NMR spin grouping and correlation exchange analysis. Application to low hydration NaDNA paracrystals

Abstract

The NMR spin-grouping technique is applied to low hydration oriented fibers of NaDNA to study the role of exchange in determining the apparent (observed) spin relaxation of the system. The analysis proceeds in three steps: first, the apparent proton relaxation is measured at high fields, with both selective and nonselective inversion pulse sequences, and in the rotating frame. The spin-grouping technique is used in all spin-lattice relaxation measurements to provide the optimum apparent relaxation characterization of the sample. Next, all apparent results are analyzed for exchange. In this analysis the results from the high field and rotating frame experiments (which probe the exchange at two different time scales) are correlated to determine the inherent (or true) spin relaxation parameters of each of the proton groups in the system. The results of selective inversion T1 measurements are also incorporated into the exchange analysis. Finally, the dynamics of each spin group are inferred from the inherent relaxation characterization. The low hydration NaDNA structure is such that the exchange between the protons on the water and those on the NaDNA is limited, a priori, to dipolar mixing. The results of the exchange analysis indicate that the dipolar mixing between water and NaDNA protons is faster than the spin diffusion within the NaDNA proton group itself. The spin-diffusion on the macromolecule is the bottleneck for the exchange between the water protons and the NaDNA protons. The water protons serve as the relaxation sink both at high fields and in the rotating frame for the total NaDNA-water spin bath. The inherent relaxation of the water is characteristic of water undergoing anisotropic motion with a fast reorientational correlation time about one axis (5 X 10(-10) less than or equal to tau r less than or equal to 8 X 10(-9)S) which is about three orders of magnitude slower than that of water in the bulk; and a slow tumbling correlation time for this axis (1.5 x 10(-7) less than or equal to tau t less than or equal to 8 x 10(-7)S) which is two orders of magnitude slower yet.

Cluster theory for water sorption in wood

“…It has been shown (Peemoeller et al 1986;Schreiner et al 1991) that the water molecule residence time at hydration sites in polymer powders is expected to be less than a microsecond. It is not unreasonable to expect a similar result for water in wood.…”

Multiple‐site fast exchange model for spin–lattice relaxation in the Fricke‐gelatin dosimeter

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Microviscosity of human erythrocytes studied using hypophosphite two-spin order relaxation

“…volume and cytoplasmic water content decreases; see Table 3). This could lead to additional complications in fitting the data because the reorientation of the hydration layer is likely to be sufficiently slow (Schreiner et al, 1991 and pertinent references therein) so as to cause the T, of HP to be outside the extreme narrowing condition, in which the random field interaction would no longer be Proton-decoupled T, values, T, values simulated with and without random field effects as well as the bulk viscosity derived from viscometry measurements are also given. The parameters used in the simulations are given in the caption to Table 1.…”