Titrations nuclear magnetic resonance

R480 R. Shivapurkar and D. Jeannerat, Determination of the Relative pKa s of Mixtures of Organic Adds Using Nuclear Magnetic Resonance Titration Experiments Based on Aliased HSQC Spectra , Anal. Methods,... 

Shortly after the reports of Jorgensen, the Zimmerman group published the first example of the DDD-AAA H-bonding pair 11.12 (Figure 4). The value of exceeded the limit of values accessible by H NMR (nuclear magnetic resonance) titrations accordingly they report a lower limit of > 10 Subsequently, Anslyn... 

Shindo, H., Hayes, M. B., and Cohen, J. S., 1976, Nuclear magnetic resonance titration curves of histidine ring protons. A direct assignment of the resonance of the active site histidine residues of ribonuclease, /. Biol. Chem. 251 2644. 

The side-chain chlorine contents of benzyl chloride, benzal chloride, and benzotrichlorides are determined by hydrolysis with methanolic sodium hydroxide followed by titration with silver nitrate. Total chlorine determination, including ring chlorine, is made by standard combustion methods (55). Several procedures for the gas chromatographic analysis of chlorotoluene mixtures have been described (56,57). Proton and nuclear magnetic resonance shifts, characteristic iafrared absorption bands, and principal mass spectral peaks have been summarized including sources of reference spectra (58). Procedures for measuring trace benzyl chloride ia air (59) and ia water (60) have been described. 

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... 

Nuclear magnetic resonance spectroscopy and magnetic titrations. . 339... 

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. 

Equivalent Weight. Three reliable analytical methods are available to determine the equivalent weight of CTPB prepolymer (1) titration by 0.1 N sodium methylate in pyridine solution to the thymol blue end point, (2) infrared spectroscopy, and (3) nuclear magnetic resonance. Satisfactory agreement has been obtained between these instrumental analyses and the acid content as determined by titration (Table XVI). 

In principle the deviation <5 can be determined by the use of usual analytical chemistry or a highly sensitive thermo-balance. These methods, however, are not suitable for very small deviations. In these cases the following methods are often applied to detect the deviation physico-chemical methods (ionic conductivity, diffusion constant, etc.), electro-chemical methods (coulometric titration, etc.), and physical methods (electric conductivity, nuclear magnetic resonance, electron spin resonance, Mossbauer effect, etc.), some of which will be described in detail. 

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 latexes were cleaned by ion exchange and serum replacement, and the number and type of surface groups were determined by conductometric titration. The molecular weight distributions of the polymers were determined by gel permeation chromatography. The stability of the latexes to added electrolyte was determined by spectrophotometry. The compositional distribution was determined by dynamic mechanical spectroscopy (Rheovibron) and differential scanning calorimetry, and the sequence distribution by C13 nuclear magnetic resonance. 

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