Dynamic anisotropy

TIR FLUORESCENCE DYNAMIC ANISOTROPY AT A UQUID/LIQUID INTERFACE... 

Three-Dimensional Model. On the other hand, if the interfacial layer is thick enough compared to the molecular size of SRIOI and if SRIOI molecules adsorbed on the interface are weakly oriented, the rotational motions of SRIOI take place in three dimensions, similar to those in a bulk phase. If this is the case, the contribution of the fluorescence with the excited dipole moment of SR 101 directed along the z-axis cannot be neglected, so that the time profile of the total fluorescence intensity must be proportional to / (0 + 2/i(t). Thus, fluorescence dynamic anisotropy is given by Equation (15), as is well known for that in a macroscopically isotropic system [10,13] ... 

It is worth noting that water/oil interfacial structures would be governed by various factors, so that a complementary study other than fluorescence dynamic anisotropy is required to obtain further detailed information about the characteristics at a water/oil interface. As a new and novel approach, therefore, excitation energy transfer d3mamics and the relevant structural (fractal) dimension analysis were introduced to elucidate the structure of a water/oil interface [4],... 

In the present study, both fluorescence dynamic anisotropy and excitation energy transfer methods were successful in providing information about the structures and... 

A water/CCU or water/DCE interface is a representative system studied by various techniques so far, invaluable information about the structure of the interface has been accumulated [20]. As an example, Benjamin and his co-workers have demonstrated that the thickness of the water/DCE or water/CCU interface is 1 nm or <1 mn, respectively [21]. The spatial resolution of fluorescence dynamic anisotropy measurements is 1 nm, so that the present results are worth comparing with the predictions from the simulations. 

The structural dimension at a water/DCE interface is d — 2.48, while short-range structural information about the interface obtained by the fluorescence dynamic anisotropy experiments suggests that the interface is three-dimensional-like. Taking the results obtained by molecular dynamics simulations into account, these results can be understood only by the fact that the water/DCE interface is thin ( 1 nm), but is rough with respect to the spatial resolution of the excitation energy transfer quenching method ( 7 nm), as shown in Figure 12.7. 

Although the structural differences between the water/CClq and water/DCE interfaces are not so large, the chemical and/or physical nature of the organic phase itself reflects on the photophysical properties of a probe molecule, indicating the novelty of the present experimental approaches. Systematic investigations are important to reveal factors governing structural and physical characteristics of water/oil interfaces. Therefore, we introduced fluorescence dynamic anisotropy and excitation energy transfer measurements to other water/oil interfacial systems the data are summarized in Table 12.3. The results are discussed in terms of the relationship between the interfacial stracture and the polarity at the water/oil interfaces (Section 12.6). 

O. Kogi, A. Fukushima, S. Ishizaka, N. Kitamura, Fluorescence dynamic anisotropy of spinach calmodulin labeled by a fluoreseein chromophore at Cys-26, Analytical Sciences 18, 689-691 (2002)... 

Fig. 16 Sample geometry for dynamic anisotropy measurements (a) perpendicular (reflection) geometry and (b) parallel (transmission) geometry...

A characteristic of small sample simulations of dense polymers under constant volume conditions is that the average pressure tensor is often anisotropic with substantial differences between the on-diagonal components and, in addition, nonzero off-diagonal terms. This has led to the use of molecular dynamics algorithms which control the pressure tensor, P, and which allow these dynamic anisotropies to be relaxed out. Once implemented such methods have the added advantage of being easily adapted to measure the response of such systems to externally applied pressure fields as we shall show later. 

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