Structure and Conformation

Neuhaus D and Williamson M 1989 The Nuclear Overhauser Effect in Structural and Conformational Analysis (New York VCH)... 

Figure 16.17 Structures and conformations of unbianched chain anions in (a) Ba[Se(S203)2].2H20, (b) Ba[Te(S203)2].2H20, and (c) (NH4)2[Te(S203)2]-...

With respect to the carrier mechanism, the phenomenology of the carrier transport of ions is discussed in terms of the criteria and kinetic scheme for the carrier mechanism the molecular structure of the Valinomycin-potassium ion complex is considered in terms of the polar core wherein the ion resides and comparison is made to the Enniatin B complexation of ions it is seen again that anion vs cation selectivity is the result of chemical structure and conformation lipid proximity and polar component of the polar core are discussed relative to monovalent vs multivalent cation selectivity and the dramatic monovalent cation selectivity of Valinomycin is demonstrated to be the result of the conformational energetics of forming polar cores of sizes suitable for different sized monovalent cations. 

Bovey, F.A. Chain Structure and Conformation of Macromolecules Wiley New York, 1982. 

Several aspects of polymer thin films have thus been investigated while many others are still unexplored. These include structural and conformational aspects where polymer thin film properties are theoretically well-treated but experimental data are generally missing. However, with further development of experimental techniques this area might become accessible in the near future. 

This area of research is still at its beginning and many aspects are not resolved. This includes in particular the structure and conformation of polymers at an interface as well as the modification of polymer dynamics by the interface. We have given several examples of the potential of surface and interface analytical techniques. They provide information on surface roughness, surface composition, lateral structure, depth profiles, surface-induced order and interfacial mixing of polymers on a molecular and sometimes subnanometer scale. They thus offer a large variety of possible surface and interface studies which will help in the understanding of polymer structure and dynamics as it is modified by the influence... 

The structures of four-membered rings are of considerable interest, owing in part to the low-frequency ring puckering vibration203. The comparison of the structures and conformational preferences of thietane oxides and dioxides discussed above with those of dithietane oxides and dioxides is therefore appropriate and will follow. 

The ESR spectra of a large variety of sulfonyl radicals have been obtained photolytically in liquid phase over a wide range of temperature. Some selected data are summarized in Table 2. The magnitudes of hyperfine splittings and the observations of line broadening resulting from restricted rotation about the C—S bond have been used successfully in conjunction with INDO SCF MO calculations to elucidate both structure and conformational properties. Thus the spin distribution in these species is typical of (T-radicals with a pyramidal center at sulfur and in accord with the solid-state ESR data. 

Interactions with xanthan were investigated for some GAX fractions of wheat bran [109]. Whereas, for lowly substituted GaMs a synergy in viscosity was observed at low total polymer concentrations, yielding a maximum of the relative viscosity at nearly equal proportions of both polysaccharides [124], the xanthan/xylan mixtures at the same experimental conditions showed no synergy. The observed decrease in the relative viscosity values upon addition of the xylan indicates that a certain interaction with xanthan takes place, but that it leads to a contraction in the hydrodynamic volume. The authors suggested that structural and conformational differences between GaM and GAX might be the reason for this observation. 

Small-angle X-ray scattering (SAXS), circular dichroism (CD), and UV spectroscopy at different temperatures were used to investigate the nature of calf-thymus DNA in aqueous solution, in the presence of [Me Sn] " (n = 1-3) species. The results demonstrate that the [MeSn(IV)] moiety does not influence the structure and conformation of the DNA double helix, and does not degrade DNA, as indicated by agarose gel electrophoresis. Inter alia, the radii of gyration, Rg, of the cross section of native calf-thymus DNA, determined by SAXS in aqueous solution in the presence of [Me Sn] " (n = 1-3) species are constant and independent of the nature and concentration of the [Me Sn] species. 

A series of (phoshinoyloxy)- [71], (phosphorylamino)- [72], (sulfonyloxy)-[73-78] and (seleninoyloxy)boranes [79] are also known, however, only monomeric or dimeric molecules with similar structures and conformations to I-III (Fig. 12) have been reported so far. 

The structures and conformational properties of a simple hemicarcerand, created earlier by Cram, see <96JA5590>, as well as the complexation and decomplexation with guest molecules have been computationally studied <96JA8056>. 

Thus, identification of all pairwise, interproton relaxation-contribution terms, py (in s ), for a molecule by factorization from the experimentally measured / , values can provide a unique method for calculating interproton distances, which are readily related to molecular structure and conformation. When the concept of pairwise additivity of the relaxation contributions seems to break down, as with a complex molecule having many interconnecting, relaxation pathways, there are reliable separation techniques, such as deuterium substitution in key positions, and a combination of nonselective and selective relaxation-rates, that may be used to distinguish between pairwise, dipolar interactions. Moreover, with the development of the Fourier-transform technique, and the availability of highly sophisticated, n.m.r. spectrometers, it has become possible to measure, routinely, nonselective and selective relaxation-rates of any resonance that can be clearly resolved in a n.m.r. spectrum. 

It is apparent from the foregoing discussion that several precautions are necessary in order to obtain accurate measurements of nonselective and selective relaxation-rates. Under these conditions, and with the availability of the modern Fourier-transform instrumentation, it is now possible to measure relaxation rates with an accuracy of 1-3%. The reward is great accurate information about the structure and conformation of molecules in the liquid phase, as will be seen in the following section. 

From the previous discussion, it is clear that relaxation experiments constitute a very powerful tool for investigation of the structure and conformation of carbohydrate molecules in solution. However, the nature of the individual problem may determine which relaxation experiment should be chosen in order to extract interproton distances to the desired accuracy of < 0.2 A. Although the limitations and relative merits of all of the various relaxation methods have not yet been systematically studied, accumulated experience provides some direct knowledge about the range of errors associated with relaxation experiments. 

Giusti, M.M., Ghanadan, H., and Wrolstad, R.E., Elucidation of the structure and conformation of red radish Raphanus sativus) anthocyanins using one- and two-dimensional nuclear magnetic resonance techniques, J. Agric. Food Chem., 46, 4858, 1998. 

Thomas, W. A. Unravelling molecular structure and conformation - the modem role of coupling constants. Prog. Nucl. Magn. Reson. Spectrosc. 1997, 30, 183-207. 

Jorgensen, P.L. (1982). Mechanism of the Na/K pump. Protein structure and conformations of the pure Na/K ATPase. Biochim. Biophys. Acta 694, 27-68. 

T. Iwashita, Y. Mino, H. Naoki, Y. Suguira, and K. Nomoto, High-resolution proton nuclear magnetic resonance analysis of solution structures and conformational properties of muguneic acids and its metal complexes. Biochemistry 22 4842 (1983). 

In order to understand polymer solution behaviour, the samples have to be characterised with respect to their molecular configuration, their molar mass and polydispersity, the polymer concentration and the shear rate. Classical techniques of polymer characterisation (light scattering, viscometry, ultracentrifugation, etc.) yield information on the solution structure and conformation of single macromolecules, as well as on the thermodynamic interactions with the solvent. In technical concentrations the behaviour of the dissolved polymer is more complicated because additional intramolecular and intermolecular interactions between polymer segments appear. 

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