Nuclear Magnetic Resonance NMR titrations

This review updates a classic and influential review by Halevi.3 What makes the current review timely is the recent development of a nuclear magnetic resonance (NMR) titration method capable of exquisite accuracy and not subject to the systematic error associated with possible impurities in one of the samples and not in the other. New values can now be compared with previous ones. 

The solution structure of recombinant mouse 25 kDa ThTPase has been determined (Song et al. 2008) and the residues responsible for binding Mg and ThTP were determined from nuclear magnetic resonance (NMR) titration experiments. While the free enzyme has an open cleft form, the enzyme-ThTP complex tends to adopt a closed tunnel-fold, resembling the p-barrel structure of yeast RNA triphosphatase. 

Several modem analytical instruments are powerful tools for the characterisation of end groups. Molecular spectroscopic techniques are commonly employed for this purpose. Nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and mass spectrometry (MS), often in combination, can be used to elucidate the end group structures for many polymer systems more traditional chemical methods, such as titration, are still in wide use, but employed more for specific applications, for example, determining acid end group levels. Nowadays, NMR spectroscopy is usually the first technique employed, providing the polymer system is soluble in organic solvents, as quantification of the levels of... 

A careful nuclear magnetic resonance (NMR) study of the titration behavior of His-35 in Az-Ade by Canters and co-workers (Groeneveld et al, 1988) confirmed the prediction that His-35 would not titrate—or, at best, was found to have an unusually low pA (4.6). Interestingly, when His-35 is protonated there seems to be no effect on the copper center, unlike the case with Az-Pae. 

Carboxyl group content is determined either by potentiometric titration of humic material or by calcium acetate titration. Calcium acetate method overestimates carboxyl content by at least 10%. Potentiometric titration of humic substances (pH 2.8) in 0.1 mol 1 KCl with a base up to pH 10 yields more precise values for carboxyl content. C nuclear magnetic resonance (NMR) (solid and liquid) can also be used for carboxyl determination. The results obtained are comparable to potentiometric titration. 

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