Hydration number relaxation rates

It is clear from the above equations that numerous parameters (proton exchange rate, kcx = l/rm rotational correlation time, tr electronic relaxation times, 1 /rlj2e Gd proton distance, rGdH hydration number, q) all influence the inner-sphere proton relaxivity. Simulated proton relaxivity curves, like that in Figure 3, are often used to visualize better the effect of the... 

The PEDM is able to explain the anomalous relaxation of solutions of ferritin and akaganeite particles, especially its linear dependence with Bq, the external magnetic field. The model is compatible with the observed dependence of the rate on pH. The relaxation rate predicted by the PEDM is proportional to the number of adsorption sites per particle (q) the values deduced for q from the adjustment of the model to experimental results (from NMR and magnetometry in solutions) are reasonable for hydrated iron oxide nanoparticles (63). 

A further application of relaxation rate measurements is that similar 1/71 ratios in a series of lanthanide complexes may be taken to indicate an isostructural series. However, this approach has the limitation that if only part of the complex is studied, perhaps an organic ligand, its 71 ratios would be independent of changes, for example changes in the extent of hydration in the remainder of the complex, provided that the conformation of the ligand relative to the lanthanide ion were preserved. An excellent example of the use of 71 data in a quite different way is its use to determine hydration numbers of lanthanide dipicolinate complexes.562... 

As we have seen above, a large number of parameters (proton exchange rate, kex = 1/Tm5 rotational correlation time, r, electronic relaxation times, 1/Ti 2e> Gd - proton distance, hydration number, q) influence the inner sphere proton relaxivity. If the proton exchange is very slow (Ti , t ), it will be the only limiting factor (Eq. (5)). If it is fast (t Ti ,), proton relaxivity will be determined by the relaxation rate of the coordinated protons,, which also depends on the rate of proton exchange, as well as on rotation and electronic relaxation. The optimal relationship is ... 

In addition to the concentration of the electrolyte solution, another barely examined factor influencing the structure and size of the hydration shells of ions is temperature. Invest tions of spin-lattice relaxation rates of and Li nuclei in aqueous LiCl solution as a function of concentration and temperature indicate that heating may destroy the tetrahedral water structure with inserted lithium cations that exists at temperatures below 30°C and enable the ions to construct a surrounding octahedral with the coordination number of 6 at temperatures above 40°C [165]. However,... 

Nuclear magnetic relaxation rates have been used to investigate the coordination number. In an investigation of the line-width broadening of La in various perchlorate solutions, Nakamura and Kawamura (1971) attributed the decreases in the values of (Av is the relaxation rate and is the relative viscosity) to a possible equilibrium between the nonahydrates and octahydrates for lanthanum ion. This conclusion was disputed by Reuben (1975) who proposed that this apparent anomaly reflected an erroneous estimate of the corrections of the linewidths for peaks due to the effect of the finite modulation amplitude and/or of partial saturation. Measurement of the transverse relaxation rates by the pulse method gave results consistent with a constant hydration number for lanthanum ion (Reuben 1975). 

The relaxivity of a responsive probe should be selectively influenced by the physiological parameter to be detected. The relaxivity is related to the microscopic properties of the contrast agent. The most important parameters that can be tailored by the chemist are the hydration number, the exchange rate of the water molecules with the surrounding water (bulk), and the motional dynamics of the molecules. All these three parameters can be modulated through supramolecular interactions. The literature on responsive probes is quite extensive here we present few examples to illustrate the importance of supramolecular interactions in the field of responsive probes. 

In sharp contrast to the large number of experimental and computer simulation studies reported in literature, there have been relatively few analytical or model dependent studies on the dynamics of protein hydration layer. A simple phenomenological model, proposed earlier by Nandi and Bagchi [4] explains the observed slow relaxation in the hydration layer in terms of a dynamic equilibrium between the bound and the free states of water molecules within the layer. The slow time scale is the inverse of the rate of bound to free transition. In this model, the transition between the free and bound states occurs by rotation. Recently Mukherjee and Bagchi [14] have numerically solved the space dependent reaction-diffusion model to obtain the probability distribution and the time dependent mean-square displacement (MSD). The model predicts a transition from sub-diffusive to super-diffusive translational behaviour, before it attains a diffusive nature in the long time. However, a microscopic theory of hydration layer dynamics is yet to be fully developed. 

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