Magnetic parameters spin probe method

Spectroscopic Methods.—Nuclear Magnetic Resonance (n.m.r.). Cohen-Addad and Ruby comment that thermodynamic polymer-solvent interaction parameters obtained from n.m.r. data should be contrasted with those obtained from other methods in the sense that the former are defined on a molecular scale only. That is, nuclear spins are local probes, sensitive to magnetic interactions averaged over volumes of molecular size. N.m.r. methods, therefore, usefully complement other methods in studying underlying statistical mechanical models for polymer-solvent mixtures at equilibrium a comment which has been amplified in relation to polymer blends. ... 

We will start by surveying the parameters that are used to describe the magnetic interactions within the nitroxide label, as well as the parameters used to characterize its motion. Because of the significant number of parameters that may be required to describe the rotational dynamics, the best means of extracting information about probe structure, orientation, and dynamics is to fit a calculated ESR spectrum to the experimental one by least-squares minimization of the model parameters. The chapter describes some of the least-squares methods that have been successfully applied to this type of analysis and concludes with some illustrative examples. Specific applications to spin-labeled polymers and interpretation of the ESR parameters obtained by this analysis are described in greater detail in Chapter 6. 

EPR spectral profiles of paramagnetic probes in solid phases are determined by the anisotropic distribution of spin packets due to the nonaveraged magnetic anisotropies. The inhomogeneously broadened bands are scarcely informative, and the so-called hyperfine methods (see below) are used in these cases to extract information on the hyperfine parameters. 

The ordering of probe molecules in liquid crystals was in fact known much earlier than 1968. It is widely used to determine various parameters of the solute and solvent liquid crystal using nuclear magnetic resonance (NMR), electron spin resonance (ESR), ultraviolet (UV), visible, and other spectroscopie teehniques. After the pioneering work of Saupe and Englert in 1963 [8], the NMR spectroscopy of molecules oriented in liquid crystals became very important in structural chemistry, as it provides the only direct method for precise determination of the molecular geometries in liquid phase. In addition to structural and confor-... 

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