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 

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 

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 cation , and only in the presence of crown ethers is the EZ form observed . The barrier to EZ -+ ZE exchange in the free carbanion is 12.9 kcal mol "S as expected quite close to that found for 29. 

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, 

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