NMR fields

Hills, B.P., Wang, Y.L., and Tang, H.R. 2001. Molecular dynamics in concentrated sugar solutions and glasses An NMR field cycling study. Mol. Phy. 99, 1679-1687. 

For spin-f nuclei, dipolar interactions may be modulated by intramolecular (DF, reorientation etc.) and/or intermolecular (TD) processes. In general, the intra- and inter-molecular processes can produce quite different Tj frequency dispersion curves. In practice, NMR field cycling experiments are often needed to extend the frequency domain from those employed in conventional spectrometers to a lower frequency range (i.e., the kHz regime) for unambiguous separation (and identification) of different relaxation mechanisms. The proton spin relaxation by anisotropic TD in various mesophases has been considered by Zumer and Vilfan.131 133,159 In the nematic phase, Zumer and Vilfan found the following expression for T ... 

Product Attribute/Disorder NMR field strength (Tesla) Methodology Ref. 

Any NMR field-cycling (FC) relaxometry experiment presumes that the sample is subject to a magnetic field of various intensities for time intervals of varying durations. More specifically, between the various intervals of a relaxation-time measurement, the external magnetic field induction... 

In a traditional magnet for NMR spectroscopy, the field Bq of the magnet is much higher than the field components originating from outside sources. Moreover, devices such as efficient NMR field stabilizers are used to suppress all interfering external fields. Consequently, the presence of such field components can be usually ignored. On the contrary, during a FFC NMR measurement the sample may be subject to very low fields (ideally down to zero) which is practically impossible when the relaxation field value becomes comparable to the environmental fields. The amplitude of such fields, if not compensated, represents the lower relaxation field limit for a reliable NMRD profile. 

Advances in NMR spectrometer and probe technology and in solid-state NMR methods, along with development of new pulse sequences have opened up the biomolecular NMR field to the study of membrane-bound proteins and large molecular weight (MW > 50 kDa) systems. In addition, studies of low-sensitivity nuclei are expected to gain in popularity as the appropriate technical and experimental expertise is developed and refined. Another important area concerns developments in protein engineering that allow preparation of biomolecules isotopically labeled either uniformly or at particular sites. The rapid and continuing development of these... 

The introduction and implementation of heteronuclear-based multidimensional techniques have revolutionized the protein NMR field. Large proteins (> 100 residues) are now amenable to detailed NMR studies and structure determination. These techniques, however, necessarily require a scheme by which and isotopes can be incorporated into the protein to yield a uniformly labeled sample. Additional complications, such as extensive covalent post-translational modifications, can seriously limit the ability to efficiently and cost effectively express a protein in isotope enriched media - the c-type cytochromes are an example of such a limitation. In the absence of an effective labeling protocol, one must therefore rely on more traditional proton homonuclear NMR methods. These include two-dimensional (1) and, more recently, three-dimensional H experiments (2,3). Cytochrome c has become a paradigm for protein folding and electron transfer studies because of its stability, solubility and ease of preparation. As a result, several high-resolution X-ray crystal structure models for c-type cytochromes, in both redox states, have emerged. Although only subtle structural differences between redox states have been observed in these... 

Fig. 2. Temperature dependence of the magnetic susceptibility x (right scale) and of the field for Pd NMR at fixed Larmor frequency Bo (left scale) for palladium. Similar to Fig. la, the NMR field shift and the susceptibility are proportional. Both are (mainly) caused by the Pauli-type paramagnetism of the d-like conduction electrons. (The temperature dependence is not predicted by the simple free-electron description of the susceptibility in metals.) [Reproduced with permission from Seitchik et al. (16). Copyright 1964 American Physical Society.]...

Many biofiuids are not chemically stable and for this reason care should be taken in their collection and storage. For example, cell lysis in erythrocytes can easily occur. In addition, if the biofiuid has been reconstituted into D2O after fireeze-drying or if a substantial amount of D2O has been added to provide an NMR field lock, then it is possible that certain H NMR resonances will be lost. These include not only NH and OH protons as expected but CH groups where the C-H bond is labile such as H2 of imidazole moieties (as in histidine or histidinyl-containing proteins such as... 

Protein Isotopic Types of NMR Field Instrument Analysis... 

The following part of the present chapter will present an introduction to the NMR field, trying to avoid deep mathematical and physical explanations, but rather presenting the conclusions of these treatments. For those interested in a deeper presentation of various topics which follow, references to more extensive books are made. 

Thus, looking to the NMR keyword in Food Sciences and Technology Abstracts, on CD-ROM, until June 1996, we could find only one book exclusively dedicated to the NMR field [14]. The same search revealed several books speciahzed in a particular food stuff or covering general analytical techniques, having a chapter in NMR. The present chapter is by no means trying to cover this gap, but only to draw attention to various aspects of NMR in food sciences, literature data being one of these aspects. 

It is difficult to make predictions on how the NMR field will develop. The variety of techniques, applications and instrumentation available today was hard to imagine only a few years ago. We will briefly mention some tendencies which could also be relevant for food sciences. But certainly the future will show much more than that. 

Recent environmental problems of Cl-containing polymers give a spotlight on chlorine. Coal contains a small amount of chlorine (50-1500 ppm) but there is no information about chemical structure in raw coals. In the NMR field, although... 

Noack F (1986) NMR field-cycling spectroscopy principles and applications. Prog NMR Spectrosc 18 171-276... 

J. Ahart, E. Palangie, W. Socher, J. Voidaender, Simulation of quadrupole disturbed NMR field spectra by using the exact solution of the Hamiltonian application to zinc, J. Chem. Phys. 78 (1983) 5468-5473. 

Single Sided NMR Field Match, Shim and dedicated sequences... 

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