NMR methodologies

The distribution of electrons around the purine skeleton affects not only its chemical properties and reactivity but also the basic parameters of its NMR spectra - chemical 

The measurement of various NMR parameters is demonstrated for 6-methoxy-A -benzylpurine in DMSO-de solution. Its H NMR spectrum is shown in Fig. 1. The H-NMR chemical shifts of selected purine derivatives 7 are summarized in Tables 1 -3. 

The chemical shifts of the purine carbon atoms are found in the range typical for heteroaromatic compounds.For purine and adenine derivatives without heavy-atom substitution, the resonances of the C-2 and C-8 atoms are located between 135 and 155 ppm. Their chemical shifts are significantly influenced by the presence of the lone 

The effect of a neighboring nitrogen atom is also observed for the C-2 resonance. While the C-2 atom in N -methylpurine and N -methylpurine resonates at — 144 ppm, the chemical shift of the same carbon atom in 2V -methylpurine and N -methyIpurine is —152 ppm. 

Atoms in molecules rarely possess spherically symmetric electron distributions due to the presence of chemical bonds or nonbonding rr-orbitals. The chemical shielding, therefore, depends on the orientation of the molecule with respect to the static magnetic field and the chemical shift is described by a second-rank tensor. The chemical-shift tensor is fully described by three principal values and three Euler angles that orient the principal axis system of the diagonalized chemical-shift tensor with respect to the molecular frame, fin, 522, and 633 (ppm) represent the three principal components of the shift tensor with the following rule 5ii 622 33. In 

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However, recent application of two types of NMR methodologies that provide long-range structural information have painted a very different picture. From these experiments, the denatured state in 0 M urea and 8 M urea appear to be highly similar, both retaining the same overall spatial positioning and orientation of the chain seen in the folded conformation. 

This review aims at giving an overview of the NMR applications in meat science. This may be an idealistic scope, as meat science is not a strictly delimited area. In studies of the conversion of muscle to meat, initialised early post mortem, the limits to in vivo muscle physiology are vague, and therefore the differentiation of which studies belong to which discipline is subjective, and consequently studies have been included where we found it natural. Overall, the review attempts to demonstrate and discuss the different NMR methodologies (relaxometry, imaging, spectroscopy) and their potential applications within meat science based on the existing literature. In the end, conclusions will be drawn, and future perspectives are considered. 

In conclusion, NMR methodologies have already proven successful within meat science with applications in many different areas. However, many unexplored areas still exist where the potential of NMR can be expected to reveal useful and valuable information. The inspiration that can be obtained from NMR studies within other disciplines, e.g., medical areas, material science, physical/chemical sciences and food science in general, should be rewarded with great attention in future in order to continue development of the use of NMR in meat science. 

Carbohydrate conformation plays a key role for molecular recognition processes, and their determination contributes to the understanding of many biological processes. The latest NMR methodological developments for conformation determination are discussed here, and representative examples are given. 

We will start by presenting new advances from the NMR methodological viewpoint to later describe some key examples of applications of NMR for sugar conformation determination, by discriminating between the free and bound state and also from natural and synthetic sugars (or mimetics thereof). 

Table 2. NMR methodology used to study quality attributes or disorders in fruit... 

The utilization of the full array of modern H and NMR methodology has led to various... 

M. E. Smith and E. R. H. van Eck, Recent advances in experimental solid state NMR methodology for half-integer spin quadrupolar nuclei. Prog. Nud. Magn. Reson. Spectrosc., 1999, 34,159-201. 

Some kinds of polypeptide blend samples (PLA/PLV, PLA/PLIL, PG/PLV and PDA/PLV) have been treated with different blend conditions, and their miscibility has been investigated by the observation of 13C NMR chemical shifts and 3H 7) data.17 27 Furthermore, we need more detailed information about the miscibility of the polypeptides to understand the polypeptide blend by using further sophisticated NMR methodology. Thus, 2D FSLG 13C- H HETCOR NMR is useful to elucidate intermolecular HB interactions between two kinds of polypeptide chains and their miscibility. 

As an NMR methodology for elucidating conformational stability in the polypeptide blends, the conformation-dependent 13C NMR chemical shift for polypeptides in the solid state has been reported. It has been elucidated that the 13C NMR chemical shifts of a number of polypeptides in the solid state, as determined by the 13C CP/MAS method, are significantly displaced, depending on their particular conformations such as a-helix, 3i-helix or p-sheet form.11,17 31... 

As an NMR methodology for elucidating miscibility in the PLA/PLV, PLA/PLIL, PDA/PLV and PG/PLV blends, the proton spin-lattice relaxation times in the rotating frame ) for homopolypeptides and their... 

Thus, it is useful to get more detailed information about the miscibility of polypeptides and to understand the polypeptide blend by using further sophisticated NMR methodology. 

Both 13C NMR and 1 FI NMR have also been used to monitor solid-phase syntheses. For 13C NMR methodologies, the main concern lies in the thousands of transients needed to properly visualize bead-attached moieties. Recently, a rapid technique has been developed.41 The method takes advan-... 

Wanasundara, U.N., Shahidi, F., and Jablonski, C.R. 1995. Comparison of standard and NMR methodologies for assessment of oxidative stability of canola and soybean oils. Food Chem. 52 249-253. 

In 1978 Cohn and Hu (1) demonstrated the isotopic effect by 180 on the Ip-nmr spectrum of inorganic phosphate. For each that replaces an 1 0, an upfield shift of 0.021 ppm results. Thus the chemical shift for HP O 58 is 0.084 ppm downfield from Hpl 04=. Based on this observation it is obvious that any chemical event that potentially involves substitution or exchange of an 0 for 16() in phosphorus containing compounds can be followed by monitoring the Ip-nmr spectrum throughout the course of the reaction. This article describes experiments from my laboratory on two enzymes that catalyze phosphoryl transfer reactions and our use of the [1 0/1 0] lp-nmr methodology to detect intermediates in the enzymic reactions. 

The application of DFT methods to the computation of transition-metal NMR has been reviewed in the past [1-4]. A short overview was recently prepared by Buhl [5], NMR calculations on heavier transition-metal complexes have further been discussed in reviews devoted to relativistic NMR methodology [6-9], Thus, the present overview does not attempt to give a full coverage of the available literature, but to present a number of illustrative examples, the present status of such computations and their accuracy and limitations, along with a description of the underlying methodology. Because of the high importance of relativistic effects on NMR parameters, which is clearly represented in the available literature on DFT NMR computations of transition-metal complexes, the reader will find that a substantial portion of this paper is devoted to this topic. 

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