Directional purely electrostatic models

General details about denatured states were discussed in Chapter 17, section B. Specific details are obtained from advanced NMR methods. But any residual native structure in CI2 under denaturing conditions is below the limits of direct structural detection by NMR. The pKa values of the 10 acidic residues in the native state of CI2 have been measured by NMR to give indirect information.28 Most of them are 2-3 units lower than they are in model compounds. The pKa values in the acid-denatured state are, on average, 0.3 unit lower than the model compound values in pure water, but the difference disappears as ionic strength increases. This indicates some compactness in the denatured state, but it could be induced by electrostatic interactions. By all criteria, the denatured state of CI2 is a relatively expanded state. 

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