Solid state chemical spectroscopy

In this chapter shock modification of powders (their specific area, x-ray diffraction lines, and point defects) measurements via analytical electron microscopy, magnetization and Mossbauer spectroscopy shock activation of catalysis, solution, solid-state chemical reactions, sintering, and structural transformations enhanced solid-state reactivity. 

Shi et al.71 have assigned the backbone and side-chain chemical shifts for 103 of 238 residues of proteorhodopsin using solid state NMR spectroscopy. Analysis of the chemical shifts has allowed determination of protonation states of several carboxylic acids as well as boundaries and distortions of trans-membrane a-helices and secondary structure elements in the loops. It has been shown that internal Asp227, making a part of the counterion, is ionised, while Glul42 located close to the extracellular surface is neutral. 

Thanks to the pioneering works of many research groups, solid-state NMR is now a well established spectroscopy for the study of biological solids, particularly for those with inherent structural disorder such as amyloid fibrils. We have provided an overview of a rather complete set of NMR techniques which have developed for samples prepared by chemical synthesis or protein expression. There are many different ways to present the materials discussed in this review. We hope that the way we have chosen can give a snapshot of some facets of the very exciting discipline of biological solid-state NMR spectroscopy. In spite of the success of solid-state NMR as a tool in biological study, it is not yet a mature technique and there is much room for further development. Below we will speculate on a few possibilities from our own perspective. 

It follows that, as used in solid state NMR spectroscopy, 13C observation may have potential advantages in that the 13C nucleus has a wider chemical shift range than 1H, making the spectral resonances of individual molecular species more easily... 

Recently, solid state nmr spectroscopy has been used to probe hydrogen-bonded materials and first reports showed that there was a direct relationship between / o o anisotropic chemical shift as bonds become... 

The isotropic chemical shift is the average value of the diagonal elements of the chemical shift tensor. Advances in solid state NMR spectroscopy allow one to determine the orientation dependence, or anisotropy, of the chemical shift interaction. It is now possible to determine the principal elements of a chemical shift powder pattern conveniently, and the orientation of the principal axes with more effort. Hence, instead of settling for just the average value of the chemical shift powder pattern, one can now aim for values of the three principal elements and the corresponding orientations in a molecular axis system. 

In our work we tried to combine solid state optical spectroscopy with the method of chemical variation, that is a systematic modification of the complexes (substitution of ligands and metals) as well as changes in the surrounding media (solvents, glasses and crystalline hosts). We are thus able to identify the nature of the excited states, and by studying the above series of related compounds we can discern the principles governing their energies relative to each other. 

Keywords 33S NMR spectroscopy 33S chemical shift 33S nuclear relaxation 33S solid state NMR spectroscopy... 

C. N. R. Rao is a Professor of Chemical Science at the Indian Institute of Science, and President of the Jawaharalal Nehru Centre for Advanced Scientific Research, Bangalore, India. He is an Honorary Professor of Chemistry at the University of Wales, Cardiff. He was Commonwealth Visiting Professor at the University of Oxford and Nehru Professor at the University of Cambridge. He is a Fellow of the Royal Society, London, Foreign Associate of the U.S. National Academy of Sciences, and Foreign member of several other academies. He is a member of the Pontifical Academy of Sciences and an Honorary Fellow of the Royal Society of Chemistry. He is a recipient of the Marlow Medal of the Faraday Society and the RSC Medal for solid-state chemistry. His main research interests are in solid-state chemistry, spectroscopy, and molecular structure and surface science. He is the author of over 500 research papers and several books in solid state chemistry. 

Polymorphism is customarily monitored by melting point or infrared spectral analysis. However, other methods, such as X-ray diffraction, thermal analytical, and solid-state Raman spectroscopy, also can be used. It is expected that the sponsor will conduct a diligent search by evaluating the drug substance recrystallized from various solvents with different properties. Either the basis for concluding that only one crystalline form exists, or comparative information regarding the respective solubilities, dissolution rates, and physical/chemical stability of each crystalline form should be provided. 

Recently, solid state nmr spectroscopy has been used to probe hydrogen-bonded materials and first reports showed that there was a direct relationship between R0...0 and cr, the anisotropic chemical shift as bonds become shorter the chemical shift moves downfield. Twenty-four compounds were examined and some, such as potassium hydrogen malonate, had a o-value below 20 ppm (Berglund and Vaughan 1980). 

Similarly, the down-field chemical shift of the proton resonance in H-NMR spectroscopy, which is a diagnostic tool for hydrogen bonding in solution, might be related to crystal structural data through the recent development of solid-state NMR spectroscopy. 

Proton NMR cannot be used as an indication of the position occupied by hydrides in HNCC in solution as the range of chemical shifts observed is enormous (441). For example, all fully characterized carbonyl clusters that contain interstitial hydrides are listed in Table II, with chemical shifts from 23.2 6 in [Co6(CO)isH]- to -24(5 in [Nii2(CO)2iH] -. The octahedral [Rue(CO).8H]- was the first reported cluster for which an interstitial hydride was assigned on the basis of X-ray (30, 31) and solid-state infrared spectroscopy studies (33). However, because of the extremely low field position of the NMR signal (16.4 S), it was suspected to be of the formyl type (417). Its interstitial position was later unequivocally established by neutron diffraction studies (32). The observation of the satellites in the... 

MAS is routinely used in solid-state NMR spectroscopy for eliminating the elfects of chemical shift anisotropy, heteronuclear dipolar interactions and first-order quadrupolar interactions. In this method the sample is rotated abont the axis inclined at 54.74° with respect to the external magnetic field Bo, so that the average of the geometric term in nnclear spin interactions (3cos 0 — 1) = Except for some specific applications of static wide-line solid-state NMR spectroscopy (i.e., for or for the determination of CSA patterns), the MAS is an essential feature of solid-state NMR spectroscopy and can also be nsed in variable temperature mode. The MAS methodology can also be nsed for high-resolntion studies of viscous hquids and soft solids. 

The transformation of plant detritus into stabilized humic substances is one of the most complex and least understood biogeochemical processes in the carbon cycle (Stevenson, 1994). Traditionally, decomposition and humification of plant residues was thought to be dominated by the mineralization of labile materials, while more recalcitrant aromatic compounds accumulate in the soil. The application of modem analytical techniques—including solid-state NMR spectroscopy, pyrolysis gas chromatography, and degradative chemical techniques—to the study of decomposition and humification has significantly altered this simple view of carbon transformation in the soil (Baldock et al., 1997 Kogel-Knabner, 1997). 

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