Molecular modeling nuclear magnetic resonance spectroscopy

This contribution to the series is a report of an initial use of nuclear magnetic resonance spectroscopy in an effort to begin to answer some of these structural questions. Also included is an outline of a molecular-based theoretical model of sidechain-counterion interactions, as suggested by the experimental results. The content of this work is concerned with Nafion in the monovalent cationic salt form, i. e.,... 

The fluid mosaic model is supported and has heen further developed by measurements with modem techniques, including nuclear magnetic resonance spectroscopy, X-ray and neutron scattering, and computer simulations. Details with molecular resolutions have now been revealed. Figure 3.5 depicts a snapshot of a fuUy hydrated ternary membrane patch composed of a 3 1 1 ratio of POPC POPA cholesterol from a large-scale, all-atom computer simulation. Several stmctural... 

Several interesting review articles have been recently published focusing on the use of NMR methods to study peptide-lipid and small molecular weight molecule interactions in model and natural membranes. Maler as well as Kang and Li highlighted the unique possibilities of solution-state NMR to investigate the structure, dynamics and location of proteins and peptides in artificial bilayers and peptide-lipid interactions. On the other hand, Renault et reviewed recent advances in cellular solid-state nuclear magnetic resonance spectroscopy (SSNMR) to follow the structure, function, and molecular interactions of protein-lipid complexes in their cellular context and at atomic resolution. 

The role of specific interactions in the plasticization of PVC between the carbonyl fimctionality of the plasticizer were proposed on the basis of results from Fourier transform infrared spectroscopy. Reported shifts in the absorption frequency of the carbonyl group of the plasticizer ester to lower wave number are indicative of a reduction in polarity. These ideas have been extended using newer analytical techniques, in particular molecular modeling and solid-state nuclear magnetic resonance spectroscopy (nmr). 

Local mode relaxation of isolated lignin and its model compounds have been detected by dynamic mechanical measurement, and broad-line nuclear magnetic resonance spectroscopy (b-NMR) [49,53], although this molecular motion has scarcely received attention in recent papers. Transition map of local mode relaxation of various kinds of polymers is found elsewhere [56]. Figure shows second moment of absorption line of b-NMR of DL in powder form. When the relaxation is from the... 

Nuclear magnetic resonance (NMR) spectroscopy is a valuable technique for obtaining chemical information. This is because the spectra are very sensitive to changes in the molecular structure. This same sensitivity makes NMR a difficult case for molecular modeling. 

These ideas have been extended using new analytical techniques, in particular molecular modeling and soHd-state nuclear magnetic resonance (nmr) spectroscopy. 

This comprehensive review of theoretical models and techniques will be invaluable to theorists and experimentalists in the fields of infrared and Raman spectroscopy, nuclear magnetic resonance, electron spin resonance and flame thermometry. It will also be useful to graduate students of molecular dynamics and spectroscopy. 

Structural information at the molecular level can be extracted using a number of experimental techniques which include, but are not restricted to, optical rotation, infra-red and ultra-violet spectroscopy, nuclear magnetic resonance in the solid state and in solution, diffraction using electrons, neutrons or x-rays. Not all of them, however, are capable of yielding structural details to the same desirable extent. By far, experience shows that x-ray fiber diffraction (2), in conjunction with computer model building, is the most powerful tool which enables to establish the spatial arrangement of atoms in polymer molecules. 

In earlier literature reports, x-ray data of a-based ceramics, the /3-like phase observed in certain silica minerals was explained by a structural model based on disordered Q -tridymite. However, others have suggested that the structure of the stabilized jS-cristobalite-like ceramics is closer to that of a-cristobalite than that of Q -tridymite, based on the 29Si nuclear magnetic resonance (NMR) chemical shifts (Perrota et al 1989). Therefore, in the absence of ED data it is impossible to determine the microstructure of the stabilized jS-cristobalite-like phase. ED and HRTEM have provided details of the ceramic microstructure and NMR has provided information about the environments of silicon atoms in the structure. Infrared spectroscopy views the structure on a molecular level. 

Liquids are difficult to model because, on the one hand, many-body interactions are complicated on the other hand, liquids lack the symmetry of crystals which makes many-body systems tractable [364, 376, 94]. No rigorous solutions currently exist for the many-body problem of the liquid state. Yet the molecular properties of liquids are important for example, most chemistry involves solutions of one kind or another. Significant advances have recently been made through the use of spectroscopy (i.e., infrared, Raman, neutron scattering, nuclear magnetic resonance, dielectric relaxation, etc.) and associated time correlation functions of molecular properties. 

---