Liquid-state NMR

Nuclear magnetic resonance (NMR) is a pre-eminent technique for molecular-level understanding because it exquisitely displays differences in and connections between chemical environments of atoms in a molecule. Many biologically relevant nuclei - H, N, N, H, Na, and more - can be usefully observed by 

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The principal dilTerence from liquid-state NMR is that the interactions which are averaged by molecular motion on the NMR timescale in liquids lead, because of their anisotropic nature, to much wider lines in solids. Extra infonnation is, in principle, available but is often masked by the lower resolution. Thus, many of the teclmiques developed for liquid-state NMR are not currently feasible in the solid state. Furthemiore, the increased linewidth and the methods used to achieve high resolution put more demands on the spectrometer. Nevertheless, the field of solid-state NMR is advancing rapidly, with a steady stream of new experiments forthcoming. 

This chapter simnnarizes the interactions that affect the spectrum, describes the type of equipment needed and the perfomiance that is required for specific experiments. As well as describing the basic experiments used in solid-state NMR, and the more advanced teclmiques used for distance measurement and correlation, some emphasis is given to nuclei with spin / > dsince the study of these is most different from liquid-state NMR. 

The structure of the second abundant component of the wood, lignin (Fig. 12) has been extensively studied using liquid state NMR and very detailed information... 

The problems involved in quantitative analysis using NMR spectroscopy, have been discussed by several authors and it is evident that it still causes a lot of problems as especially pointed out by Hays55 in his excellent review on the subject. Thus in liquid state NMR spectroscopy the quantitative estimation of atoms and groups involves the use of normal analytical method. In the case of solid state NMR spectroscopy, however, the application of the cross-polarization technique results in signal enhancements and allows repetition rates faster than those allowed by the carbon C-13 Tl. Therefore, the distortion of relative spectral intensities must always be considered a possibility, and hence quantitative spectra will not always be obtained. 

In liquid-state NMR spectroscopy only the isotropic component of the chemical shift tensor is measurable. Upon ahgnment the situahon changes and the so-called zz-component of the chemical shift tensor includes anisotropic components. 

We have referred to the various interactions which can cause line broadening in the solid state. One of these, which is normally not a problem in liquid state NMR, is due to the fact that the chemical shift itself is a tensor, i.e. in a coordinate system with orthogonal axes x, y and z its values along these axes can be very different. This anisotropy of the chemical shift is proportional to the magnetic field of the spectrometer (one reason why ultra-high field spectrometers are not so useful), and can lead in solid state spectra to the presence of a series of spinning sidebands, as shown in the spectra of solid polycrystalline powdered triphenylphosphine which follows (Fig. 49). In the absence of spinning, the linewidth of this sample would be around 75 ppm ... 

The price to pay for getting the higher intermediate frequency in such a convenient way would be the less clock-jitter tolerance, so that the apparent resolution of the resonance line can be degraded compared with that obtained in the conventional detection scheme. For this reason, we demonstrated the high-resolution liquid-state NMR experiment, in which the resonance line width was on the order of Hz. In fact, we observed a drift of the peak position when we used a less stable clock... 

Microporous nanoparticles with ordered zeolitic structure such as Ti-Beta are used for incorporation into walls or deposition into pores of mesoporous materials to form the micro/mesoporous composite materials [1-3], Microporous particles need to be small enough to be successfully incorporated in the composite structure. This means that the zeolite synthesis has to be stopped as soon as the particles exhibit ordered zeolitic structure. To study the growth of Ti-Beta particles we used 29Si solid-state and liquid-state NMR spectroscopy combined with x-ray powder diffraction (XRPD) and high-resolution transmission electron microscopy (HRTEM). With these techniques we monitored zeolite formation from the initial precursor gel to the final Ti-Beta product. 

We note that optimal control is a universal tool for experiment design and has also, in solid-state NMR spectroscopy, found additional applications in the design of homonu-clear dipolar recoupling [41], broadband rf pulses and quantum gates [71], building blocks of symmetry-based recoupling experiments [129], quadrupolar multiple-quantum MAS experiments [165], and improved pulses for quadrupolar nuclei [166]. Numerous references to further applications with regard to liquid-state NMR can be found in [72]. 

In general, liquid-state NMR is preferable as a starting point over SSNMR for several compelling reasons. The primary reason is due to the ability of liquid-state NMR to yield much narrower lines. In practice, liquid-state NMR line shapes are typically an order of the magnitude or more narrower than the solid state. This provides much greater spectral resolution and often an apparently greater signal-to-noise ratio for liquids spectra as compared with solids spectra. NMR... 

Hietala, S., Maunu, S.L., Sundholm, F., Jamsa, S. and Viitaniemi, P. (2002). Structure of thermally modified wood studied by liquid state NMR measurements. Hol orschung, 56(5), 522-528. 

The main experiments performed with the two different silica sources are reported in Table 1 and the Si liquid state NMR spectra of experiments 3, 4, and 11 (Table 1) are given in Figure 1. 

Figure 1 Si liquid state NMR spectra of surfactant-silicate mixtures a) waterglass 0.5M Si02 0.1M CTAB 0.9M NaOH, experiment 3, Table 1, b) octameric silicate species (D4R) 0.5M SiC>2 0.1M CTAB 1.0M TMAOH 21vol% MeOH, experiment 11, Table 1 and c) waterglass 0.5M Si02 0.1M CTAB 0.4M NaOH 0.6M TMAOH 21vol% MeOH experiment 4, Table 1 ( external reference)...

The Si liquid state NMR spectrum of experiment 11 (Figure lb) displays mainly one sharp and intense line at -99.4ppm corresponding to the D4R units. It is worthy to note that in the presence of a large amount of sodium cations (experiment 4), the concentration of D4R species considerably decreases (see Figure lc), such a result being already mentioned in the literature [15]. 

Liquid-state NMR spectroscopy (Davidson and Ripmeester, 1984) Yes Water mobility vs. time (mins) 15 psi Reorientation and diffusion... 

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