Magnetic resonance systems temperature measurement

The most powerful technique for studying molecular motions in protein-water systems below 0°C is magnetic resonance. Dielectric relaxation measurements can be used, but these measurements are more suitable at higher temperatures in homogenous solutions (13). Recently, the frequency dependence of the mehcanical properties of biopolymers has been shown to yield considerable kinetic information (14). I will limit discussion to the salient results attainable from these techniques. 

Nuclear Magnetic Resonance (NMR) Spectroscopy. Longitudinal and transverse relaxation times (Ti and T2) of 1H and 23Na in the water-polyelectrolytes systems were measured using a Nicolet FT-NMR, model NT-200WB. T2 was measured by the Meiboom-Gill variant of the Carr-Purcell method (5). However, in the case of very rapid relaxation, the free induction decay (FID) method was applied. The sample temperature was changed from 30 to —70°C with the assistance of the 1180 system. The accuracy of the temperature control was 0.5°C. 

Comparison of Infrared and Nuclear Magnetic Resonance Methods. The NMR measurements of H bonding systems are few in number but great in promise. Effective use of this technique depends rather critically upon the possibility of varying the sample temperature. At high temperatures, dissociation of the H bonded complexes can be obtained even at the rather high concentrations necessary for detection. At low temperatures the different H bonded species may be observable individually. 

The results of nuclear magnetic resonance (NMR) measurements on alkali fullerides K cC o reported. The NMR spectra demonstrate that material with 0 < X < 3 is in fact a two-phase system at equilibrium, with x = 0 and x = 3. NMR lineshapes indicate that C o Ions rotate rapidly in the KsC q phase at 300 K, while 50 ions in the insulating KaC o phase are static on the time scale of the lineshape measurement. The temperature dependence of the spin-lattice relaxation rate in the normal state of is found to be characteristic of a metal, indicating the... 

NMR. Magnetic resonance experiments at low temperatures have been limited largely to proton and deuteron NMR of the water molecules in water-polymer preparations. This is reasonable because of the sensitivity attainable and because the most rapidly moving molecular species (water) is the most easily detected. I will discuss only systems without macroscopic order (e.g., frozen solutions of globular proteins) but the interested reader will find intriguing reports of nmr measurements on protein crystals and on fibrous or layered materials (15,16,17). 

In Fig. 4, we plot the volume dependences of the diffusivities of various model systems, all calculated for argonlike particles, and for the laboratory system methyl cyclohexane, which seems to be representative. Data for the latter are available for two temperatures from the accurate nuclear magnetic resonance (NMR) spin-echo measurements of Jonas et al. To group the data for different systems for better comparison of their behavior, we have obtained a reducing parameter for each liquid by taking advantage of the observations of Batchinski and Hildebrand that fluidities , and diffusivities D of highly fluid molecular liquids vary linearly with volume. 

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