highly resilient systems. One practical consequence is many seemingly obvious mutations fail to work as intended when metabolic engineering is attempted. Alternately, mutations distal from where an effect on metabolism is sought prove to be effective. The existence of viable and alternate flux solutions can also confound the interpretation of 13C NMR experiments. Unless 13C label design for a precursor such as glucose is correctly done, wrong answers can be obtained concerning the effect of a mutation when one goes numerically from NMR data to the values of the metabolic fluxes. From the practical stand point, such incorrect answers can then (i) cause one to reject a mutation strategy that is actually successful or (ii) lead to formulating incorrect next steps for the round(s) of mutation. After summarizing different ways to analyze metabolic networks (e.g. mixed integer programming), this presentation will first present exam...

A new tracer technique, in which a 13C-labeled compound as a biological tracer and 13C nuclear magnetic resonance (NMR) as an analytical tool are used, is proposed. In order to verify the applicability of the method to clinical chemistry. [1-13C]benzoic acid was administered and [1'-13C]hippuric acid excreted in the urine was quantitated by NMR, by using [1-13C]hippuric acid as an internal standard.

This work demonstrates a solid-state NMR strategy for extracting multiple interatomic distance and angle constraints from moderately complex solid organic compounds containing a single (13)C label and a single (15)N label. It is shown that the constraints obtained for the compound cimetidine, with the labels placed at positions directed by the standard synthetic route, are sufficient to provide reliable estimates of 5 of the 8 torsional degrees of freedom in the molecule and are consistent with a molecular conformation close to that determined by crystallography. This strategy will be useful for determining the conformations of sparsely-labelled small molecules in motionally restrained environments, such as within the binding sites of membrane-embedded receptors.

2 páginas, esquemas., 2,6-Dimethyl-substituted anisoles can be converted into the corresponding 2-ethyl-6-methylphenols in a several-step reaction mediated by a TpMe2Ir(III) complex; use of the 13C-enriched anisoles, ArO13CH3, shows that the 13C label distributes across the two ethyl sites with a preference for the terminal position., Financial support from the DGI (Project CTQ 2004-00409/BQU, FEDER support), the Junta de Andalucía, and cooperation project CSIC-CONACyT are gratefully acknowledged. L.L.S. and P.L. thank the MEC for research grants.

Origin of the Methyl Substituents of F Acids Feeding experiments with L-[methyl-13C]methionine on suspension cultures of Saccharum spec. demonstrate that the furan methyl groups of F acids 1 are derived from methionine. Specific incorporation of 13C label was confirmed by GC/MS analysis of the tetrahydrofuran derivatives 2.

Incorporation of 13C label from either [1-13C]glucose to glutamate C-4 and lactate C-3 or from [2-13C]acetate to glutamate C-4 was monitored in situ in a superfused brain slice preparation by using 1H-detected/13C-edited (1H/13C) n.m.r. spectroscopy. The fractional enrichments of both metabolites were determined by this means in both brain slices and acid extracts of the preparations in order to assess their 1H-n.m.r. detectabilities. The 1H/13C satellite resonances from glutamate C-4 and lactate C-3 in brain tissue were followed from 4 min onwards in the presence of 5 mM [1-13C]glucose. Fractional enrichment of glutamate C-4 in the slice preparations was higher than in their acid extracts throughout the incubation of 100 min; at 30 min the enrichment was 15.9 +/- 0.6% in the slice preparations and 10.6 +/- 0.9% in extracts and at 100 min 24.5 +/- 1.7% compared with 19.7 +/- 0.4%, respectively. In contrast, lactate C-3 reached a steady-state fractional enrichment of approx. 43% by 15 min and there was no difference between the values determined in the slice preparations and the acid extracts. There was a significant difference between the glutamate C-4 fractional enrichments in the brain slices (7.4 +/- 0.6%) and extracts (5.1 +/- 0.3%) after 60 min of incubation with [2-13C]acetate. Thus 13C label from both glucose and exogenous acetate enters a pool of glutamate that is more amenable to 1H n.m.r. detection than total acid-extracted brain biochemical glutamate, whereas lactate is labelled with full 1H n.m.r. visibility. The results are discussed in the light of the biochemical factors that affect glutamate 1H-n.m.r. susceptibility and thus its n.m.r. visibility.

An approach to a synthesis of stereoselective 5'-monodeuterated nucleoside combined with 13C label is described. A preparation of (5R)-D-[5-(2)H1;5-(13)C]ribose derivative of 1,2:5,6-di-O-isopropyliden-alpha-D-allofranose was successfully achieved by a 13C Wittig reaction using Ph3P13CH3I-BuLi to 5-oxoribose derivative and subsequent transformation into D-[5-(13)C]ribose derivative with an AD reaction, selective acylation, oxidation with NaIO4, and a stereoselective deuteride transfer reaction from Alpine-Borane-d to 5-oxo-D-[5-(13)C]ribose derivative as the main reaction. (5'R)-[5'-(2)H1;5'-(13)C]nucleosides were synthesized in the established manner from this 5-(13)C/2H1-double-labeled ribose.

This paper presents the synthesis of 1-13C- and 4-13C-plastoquinone-9 and their characterization with NMR spectroscopy and mass spectrometry. The synthetic scheme has been further adapted to introduce 13C-labeled plastoquinones on all individual and on each combination of positions in the quinone ring. Also a two-step scheme is disclosed to prepare unlabeled plastoquinone-9. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Methods for the introduction of a radioactive 13C label into N-(2-chlorophenyl-sulfonyl)-N'-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)urea, which has herbicidal activity, are described.

The food web of Izembek Lagoon, Alaska draws most of its carbon from eelgrass (Zostera marina) and phytoplankton. The13C:12C ratios of these primary producers are sufficiently different to enable their contributions to consumers to be estimated from consumer13C:12C ratios. Although the technique is conceptually simple, carbon inputs from other sources and isotope fractionations occurring in the food web limit its precision. Isotopic data nevertheless helps to establish the major carbon fluxes through the community and to assess the importance of eelgrass carbon to individual animals. It is particularly useful when dealing with detritus food chains, where direct observations of animal feeding habits are difficult to make. The Izembek community draws much of its carbon from eelgrass. Detritus food chains provide the major pathway for assimilation of eelgrass carbon by the community, but grazers are also important. Eelgrass carbon is more important to benthic animals than to the eelgrass epibiota and the fishes, which depend mainly on phytoplankton carbon.

Determination of glycolic acid by stable isotope dilution was applied to the measurement of the glycolic acid pool size in tomato and maize leaves during photorespiration. Detached leaves were maintained in the presence of 18O2; [13C]glycolate was added to the foliar extract as an internal standard and the mixture of biological glycolate and [13C]glycolate was analyzed by combined gas chromatography-mass spectrometry. The level of foliar glycolate pool was measured via the 13C label, and 18O incorporation was determined.

Reaction of (E,Z)-or (E)-2-anisyl-1,2-ditolyl[2-13C]vinyl bromides ((E,Z)- or (E)-6-Br-2-13C) with HOAc–AgOAc gave a 1:1 mixture of (E)- and (Z)-2-anisyl-1,2-ditolyl[1,2-13C]vinyl acetates ((E,Z)-6-OAc-1,2-13C), with about 37.4% scrambling of the label from C-2 to C-1 arising from degenerate 1,2-anisyl shifts in the 2-anisyl-1,2-ditolyl[2-13C]vinyl cation (6-2-13C). No detectable amount of 1-anisyl-2,2-ditolylvinyl acetate was formed, indicating no nondegenerate 1,2-tolyl shift in cation 6 to give the more stable 1 -anisyl-2,2-ditolylvinyl cation (10) in the reaction with HOAc–AgOAc. Reaction of (E)-6-Br-2-13C with 2,2,2-trifluoroethanol (TFE) in the presence of 2,6-lutidine gave as major product 1-anisyl-2,2-ditolyl[1,2-13C]vinyl 2,2,2-trifluoroethyl ether (10-OTFE-1,2-13C) and a 1:1 mixture of (E)- and (Z)-2-anisyl-1,2-ditolyl[1,2-13C]vinyl 2,2,2-trifluoroethyl ethers ((E,Z)-6-OTFE-1,2-13C) as minor products, the ratio of 10-OTFE to (E,Z)-6-OTFE being about 80:20. Scrambling on the 13C label in the major product, 10-OTFE-1,2-13C, was 48.8 ± 0.9% and scrambling in the minor products, (E,Z)-6-OTFE-1,2-13C, was 47.2 ± 1.4%. The present work with cation 6 completes the series of nine possible triarylvinyl cations, with various combinations of phenyl (Ph), p-tolyl (Tol), and (or) p-anisyl (An) as the three aryl groups, that can give rise to degenerate 1,2-aryl shifts across the double bond, and the present results are discussed in conjunction with data from previous work on the other eight triarylvinyl cationic systems.

The synthesis of six 1-X- (X = OH, OCH3, OCOCH3, CH3, CHO and CN) phenanthrene derivatives with a 13C label at C-1 is described. An analysis of the 13C13C spin coupling constants shows the importance of π-interaction for the coupling constant transmission. Small 13C13C spin coupling constants over 6 bonds are reported.

Standard samples of pure (+)-salutaridine and (−)-thebaine required to study the mammalian origin of morphine, were prepared from (+)-6-demethylsalutaridine by published procedures and were characterized by CD spectra and physical data. Reductive N-methylation of (−)-northebaine afforded (−)-thebaine, and when 13C-labeled formalin was used, (−)-thebaine with a 13C label on the N-methyl carbon atom resulted. The latter represents a model procedure to prepare ultimately N-14CH3-labeled (−)-thebaine and 14C-labeled congeners.

When labelled sugars are produced by in vivo photosynthesis in the presence of 13CO2 the resulting material is often a combination of at least two types of isotopic species, the endogenous material containing 13C in natural abundance and the enriched material. Before such materials can be used in clinical applications where quantitative studies are being carried out, it is necessary to determine the enrichment of the various isotopic components. The analyses described in this work were designed to measure: 1. The relative amounts of unenriched and uniformly labelled material. 2. The uniformity of the 13C label in the enriched material. 3. The enrichment in the labelled material. These measurements were done with a combined gas chromatographmass spectrometer (GC-MS) operating in the selected ion monitoring mode. This technique is especially useful for isotopic analyses because it can be successfully used to obtain quantitative data even on microgram quantities of complex mixtures.

Resonances from 13C, 31P and 1H have been detected simultaneously in suspensions of human erythrocytes using a modified NMR spectrometer equipped with a probe tuned to four different frequencies. The utility of multinuclear NMR in the study of cellular metabolism is demonstrated with an investigation of 13C label flux through the 2,3-bisphosphoglycerate bypass in human erythrocytes. In a single experiment, the respective contributions of this bypass and the pentose-phosphate shunt were found to be 27 and 10% of the total glycolytic rate.

The halogenation of 2-phenylethanol-1-14C and -1-13C was carried out with halogenphosphorus or phosphorus trihalide under various conditions. The resulting 2-phenylethyl halides showed isotopic scrambling of the 14C and 13C label from C-1 to C-2. The degree of rearrangement increased with the rise of reaction temperature. In a given temperature, the rearrangement in iodination was more than that found in bromination or chlorination.

Phenylisothiocyanate, enriched with 13C at the isothiocyanate carbon, has been synthesized and utilized as a 13C NMR probe of proteins for the first time. The reagent has been used to label the amino groups of oxidized glutathione, and the resulting 13C NMR spectrum shows a prominent thiocarbonyl peak after a single NMR scan. The reagent is also capable of differentiating amino groups on the insulin molecule with distinct peaks corresponding to the amino groups on the A and B chains of insulin. This study illustrates the potential of using a new 13C label to functionalize amino groups of proteins and to study the labeled proteins with 13C NMR.

Imaging of the metabolism of hyperpolarized [1-13C]pyruvate has shown considerable promise in preclinical studies in oncology, particularly for the assessment of early treatment response. The repeatability of measurements of 13C label exchange between pyruvate and lactate was determined in a murine lymphoma model in fasted and non-fasted animals. The fasted state showed lower intra-individual variability, although the [1-13C]lactate/[1-13C]pyruvate signal ratio was significantly greater in fasted than in non-fasted mice, which may be explained by the higher tumor lactate concentrations in fasted animals. These results indicate that the fasted state may be preferable for the measurement of 13C label exchange between pyruvate and lactate, as it reduces the variability and therefore should make it easier to detect the effects of therapy. © 2016 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.

1-Hydroxy- and 1-acetoxy-naphthalene with a 13C label at the α-position have been synthesized; the 13C–13C spin coupling constanta have been measured by Fourier transform n.m.r. spectroscopy and interpreted in terms of INDO and Huckel calculations.

The mass spectra of the 3-ethylene ketal of delta 5-pregnan[20-13C]methylene-3-one and 17 beta-acetoxyl[3-13C]methyleneandrost-1-ene have been examined. In both cases there are some fragments which show either relatively large retention or elimination of 13C label and these can be assigned to some fragmentation paths which generally follow those found for diterpenic and steroidal hydrocarbons, and are in good agreement with the empirical fragmentations rules in mass spectrometry.

Recently we reported that rates of protein turnover in intravenously fed neonates were approximately 69% of the value in enterally fed babies. We speculated that this difference ( 4g/kg/d) represented gut protein synthesis. However we were concerned that these differences might be related to methodology rather than to a real biological difference. In order to resolve this problem we studied protein turnover in IV fed neonates using 1-13C-leucine simultaneously with 15N-glycine (the previous label). Twelve babies were studied. BW 2.34±0.16kg. Intakes: protein 3.2±0.2 g/kg/d; energy 88 3kcal/kg/d; N balance 284 19mgN/kg/d. The rates of flux (Q), protein synthesis (S) and breakdown (B) are shown. Turnover rates derived from the 13C label studies are significantly lower (p