Anisotropy measurement

The quantitative assessment of the overall orientation of PET fibers is generally made on the basis of fiber optical anisotropy measurements, i.e., measurements of the optical birefringence of the fiber. The determination of the value of optical birefringence makes it possible to determine the value of Hermans function of orientation based on the equation ... 

Simultaneous weight-change and diamagnetic-anisotropy measurements upon adsorption and desorption of bromine in PG have been carried out (M4). They showed that final susceptibility values are reached well before full bromine saturations, and remain until 80% desorption is attained. 

Deslouis C, Maurin G, Pebere N, Tribollet B (1988) Investigation of tellurium electrocrystal-Uzation by EHD impedance technique. J Appl Electrochem 18 745-750 Yagi I, Nakabayashi S, Uosaki K (1998) In situ optical second harmonic rotational anisotropy measurements of an Au(l 11) electrode during electrochemical deposition of tellurium. J Phys Chem B 102 2677-2683... 

In practice, fluorescence anisotropy measurements are carried out as described by Larsson et al. [134] using ... 

Second, we analyze the nature of the next, strong 2PA bands. The positions of their final states correspond to one-photon symmetry forbidden bands and can be found from excitation anisotropy measurements, as illustrated in Figs. 6,19, and 23. Excitation anisotropy spectra for all cyanine-like molecules typically reveal a large alternation of maximum and minimum features suggesting the positions of the 1PA and 2PA transitions. Two-photon excitation into final states involves two dipole moments, fi0i and /i (i. 

Recently, rapid kinetics have been observed in anisotropy measurements applied to the P and B bands [10,21,31,39,51], It is found that prior to ET, there exist a few steps in the P and B bands. These measurements provide detailed information on the P and B bands, especially for the nature of the electronic... 

It should be noted that the calculated anisotropy may not be applied to fs time-resolved anisotropy measurements because fs time-resolved experiments involve pumping and probing conditions and may involve overlapping between the vibronic structures of several electronic states due to the use of fs laser pulses. Nevertheless, we think the calculated anisotropy using Eq. (2.54) can provide a reference in comparing models. 

Ultrafast emission measurements are possible with the dendrimer metal nanocomposites. The gold and silver internal dendrimer nanocomposites showed a fast emission decay of approximately 0.5 ps, which was followed by a slower decay process. The fast decay emission is attributed to decay processes of the gold (or silver) metal nanoparticles. Ultrafast emission anisotropy measure-... 

Quantitative information can be obtained only if the time-scale of rotational motions is of the order of the excited-state lifetime r. In fact, if the motions are slow with respect to r(r ro) or rapid (r 0), no information on motions can be obtained from emission anisotropy measurements because these motions occur out of the experimental time window. 

Dr can be determined by time-resolved fluorescence polarization measurements, either by pulse fluorometry from the recorded decays of the polarized components I l and 11, or by phase fluorometry from the variations in the phase shift between J and I as a function of frequency (see Chapter 6). If the excited-state lifetime is unique and determined separately, steady-state anisotropy measurements allow us to determine Dr from the following equation, which results from Eqs (5.10) and (5.41) ... 

Steady-state anisotropy measurements are then insufficient for fully characterizing rotational motions and time-resolved experiments are required. 

Time-dependent anisotropy measurements 6.2.7.1 Pulse fluorometry... 

Time-resolved emission anisotropy measurements are more straightforward in pulse fluorometry. 

In Chapter 5, devoted to fluorescence polarization, it was shown that information on the rotational motions of a fluorophore can be obtained from emission anisotropy measurements. Application to the evaluation of the fluidity of a medium, or molecular mobility, is presented below. 

Steady-state and time-resolved emission anisotropy measurements also allows distinction of single molecules on the basis of their rotational correlation time. 

The results of fluorescence polarization studies of proteins were discussed above. Time-resolved anisotropy measurements often permit, without any additional variation of experimental conditions, intramolecular rotations to be distinguished from rotation of the whole protein molecule and characterized,... 

H. Kirn and W. C. Galley, Rotational mobility associated with the protein moiety of human serum lipoproteins from tryptophan phosphorescence anisotropy measurements, Can. J. Biochem. Cell Biol. 61, 46-53 (1983). 

J. W. Berger and J. M. Vanderkooi, Intrinsic phosphorescence anisotropy measurements of the tobacco mosaic virus, work in progress. 

The first decision to be made in designing an experiment to measure the motional properties of membrane lipids concerns the type of probe molecule. Too often, this choice is made from the point of view of convenience or tradition rather than suitability, although there is now a considerable range of suitable fluorophores from which to choose. The second consideration is the type of measurement to be made. The most detailed and complete motional information is obtained from a time-resolved fluorescence anisotropy measurement which is able to separate the structural or orientational aspects from the dynamic aspects of fluorophore motion. Steady-state anisotropy measurements, which are much easier to perform, provide a more limited physical parameter relating to both of these aspects. 

In time-resolved anisotropy measurements, the static or orientational components of motion and the rate of motion are derived. The time-resolved derivation of rs is revealed as... 

The rx term is the anisotropy at times long compared to the fluorescence lifetime, whereas in Eq. (5.9) 2 will be long. If there is no rM, then Eq. (5.8) reduces to the familiar Perrin equation for an isotropic rotator. Earlier, some confusion existed in this field since it was not recognized that an rro term was required for the case of membrane lipid bilayers. For the most part, time-resolved anisotropy measurements have a short rotational correlation time and an term. However, it has been recognized that a more adequate description may be to use two rotational correlation times, where the second may be quite long but not infinite as the rm implies/35 36 ... 

At the present time, two methods are in common use for the determination of time-resolved anisotropy parameters—the single-photon counting or pulse method 55-56 and the frequency-domain or phase fluorometric methods. 57 59) These are described elsewhere in this series. Recently, both of these techniques have undergone considerable development, and there are a number of commercially available instruments which include analysis software. The question of which technique would be better for the study of membranes is therefore difficult to answer. Certainly, however, the multifrequency phase instruments are now fully comparable with the time-domain instruments, a situation which was not the case only a few years ago. Time-resolved measurements are generally rather more difficult to perform and may take considerably longer than the steady-state anisotropy measurements, and this should be borne in mind when samples are unstable or if information of kinetics is required. It is therefore important to evaluate the need to take such measurements in studies of membranes. Steady-state instruments are of course much less expensive, and considerable information can be extracted, although polarization optics are not usually supplied as standard. 

FIGURE 5.20 (See color insert following page 280.) Temperature influence for fluorescence anisotropy measurements on C22-modified sihca. (a) Decay cnrves for DPH at different temperatures, (b) schematic of wobble motion of DPH and resulting finorescence lifetimes (xp) and half-cone angles ). (Reprodnced from Pursch, M., et al., J. Am. Chem. Soc., 121, 3201, 1999. With permission.)... 

The arguments advanced here apply equally well to 110 facets. This conclusion is illustrated schematically in Fig. 4. Figure 4a shows the y-plot obtained by Heyraud and Metois for pure Pb . Figure 4b is a modification of Fig. 4a, in which the cusps at 111 and 100 have been deepened, and new cusps have been created at 227) and 110) orientations. The depth of the cusps has been adjusted to produce an equilibrium form by means of the Wulff constmction (Fig. 4c) that matches the experimental equilibrium form of Fig. 2d. The deepening of the cusps needed to produce the desired shape is of the order of a few percent, and falls within the general range of anisotropy measured previously in the case of pure Pb. 

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