The effect of Magic Angle Spinning on proton spin-lattice relaxation times in some organic solids

Proton spectra of solids are usually broadened by strong proton homonuclear dipolar interactions. However, substantial line narrowing may be achieved by Magic Angle Spinning (MAS) in systems of low proton density or in systems in which rapid molecular motions occur. In such conditions, T1(H) measurements are often used to characterise the dynamics of each resolved proton site. We show that T1(H) values measured for solid organic compounds with high proton abundance, such as adamantane and glycine, may be strongly dependent on the spinning rate employed, so that care is required when values are compared. The effects of molecular motion and proton density on T1(H) and its dependence on spinning rate were investigated. We found that an increase in molecular motion leads to an increase of T1(H) at higher spinning rates. The opposite is found for systems with low proton densities which show relatively lower T1(H), at higher spinning rates. A possible interpretation is suggested in terms of the reduced spin diffusion efficiency at higher spinning rates.     

Measurement of spin-lattice relaxation times and kinetic rate constants in rat muscle using progressive partial saturation and steady-state saturation transfer

The determination of neomycin sulfate by liquid chromatography using a column packed with a poly(styrenedivinylbenzene) co-polymer and pulsed electrochemical detection on a gold electrode is described. The mobile phase consisted of an aqueous solution containing 70 g/l of sodium sulfate, 1.4 g/l of sodium 1-octanesulfonate and 50 ml/l of a 0.2 M phosphate buffer (pH 3.0). Sodium hydroxide was added post-column. The influence of the different chromatographic parameters on the separation was investigated. The method shows good linearity and repeatability and is stability indicating. A number of commercial samples was analyzed using this method and the results were compared with results obtained with the European Pharmacopoeia method and a previously described thin-layer chromatographic method.     

Binding of Ru(II) polyazaaromatic complexes to DNA: A 23Na NMR spin-lattice relaxation study

The possibility of using sodium-23 spin-lattice relaxation rate measurements to probe the interaction modes of Ru11 polyazaaaromatic complexes with DNA is investigated. The following complexes are considered: Ru(phen)3(2+) (phen = 1.10-phenanthroline), Ru(phen)2HAT2+ (HAT = 1,4,5,8,9,12-hexaazatriphenylene), and Ru(diMeTAP)3(2+) (diMeTAP = 2,7-dimethyl-1,4,5,8-tetraazaphenanthrene). The addition of Ru(diMeTAP)3(2+) to a solution of NaDNA leads to a decrease in the sodium-23 spin-lattice relaxation rate (R1) similar to the effect observed upon addition of Mg2+. This indicates that Ru(diMeTAP)3(2+) interacts like Mg2+ with DNA and consequently that the electrostatic interaction dominates the association with DNA, Ru(phen)3(2+) and Ru(phen)2HAT2+ diminish R1 more efficiently than Mg2+, in a manner similar to ethidium bromide, which is known for its intercalation properties. Thus interactions other than electrostatic occur between these two complexes and DNA. These results are in agreement with data obtained from other techniques, according to which Ru(phen)3(2+) and Ru(phen)2HAT2+ are located partially inside the DNA double helix, in contrast to Ru(diMeTAP)3(2+) which remains in the ionic atmosphere around the phosphate backbone.     

Frequency dependence of MR relaxation times. I. Paramagnetic ions

T1 and T2 of paramagnetic ions in free and chelated form were measured over the range of clinical magnetic resonance imaging field strengths (0.02-1.5 T). T1 values agreed with published data; however, to our knowledge, the field dependence of T2 has not been systematically studied before Mn2+, Cr3+, and Fe3+ all showed T2 reduction at high field strengths, although reduction due to Fe3+ was minimal. This is believed to be due to "contact" interactions, which have been previously noted for manganese. No such T2 reduction was seen in the chelates, except that dysprosium chelate (but not free ion) showed an anomalous decrease in T2 at high field strengths, which may possibly be explained by a dephasing effect caused by the large magnetic moment of Dy3+.     

1H spin-lattice relaxation parameters in the length of human intestine resected for cancer

1H spin-lattice relaxation curves were acquired for samples of intestinal adenocarcinoma (B) and of uninvolved tissue at the upper (A) and lower (C) resection margin of lengths of intestine taken at surgery from 20 patients. Each sample showed a wide distribution of relaxation times with the order of 90% of the signal in a single peak at long times. Several different single-parameter relaxation times computed from discrete-exponential analysis showed that most of the relaxation times for C and B are in the upper two-thirds of the range of times for A. The mean time for the tumor is about 10% longer (with p < 0.01) than for the upper resection margin. The difference between the tumor and the lower resection margin is not significant. Distribution width parameters associated with A and C were significantly larger than those associated with the tumors. Two-exponential fits indicate that the fast-relaxing component represents a smaller signal fraction for the tumor B than for A or C.     

Muscle proton T2 relaxation times and work during repetitive maximal voluntary exercise

We studied the effects of progressive maximal voluntary handgrip contractions (MVCs) on muscle proton spin-spin (T2) relaxation times and work, measured as the integrated force vs. time curve (FTI). Six healthy volunteers performed 10, 20, 40, and 80 MVCs in a 0.35-T magnet on four separate occasions. Repeated measures analyses of variance of increases in T2 and FTI during successive bouts were significant (P < 0.005 and P < 0.001, respectively). FTI increased with successive bouts to a greater extent than did muscle T2 (P < 0.05). For T2, the Helmert contrast judged the 10-MVC response lower than the mean of the remaining responses (P < 0.005), and the differences between all others compared with the means of subsequent responses were not significant, indicating a "flattening" of the T2 response after the increase from 10 to 20 repetitions. For FTI, all the single degree of freedom Helmert contrasts were significant (P < 0.001), indicating a continual increase in response over increased MVCs. The curved nature of the T2 response conformed best to a hyperbolic function, suggesting that a limit of approximately 32% exists for the change in T2 during progressively longer bouts of MVCs. A limit in the T2 response is consistent with the existence of a limit in the amount of water that muscle can take up from the vasculature during exertion.