Nuclear relaxation rate

N-protonation the absolute magnitude of the Ad values is larger than for Af-methylation <770MR(9)53>. Nuclear relaxation rates of and have been measured as a function of temperature for neat liquid pyridazine, and nuclear Overhauser enhancement has been used to separate the dipolar and spin rotational contributions to relaxation. Dipolar relaxation rates have been combined with quadrupole relaxation rates to determine rotational correlation times for motion about each principal molecular axis (78MI21200). NMR analysis has been used to determine the structure of phenyllithium-pyridazine adducts and of the corresponding dihydropyridazines obtained by hydrolysis of the adducts <78RTC116>. 

In addition to the standard constraints introduced previously, structural constraints obtainable from the effects of the paramagnetic center(s) on the NMR properties of the nuclei of the protein can be used (24, 103). In iron-sulfur proteins, both nuclear relaxation rates and hyperfine shifts can be employed for this purpose. The paramagnetic enhancement of nuclear relaxation rates [Eqs. (1) and (2)] depends on the sixth power of the nucleus-metal distance (note that this is analogous to the case of NOEs, where there is a dependence on the sixth power of the nucleus-nucleus distance). It is thus possible to estimate such distances from nuclear relaxation rate measurements, which can be converted into upper (and lower) distance limits. When there is more than one metal ion, the individual contributions of all metal ions must be summed up (101, 104-108). If all the metal ions are equivalent (as in reduced HiPIPs), the global paramagnetic contribution to the 7th nuclear relaxation rate is given by... 

Methods for measuring Ti and T2 are discussed in Chapter 5 of reference 21. Suffice it to say here that understanding the method for measuring T2 (the Carr-Purcell pulse sequence or spin-echo method) becomes important for discussing two-dimensional NMR spectra. When spin-spin coupling is present, a modulation of spin echoes is produced, and it is this fact that is important in 2-D NMR spectroscopy. Nuclear relaxation rates and mechanisms become important when discussing the effect of paramagnetic metal centers on NMR spectroscopy. 

The Bloembergen-Morgan equations, Eqs. (14) and (15), predict that the electron spin relaxation rates should disperse at around msTy = 1. This will make the correlation times for the dipolar and scalar interaction, %ci and respectively, in Eq. (11) dependent on the magnetic field. A combination of the modified Solomon-Bloembergen equations (12) and (13), for nuclear relaxation rates with the Bloembergen-Morgan equations for the field dependence... 

Longitudinal and transverse nuclear relaxation profiles differ in the high field part. In fact, the equation for the transverse nuclear relaxation rates contains a non-dispersive term, depending only on Xd. Therefore the transverse relaxation does not go to zero at high fields, as longitudinal relaxation does, but increases because Tie increases (until it increases to the point where it becomes longer than x or Xm)-... 

The Florence NMRD program (8) (available at www.postgenomicnmr.net) has been developed to calculate the paramagnetic enhancement to the NMRD profiles due to contact and dipolar nuclear relaxation rate in the slow rotation limit (see Section V.B of Chapter 2). It includes the hyperfine coupling of any rhombicity between electron-spin and metal nuclear-spin, for any metal-nucleus spin quantum number, any electron-spin quantum number and any g tensor anisotropy. In case measurements are available at several temperatures, it includes the possibility to consider an Arrhenius relationship for the electron relaxation time, if the latter is field independent. 

Nuclear relaxation rates, iron-sulfur proteins, 47 267-268 Nuclear resonance boron hydrides and, 1 131-138 fluorescence, 6 438-445 Nuclear spin levels, 13 140-145 Magnetic properties of nuclei, 13 141-145 Nuclear testing... 

Hydrol5dic polymerization in the ferric citrate system can be prevented if sufficient excess citrate is present in solution 66). Approximately 20 millimolar excess citrate is sufficient to supress pol3mier-ization of 1 millimolar iron, as indicated by dialysis and spectrophotomet-ric measurements. From pH titration in high citrate solutions, it was concluded 66) that a dicitrate complex of iron is formed at high pH. Presumably formation of the dicitrate chelate is competitive with hydrolytic polymerization. The fraction of polymer formed in ferric citrate solutions was found to decrease smoothly as the citrate content was increased up to 20 millimolar. The nuclear relaxation rate of the water protons in ferric citrate solutions increases with the citrate concentration. 

A second steady-state method involves the analysis of the broadening of the nuclear magnetic resonance spectra of phospholipids in bilayers containing low concentrations of spin-labeled phospholipids. A theoretical analysis of the relation between this line broadening and diffusion rates has been given by Brulet and McConnell.3 [In this paper (6) is not correct the subsequent equations are nonetheless correct. For an alternative derivation, see Brulet.2] In this paper it is shown that a number of measurements of nuclear relaxation rates T71 of nuclei in phospholipids are consistent with lateral diffusion constants in the range 10 7 to 10 R cm2/s. 

The structural information derived from relaxation enhancement studies depends somewhat on the model chosen to describe the interaction of solvent protons with the protein molecules. For example even if the experiments indicated that the dispersion of Tfpr were essentially determined by the correlation time for rotational tumbling of the protein the tumbling of the hydration waters would not necessarily have to be restricted to that of the entire hydrated protein. Evidence was found that fast intramolecular tumbling about an axis fixed with respect to the surface of the hydrated species reduced the proton and O17 nuclear relaxation rates even in extremely stable aquocomplexes of Al3+ and other metal ions (Connick and Wiithrich (21)). The occurrence of similar... 

Electronic relaxation times of some common paramagnetic metal ions and nuclear relaxation rates for a proton at 5 A from the metal, at 800 MHz H resonance frequency, due to dipolar and Curie relaxation, estimated from Eqs. (3.16), (3.17), (3.29) and (3.30), with rc = rs... 

THE INDUCED MAGNETIC MOMENT PER METAL ION IN POLYMETALLIC SYSTEMS, THE HYPERFINE CONTACT SHIFT, AND THE NUCLEAR RELAXATION RATES... 

The resulting assignment, which is one of the most successful in paramagnetic metalloproteins, is reported in Table 6.3. The nuclear relaxation rates, which are... 

For any nucleus i of a paramagnetic lanthanide complex in the absence of significant chemical exchange, the experimental longitudinal (l/7 p) and transversal (1 /7 xp) nuclear relaxation rates are given by eqs. (4), (5) in which 7]dia corresponds to the characteristic relaxation times of the same nucleus i in the analogous diamagnetic complex (R = La, Y, Lu) and 7)para are... 

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