2H relaxation

Sine l3C and 2H relaxation are the consequence of intramolecular interactions, the relaxation times f of 13C and 2H within a given molecule may be compared directly with the help of eqs. (3.22) and (3.27) ... 

In a study combining 2H relaxation-time measurements and use of paramagnetic lanthanide shift reagents, the ratio of the relaxation times of axial and equatorial deuterons in 2,2,6,6-tetradeuterio-4-t-butylcyclohexanone [20]... 

In summary, for this area to move forward, methods need to be introduced to provide information additional to 2H lineshapes when studying more complex systems. Calculations such as those just described are one real possibility experimental possibilities include use of magic-angle spinning 2H NMR, and using the full anisotropy of 2H 7j measurements and 13C NMR. A very nice illustration of the use of several different techniques in a motional study examined the slow alkane motions in a urea/alkane inclusion compound via 2H relaxation measurements, selective inversion experiments and two-dimensional 2H exchange.125... 

One of the most widely used tools to assess protein dynamics are different heteronuclear relaxation parameters. These are in intimate connection with internal dynamics on time scales ranging from picoseconds to milliseconds and there are many approaches to extract dynamical information from a wide range of relaxation data (for a thorough review see Ref. 1). Most commonly 15N relaxation is studied, but 13C and 2H relaxation are the prominent tools to characterize side-chain dynamics.70 Earliest applications utilized 15N Ti, T2 relaxation as well as heteronuclear H- N) NOE experiments to characterize N-H bond motions in the protein backbone.71 The vast majority of studies applied the so-called model-free approach to translate relaxation parameters into overall and internal mobility. Its name contrasts earlier methods where explicit motional models of the N-H vector were used, for example diffusion-in-a-cone or two- or three-site jump, etc. Unfortunately, we cannot obtain information about the actual type of motion of the bond. As reconciliation, the model-free approach yields motional parameters that can be interpreted in each of these motional models. There is a well-established protocol to determine the exact combination of parameters to invoke for each bond, starting from the simplest set to the most complex one until the one yielding satisfactory description is reached. The scheme, a manifestation of the principle of Occam s razor is shown in Table l.72... 

Picullel L, Halle B (1986) Water spin relaxation in colloidal systems. Part 2., 70 and 2H relaxation in protein solutions. J Chem Soc Faraday Trans I 82 401-414... 

Interactions between oppositely charged micelles in aqueous solutions spontaneously form vesicles. The self-diffusion coefficient of water and 2H relaxation of 2H-labeled dodecyl trimethyl ammonium chloride of the dodecyl trimethyl ammonium chloride-sodium dodecyl benzenesulfonate systems show that in these mixtures there is limited growth of the micelles with changes in composition. The vesicles abruptly begin to form at a characteristic mixing ratio of the two surfactants. The transition is continuous.205 Transformation from micelle to vesicle in dodecyl trimethyl ammonium chloride-sodium perfluoro-nonanoate aqueous solution has been studied by self-diffusion coefficient measurements, and it was found that at a concentration of 35 wt% with a molar ratio of 1 1, the self-diffusion coefficient of the mixed micelles is far smaller than that of the two individual micelles.206 The characteristics of mixed surfactant... 

A number of studies relating anionic polymer and cationic surfactants have been performed by >H chemical-shift, multi-field relaxation differential line broadening, diffusion ordered spectroscopy, and 2H relaxation methods.286-294... 

Various models have been proposed relating quadrupolar relaxation times to the correlation times of molecular motions, (lc) The more sophisticated the model considered the greater the number of parameters involved and thus the necessity for more independent NMR measurements. These may be obtained from a consideration of both14N and 2H relaxation data on a series of closely related molecules. Ordinary and... 

The frequency dependence of the water 2H relaxation data of solubilized bR at 4°C (Fig. 25) arising from biLorentzian curves were measured and the low-frequency step was studied by... 

N and 2H relaxation can be employed to detect fluctuations of backbone dynamics of protein kinases on the nano- to picosecond and milli- to microsecond timescales. Analysis of the relaxation data allows for a semiquantitative estimation of the conformational entropy change for the main chain of protein kinases dependent on ligand binding or point mutation. 

In contrast to 2H, relaxation is far more complex to describe for IH or 13C With spin Vs nuclei, the main relaxation mechanism is dipolar relaxation, where again complex sums over all interacting pairs of spins complicate the expressions for Ri and / 2- IH relaxation data determined for adsorption systems are interpreted qualitatively as a measure for mobility, since the proportionality to the spectral density function still holds. 

One possibility is to determine the time scale for diffusion around a spherical particle by relaxation experiments, since transverse relaxation rates are sensitive to slow motional time scales. The 2H relaxation time T2 was measiued in a quadrupolar CPMG experiment, in which the delay between pulses, r, in the pulse sequence was varied. With increasing r, the experiment increasingly allows for diffusion as a slow motional mode to contribute to the relaxation rate, and to decrease T2. With this principle, from the dependence of R2 = T2 against the diffusion coefficient D is extracted, as shown in fig. 15, where the slope is proportional to D [52], Diffusion coefficients of the phospholipid POPC were determined at different temperatures [52], the diffusion of the inner and outer monolayer of DPPC on silica could be separated [53], and recently a diffusion coefficient was determined for lipid bilayers on polymeric support [54],... 

Fig. 19 Left 2H relaxation times for PMA-d in toluene solution (open symbols) and in swollen adsorption layers (filled symbols), squares TI, circles T2. Right Mean correlation times for PMA-d in toluene solution (circles) and in swollen adsorption layers (squares) as evaluated fix>m a log-normal distribution of Tj. Both figures taken from [14] with permission.

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