NMR relaxation parameters

Since NMR relaxation in proteins is determined by dynamics on the picosecond to nanosecond time scale, experimental NMR relaxation parameters can provide important information concerning picosecond motions. Time correlation func-... 

Proton NMR relaxation parameters have also been determined for polyethylene ( ) and polyethylene oxide (39) in the melting region. The apparent contradiction between the proton spin-lattice relaxation parameter for a high molecular weight linear polyethylene sample at its melting point, with the relaxation measurements, has previously been pointed out. (17) This discrepancy is still maintained with the more detailed results reported here for both types of polyethylene. For the proton relaxation a small, but distinct, discontinuity is reported at the melting teirperature. (38)... 

Meltzer AD, Tirrell DA, Jones AA, Inglefield PT, Hedstrand DM, Tomalia DA. Chain dynamics in poly(amidoamine) dendrimers a study of carbon-13 NMR relaxation parameters. Macromolecules 1992 25 4541-4548. 

As will be shown later, the NMR relaxation parameters are frequency-dependent quantities. Therefore, we are interested in ways to measure these frequencies associated with the nature of the rotational motion. The Fourier transform of the TCF, which evolves in the time domain, yields a spectrum of motional frequencies in which the value of the function, J((o), at each frequency is known as the spectral density423... 

It is evident that simple theories of molecular motion are not adequate to explain experimental nmr relaxation parameters in certain polymer systems as well as in some highly associated small molecules. As field dependent nmr relaxation studies become more widespread, the observation of these relaxation characteristics will undoubtedly be found more general than is currently thought. 

Van Dorsten FA, Olah L, Schwindt W, Grune M, Uhlenkuken U, Pillekamp F, Hossmann KA, Hoehn M (2002) Dynamic changes of ADC, perfusion, and NMR relaxation parameters in transient focal ischemia of rat brain. Magn Reson Med 47 97-104... 

What is the mechanism of spins dropping down from the state to the a state and fanning out around the two cones, and what determines the rates (R = HT and/ 2 = 1/72) of NMR relaxation These processes are intimately tied to the motion of molecules as they tumble ( reorient ) in solution in their rapid Brownian motion, and measurement of the NMR relaxation parameters T and T2 can even give us detailed information about molecular dynamics (motion) from the point of view of each spin in the molecule. A simplified model... 

Often the information on NMR relaxation parameters carried by image contrast is insufficient to address a particular problem. We can then look to the rich information content of the spectrum itself. Generally, spectroscopy of the entire body is not of much value, and in vivo spectroscopy is usually carried out as localized spectroscopy, that is, over a part of the body. There are various ways of restricting the operation of the spectrometer to a particular region, and they fall into two broad classes those that depend on the physical dimensions of the rf coil and those that use field gradients in the pulse sequences. Often these approaches are combined. At this time, the use of spectroscopic examinations has not become part of the repertoire of clinical practice, despite a history of in vivo spectroscopy almost as old as MRI itself. In vivo spectroscopy has had a number of landmark successes in solving problems in metabolism research in both animals and humans, but there have been no spectroscopic applications that have been demonstrated to be more effective than other methods for the routine diagnosis of disease. 

Fig. 17. Longitudinal H NMR relaxation parameters at 30 MHz for water adsorbed on lysozyme powders derived from the cross-relaxation model after setting the protein relaxation rate equal to 0. Tis the water proton relaxation time and 7", is the time constant characterizing spin transfer between the protein protons and the water protons. From Hilton etal. (1977).

C-NMR relaxation parameters may also be employed to access the rates of overall and internal motions for saccharide molecules.230 Longitudinal and transversal heteronuclear relaxation times as well as hetero-nuclear NOEs depend on the molecular motion of the molecule, including overall and internal motions. Thus, careful analysis of these parameters can be employed to demonstrate the presence of conformational heter-eogeneity and/or dynamics, as well as the restriction to motion and the timescale of the existing fluctuations. Different examples of application of this methodology to trisaccharides,231 232 tetrasaccharides,233 pentasaccharides,234 and polysaccharides235,236 have been described. 

Some of the earliest chemometric NMR analysis of materials involved the PCA of organic peat using C CPMAS NMR spectra,and the analysis of H and C NMR relaxation parameters in coal. Chemometrics and C CPMAS has also been applied to classify soil organic matter. Clayden and co-workers have used FA of the time domain F NMR signal in poly(tetrafluoroethane), PTFE polymers as a method to measure crystallinity. It was demonstrated that the dominant principal component did not correlate well, but that the scores of second and third principal component show an excellent correlation with the PTFE crystallinity. PLS methods have also been used to determine... 

Prompers and Briischweiler showed by quasiharmonic analysis that the conformational partition function of a globular protein sampled on the ns time scale can be factorized in good approximation into purely reorientational part, which determines heteronuclear NMR spin relaxation, and a remaining part that includes other types of intramolecular motions. Thus a thermodynamic interpretation of NMR relaxation parameters in proteins in the presence of motional correlations can be given. 

We have also begun to structurally characterize fibrillar states of a-synuclein (140 residues) and of the K19 domain of protein tau. Both systems are involved in possibly related neuro-degenerative diseases.Preliminary results of two- and three-dimensional correlation spectroscopy, as outlined above, reveal that many of the NMR detectable resonances exhibit narrow or line widths, consistent with the occurrence of well-ordered domains in both proteins. On the other hand, other segments of the considered proteins cannot readily be detected suggesting that they may display static or dynamic disorder under the experimental conditions considered. While the effect of molecular dynamics of NMR relaxation parameters has been studied in the context of solution- or solid-state NMR for a long time, recent progress in the study of uniformly labelled proteins by MAS NMR has created novel means by which to study dynamics of entire polypeptide sequences using 2D methods. For example, Bockmann and Emsley have... 

The measurements of NMR relaxation parameters (Tu T2, and NOE) provide information concerning the time scales and the amplitudes of atomic motions. Under most circumstances, the relaxation behavior of the nuclear spins ( H,, 3C) in a protein is governed by dipolar interactions between the various spins.422,423 The dipolar couplings depend on the relative positions of the coupled nuclei and on their relative motions.423,424 We consider spin 1/2 nuclei... 

Levy, R.M., Karplus, M., Wolynes, RG. NMR relaxation parameters with internal motion Exact Langevin trajectory results compared with simplified relaxation models. J. Am. Chem. Soc. 1981, 103, 5998-6011. 

Physical properties of the first-shell water of macromolecular water shell differ from the bulk water properties. Some of them can be measured experimentally. They are the phase transition temperature, dielectric constant, NMR relaxation parameters, calorimetric characteristics, kinetic characteristics, such as self-diffusion coefficient and some others. The rrrain factors that define protein structure are residue sequence, hydration, iorric arrd hydrophobic irrleractions. 

The normal case with a molten or dissolved polymer is that its conformational jumps are quite rapid, compared with the tumbling and looping motions of entire chains. A typical barrier to a conformational jump in a vinyl polymer chain without external constraints is only approximately 12-20 kJ mol and is therefore readily surmounted at room temperature, typically at least 10 times per second. In this case, the local motions will contribute to the NMR relaxation parameters of the polymer, such as T, T2 and NOE. Similar motions will occur in the gel state and in the flexible solid, above Tg. 

Globular and membrane proteins in aqueous solution or Hpid bilayers/ biomembranes could undergo a wide range of motions at ambient temperatures. Such motions can be characterized by several types of NMR relaxation parameters, chemical exchange, dynamic interference including SRI [27—29]. Detection ranges for motions by the respective parameters are schematically illustrated in Fig. 1.1 for solution and soUd state NMR approaches. Naturally, fast motions are solely examined by solution NMR techniques for any portions of proteins. The experimental approaches to be able to detect intermediate or slow motions are obviously different between the solution and solid state NMR methods. 

Fig. Ic), therefore suggesting a relationship between survival rate and NMR relaxation parameters exists.

Low field NMR equipment is used in many food laboratories to measure Solid Fat Content. This measurement is only based on proton signal intensities. New prospects are opening up for this technique with the measurement of NMR relaxation parameters, espeeially spin-lattice relaxation times making it possible to establish a relationship between Ti and crystal size. This could be usefiil to follow the evolution of crystal size as a function of time or to determine crystal size distribution profiles. Knowing that crystal size monitors the physieal properties of fats, this relationship could be used to determine some physical properties of high fat content food products. 

R. M. Levy, M. Karplus, and P. G. Wolynes, /. Am. Chem. Soc., 103, 5998 (1981). NMR Relaxation Parameters in Molecules with Internal Motion Exact Langevin Trajectory Results Compared with Simplified Relaxation Models. 

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