Fluorescence correlation spectroscopy relaxation methods

Studies on the dynamics of complexation for guests with cyclodextrins have been carried out using ultrasonic relaxation,40 151 168 temperature jump experiments,57 169 183 stopped-flow,170,178,184 197 flash photolysis,57 198 202 NMR,203 205 fluorescence correlation spectroscopy,65 phosphorescence measurements,56,206 and fluorescence methods.45,207 In contrast to the studies with DNA described above, there are only a few examples in which different techniques were employed to study the binding dynamics of the same guest with CDs. This probably reflects that the choice of technique was based on the properties of the guests. The examples below are grouped either by a type of guest or under the description of a technique. 

Keywords Block copolymer micelles Fluorescence anisotropy Fluorescence correlation spectroscopy Molecular dynamics simulations Monte Carlo simulations Solvent relaxation method Time-resolved fluorescence... 

As shown above, the intrinsic fluorescence spectra of proteins as well as coenzyme groups and probes shift within very wide ranges depending on their environment. Since the main contribution to spectral shifts is from relaxational properties of the environment, the analysis of relaxation is the necessary first step in establishing correlations of protein structure with fluorescence spectra. Furthermore, the study of relaxation dynamics is a very important approach to the analysis of the fluctuation rates of the electrostatic field in proteins, which is of importance for the understanding of biocatalytic processes and charge transport. Here we will discuss briefly the most illustrative results obtained by the methods of molecular relaxation spectroscopy. 

Dielectric spectroscopy techniques (3) represent an exception to this limitation. In fact, Senturia et al. (4) recently described a microdielectrometric method for in situ measurement of epoxy cure. Using a novel microdielectric probe, they studied isothermal cures of digylcidyl ether bisphenol-A (DGEBA) epoxy in which the low-frequency dielectric relaxation time, r, is correlated with the bulk viscosity (4). In this paper we report preliminary results on the utilization of a viscosity-dependent fluorescence probe as an alternative (and possibly complementary) new approach with potential for in situ monitoring of epoxy cure kinetics. We also report the observation of a unique fluorescence "self-probe capability of tetraglycidyl-diaminodiphenyl methane (TGDDM) epoxy which has not been reported previously. 

A useful and common way of describing the reorientation dynamics of molecules in the condensed phase is to use single molecule reorientation correlation functions. These will be described later when we discuss solute molecular reorientational dynamics. Indirect experimental probes of the reorientation dynamics of molecules in neat bulk liquids include techniques such as IR, Raman, and NMR spectroscopy. More direct probes involve a variety of time-resolved methods such as dielectric relaxation, time-resolved absorption and emission spectroscopy, and the optical Kerr effect. The basic idea of time-resolved spectroscopic techniques is that a short polarized laser pulse removes a subset of molecular orientations from the equifibrium orientational distribution. The relaxation of the perturbed distribution is monitored by the absorption of a second time-delayed pulse or by the time-dependent change in the fluorescence depolarization. 

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