Solution NMR Spectroscopy

The formation of such materials may be monitored by several techniques. One of the most useful methods is and C-nmr spectroscopy where stable complexes in solution may give rise to characteristic shifts of signals relative to the uncomplexed species (43). Solution nmr spectroscopy has also been used to detect the presence of soHd inclusion compound (after dissolution) and to determine composition (host guest ratio) of the material. Infrared spectroscopy (126) and combustion analysis are further methods to study inclusion formation. For general screening purposes of soHd inclusion stmctures, the x-ray powder diffraction method is suitable (123). However, if detailed stmctures are requited, the single crystal x-ray diffraction method (127) has to be used. 

Typical characterization of the thermal conversion process for a given molecular precursor involves the use of thermogravimetric analysis (TGA) to obtain ceramic yields, and solution NMR spectroscopy to identify soluble decomposition products. Analyses of the volatile species given off during solid phase decompositions have also been employed. The thermal conversions of complexes containing M - 0Si(0 Bu)3 and M - 02P(0 Bu)2 moieties invariably proceed via ehmination of isobutylene and the formation of M - O - Si - OH and M - O - P - OH linkages that immediately imdergo condensation processes (via ehmination of H2O), with subsequent formation of insoluble multi-component oxide materials. For example, thermolysis of Zr[OSi(O Bu)3]4 in toluene at 413 K results in ehmination of 12 equiv of isobutylene and formation of a transparent gel [67,68]. 

Ippel, J. H., Olofsson, A., Schleucher, J., Lundgren, E., and Wijmenga, S. S. (2002). Probing solvent accessibility of amyloid fibrils by solution NMR spectroscopy. Proc. Natl. Acad. Sci. USA 99, 8648-8653. 

The TMEDA and THE complexes of the very sterically crowded methyllithium derivative tris(trimethylsilyl)methyUithium (9, Scheme 1) were studied by multinuclear solid state NMR spectroscopy in combination with solution NMR spectroscopy and X-ray crystallography to reveal the strucmre and dynamic behaviour of the complexes . In the solid state, this complex crystallizes as an ate-complex, with one lithium cation interacting with two substituted methyl anions while the other lithium cation is complexed by two TMEDA ligands. In solution, the afe-complex is partly transformed into solvated monomers or aggregates, depending on the experimental conditions. 

In solution NMR spectroscopy, dipolar interactions and anisotropic effects are averaged out by the molecular motion, but this is not so in the solid state, and the NMR spectra of solids tend to be broadened by three main effects ... 

It is particularly important to be able to distinguish between cis and trans isomers. In solution, NMR spectroscopy (2H, 31P, 13C) is the most useful technique in the solid state the far-IR spectra are usually diagnostic, since both the number of bands (two for cis, one for trans) and the frequency of absorption (vPd x) are characteristic of the isomer present. 

There has been long controversy regarding the bioactive conformation of PTX due to the difficulties to obtain high-resolution structural data from PTX bound to MT. Before the EC structure of PTX-stabilized tubulin polymer sheets [11] was available, solution NMR spectroscopy was used to derive candidate conformations for the tubulin-bound state of PTX. Early solution NMR studies on PTX have been reviewed by Jimenez-Barbero et al. [51] and only the fundamental results are summarized here. 

Two conformations of EpoA in complex with tubulin have been proposed on the basis of EC [26] and NMR [76, 96] data, respectively (Fig. 11). The tubulin-bound conformation of EpoA was determined by solution NMR spectroscopy [96] before the EC structure of EpoA bound to tubulin was available. The observation that, in a 100 1 mixture with tubulin, NOE cross-peaks of EpoA have negative sign, indicated that there is a fast exchange equilibrium in solution. This offered the opportunity to measure transferred NMR experiments, that report on the bound conformation of the ligand. A total of 46 interproton distances were derived from cross-peak volumes in tr-NOE spectra. However, these distance restraints did not suffice to define a unique conformation, as several distinct structures were consistent with them. Transferred cross-correlated relaxation (Sect. 2.2.1.3) provided the additional dihedral restraints that were crucial to define the bound conformation [96, 97], One requirement to measure CH-CH dipolar and CH-CO dipolar-CSA CCR rates is that the carbon atoms involved in the interaction are labeled with 13C. The availability of a 13C-labeled sample of EpoA offered the opportunity to derive seven of these dihedral angle restraints from tr-CCR measurements (Fig. 12). 

The conformation of laulimalide in the free state has been studied by X-ray crystallography [129, 130] and solution NMR spectroscopy [64, 134],... 

Bovey, F. A., Structure of Chains by Solution NMR Spectroscopy , in Comprehensive Polymer Science, Pergamon Press, Oxford, 1989, Vol. 1, pp. 339-375. 

From the outset, it was clear that Si MASNMR resonances were, to some degree, structure-sensitive. The correlation charts of Lippmaa et al (5.9) and our own (7, 10) show a range of values at which a 2 si nucleus in a particular environemnt (Si(0Al) (OSi) with n = 0, 1, 2, 3> or k) was expected to resonate his point emerges clearly from Table 1. In this respect MASNMR is similar to IR, UV and Raman and solution NMR spectroscopies for which there are comparable charts that are constructed, as in 29sI MASNMR, solid-state spectroscopy, largely on the basis of accumulated practical experience, rather than on theoretical calculations. ... 

Solid-state NMR is used in the analysis of ceramics (they are neither soluble nor meltable), biological cell membranes, wood, cellulose and other plant materials, bone, and even gemstones (any volunteers for solution NMR spectroscopy of... 

Evenas, J., Tugarinov, V., Skrynnikov, N. R., Goto, N. K., Muhandiram, R., and Kay, L. E. (2001). Ligand-induced structural changes to maltodextrin-binding protein as studied by solution NMR spectroscopy./. Mol. Biol. 309, 961-974. 

Solution NMR spectroscopy is the most widely used technique to determine the equihbrium constant of supramolecular polymers [23,24,59,123, 148,149,158,197], either directly or with the help of a monofunctional model compound, hi the usual case of a fast exchange between free and hydrogen bonded extremities, the equihbrium constants of a particular association model are derived from the analysis of the evolution of the chemical shift versus concentration (for self-complementary functions) or versus stoichiometry (for complementary functions). Equihbrium constants in the range below 10 are reliably accessible. 

X-ray crystallographic analyses usually provide structural information that correctly represents the actual structures of metal ion-nucleic acid complexes in the crystal this usually represents an environment that is drastically different from normal solution conditions. Obviously, such analyses are limited to complexes that are both stable and amenable to crystallization. In comparison, solution NMR spectroscopy data are much more generally applicable to the analysis of metal ion-nucleic acid structure, " " but can be more easily misinterpreted owing to factors such as the distribution of metal ions among several binding sites and the intrinsically weaker nature of some of the interactions that are studied. Also, nucleic acid crystallization requires the formation of ordered and uniform intermolecular interactions between nucleic acids. These intermolecular interactions may either compete or interfere with the formation of certain metal-nucleic complexes and promote the formation of unnatural metal binding centers. ... 

In the decade or so since the first edition of this encyclopedia, there has been a considerable growth in the synthesis and structural characterization of unusually large polyoxometalates. In most cases, these have stability in solution (NMR spectroscopy) as well as in the solid state, and can be considered as linked assemblies of polyoxoanion building blocks. 

Liang B, Bushweller JH, Tamm LK. Site-directed parallel spinlabeling and paramagnetic relaxation enhancement in structure determination of membrane proteins by solution NMR spectroscopy. J. Am. Chem. Soc. 2006 128 4389-4397. 

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