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1,4,52-Deoxy-D-glucose (2DG) is a known surrogate molecule that is useful for inferring glucose uptake and metabolism. Although 13 C-labeled 2DG can be detected by nuclear magnetic resonance (NMR), its low sensitivity for detection prohibits imaging to be performed. Using chemical exchange saturation transfer (CEST) as a signal-amplification mechanism, 2DG and the phosphorylated 2DG-6-phosphate (2DG6P) can be indirectly detected in 1 H magnetic resonance imaging (MRI). We showed that the CEST signal changed with 2DG concentration, and was reduced by suppressing cerebral metabolism with increased general anesthetic. The signal changes were not affected by cerebral or plasma pH, and were not correlated with altered cerebral blood flow as demonstrated by hypercapnia; neither were they related to the extracellular glucose amounts as compared with injection of D-and L-glucose. In vivo 31 P NMR revealed similar changes in 2DG6P concentration, suggesting that the CEST signal reflected the rate of glucose assimilation. This method provides a new way to use widely available MRI techniques to image deoxyglucose/glucose uptake and metabolism in vivo without the need for isotopic labeling of the molecules. Keywords: 2-deoxyglucose; glucose; glucoCEST; magnetic resonance imaging; metabolism INTRODUCTIONThe rate of glucose uptake and its conversion into subsequent metabolites are important biomarkers of cellular function. Since the seminal work of Sokoloff et al, 1 isotopically labeled 2-deoxy-Dglucose (2DG) has been established as a way to measure glucose metabolism; this is based on the observation that 2DG enters cells by the same transporters as glucose (e.g., mostly GLUT-1 and GLUT-3 in the brain). It is phosphorylated by hexokinase into 2DG-6-phosphate (2DG6P) but only minimally metabolized further via glucose-6-phosphate dehydrogenase in the oxidative pentose phosphate pathway, and glucose-6-phosphate isomerase in the glycolytic pathway, because of the lack of a hydroxyl group on carbon atom 2 (C2). As the amount of glucose-6-phosphatase that catalyzes the hydrolysis of 2DG6P to 2DG is low in mammalian brain, and having low membrane permeability 2DG6P becomes trapped in brain cells for many hours.2 By quantifying the amount of 2DG and 2DG6P, the glucose metabolic rate can be estimated via compartmental modeling.

While NMR is the most used analytical method for determining the molecular structure of isolated chemical entities, small compounds as well as macromolecules, its capability of analysing complex mixtures is less known. The advent of Diffusion Ordered SpectroscopY (DOSY) NMR has made diffusion experiments popular, enabling diffusion coefficients to be routinely measured and used to characterize chemical systems in solution. Indeed, since the translational diffusion coefficients of molecular species reflect their effective sizes and shapes, DOSY NMR allows the separation of the chemical entities present in multicomponent systems and, as in all diffusion NMR experiments, provides information on their intermolecular interactions as well as on their size and shape. The main aim of this review is to present an overview of the DOSY NMR mapping and its applications. The paper starts with a brief introduction to pulsed-field gradient (PFG) NMR and then focuses on the methodological procedures that can be used to perform good diffusion data acquisition and to obtain good-quality DOSY maps. The second part describes, through selected literature examples, different applications of DOSY NMR to demonstrate the potential of the method for (i) unravelling the components of complex matrices comprising pharmaceuticals, dietary supplements, foods and beverages, and biological extracts, and (ii) probing intermolecular interactions and evaluating association constants between different hosts and guests, as well as estimating the sizes and molecular weights of molecular species.

The binding of block copolymer Pluronic F-127 in aqueous dispersions of single- (SWCNT) and multiwalled (MWCNT) carbon nanotubes has been studied by pulsed-field-gradient (PFG) (1)H NMR spectroscopy. We show that a major fraction of polymers exist as a free species while a minor fraction is bound to the carbon nanotubes (CNT). The polymers exchange between these two states with residence times on the nanotube surface of 24 ± 5 ms for SWCNT and of 54 ± 11 ms for MWCNT. The CNT concentration in the solution was determined by improved thermal gravimetric analysis (TGA) indicating that the concentration of SWCNT dispersed by F-127 was significantly higher than that for MWCNT. For SWCNT, the area per adsorbed Pluronic F-127 molecule is estimated to be about 40 nm(2).

Several investigations have recently reported the combined use of pulsed field gradient (PFG) with magic angle spinning (MAS) for the analysis of molecular mobility in heterogeneous materials. In contrast, little attention has been devoted so far to delimiting the role of the extra force field induced by sample rotation on the significance and reliability of self-diffusivity measurements. The main purpose of this work is to examine this phenomenon by focusing on pure liquids for which its impact is expected to be largest. Specifically, we show that self-diffusion coefficients can be accurately determined by PFG MAS NMR diffusion measurements in liquids, provided that specific experimental conditions are met. First, the methodology to estimate the gradient uniformity and to properly calibrate its absolute strength is briefly reviewed and applied on a MAS probe equipped with a gradient coil aligned along the rotor spinning axis, the so-called 'magic angle gradient' coil. Second, the influence of MAS on the outcome of PFG MAS diffusion measurements in liquids is investigated for two distinct typical rotors of different active volumes, 12 and 50 microL. While the latter rotor led to totally unreliable results, especially for low viscosity compounds, the former allowed for the determination of accurate self-diffusion coefficients both for fast and slowly diffusing species. Potential implications of this work are the possibility to measure accurate self-diffusion coefficients of sample-limited mixtures or to avoid radiation damping interferences in NMR diffusion measurements. Overall, the outlined methodology should be of interest to anyone who strives to improve the reliability of MAS diffusion studies, both in homogeneous and heterogeneous media.

The pulsed field gradient spin‐echo nuclear magnetic resonance method is used to measure the translational diffusion of solvents and solutes in homogeneous and heterogeneous systems. It is widely used in the characterization of molecules and materials in general, via phenomena such as ‘diffusion interference’. It is also the basis of tissue discrimination in magnetic resonance imaging, via diffusion tensor imaging. The mathematical equation used to analyze data from a simple noninteracting solute (using a pair of magnetic field gradient pulses that are applied in the experiment) was first derived by Stejskal and Tanner. However, in the article and in subsequent presentations the basic derivation, which we call the the “theoretical physics” of the theory, is not presented in extenso. Conversely, many papers in which the exploration of the effects of magnetic field gradient pulses of shapes other than simple rectangles generally begin with the time‐dependent integral that emerges from the original theoretical physics. To fill this “pedagogical gap” we use here a rigorous step‐by‐step approach to the theoretical physics of the Stejskal–Tanner equation and indicate how it was based on earlier theories. We also take the opportunity to indicate a contemporary approach to deriving new relationships between user‐defined magnetic field gradient pulse shapes and the diffusion coefficient; and we show how these can be rapidly and accurately derived using symbolic computation. © 2012 Wiley Periodicals, Inc. Concepts Magn Reson Part A 40A: 205–214, 2012.

Ion flow in many voltage-gated K؉ channels (VGK), including the (human ether-a-go-go-related gene) hERG channel, is regulated by reversible collapse of the selectivity filter. hERG channels, however, exhibit low sequence homology to other VGKs, particularly in the outer pore helix (S5) domain, and we hypothesize that this contributes to the unique activation and inactivation kinetics in hERG K ؉ channels that are so important for cardiac electrical activity. The S5 domain in hERG identified by NMR spectroscopy closely corresponded to the segment predicted by bioinformatics analysis of 676 members of the VGK superfamily. Mutations to approximately every third residue, from Phe 551 to Trp 563 , affected steady state activation, whereas mutations to approximately every third residue on an adjacent face and spanning the entire S5 segment perturbed inactivation, suggesting that the whole span of S5 experiences a rearrangement associated with inactivation. We refined a homology model of the hERG pore domain using constraints from the mutagenesis data with residues affecting inactivation pointing in toward S6. In this model the three residues with maximum impact on activation (W563A, F559A, and F551A) face out toward the voltage sensor. In addition, the residues that when mutated to alanine, or from alanine to valine, that did not express (Ala 561 , His 562 , Ala 565 , Trp 568 , and Ile 571 ), all point toward the pore helix and contribute to close hydrophobic packing in this region of the channel.

Break it up: Ordinarily, silica gel produces no separation in a mixture of aromatic molecules by HPLC; however, solid‐enhanced DOSY NMR spectroscopy succeeds in this task, although its separation capabilities concern just the spectral components. Chromatographic NMR spectroscopy may thus prove a simple complement to HPLC in favorable cases. MAS=magic‐angle spinning.