NMR signals of water

Sorbed Water. Because Nafion is a perfluorinated material, it is straight-forward to observe the NMR signal of water hydro-... 

FIGURE 3.49 Broad (a) and narrow (b) component intensities of H NMR signal of water bound in 1.4 wt% GO dispersion as a function of concentration of organic additives. 

High temperature-high pressure NMR techniques provide useful information on the intermolecular interactions of SCW. The NMR signal of water observed at 30°C was sharp and shifted toward the low field side with temperature at constant density (p = 0.4 g cm at high temperatures and pressures the pressure was changed in an NMR tube with a constant volume) [62, 63]. The signal was broadened with the increase in the temperature as seen in Fig. 17a. The chemical shift cr of water is plotted against temperature in the liquid and gas phases in Fig. 17b. 

Fig. 17. H NMR signals of water, (a) The shape and position of H NMR signals at various temperatures, (b) H NMR chemical shift 6 as a function of temperature and density. The filling factor of water is 0.4, which makes density of supercritical water to be...

Researchers have show that the application of dynamic nuclear polarization (DNP) at X-band on NMR signal of water under ambient condition, in combination with continuous-wave (cw) ESR, is a new and potentially powerful approach to study hydration and fluid dynamics of soft macromolecular assemblies. The source to amplify NMR signal is stable nitroxide radicals, also known as spin labels, that serve as reporter species to... 

A novel analytieal tool for the selective detection of local water inside soft mol. assemblies (hydrophobic cores, vesicular bilayers, and micellar structures) suspended in bulk water has been presented. Through the use of dynamic nuclear polarization (DNP), the NMR signal of water is ampUfied, as it interacts with stable radicals that possess about 658 times higher spin polarization. Stable nitroxide radicals covalently attached along the hydrophobic tail of stearic acid molecules that incorporate themselves into surfactant-based micelle or vesicle structures have been used, allowing to study the local water content and fluid viscosity inside oleate micelles and vesicles and Triton X-100 micelles to serve as model systems for soft molecular assembhes. ... 

It should be emphasized that the ester carbonyl group in the interfacial zone II is most crucial and susceptible to the anesthetic action of the drugs. In our NMR study, we have found that the ester carbonyl site in zone II is particularly susceptible to the extent of hydration [51]. Above the G/LC transition temperature, the carbonyl is the innermost site where the water can penetrate. The strong perturbation of the NMR signal of the... 

It is expected that the neutral species of the anesthetics can penetrate more deeply into the hydrophobic bilayer interior than the cationic ones. From the H and C NMR, we have demonstrated that the neutral species, DEC and PRC, are trapped deeply in the bilayer DEC can penetrate into the hydrophobic core of the bilayer, zone III, and PRC can penetrate into the inside of the bilayer preferentially trapping from zone II to the middle of zone III [48]. This information is valuable in the sense that it is difficult to observe the NMR signal of the neutral species in water because of the extremely low solubility. The preferential location is in accordance with the solubility in water the neutral species of DEC and PRC, sparingly soluble in water, are expected to favor the hydrophobic bilayer interior. 

Quantitative NMR analysis may also be applied to water-soluble polymers or copolymers in some cases. Polymers usually have large molecular weights and are heterogeneous in size. However, the proton NMR signals of some polymers... 

Independent analysis of the bound water NMR signal of each species. 

Useful information about enzymes can sometimes be obtained by observing effects of paramagnetic ions on the NMR signal of protons in the solvent water. 

It is well known that high-silica zeolites such as silicalite are hydrophobic. Addition of hexane to ZSM-5 does not affect the NMR signal from water, but addition of butanol has a very marked influence. This indicates that butanol displaces water from the intracrystalline space to the outer surface of the zeolite particles. 

Fig. 5.42. 600 MHz H NMR spectrum of water solutions of the Thermits Cua domain at pH 8 and 278 K. Signal i is observable at lower pH (adapted from [120]).

DOTA-type complexes exist in two diastereomeric forms (m and M) which may have remarkably different water exchange rates as found for [Eu(D0TAM)(H20)]3+ [58,59]. In this 170 and H NMR study performed in acetonitrile-water solvent, it was possible to detect the NMR signals of the coordinated water molecules in both isomers. In a general case, the observation of the bound water signal for Ln(III) poly(amino carboxylates) is not possible due to the fast exchange, and for Gd(III) complexes, to the slow electronic relaxation. 

One aspect of the experimental conditions under which these spectra were obtained is important to understand so that the spectra can be rationally interpreted. For solubility and stability purposes, peptides are generally dissolved in buffered water. Recall from Chapter 3 that compounds prepared for NMR experiments are almost always dissolved in deuterated solvents. The need for deuterated solvents is so that the spectrometer can remain stable for the duration of the experiment by way of the field/frequency lock. The lock signal comes from the deuterium NMR signal of... 

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