Polarization properties measurement techniques

The choice of an appropriate measurement technique (e.g., chromatographic separation) depends on the physicochemical properties of the analyte (Fig. 14.1). According to the Giger definition, apart from molecular mass, chemical character, and polarity, the volatility of analytes must also be considered [1]. This factor determines the applicability of GC for the final determination of analytes of molecular masses up to 1000 Da and high vapor pressure. 

The changes have been used to provide information about the enviromnent of the fluorescent probe and to follow changes in conformation of the macromolecule. In other work the study of the fluorescence polarization properties of the attached probe under steady state illumination and the application of Perrin s equation enable calcu-latnn of the rotary Brownian motion of the polymer. This technique has been extended by Jablonski and Wahl to the use of time-resolved fluorescence polarization measurements to calculate rotational relaxation times of molecules These experiments are discussed fiilly in the fdlowing section of this review. 

The helix-coil transition can be demonstrated by polarization of fluorescence techniques, and the results may be compared with spectroscopic measurements to correlate the change in the hydrodynamic properties of the molecule with the change of its conformational structure. It is clear that the hydrodynamic and conformational changes do not necessarily parallel one another. Ion adsorption, breaks in the helix, and changes in helical type can occur without being reflected in the optical rotation parameters. 

A study of the structures of molecules requires techniques that are sensitive to the three-dimensional shapes, and ideally the property of handedness. Handed molecules that have been separated, at least in part, from their antipodes, are said to be optically active in that they behave di rently toward the right and left components of circularly polarized light (CPL). All biological molecules of any complexity have this characteristic. The di rential interaction with CPL may manifest itself as a differential scattering, which is measured as a non-zero rotation of the plane of polarization of plane polarized light, measurable with a polarimeter at specific wave lengths, or as a function of wave length, X., as optical rotatory dispersion (ORD). 

Fluorescence measurements and detection can either be made under steady-state or time-resolved conditions. Some of the commonly used measurement techniques focus on changes in optical properties such as fluorescence intensity quenching, phase fluorometry (lifetime), polarization, surface plasmon resonance (SPR), and evanescent waves. Here, we will present detector systems based for (a) fluorescence intensity quenching and (b) phase fluorometry in detail. A few example references of integrated optical sensor systems based on the various optical measurement techniques are given in Table 1 and the reader is encourage to review those papers if more details are desired. 

Both molecular and transition dipole moment orientation can be probed within the solid state samples, especially upon combining structural information with polarized absorption measurements. Small-area electron diffraction experiments are also effective since they allow the orientation of crystalline regions within polymer nanofibers to be probed. Most of these techniques are already well established from the study of polymer alignment in thin-films. Improved analysis methods, which make use of combined polarized Raman spectroscopy and UV-visible absorption data, are especially worthwhile to be mentioned as valuable tools to investigate the orientational properties of light-emitting polymer systems. We will come back in depth to optical properties of polymer nanofibers in Chapter 5. 

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