ZZ-Exchange

Li Y, Palmer AG (2009) TROSY-selected ZZ-exchange experiment for characterizing slow chemical exchange in large proteins. J Biomol NMR 45 357-360... 

The delocalization in the donor and acceptor parts of case 2 systems leads to considerably hindered rotations around the formal single bonds. The acceptor part of a compound like 13 is similar to the anion of a /J-diketone. While the dynamics of the latter one is difficult to study without the intervention of a chelated cation, the acceptor part of 13 is more similar to an isolated /J-diketonate ion. A study of 13 by dynamic 11 NMR revealed exchange between three rotamers (EZ, ZE and EE, Scheme 2). The fourth rotamer, ZZ,... 

The conformational situation for twisted 2,2-diacyl compounds of type 29 is quite different from that for sodium or lithium 1,3-diketone enolates. In the latter, the ZZ form is stabilized by complexation with the cation75, and only in the presence of crown ethers is the EZ form observed76. The barrier to EZ - ZE exchange in the free carbanion is 12.9 kcal mol-1, as expected quite close to that found for 29. 

Table 5 Spin levels (Ei,i = 1 ), /T (in cm. K/mol) values at (in °K) corresponding to maximum anisotropy of the main values of the susceptibility /ii(ii = xx, yy, zz) tensor, /avr[Xav = (l/3)(Xxx + Xyy + Xzz)] and anisotropic D12 and A12 tensor parameters of a Fe -CN-Cu" model complex with and without trigonal Jahn-TeUer distortions from model calculations accounting for the difference of Je and Jb2 exchange coupling parameters (exchange anisotropy) or alternatively, assuming an isotropic Heisenberg exchange (1 = 1e = 1b2)...

Three liquids, having bulk solute i concentration [CJp, [C,]e, and [C,]r, constant volumes l-p, and Fr, respectively, are separated by two membranes with the same working area. S. Stirring of bulk liquids is effective in such a way that the aqueous (Zzfe, Zz e) and the organic her) boundary layers become sufficiently thin and constant. Concentration profiles with hydrophobic membranes are demonstrated in Fig. 5.2, while those containing hydrophilic or ion-exchange membranes are in Fig. 5.3. Using the concept of the one-dimensional series of diffusion resistances, and... 

Vysotskii ZZ, Strazhesko DN (1973) Isoelectric state of disperse silicas and ion exchange in acid solutions, adsorption and adsorbents, 1st edn. WUey, New York, pp 55-71... 

In this expression, i represents the electrode current density, Zq is the exchange current density, R is the gas constant, T is the temperature, the anode and cathode charge transfer coefficients are often related by -I- = 1, zz is the number... 

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