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Different folivorous marsupials select their food from different subgenera of Eucalyptus, but the choices cannot be explained by known antifeedants, such as formylated phloroglucinol compounds or tannins, or by nutritional quality. Eucalypts contain a wide variety of plant secondary metabolites so it is difficult to use traditional methods to identify the chemicals that determine food selection. Therefore, we used a metabolomic approach in which we employed (1)H nuclear magnetic resonance spectroscopy to compare chemical structures of representatives from the two subgenera and to identify chemicals that consistently differ between them. We found that dichloromethane extracts of leaves from most species in the subgenus Eucalyptus differ from those in Symphyomyrtus by the presence of free flavanones, having no substitution in Ring B. Although flavanoids are known to deter feeding by certain insects, their effects on marsupials have not been established and must be tested with controlled feeding studies.

The SPACE volume-selection technique has been used to acquire high-resolution 1H spectra from the brain of neonate mice at 11.7 T (500 MHz). Spectra were acquired from voxels smaller than 20 μl. The spectra display elevated intensities of resonances arising from taurine and reduced intensities of those arising from N-acetylaspartate, when compared to those of mature animals, correlating well with in vitro studies. An integrated probe design consisting of separate transmission and reception RF coils and linear gradient coils is described. Comments are made concerning the advantages and disadvantages of performing gradient-encoded localized spectroscopy at this field strength.

Theoretical and experimental results are presented demonstrating that the slice intensity resulting from a self‐refocusing 270° Gaussian pulse (L. Elmsley and G. Bodenhausen, Magn. Reson. in Med. 10, 273, 1989) is approximately 60% of that following an appropriately refocused 90° Gaussian pulse.

The improved understanding and control of induced eddy current effects has led to the increased application of pulsed field gradients in high-resolution 2D NMR spectroscopy. Of particular interest is the ability to select specific coherences in a single acquisition with concomitant "quadrature detection" in the F1 dimension. A product-operator analysis of this effect for an AX spin system which describes the selection of N-type or P-type signals using appropriate gradient episodes in the COSY and 2D double-quantum experiments is presented.

A globally optimal superconducting magnet coil design procedure based on the Minimum Stored Energy (MSE) current density map is outlined. The method has the ability to arrange coils in a manner that generates a strong and homogeneous axial magnetic field over a predefined region, and ensures the stray field external to the assembly and peak magnetic field at the wires are in acceptable ranges. The outlined strategy of allocating coils within a given domain suggests that coils should be placed around the perimeter of the domain with adjacent coils possessing alternating winding directions for optimum performance. The underlying current density maps from which the coils themselves are derived are unique, and optimized to possess minimal stored energy. Therefore, the method produces magnet designs with the lowest possible overall stored energy. Optimal coil layouts are provided for unshielded and shielded short bore symmetric superconducting magnets.

MRI of the lung using hyperpolarized helium as an inhaled contrast agent has important research applications and clinical potential. Owing to the limited availability of hyperpolarized helium, this type of imaging has not been performed in the human lung outside of North America or Europe. The objective of this study was to test the feasibility of imaging human lungs in Australia using hyperpolarized helium gas imported from Germany.A Bruker 2-Tesla whole-body magnetic resonance scanner located in Brisbane, Australia was adapted with a helium-3 radiofrequency transceiver coil. Helium-3 was hyperpolarized to 72% in Mainz, Germany and airfreighted to Brisbane. The time taken for the journey was 32 h and scanning was performed 36-40 h after departure from Mainz, with an estimated polarization level of 44%. Procedures were developed to transfer 300 mL of the hyperpolarized helium to Tedlar bags filled with 700 mL of nitrogen. Healthy volunteers inhaled the 1 L helium/nitrogen mixture from FRC, and imaging was performed with a 10 s breathhold.Imaging showed very detailed and even ventilation of all regions of the lung with a good signal-to-noise ratio. No adverse effects of inhaling the gas mixture were noted.This report of MRI of the human lung using hyperpolarized helium demonstrates the feasibility of long distance gas transport from Germany to Australia. This will help to facilitate research and clinical application of this innovative functional lung imaging technique.

A cyclitol galactoside was isolated from the seeds of Vigna angularis and shown to be identical with galactosylononitol. However, detailed 2D NMR data and methylation analysis resulted in the revision of the structure of galactosylononitol to O-alpha-D-galactopyranosyl-(1-->3)-4-O-methyl-D-myo-inositol (1). Thus, compound 1 represents the only naturally occuring methylated derivative of galactinol.

A digalactosyl ononitol was isolated from seeds of adzuki bean (Vigna angularis [Willd.] Ohwi et Ohasi). Analysis of hydrolysis products and NMR spectroscopy established its structure as O-alpha-D-galactopyranosyl-(1-->6)-O-alpha-D-galactopyranosyl-(1-->3)-O-methyl- D-myo-inositol. (C) 2003 Elsevier Ltd. All rights reserved.

Read-only-memory-based (ROM-based) quantum computation (QC) is an alternative to oracle-based QC. It has the advantages of being less "magical," and being more suited to implementing space-efficient computation (i.e., computation using the minimum number of writable qubits). Here we consider a number of small (one- and two-qubit) quantum algorithms illustrating different aspects of ROM-based QC. They are: (a) a one-qubit algorithm to solve the Deutsch problem; (b) a one-qubit binary multiplication algorithm; (c) a two-qubit controlled binary multiplication algorithm; and (d) a two-qubit ROM-based version of the Deutsch-Jozsa algorithm. For each algorithm we present experimental verification using nuclear magnetic resonance ensemble QC. The average fidelities for the implementation were in the ranges 0.9-0.97 for the one-qubit algorithms, and 0.84-0.94 for the two-qubit algorithms. We conclude with a discussion of future prospects for ROM-based quantum computation. We propose a four-qubit algorithm, using Grover's iterate, for solving a miniature "real-world" problem relating to the lengths of paths in a network.

The ligand-binding region of the low-density lipoprotein (LDL) receptor is formed by seven N-terminal, imperfect, cysteine-rich (LB) modules. This segment is followed by an epidermal growth factor precursor homology domain with two N-terminal, tandem, EGF-like modules that are thought to participate in LDL binding and recycling of the endocytosed receptor to the cell surface. EGF-A and the concatemer, EGF-AB, of these modules were expressed in Escherichia coli. Correct protein folding of EGF-A and the concatemer EGF-AB was achieved in the presence or absence of calcium ions, in contrast to the LB modules, which require them for correct folding. Homonuclear and heteronuclear 1H-15N NMR spectroscopy at 17.6 T was used to determine the three-dimensional structure of the concatemer. Both modules are formed by two pairs of short, anti-parallel beta-strands. In the concatemer, these modules have a fixed relative orientation, stabilized by calcium ion-binding and hydrophobic interactions at the interface. 15N longitudinal and transverse relaxation rates, and [1H]-15N heteronuclear NOEs were used to derive a model-free description of the backbone dynamics of the molecule. The concatemer appears relatively rigid, particularly near the calcium ion-binding site at the module interface, with an average generalized order parameter of 0.85+/-0.11. Some mutations causing familial hypercholesterolemia may now be rationalized. Mutations of D41, D43 and E44 in the EGF-B calcium ion-binding region may affect the stability of the linker and thus the orientation of the tandem modules. The diminutive core also provides little structural stabilization, necessitating the presence of disulfide bonds. The structure and dynamics of EGF-AB contrast with the N-terminal LB modules, which require calcium ions both for folding to form the correct disulfide connectivities and for maintenance of the folded structure, and are connected by highly mobile linking peptides.

Circular dichroism and NMR spectroscopy have been used to determine the structure of the low-density lipoprotein (LDL) receptor-binding peptide, comprising residues 130-152, of the human apolipoprotein E. This peptide has little persistent three-dimensional structure in solution, but when bound to micelles of dodecylphosphocholine (DPC) it adopts a predominantly alpha-helical structure. The three-dimensional structure of the DPC-bound peptide has been determined by using 1H-NMR spectroscopy: the structure derived from NOE-based distance constraints and restrained molecular dynamics is largely helical. The derived phi and psi angle order parameters show that the helical structure is well defined but with some flexibility that causes the structures not to be superimposable over the full peptide length. Deuterium exchange experiments suggest that many peptide amide groups are readily accessible to the solvent, but those associated with hydrophobic residues exchange more slowly, and this helix is thus likely to be positioned on the surface of the DPC micelles. In this conformation the peptide has one hydrophobic face and two that are rich in basic amino acid side chains. The solvent-exposed face of the peptide contains residues previously shown to be involved in binding to the LDL receptor.

A novel furanoterpene (2), iso-dehydrodendrolasin, has been isolated from the tropical marine sponge Euryspongia deliculata and characterized by 2D NMR.

Chemical synthesis was used to prepare the HIV-1 protease specifically 13C-labelled in the catalytically essential Asp 25 in each monomer. The NMR chemical shift of the 13C-enriched homodimeric enzyme was measured in the presence of the inhibitor pepstatin, a mimic of the tetrahedral intermediate formed in enzyme catalysis. In this complex, the catalytic carboxyls do not titrate in the pH range where the enzyme is active; throughout the range pH 2.5-6.5, one Asp 25 side chain is protonated and the other deprotonated. By contrast, in the absence of inhibitor the two Asp side chains are chemically equivalent and both deprotonated at pH 6, the optimum for enzymatic activity. These direct observations of the chemical properties of the catalytic apparatus of the enzyme provide concrete information on which to base the design of improved HIV-1 protease inhibitors.

In vivo, volume-selected H-1 NMR spectroscopy employing the SPACE technique was used to monitor biochemical changes in the thiamin deficient rat brain in response to glucose loading. The concentrations of brain N-acetylaspartate, glutamate/glutamine/gamma-aminobutyric acid, lactate and glucose differed significantly from those of control animals. The results are consistent with a metabolic block at the reaction catalyzed by the thiamin dependent enzyme alpha-keto glutarate dehydrogenase soon after the onset of neurological symptoms of thiamin deficiency, and a further block at pyruvate dehydrogenase arising late in the course of thiamin deficiency.

In Vivo, high‐resolution, volume‐selected H NMR spectroscopy was used to monitor the concentration of ethanol in the dog brain following intravenous injection of ethanol. Equilibration of ethanol in the body water should result in approximately equivalent concentrations of ethanol in the blood and brain. However, the mean equilibrium brain ethanol concentration determined using N‐acetylaspartate as an internal standard was only 23 ± 5% of the blood ethanol concentration. The disparity between blood and brain ethanol concentrations was attributed to underestimation of the ethanol concentration due to overlapping resonances with NAA and to T attenuation or possible nondetection of the H signal from ethanol bound at the surface of cell membranes and partitioned into the hydrophobic core of membrane lipids. © 1991 Academic Press, Inc.

Volume-selected 1H NMR spectroscopy was combined with spectral editing to selectively detect brain metabolites. The SPACE localization sequence was used to create a voxel of zeta-magnetization which could then be edited for any scalar coupled metabolite by the use of selective excitation in the ECZOTIC sequence to generate longitudinal spin order. The sequence returns an edited signal with no intrinsic loss of magnetization. The method was applied to observe approximately 10 mM ethanol and 17 mM lactate in the brain of a dog.

The volume selection technique SPACE has been combined with a two-dimensional multiple-quantum editing sequence to uniquely detect certain J-coupled cerebral metabolites. In vivo results demonstrating edited glutamate/glutamine and lactate from 0.4 ml of a rat's brain at 4.7 T are presented. The sequence was optimized to balance multiple-quantum generation and signal loss due to T2 relaxation. Without due regard to T2 relaxation little signal is observed.

We present theory and simulations for a spectral narrowing scheme for laser diode arrays (LDAs) that employs optical feedback from a diffraction grating. We calculate the effect of the so-called smile of the LDA and show that it is possible to reduce the effect by using a cylindrical lens set at an angle to the beam. The scheme is implemented on a 19-element LDA with smile of 7.6 microm and yields frequency narrowing from a free-running width of 2 to 0.15 nm. The experimental results are in good agreement with the theory.

Two new polypropionates, caloundrin B (11), systematic name (1″R,2R,3″R,4R,5S,5″R,6S,-7″R,8″S,9″S,10″R)-2-(6′-ethyl-3′,5′-dimethyl-4′-oxopyran-2′-yl)-6-(5″-ethyl-7″-hydroxy-8″,9″,10″-trimethyl-2″,4″,6″-trioxatricyclo[3.3.1.13,7]dec-3″-yl)-5-hydroxy-4-methylheptan-3-one, and funiculatin A (12), systematic name (2ξ,1′S,4R,5′S,6′S)-2-(1′-ethyl-4′,6′,8′-trimethyl-2𔈀,9′-dioxabicyclo[3.3.1]nona-3′,7′-dien-3′-yl)-4,6-dimethylnon-6-en-3-one, have been isolated from Siphonaria zelandica and S. funiculata respectively. The structures of the new compounds were deduced by two-dimensional n.m.r. spectroscopy, particularly long-range 13C- 1H correlation spectroscopy (HMBC), by biosynthetic reasoning and by comparison with the known polypropionates denticulatin A (5), siphonarin B (8), muamvatin (9) and baconipyrone C (14). Information about the relative stereochemistry of the tricyclic ring system of (11) and the bicyclic ring system of (12) was deduced from coupling constant values, and by n.O.e. difference and NOESY experiments, and was confirmed by molecular modelling studies. The relative stereochemistry of the side chains and the absolute stereochemistry were inferred from biosynthetic comparison with the above known polypropionates, and by correlation of funiculatin A with denticulatin A (5) of known absolute stereochemistry. The stereochemistry at C10 of funiculatin A (position 2 of the non-6-en-3-one chain) could not be unambiguously determined. A third new polypropionate funiculatin B, epimeric with funiculatin A at C10, was isolated and partially characterized.

Exploitation of mu ltiple-quantum (MQ) and zero-quantum (ZQ) coherences generated between scalar-coupled nuclei for selective spectral editing of metabolite signals has recently received much attention (I-4). Perhaps the ma in disadvantages associated with reported methods are their reliance on accurate subtraction ( 1)) a ma jor concern for in vivo applications where dominant water and lipid resonances may interfere, and the need for two-dimensional spectroscopy to extract the metabolite signal (2). In a one-dimensional method (3, 4)) selective excitation and pulsed field gradients were emp loyed to select ZQ coherence exclusively, giving good spectral editing and solvent suppression in a single scan. However, these methods suffer significant signal-to-noise loss since both ZQ and MQ coherences are generated but only one is eventually converted to an observable single-quantum (SQ) signal, the other being dephased by a field gradient or eliminated by phase cycling. In the case of ZQ coherence selection, a maximum of one-quarter of the coherence is available following gradient application and the efficiency of a desired MQ coherence formation may be dependent upon the mu ltiplicity of the spin-spin coupling, for example, in ethanol, where SQ and triple-quantum (TQ) components are lost (4). Selective polarization transfer methods have also been proposed but these also result in reduced signal due to the direction of the transfer (5) or through the dependency of the polarization transfer efficiency on RF pulse angle (4) and may require extensive phase cycling (6). Here we describe a procedure, ECZOTIC (editing via correlated z order with total inherent coherence), in which all metabolite coherence is selectively converted to correlated z order, or longitudinal two-spin order ( 7)) in a manner similar to that of the INEPT experiment (8), and, following pulsed field gradient dephasing of other signals, is converted to observable SQ coherence with maximum signal return. The insensitivity of ZQ coherence to field inhomogeneity is well known and is the basis of the editing techniques ment ioned above (2-4). However, correlated z order, like all longitudinal magnetization, is also invariant in the presence of a field gradient and provides an alternative approach to spectral editing. The method is readily applied

Induction of iron overload in mice using 1% (w/w) dietary carbonyl iron resulted in marked decreases in 1H and 31P NMR relaxation times. Natural-abundance deuterium (2H) NMR spectroscopy has been used to measure 2H T1 values in vivo in the presence of body paramagnetic iron. This procedure offers a method for noninvasive determination of body iron stores.

A new method for selective observation of scalar coupled metabolites by either zero-quantum coherence transfer or polarization transfer with concurrent water suppression in a single acquisition was developed. Gaussian shaped RF pulses were used to selectively generate multiple-quantum and zero-quantum coherence in the metabolite of interest, single quantum (including water) and double quantum coherences were then dephased under the influence of a B0 field gradient and the surviving zero-quantum coherence was converted to observable metabolite signal. The duration of the gradient application and the frequency and angle of the final selective read pulse determined whether a polarization transfer or a coherence transfer signal was observed. Water suppression factors of around 8000 were achieved which allowed operation of the receiver at high gain levels resulting in greatly improved signal to noise in the metabolite spectra. The CH3 and CH resonances of lactate in a mouse brain homogenate were selectively edited and the method was also applied to selective editing of ethanol.

A single slice of z-magnetization is used to generate high-speed images. The slice selection step is achieved using two sin-sinc pulses. This procedure eliminates the need for continual slice gradient reversal, a requirement for the FLASH technique. The RAPID imaging method has less inherent T1 and/or T2 dependence than current fast imaging methods and is more sensitive.

Water-suppression techniques can be divided into two types, those that result in zero net excitation of the water resonance and those in which the water magnetization is randomized prior to observation of the spectrum of interest. The randomization mechanism may involve selective irradiation, use of natural spin relaxation, or application of a homospoil gradient pulse to dephase selectively excited transverse spin coherence. Destruction techniques considered in this paper will involve the latter of these processes. Nonexcitation methods usually involve a binomial-type pulse cluster which results in off-resonance excitation but zero net rotation on resonance ( 1). Although the water-suppression factor of these methods is usually high ( > 1000)) they suffer from the major limitation that the spectral response is either not flat and/ or there is a large linear phase distortion of the spectrum. Destruction techniques are attractive because the final read pulse can be a hard 90” pulse which ensures uniform excitation of the spectrum with minimal phase distortion. The aim of these methods is the establishment of (S,) = (3,) = (&) = 0 over some selective band in frequency space. For those that utilize a pulsed field gradient, selectivity is achieved by the application of a shaped RF pulse which generates transverse spin coherence over a narrow band and the coherence is dephased by the field gradient. In a previous paper (2) we discussed the difficulties of maintaining high-resolution conditions (Au < 1 Hz) during data acquisition following a field gradient pulse. The major problems can be overcome by preemphasis of the gradient pulse and by applying a correction current through the Z0 coil during data acquisition to ensure that the static magnetic field is stable. Decoupling of the gradient coils from the magnet, shim set, and bore tubes by shielding and isolation may also alleviate these induced eddy current problems. In this paper we consider the nature of the shaped pulse to achieve the optimum water suppression. As well, we introduce a new mechanism to achieve water suppression using a pulsed field gradient and a selective noise pulse. All spectra were obtained on a Bruker MSL-200 spectrometer interfaced to an Oxford Instruments 4.7 T, 13 cm vertical bore magnet. Gradient pulses and Z0 correction were controlled by a Bruker MSL preemphasis unit and were applied to the

The apparent stability constants (K) of the cryptates [AgβC21C5]+ and [Na·C21C5]+ (C21C5 = 4,7,13-trioxa-1,10-diazabicyclo[8.5.5]eicosane) have been determined in a range of solvents. For [Na·C21C5]+ log (K/dm3 mol−1) = 2.87, 3.72, 3.76, 3.98, 5.08 and 5.12 at 298.2 K in dimethylformamide, pyridine, methanol, acetone, acetonitrile and propylene carbonate, respectively, in the presence of 0.05 mol dm−3 tetraethylammonium perchlorate supporting electrolyte. These values are substantially lower than those observed for [Na·C211]+ (C211 = 4,7,13,18-tetraoxa-1,10-diazabicyclo[8.5.5]eicosane) and this is attributed to the presence of one less oxygen atom in C21C5 than in C211. A similar relationship is observed for [Ag·C211]+ and [Ag·C21C5]+, where, for the latter cryptate, log (K/dm3 mol−1) = 5.19

1H NMR studies of glycolysis in washed cell suspensions of Streptococcus faecalis indicated that intracellular lactate is not 1H NMR visible. Evidence for this was gained from time course studies of glycolysis at increasing concentrations of glucose. A close correlation existed between the relative increase in the lactate integral and the enzymatically determined extracellular lactate concentration [Lo]. When ionophores which cause the collapse of the positive intracellular/extracellular lactate gradient were added to cell suspensions following fermentation of 5, 10 and 50 mM glucose, the increase in the lactate integral was proportional to the respective increase in [Lo]. A more direct method for determining the origin of the lactate signal involved centrifugation of a cell suspension after fermentation of 50 mM glucose and measurement of lactate in the extracellular and intracellular fluid. 1H spectra of the cell suspension, supernatant and sonicated pellet revealed that the lactate observed in the cell suspension was equivalent to the lactate in the supernatant alone. The intracellular lactate contained in the pellet represented 42% of the total lactate, indicating that only 58% of lactate is detected by in vivo 1H MRS of S. faecalis. This result is in contrast with the high percentage (70-90%) of in vitro lactate which is detected by in vivo 1H MRS of mammalian brain tissue (Williams S. R. et al. Magn. Res. Med. 7, 425-431, 1988). This may be due to a higher proportion of extracellular lactate in mammalian tissue or differences in the intracellular environments of bacterial and mammalian cells.

Successful in vivo NMR spectroscopy requires a combination of techniques to address the problems of volume selection, water suppression, and resolution. All this needs to be done in the very heterogeneous environment found in living organisms. Previously published techniques are used to obtain H spectra from a dog brain, observing metabolites with concentrations below 1 mM. Measurements of spin‐lattice relaxation times (T) are also presented. The H relaxation times are long (T > 1.0 s) yielding information about the fluidity of the molecular environment. Comments are made concerning the achievable linewidth in vivo and the deficiencies that phase‐encoding spectroscopic methods may have in obtaining high‐resolution H spectra. © 1989 Academic Press, Inc.

Natural abundance deuterium NMR spectroscopy can be used to characterise in vivo2H signals arising from water and fat in mice, with acquisition times of less than two minutes. Administration of D2O (10% V V ) in the drinking water enhances these signals so that excellent spectra can be obtained with one scan. Using these procedures the in vivo turnover of 2H in water and fat in mice has been determined. This procedure may be of particular importance in studies of fat turnover in obesity.

A method based on zero-quantum coherence transfer for spectral editing of metabolites in aqueous solution in a one-dimensional experiment is described. Water suppression factors of approximately 8000 were achieved by the use of pulsed B0 field gradients and excellent editing was obtained in a single acquisition. The methyl resonances of both lactate and acetaldehyde were readily observed in a mouse brain homogenate by generating zero-quantum coherence using Gaussian pulses for selective excitation of the respective CH resonances.

When developing new techniques for NMR imaging and in vivo spectroscopy it is a major advantage to be able to calculate the magnetization slice profiles, at any point during a pulse sequence in the presence of a field gradient. While this has frequently been done by treating the problem as a number of discrete resonances, it is sometimes necessary to consider the continuous nature of the magnetization profiles. This paper describes a method used to simulate the free-induction decay at any point during the NMR experiment.

A method (NIMBLE) for obtaining optimum B0 field homogeneity at voxels located away from the magnet isocenter for use in volume-selected NMR spectroscopy is described. Voxels may be shimmed using only first-order X, Y, and Z shims to produce three-dimensional shim current maps, thus avoiding shim coupling problems. NIMBLE shimming prior to volume selection ensures optimum spectral resolution and improves the efficiency and accuracy of the volume-selection experiment. The benefits of the technique are illustrated by a high-resolution volume-selected spectrum of human tibia marrow.

A novel method for reducing the rf power requirements of selective pulses employed for z magnetization slice inversion in localized NMR spectroscopy is presented. Following slice preparation by the use of frequency‐incremented sine pulses, the slice gradient is reduced, which narrows the frequency width of the slice. This allows the use of relatively low‐power selective inversion pulses, an important consideration for in vivo applications. © Academic Press, Inc.

In the solid and solution state Li+ and Na+ form inclusive and exclusive cryptâtes respectively with C21Cs, in which Li+ resides inside and Na+ resides outside the C2IC5 cavity. Similar inclusive and exclusive structures are observed for [Li.C211]+ and [Na.C211]+. The logarithms of the stability constants in dimethylformamide for [Li.C21C5] +, [Li.C211]+, [Na.C21C5]+ and [Na.C211]+ are: 2.80, 6.99, 2.87 and 5.20; and the corresponding decomplexation rate constants are: 107, 0.013, 28800 and 12 s-1 at 298.2 K. The relationships between cryptate structure, stability and lability are considered, as are solvent influences.

The combination of a frequency nonselective excitation suppression method (1331 sequence) with selective excitation followed by gradient‐induced dephasing of water transverse magnetization yielded suppression ratios of greater than 10,000:1. The need for gradient preemphasis and correction of Bo field shifts is discussed. The suppression efficiency of this method compared favorably to results obtained using the CPMG spin‐ echo technique to observe metabolite resonances in a urine sample. © 1989 Academic Press, Inc.

Four of the techniques proposed for in vivo volume‐selected NMR spectroscopy have been compared using a simple phantom with a large background water signal which was outside the region of interest. The methods VSE, SPACE, SPARS, and DIGGER all use pulsed field gradients for spatial encoding and were tested with a symmetric and an asymmetric phantom. SPACE was used to obtain volume‐selected H NMR spectra of a human leg, demonstrating excellent discrimination between bone marrow and muscle. © 1987 Academic Press, Inc.

An apparatus is described that facilitates the determination of incorporation levels of isotope labelled, gaseous precursors into volatile insect-derived metabolites. Atmospheres of varying gas compositions can be generated by evacuation of a working chamber followed by admission of the required levels of component gases, using a precision, digitised pressure read-out system. Insects such as fruit-flies are located initially in a small introduction chamber, from which migration can occur downwards into the working chamber. The level of incorporation of labelled precursors is continuously assayed by the Solid Phase Micro Extraction (SPME) technique and GC-MS analyses. Experiments with both Bactrocera species (fruit-flies) and a parasitoid wasp, Megarhyssa nortoni nortoni (Cresson) and oxygen-18 labelled dioxygen illustrate the utility of this system. The isotope effects of oxygen-18 on the carbon-13 NMR spectra of 1,7- dioxaspiro[5,5]undecane are also described.

Volume-localized proton nuclear magnetic resonance spectroscopy was used as an assay of regional biochemistry in the isolated perfused rat kidney. This model eliminated artifacts caused by respiratory and cardiac motion experienced in vivo. Immersion of the kidney under its venous effluent reduced the susceptibility artifacts evoked by tissue-air interfaces. The rapid acquisition with relaxation enhancement imaging sequence was used for scout imaging. This gave excellent spatial resolution of the cortex, outer medulla, and inner medulla. Spectra were then acquired in 10 minutes using the volume-selective multipulse spectroscopy sequence from voxels with a volume of approximately 24 microL located within the cortical or medullary regions. Spectral peaks were assigned by the addition of known compounds to the perfusion medium and by comparison with spectra of protein-free extracts of cortex and medulla. The medullary region spectra were characterized by signals from the osmolytes betaine, glycerophosphorylcholine, and inositol. The spectra from the cortex were more complex and contained lesser contributions from osmolytes.

Brown allylation methodology has been employed to provide seven of the eight possible isomers of the (ZE)(EZ) spiroacetal system representing the CD ring fragment (C17-C28) of spongistatin 1. The stereochemistry of the isomers follows from high-field NMR examinations which furnish insights into the trends in the NMR data for these ketal structures.

Sodium-23 n.m.r. studies of the exchange of Na+ between the solvated and Na+·C211 environments show that the cryptate dissociation rate constant kd(335 K)= 1053.6±4.1, 832.7±5.0 and 554.8±3.2, ΔH‡= 67.2±0.3, 69.5±0.4 and 83.5±0.5 kJ mol–1 and ΔS‡= 12.6±0.7, 17.4±1.2 and 55.9±1.2 J K–1 mol–1 in water, dimethyl sulphoxide and dimethylformamide, respectively. Both 13C and 23Na n.m.r. studies indicate that Na+·C211 exists predominantly in the exclusive form in solution whereas Li+·C211 exists predominantly in the inclusive form. These data are discussed in terms of the two sequential equilibria: [graphics ommitted]. Mechanistic discussion is also extended to larger cryptates.

19 F n.m.r. studies of the inclusion of o-, m-, p- and α-fluoro-trans-cinnamates and o, p- and α,p-difluoro-trans-cinnamates by α-cyclodextrin (αCD) have shown that two inclusion equilibria [graphic omitted] are established in D2O solution at pD = 8.5 ± 0.1. Typically at 294 K, K1= 111 ± 13 dm3 mol–1 and K2= 23 ± 2 dm3 mol–1 for α,p-difluoro-trans-cinnamate. Chemical-shift and other data indicate that the predominant S·αCD complex is that in which the carboxylate group of the fluorocinnamate enters the wide end of the αCD cavity, delineated by twelve secondary hydroxy groups, first. The S·(αCD)2 complex probably has a structure in which the fluoro-trans-cinnamate is encapsulated by two αCD with the wide ends of their cavities in close proximity.

The crystal structures of the cryptates formed between sodium ion and 4,7,1 3,18-tetraoxa-1,10-diazabicyclo[8.5.5]icosane, [Na(L1)(NCS)], and 4,7,13-trioxa-1,10-diazabicyclo[8.5.5]icosane, [Na(L3)(NCS)], have been determined by single-crystal X-ray diffraction methods at 295 K and refined by least-squares methods to conventional R values of 0.069 and 0.039 for 1 417 and 2 259 reflections respectively. The respective crystals were of space group Pcab with a= 14.686(3), b= 15.699(4), c= 16.522(5)A, and Z= 8; and P21/n with a= 9.947(2), b= 15.681(4), c= 12.460(3)A, β= 95.27(2)°, and Z= 4. Both [Na(L1)(NCS)] and [Na(L3)(NCS)] exist in the ‘exclusive’ form in which Na+ is located 0.14 and 0.37 A respectively above the planes defined by the three oxygen atoms of the 15-membered cryptand rings. The 13C n.m.r. spectra of these cryptates are consistent with the retention of the exclusive structures in solution whilst the 13C n.m.r. spectra of the analogous Li+ cryptates indicate that they possess ‘inclusive’ structures in solution. Preliminary 23Na n.m.r. data show the rate of Na+ dissociation from [Na(L1)]+ to be significantly less than that from [Na(L3)]+ as indicated by dissociation rate constants (298.2 K) of 12.1 ± 0.2 and (2.88 ± 0.02)× 104 s–1 respectively determined in N,N-dimethylformamide solvent.