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In vivo MRS is a non-invasive measurement technique used not only in humans, but also in animal models using high-field magnets. MRS enables the measurement of metabolite concentrations as well as metabolic rates and their modifications in healthy animals and disease models. Such data open the way to a deeper understanding of the underlying biochemistry, related disturbances and mechanisms taking place during or prior to symptoms and tissue changes. In this work, we focus on the main preclinical (1)H, (31)P and (13)C MRS approaches to study brain metabolism in rodent models, with the aim of providing general experts’ consensus recommendations (animal models, anesthesia, data acquisition protocols). An overview of the main practical differences in preclinical compared with clinical MRS studies is presented, as well as the additional biochemical information that can be obtained in animal models in terms of metabolite concentrations and metabolic flux measurements. The properties of high-field preclinical MRS and the technical limitations are also described.

The good performance of N‐heterocyclic carbenes (NHCs), in terms of versatility and selectivity, has called the attention of experimentalists and theoreticians attempting to understand their electronic properties. Analyses of the Au(I)–C bond in [(NHC)AuL]+/0 (L stands for a neutral or negatively charged ligand), through the Dewar–Chatt–Duncanson model and the charge displacement function, have revealed that NHC is not purely a σ‐donor but may have a significant π‐acceptor character. It turns out, however, that only the σ‐donation bonding component strongly correlates with one specific component of the chemical shielding tensor. Here, in extension to earlier works, a current density analysis, based on the continuous transformation of the current density diamagnetic zero approach, along a series of [(NHC)AuL]+/0 complexes is presented. The shielding tensor is decomposed into orbital contributions using symmetry considerations together with a spectral analysis in terms of occupied to virtual orbital transitions. Analysis of the orbital transitions shows that the induced current density is largely influenced by rotational transitions. The orbital decomposition of the shielding tensor leads to a deeper understanding of the ligand effect on the magnetic response properties and the electronic structure of (NHC)‐Au fragments. Such an orbital decomposition scheme may be extended to other magnetic properties and/or substrate‐metal complexes., (NHC) carbon chemical shielding tensor decomposition into orbital contributions. The current density is largely influenced by rotational transitions involving occupied and virtual orbitals localized on the (NHC) carbon atom with a 1 and b 1 symmetries, respectively.John Wiley & Sons, Ltd.

International audience; Individual molecular components of soil organic matter (SOM) have been studied since the early 19th century. Their characterization is essential, because knowledge of the molecular structures constituting SOM allows for the detailed understanding of its origin and the processes implicated in soil C sequestration. This provides the basis for target-oriented development of management practices to optimize ecosystem services provided by soil. The aim of this review is to give an overview about the major analytical developments and the information gain that could be achieved by application of molecular methods in SOM research. Up to the 1980s, studies concentrated on the characterization of the chemical nature of SOM. Analyses were mainly based on soluble OM compounds, which were fractionated chemically into humic and fulvic acids. During the 1990s, the focus changed and scientists were more interested in biological processes controlling SOM formation and its dynamics. Introduction of physical fractionation and combination of molecular and isotopic techniques allowed assessment of composition, origin, and turnover of SOM within specific localizations in the mineral soil matrix. Analyses of the dynamics of single molecules led to a massive change of paradigms. Long residence times of SOM are no longer explained by chemical recalcitrance but by microbial products being stabilized by the interaction with soil minerals and microbial inaccessibility. In recent years, techniques yielding results with high molecular and spatial resolution were introduced, which will allow the acquisition of much more detailed information, moving a step further toward elucidating the nature and properties of SOM.

The ability to avoid blue-light radiation is crucial for bacteria to survive. In Halorhodospira halophila, the putative receptor for this response is known as photoactive yellow protein (PYP). Its response to blue light is mediated by changes in the optical properties of the chromophore para-coumaric acid (pCA) in the protein active site. PYP displays photocycle kinetics with a strong pH dependence for ground-state recovery, which has remained enigmatic. To resolve this problem, a comprehensive pK(a) determination of the active-site residues of PYP is required. Herein, we show that Glu-46 stays protonated from pH 3.4 to pH 11.4 in the ground (pG) state. This conclusion is supported by the observed hydrogen-bonded protons between Glu-46 and pCA and Tyr-42 and pCA, which are persistent over the entire pH range. Our experimental results show that none of the active-site residues of PYP undergo pH-induced changes in the pG state. Ineluctably, the pH dependence of pG recovery is linked to conformational change that is dependent upon the population of the relevant protonation state of Glu-46 and the pCA chromophore in the excited state, collaterally explaining why pG recovery is slow.

Astrocytes have various important roles in brain physiology. To further elucidate the details of astrocytic functions under normal and pathological states, astrocyte-specific measurements are mandatory. For studying brain energy metabolism, the use of the astrocyte-specific energy substrate acetate has proven to be of great value. Since the first applications of labeled acetate for brain studies about 50 years ago, numerous methodologies have been developed and employed in compartment-specific investigations of brain metabolism. Here, we provide an overview of these different methodological approaches and review studies employing acetate labeled with the most commonly used carbon isotopes. Journal of Cerebral Blood Flow & Metabolism (2011) 31, 1668-1674; doi:10.1038/jcbfm.2011.84; published online 8 June 2011

We hypothesised that, during occlusion inside granular aggregates of oxide-rich soils, the light fraction organic matter would undergo a strong process of decomposition, either due to the slow process of aggregate formation and stabilisation or due to digestion in the macro- and meso-fauna guts. This process would favour the accumulation of recalcitrant materials inside aggregates. The aim of this study was to compare the dynamics and the chemical composition of free and occluded light fraction organic matter in a natural cerrado vegetation (woodland savannah) and a nearby pasture (Brachiaria spp.) to elucidate the transformations during occlusion of light fraction in aggregates of a clayey Oxisol. Nuclear Magnetic Resonance of the 13C, with Cross Polarisation and Magic Angle Spinning (13C-CPMAS-NMR), and 13C/12C isotopic ratio were combined to study organic matter composition and changes in carbon dynamics, respectively. The occluded light fraction had a slower turnover than the free light fraction and the heavy fraction. Organic matter in the occluded fraction also showed a higher degree of decomposition. The results confirm that processes of soil organic matter occlusion in the typical "very fine strong granular" structure of the studied oxide-rich soil led to an intense transformation, selectively preserving stable organic matter. The small amount of organic material stored as occluded light faction, as well as its stability, suggests that this is not an important or manageable sink for sequestration of atmospheric CO2. O presente estudo tomou, como referência, a hipótese de que, durante a oclusão dentro de agregados granulares de solos ricos em óxidos, a fração leve da matéria orgânica do solo passa por um intenso processo de decomposição, decorrente do lento processo de formação desses agregados ou da digestão no trato digestivo da meso e macrofauna. O objetivo deste trabalho foi comparar a dinâmica e a composição química das frações leves (livre e oclusa)s de um solo sob vegetação de cerrado e uma pastagem (Brachiaria spp.) adjacente, para elucidar as transformações durante o processo de oclusão da fração leve em agregados de um Oxissol argiloso. As técnicas de Ressonância Magnética Nuclear do 13C, com Polarização Cruzada e Ângulo Mágico de Rotação (13C-RMN-PCAMR), e de análise da relação isotópica 13C/12C para acessar, respectivamente, a composição e dinâmica dos materiais orgânicos presentes. A fração leve oclusa apresentou um tempo de ciclagem bem maior, quando comparada à fração leve livre e a pesada. A matéria orgânica nessa fração também apresentou maior grau de decomposição. Segundo os resultados, o processo de oclusão de matéria orgânica nas típicas estruturas "granulares fortes muito pequenas" dos solos ricos em óxidos levou esse material a sofrer uma intensa transformação, preservando seletivamente matéria orgânica estável. As pequenas quantidades de carbono acumuladas na fração leve oclusa, assim como sua estabilidade, indicaram não representar essa fração importante e manejável sumidouro de CO2 atmosférico.

Quantity and quality of soil organic matter (SOM) affect physical, chemical, and biological soil properties, and are pivotal to productive and healthy grasslands. Thus, we analyzed the distribution of soil aggregates and assessed quality, quantity, and distribution of SOM in two unimproved and improved (two organic and two conventional) grasslands in subarctic Iceland, in Haplic and Histic Andosols. We also evaluated principal physicochemical and biological soil properties, which influence soil aggregation and SOM dynamics. Macroaggregates (>250 µm) in topsoils were most prominent in unimproved (62–77%) and organically (58–69%) managed sites, whereas 20–250 µm aggregates were the most prominent in conventionally managed sites (51–53%). Macroaggregate stability in topsoils, measured as mean weight diameter, was approximately twice as high in organically managed (12–20 mm) compared with the conventionally managed (5–8 mm) sites, possibly due to higher organic inputs (e.g., manure, compost, and cattle urine). In unimproved grasslands and one organic site, macroaggregates contributed between 40% and 70% of soil organic carbon (SOC) and nitrogen to bulk soil, whereas in high SOM concentration sites free particulate organic matter contributed up to 70% of the SOC and nitrogen to bulk soil. Aggregate hierarchy in Haplic Andosols was confirmed by different stabilizing mechanisms of micro- and macroaggregates, however, somewhat diminished by oxides (pyrophosphate-, oxalate-, and dithionite-extractable Fe, Al, and Mn) acting as binding agents for macroaggregates. In Histic Andosols, no aggregate hierarchy was observed. The higher macroaggregate stability in organic farming practice compared with conventional farming is of interest due to the importance of macroaggregates in protecting SOM and soils from erosion, which is a prerequisite for soil functions in grasslands that are envisaged for food production in the future.

A method for in vivo carbon-edited detection with proton echo-planar spectroscopic imaging (ICED PEPSI) is described. This method is composed of an echo-planar based acquisition implemented with C-13-H-1 J editing spectroscopy and is intended for high temporal and spatial resolution in vivo spectroscopic imaging of C-13 turnover, from D-[1,6-C-13]glucose to glutamate and glutamine, in the brain. At a static magnetic field strength of 7 T, both in vitro and in vivo chemical shift imaging data are presented with a spatial resolution of 8 mu L (i.e., 1.25 x 1.25 x 5.00 mm(3)) and a maximum spectral bandwidth of 5.2 ppm in H-1. Chemical shift imaging data acquired every 11 minutes allowed detection of regional [4-(CH2)-C-13]glutamate turnover in rat brain. The [4-(CH2)-C-13]glutamate turnover curves, which can be converted to tricarboxylic acid cycle fluxes, showed that the tricarboxylic acid cycle flux (V-TCA) in pure gray and white matter can range from 1.2 +/- 0.2 to 0.5 +/- 0.1 mu mol/g/min, respectively, for morphine-anesthetized rats. The mean cortical V-TCA from 32 voxels of 1.0 +/- 0.3 mu mol/g/min (N = 3) is in excellent agreement with previous localized measurements that have demonstrated that V-TCA can range from 0.9-1.1 mu mol/g/min under identical anesthetized conditions. (C) 1999 Wiley-Liss, Inc.

13C CP/MAS NMR spectra of the metal carbonyl complexes Cr(CO)6, Fe(CO)5 and Mn2(CO)10 included in β- and γ-cyclodextrin (CD) cavities have been studied in the temperature range 133 to 423 K. Cr(CO)6 molecules reorient effectively isotropically within γ-cyclodextrin, Fe(CO)5 molecules in β-cyclodextrin reorient effectively isotropically and show rapid axial–equatorial exchange, but Mn2(CO)10 in the super-cage defined by two γ-cyclodextrin molecules shows MAS sidebands at lower temperatures indicative of a more restricted motion such as molecular gyration. The important role of guest and host molecular shape and symmetry match in the reorientational dynamics of the metal carbonyls is discussed.

Despite the potentially large contribution of black carbon (BC) to the recalcitrant soil organic matter pool, the molecular-level composition of aged BC has hardly been investigated. Pyrolysis-GC/MS, which provides structural information on complex mixtures of organic matter, was applied to the NaOH-extractable organic matter of an acidic colluvial soil (Atlantic ranker) sampled with high resolution (5 cm) that harbours a fire record of at least 8.5 ka. Additionally, 5 charcoal samples from selected soil layers were characterised using pyrolysis-GC/MS for comparison. Pyrolysis-GC/MS allowed distinguishing between BC and non-charred organic matter. It is argued that a large proportion of the polycyclic aromatic hydrocarbons (PAHs), benzenes and benzonitrile in the pyrolysates of the extractable organic matter, together accounting for 21–54% of total identified peak area, derived from BC. In charcoal samples, these compounds accounted for 60–98% of the pyrolysis products. The large quantity of BC in almost all samples suggested a key role of fire in Holocene soil evolution. The high C content of the soil (up to 136 g C kg−1 soil) may be attributed to the presence of recalcitrant organic C as BC, in addition to the sorptive preservation processes traditionally held responsible for long-term C storage in acid soils. Interactions between reactive Al hydroxides and BC could explain the longevity of BC in the soil. This work is the first thorough pyrolysis-GC/MS based study on ancient fire-affected organic matter.

Soil organic matter (SOM) in allophanic soils is supposed to accumulate due to protection caused by binding to allophane, aluminium and iron. We investigated a catena of allophanic and non-allophanic soils in Costa Rica to determine the effect of such binding mechanisms on SOM chemistry. These soils contain no contribution of black carbon. Molecular characterization of litter, extractable and dispersed organic matter was done by Curie-point pyrolysis-GC/MS. The molecular chemistry of the organic fractions indicates a strong decomposition of plant-derived organic matter and a strong contribution of microbial sugars and N-compounds to SOM. Both the decomposition of plant-derived SOM ¿ including that of relatively recalcitrant compounds ¿ and the relative contribution of microbial SOM were greater in allophanic samples than in non-allophanic ones. This suggests that chemical protection does not act on primary OM, although it may influence the accumulation of secondary OM in these soils. The effect of allophane on SOM contents in such perhumid soils is probably through incorporation of decomposition products and microbial SOM in very fine aggregates that ¿ in a perhumid environment ¿ remain saturated with water during much of the year. Greater concentrations of aliphatics are found in allophanic residues, but there is no evidence of any specific mineral-organic binding. The results do not support the existing theory of chemical protection of plant-derived components through binding to allophane, iron and aluminium.

NaOH and Na4P2O7 extractable organic matter fractions of two volcanic ash profiles (Azores Islands) were studied by pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). The soils did not have melanic horizons and were not affected by burning. The pyrolysates of all samples were dominated by polysaccharide-derived compounds. The Na4P2O7 extractable fractions were relatively enriched by markers of lignin, proteins, and lipids. Only in the topsoils (A horizons) did lignin appear to be present in significant amounts and, although present with a high degree of side-chain oxidation, the distribution of lignin-derived products could be related to the overlying vegetation. A similar trend was observed for lipids, in particular the high abundance of C26 alkanol in profile EUR05 clearly reflecting grass. Below the topsoils, lignin and lipids were hardly detectable. With depth, markers of intact polysaccharides decreased relatively to smaller polysaccharide pyrolysis products. The same is true for chitin. Compared with other soils, the relative abundance of lignin and lipids was remarkably low. The occurrence of large amounts of polysaccharides including chitin points to an important in situ production of soil organic matter by fungi and/or arthropods. There is no indication of preservation of plant-derived organic matter by allophane or Al3+, but the presence of large amounts of (microbial) polysaccharides and chitin suggests that these secondary organic matter products are indeed stabilized.

To gain understanding about the process of global warming, it is essential to study the global C cycle. In the global C cycle, soil organic matter (SOM) is a major source and sink of atmospheric C. Turnover times of C in these soil organic compounds vary from hours to thousands of years. Clay minerals can stabilize SOM through the formation of organo-mineral bonds. The aim of this research was first, to determine the mean residence time (MRT) of organic matter that is bound to different clay mineral surfaces, and second, to explain the variance in the measured MRTs using multilinear regression. We especially studied organic matter that is bound to kaolinite or smectite. We analyzed the 14C activity of organic matter in the whole and heavy clay-size fraction of kaolinite- and smectite-dominated soils from N'Ropa, in northern Mozambique. The soils originated from natural savanna systems and bamboo forest. We assumed that C inputs and outputs are in equilibrium in such soils, so that the 14C age equals the MRT of the organic C. For both kaolinite- and smectite-dominated soils, the organic matter in the whole and heavy clay-size fraction and extracts had a fast turnover (400¿500 yr on average). The MRT of kaolinite-bound organic matter did not differ significantly from that of smectite-bound organic matter. Multiple linear regression indicates that the effective cation-exchange capacity (ECEC) is the main factor to explain variance in the MRT of the extracted SOM. These results agree with previously found trends in organic matter turnover of kaolinite and smectite-associated clay.

A method for in vivo carbon-edited detection with proton echo-planar spectroscopic imaging (ICED PEPSI) is described. This method is composed of an echo-planar based acquisition implemented with C-13-H-1 J editing spectroscopy and is intended for high temporal and spatial resolution in vivo spectroscopic imaging of C-13 turnover, from D-[1,6-C-13]glucose to glutamate and glutamine, in the brain. At a static magnetic field strength of 7 T, both in vitro and in vivo chemical shift imaging data are presented with a spatial resolution of 8 mu L (i.e., 1.25 x 1.25 x 5.00 mm(3)) and a maximum spectral bandwidth of 5.2 ppm in H-1. Chemical shift imaging data acquired every 11 minutes allowed detection of regional [4-(CH2)-C-13]glutamate turnover in rat brain. The [4-(CH2)-C-13]glutamate turnover curves, which can be converted to tricarboxylic acid cycle fluxes, showed that the tricarboxylic acid cycle flux (V-TCA) in pure gray and white matter can range from 1.2 +/- 0.2 to 0.5 +/- 0.1 mu mol/g/min, respectively, for morphine-anesthetized rats. The mean cortical V-TCA from 32 voxels of 1.0 +/- 0.3 mu mol/g/min (N = 3) is in excellent agreement with previous localized measurements that have demonstrated that V-TCA can range from 0.9-1.1 mu mol/g/min under identical anesthetized conditions. (C) 1999 Wiley-Liss, Inc.

The purpose of this study was to develop a two-compartment metabolic model of brain metabolism to assess oxidative metabolism from [1-C-11] acetate radiotracer experiments, using an approach previously applied in C-13 magnetic resonance spectroscopy (MRS), and compared with an one-tissue compartment model previously used in brain [1-C-11] acetate studies. Compared with C-13 MRS studies, C-11 radiotracer measurements provide a single uptake curve representing the sum of all labeled metabolites, without chemical differentiation, but with higher temporal resolution. The reliability of the adjusted metabolic fluxes was analyzed with Monte-Carlo simulations using synthetic C-11 uptake curves, based on a typical arterial input function and previously published values of the neuroglial fluxes V-tca(g), V-x, V-nt, and V-tca(n) measured in dynamic C-13 MRS experiments. Assuming V-x(g)=10xV(tca)(g) and V-x(n)=V-tca(n), it was possible to assess the composite glial tricarboxylic acid (TCA) cycle flux V-gt(g) (Vgtg = V(x)(g)xV(tca)(g)/(V-x(g) + V-tca(g))) and the neurotransmission flux V-nt from C-11 tissue-activity curves obtained within 30 minutes in the rat cortex with a beta-probe after a bolus infusion of [1-C-11] acetate (n = 9), resulting in V-gt(g) = 0.136 +/- 0.042 and V-nt = 0.170 +/- 0.103 mu mol/g per minute (mean +/- s.d. of the group), in good agreement with 13C MRS measurements. Journal of Cerebral Blood Flow & Metabolism (2012) 32, 548-559; doi: 10.1038/jcbfm.2011.162; published online 30 November 2011

Hippocampus plays a critical role in linking brain energetics and behavior typically associated to stress exposure. In this study, we aimed to simultaneously assess excitatory and inhibitory neuronal metabolism in mouse hippocampus in vivo by applying (18)FDG-PET and indirect C-13 magnetic resonance spectroscopy (H-1-[C-13]-MRS) at 14.1 T upon infusion of uniformly C-13-labeled glucose ([U-C-13(6)]Glc). Improving the spectral fitting by taking into account variable decoupling efficiencies of [U-C-13(6)]Glc and refining the compartmentalized model by including two gamma-aminobutyric acid (GABA) pools permit us to evaluate the relative contributions of glutamatergic and GABAergic metabolism to total hippocampal neuroenergetics. We report that GABAergic activity accounts for similar to 13% of total neurotransmission (V-NT) and similar to 27% of total neuronal TCA cycle (V-TCA) in mouse hippocampus suggesting a higher V-TCA/V-NT ratio for inhibitory neurons compared to excitatory neurons. Finally, our results provide new strategies and tools for bringing forward the developments and applications of C-13-MRS in specific brain regions of small animals.