Differentiating brown and white adipose tissues by high-resolution diffusion NMR spectroscopy.

There are two types of fat tissues, white adipose tissue (WAT) and brown adipose tissue (BAT), which essentially perform opposite functions in whole body energy metabolism. There is a large interest in identifying novel biophysical properties of WAT and BAT by a quantitative and easy-to-run technique. In this work, we used high-resolution pulsed field gradient diffusion NMR spectroscopy to study the apparent diffusion coefficient (ADC) of fat molecules in rat BAT and WAT samples. The ADC of fat in BAT and WAT from rats fed with a chow diet was compared with that of rats fed with a high-fat diet to monitor how the diffusion properties change due to obesity-associated parameters such as lipid droplet size, fatty acid chain length, and saturation. Feeding a high-fat diet resulted in increased saturation, increased chain lengths, and reduced ADC of fat in WAT. The ADC of fat was lower in BAT relative to WAT in rats fed both chow and high-fat diets. Diffusion of fat was restricted in BAT due to the presence of small multilocular lipid droplets. Our findings indicate that in vivo diffusion might be a potential way for better delineation of BAT and WAT in both lean and obese states.

Long-lived spin state of a tripeptide in stretched hydrogel.

The longitudinal (T 1), transverse (T 2), and singlet state (T s) relaxation times of the geminal backbone protons (CH2) of L-Leu-Gly-Gly were studied by NMR spectroscopy at 9.4 T in a bovine hide gelatin gel composed in D2O at 25 °C. Gelatin granules were dissolved in a hot solution of the tripeptide and then the solution was allowed to gel inside a flexible silicone tubing. With increases in gelatin content, the T 2 and T s of the CH2 protons correspondingly decreased (T s/T 2 ~ constant), while the change in T 1 was relatively small. The largest observed T s/T 1 value was 3.3 at 46% w/v gelatin that was the lowest gelatin content examined. Stretching the tubing, and hence the gel, brought about anisotropic alignment of the constituents resulting in residual quadrupolar splitting of the resonance from D2O in (2)H NMR spectra, and residual dipolar splitting of the CH2 resonance in (1)H NMR spectra. WALTZ-16 decoupling during the relaxation intervals extended the singlet state relaxation time, but the efficacy diminished as the gels were stretched. Theoretically predicted T 1, T 2, and T s values, assuming intramolecular dipolar coupling as the only source of relaxation, were within the same order of magnitude as the experimentally observed values. Overall we showed that it is possible to observe a long-lived spin state in an anisotropic medium when T 2 is shorter than T 1 in the presence of non-zero residual dipolar couplings.

From sulfur-amine solutions to metal sulfide nanocrystals: peering into the oleylamine-sulfur black box.

In this Article, we present our findings on the formation of metal sulfide nanocrystals from sulfur-alkylamine solutions. By pulsed field gradient diffusion NMR along with the standard toolbox of 1D and 2D NMR, we determined that sulfur-amine solutions used as a sulfur precursor exist as alkylammonium polysulfides at low temperatures. Upon heating to temperatures used in nanocrystal synthesis, the polysulfide ions react with excess amine to generate H(2)S, which combines with the metal precursor to form metal sulfide. Four different reaction pathways were found, each of which produced H(2)S and the byproducts identified in this Article. Thioamides were identified as an intermediate and were shown to exhibit much more rapid kinetics than sulfur-alkylamine solutions at low temperatures in the synthesis of metal sulfide nanocrystals.

Optimum pulse flip angles for multi-scan acquisition of hyperpolarized NMR and MRI.

The optimum pulse flip angles were calculated for multi-scan acquisition of hyperpolarized NMR and MRI. The derived formulae could be correlated with the best angle for ordinary steady-state acquisition, the so-called Ernst angle. Although single-scan acquisition has been popular in hyperpolarized measurements, signal accumulation by increasing scans may become very effective for improving the total signal gain, especially when the sample's longitudinal spin relaxation time is long. The optimum angles were calculated from theoretical relations between the exponential of the pulse repetition time/relaxation time ratio and the total scan counts. Constant and variable flip angle cases are presented, both of which yield similar cumulative signal amplitudes. For the constant angle case, a numerically calculated semi-universal curve is presented for the rough estimation of the best angle, as the results were not significantly dependent upon the degree of hyperpolarization within the realistic range. Meanwhile, for the variable angle case, the best angles were approximated from a clean trigonometric series relation, in which the initial pulse became near the Ernst angle and the last pulse was always 90 degrees . A modification of the variable angle scheme enables the acquisition of uniform signal amplitude throughout all scans.