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Dynamics water exchange

Gd + complexes with macrocyclic and acyclic polyaminocarboxylic acid ligands 78-80, 8 are typical MRI contrast agents (Caravan et al., 1999). Although they effectively encapsulate the Gd + cation and form stable complexes in water (log K = 16-25), their metal centers have free coordination sites for water molecules and their unpaired electrons reduce the relaxation times Ti and T2 (fig. 29) (Rulofif et al., 1998 Aukmst et al., 2001 Dubost et al., 1991 Kumar et al., 1994). The exchange processes of the coordinated water molecules (inner-sphere water) and hydrogen-bonded water molecules (2nd-sphere water) with bulk water molecules have a significant influence on the reduction of the relaxation times (fig. 30). Therefore, the structural and electronic factors of the Gd + complex should be controlled to attain dynamic water exchange. [Pg.319]

Compensarion temperature, 199,271,272 for reversed-phaM chromatography, 273 for solubility of hydrocabons in water, 273 Complex exchange with displacement of hetaeron, 254 see also Dynamic complex exchange... [Pg.165]

Anand, K., Damodaran, S. (1996). Dynamics of exchange between asi-casein and p-casein during adsorption at air-water interface. Journal of Agricultural and Food Chemistry, 44, 1022-1028. [Pg.345]

You have worked hard to study the internal dynamics of tetrachloroethene (PCE) and to calculate vertical turbulent diffusion coefficients in lakes. A friend of yours is more interested in the process of air-water exchange. One day, she sees some of your PCE data lying on your desk. She is very happy with the table below and... [Pg.942]

In Box 21.2 we analyzed the dynamics of PCE in Greifensee and found that the air-water exchange velocity, v/a/w, which explains the observed concentration, turned out to be unrealistically small. One reason could be that the lake is stratified during the summer and thus the surface concentration of PCE, which determines the size of both air-water exchange and loss at the outlet, is overestimated. Use the physical characteristics of Greifensee listed in Table 21.1. Total input of PCE is /,tot = 0.90 mol d-1. The PCE concentration in air is smaller than 10 8molnT3. Note that the air-water exchange velocity of PCE at u10 = lm s-1 is via/w = 4.9 x 10-6 m s 1 (Table 21.1). [Pg.987]

One could try to determine r such that the mean concentration C(, calculated with the realistic air-water exchange velocity, corresponds to the measured value. In fact, PCE in Greifensee is never at steady-state. Thus, rather than trying to optimize rj, in Illustrative Example 21.6 we will analyze the dynamic behavior of the PCE concentration in the lake under the influence of changing stratification regimes. [Pg.990]

In these equations, the symbols have their customary meanings (see Toth et al. in this volume for an excellent review of the topic), and the correlation times given in Eq. (3) have the following typical values at 50 MHz in water Tle (electron spin-lattice relaxation time) =10 ns, T2e (electron spin-spin relaxation time) = 1 ns, rm (inner sphere water exchange correlation time) = 130 ns [3], and rR = 60 ps. These values, in the context of Eq. (1 - 3), show why rotational dynamics control relaxivity for such chelates. [Pg.203]

The circulation of water in the Arctic Basin is a complex system of cycles and currents with different scales. Block HB simulates the dynamics of Arctic Basin water by the system of sub-blocks presented in Figure 6.2. The water dynamics in 2 is presented by flows between compartments Eijk. The directions of water exchanges are represented on every level zk = z0 + (k — 1 )A k according to Aota et al. (1992) in conformity with the current maps assigned as SSMAE input. The external boundary of 2 is determined by the coastline, the sea bottom, the Bering Strait, the southern boundary of the Norwegian Sea, and the water-atmosphere interface. [Pg.372]

Swenson, E.M., and Sasser, C.E. (1992) Water level fluctuations in the Atchafalaya Delta, Louisiana tidal forcing versus river forcing. In Dynamics and Exchanges in Estuaries and the Coastal Zone, Coastal and Estuarine Studies 40 (Prandle, D., ed.), pp. 191-208, American Geophysical Union, Washington, DC. [Pg.670]


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