Proton-decoupled partially relaxed Fourier transform (PRFT) NMR of carbon-13 in natural abundance was used to determine spin–lattice relaxation times (T1) of individual carbons in solutions of cholesteryl chloride, sucrose, and adenosine 5′-monophosphate (AMP) at 15.08 MHz and 42°C. With the exception of a few side-chain groups, all protonated carbons have T1 values of less than 1 sec. Some side-chain carbons on cholesteryl chloride show evidence of internal reorientation and have relaxation times of up to 2 sec. Nonprotonated carbons have T1 values in the range 2–8 sec. These relaxation times are sufficiently short to make ordinary Fourier transform NMR a very sensitive technique in the study of complex molecules without the need for spin-echo refocusing schemes. Integrated intensities and nuclear Overhauser enhancements prove that, except for two of the three nonprotonated carbons in AMP, all 13C nuclei in these compounds relax mainly through 13C–1H dipolar interactions. Measured T1 values of protonated carbons were used to determine rotational correlation times. The ring backbone of 1M cholesteryl chloride in CCl4 reorients isotropically with a correlation time of 9 × 10−11 sec. Methyl groups directly attached to the backbone show evidence of internal motion with a correlation time ≲ 5 × 10−12 sec. A comparison of T1 values on the side group attached at C-17 indicates that the effect of internal motion is greatest for carbons near the free end. The two rings in sucrose behave as a single rigid entity reorienting isotropically with correlation times of 7 × 10−11 and 3 × 10−10 sec for 0.5M and 2M aqueous solutions, respectively. There is evidence for internal reorientation of the CH2OH side chains, with a correlation time much longer than that of methyl groups in cholesteryl chloride. The adenine group of 1M aqueous AMP is more restricted in its rotational motion than the sugar moiety. It appears that PRFT NMR spectra will be a useful addition to the arsenal of spectrochemical techniques. Relaxation times measured from PRFT spectra can be used in assignments. Furthermore, resonances that are unresolved in the normal spectrum, can be separated in PRFT spectra if the overlapping peaks arise from carbons with appreciably different T1 values.

Sodium-23 N M R at 26.46 M H z has been used to study cation binding in a perfluorosulfonate ion exchange resin (Nafion) as a function of water content and temperature. A large chemical shift change (-130 ppm) and line width increase are seen upon decreasing the water content from 30 to 1%. These effects are reversed with increasing temperature. The data can be interpreted in terms of a fast equilibrium between bound and unbound, but loosely associated, cations in the hydrophilic regions of the material. A larger fraction of cations is bound with decreasing water content and temperature. The large change in chemical shift points to the formation of contact ion pairs. The data suggest the presence of three or four water molecules in the first hydration sphere of the sodium ions. The 23Na N M R behavior is consistent with a reversed micelle model of Nafion.

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Recent findings using volumetric MRI techniques have revealed that patients with combat-related and noncombat-related posttraumatic stress disorder (PTSD) have reductions in right hippocampal volume. Twenty-one veterans with PTSD and eight age-matched control veterans were studied using proton magnetic resonance spectroscopy to test the hypothesis that the N-acetyl-L-aspartic acid/creatine (NAA/Cr) ratio would be decreased in the right medial temporal lobe structures of patients with PTSD compared to controls. Patients with PTSD displayed significantly lower NAA/Cr ratio for the right medial temporal lobe relative to the left (P < or = 0.011). Patients with PTSD also had lower NAA/Cr in right medial temporal lobe (P < or = 0.013) and lower choline/Cr in left medial temporal lobe (P < or = 0.030) compared to control subjects. Because NAA is regarded as an indicator of neuronal density, this finding suggests that the neuronal density of right-sided medial temporal structures in patients with combat-related PTSD may be decreased.

The behavior of the lithium (Li) ion in normal human erythrocytes has been studied by 7Li NMR. The uptake of Li into the cells was followed as a function of solution conditions, temperature, hematocrit, and blood age using dysprosium tripolyphosphate shift reagent. Under our conditions the uptake of Li increases with increasing hematocrit and blood age. For packed cells the extracellular 7Li spin-lattice relaxation time was only slightly longer than the intracellular relaxation time. Thus, T1 may not be useful for separate observation of intra- and extracellular Li in vivo. The intra- and extracellular T2s were substantially shorter than the corresponding T1s. Also, the intracellular T2 was considerably shorter than that for the extracellular compartment, suggesting that T2 may provide a noninvasive handle for observation of intracellular Li. Nuclear Overhauser enhancements could be observed for both extra- and intracellular 7Li, confirming that dipolar coupling to 1H is a contributing relaxation mechanism. The 7Li NMR visibility was essentially 100% at high Li concentrations, decreasing to about 84% at 1 mM Li. Based on time course studies of the invisibility, and a comparison of NMR and inductively coupled plasma results, it appears that the invisibility of the intra- and extracellular compartments for packed cells is the same. Although a 23Na double-quantum signal could be observed for red blood cells, no double-quantum signal was observed for 7Li.