A selective excitation/B0 gradient technique for high-resolution 1H NMR studies of metabolites via zero-quantum coherence and polarization transfer.

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

Quadrature detection in F1 induced by pulsed field gradients

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

Localized 1H NMR spectroscopy of rat spinal cord in vivo

A movable, actively decoupled surface coil has been employed to obtain a localized H-1 NMR spectrum from the lumbosacral spinal cord of a live Lewis rat. A volume selective 'VOSY' normally spelled out as 'volume selective spectroscopy' spectroscopy pulse sequence that incorporates ''phase ramped'' selective RF pulses, has been used to minimize random phase jitter in the NMR signal as a result of the large frequency shifts required to locate the voxel in the center of the cord while using intense gradient pulses. Spectra from 13-mu l voxels in healthy rats and in rats inoculated with guinea pig spinal cord and complete Freund's adjuvant, resulting in experimental autoimmune encephalomyelitis, are shown

The 1H NMR visibility of intracellular lactate in Streptococcus faecalis

H NMR studies of glycolysis in washed cell suspensions of Streptococcus faecalis indicated that intracellular lactate is not H 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. H 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 H 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 H 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

Fugitive emission source characterization using a gradient-based optimization scheme and scalar transport adjoint

Fugitive emissions are important sources of greenhouse gases and lost product in the energy sector that can be difficult to detect, but are often easily mitigated once they are known, located, and quantified. In this paper, a scalar transport adjoint-based optimization method is presented to locate and quantify unknown emission sources from downstream measurements. This emission characterization approach correctly predicted locations to within 5 m and magnitudes to within 13% of experimental release data from Project Prairie Grass. The method was further demonstrated on simulated simultaneous releases in a complex 3-D geometry based on an Alberta gas plant. Reconstructions were performed using both the complex 3-D transient wind field used to generate the simulated release data and using a sequential series of steady-state RANS wind simulations (SSWS) representing 30 s intervals of physical time. Both the detailed transient and the simplified wind field series could be used to correctly locate major sources and predict their emission rates within 10%, while predicting total emission rates from all sources within 24%. This SSWS case would be much easier to implement in a real-world application, and gives rise to the possibility of developing pre-computed databases of both wind and scalar transport adjoints to reduce computational time

A precision apparatus, with solid phase micro-extraction monitoring capability, for incorporation studies of gaseous precursors into insect-derived metabolites

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