Anisotropy times

Comparative Analysis of Fluorescence Reporter Signals Based on Intensity, Anisotropy, Time-Resolution,... 

Demchenko AP (2010) Comparative analysis of fluorescence reporter signals based on intensity, anisotropy, time-resolution and wavelength-ratiometry. In Demchenko AP (ed) Advanced Fluorescence Reporters in Chemistry and Biology I. Springer Ser Fluoresc 8 3-24... 

Figure 9. Experimental [59] and theoretical values of the polarization anisotropy time correlation function at 100 fs, as a function of OD stretch frequency, for three different temperatures. See color insert.

Table 1. Expressions for the anisotropy time dependence used through the paper...

FigureBl.5.16 Rotational relaxation of Coumarin 314 molecules at the air/water interface. The change in the SFI signal is recorded as a fimction of the time delay between the pump and probe pulses. Anisotropy in the orientational distribution is created by linearly polarized pump radiation in two orthogonal directions in the surface. (After [90].)...

MAS Si speetnim of a sample of sodium disilieate (Na Si O,) erystallized from a glass is shown as an example. Whilst the statie speetnim elearly indieates an axial ehemieal shift powder pattern, it gives no evidenee of more than one silieon site. The MAS speetnim elearly shows four resolved lines from the different polymorphs present in die material whose widths are 100 times less than the ehemieal shift anisotropy. 

Small molecules in low viscosity solutions have, typically, rotational correlation times of a few tens of picoseconds, which means that the extreme narrowing conditions usually prevail. As a consequence, the interpretation of certain relaxation parameters, such as carbon-13 and NOE for proton-bearing carbons, is very simple. Basically, tlie DCC for a directly bonded CH pair can be assumed to be known and the experiments yield a value of the correlation time, t. One interesting application of the measurement of is to follow its variation with the site in the molecule (motional anisotropy), with temperature (the correlation... 

The methods diseussed so far, fluoreseenee upeonversion, the various pump-probe speetroseopies, and the polarized variations for the measurement of anisotropy, are essentially eonventional speetroseopies adapted to the femtoseeond regime. At the simplest level of interpretation, the infonnation eontent of these eonventional time-resolved methods pertains to populations in resonantly prepared or probed states. As applied to ehemieal kineties, for most slow reaetions (on the ten pieoseeond and longer time seales), populations adequately speeify the position of the reaetion eoordinate intemiediates and produets show up as time-delayed speetral entities, and assignment of the transient speetra to ehemieal stnietures follows, in most oases, the same prinoiples used in speotrosoopio experiments perfomied with oontinuous wave or nanoseoond pulsed lasers. 

Cross A J and Fleming G R 1984 Analysis of time-resolved fluorescence anisotropy decays Blophys. J. 46 45-56... 

Matro A and Cina J A 1995 Theoretical study of time-resolved fluorescence anisotropy from coupled chromophore pairs J. Phys. Chem. 99 2568-82... 

This method has been devised as an effective numerical teclmique of computational fluid dynamics. The basic variables are the time-dependent probability distributions f x, f) of a velocity class a on a lattice site x. This probability distribution is then updated in discrete time steps using a detenninistic local rule. A carefiil choice of the lattice and the set of velocity vectors minimizes the effects of lattice anisotropy. This scheme has recently been applied to study the fomiation of lamellar phases in amphiphilic systems [92, 93]. 

Radiation Effects. Alpha sihcon carbide exhibits a small degree of anisotropy in radiation-induced expansions along the optical axis and perpendicular to it (58). When diodes of sihcon carbide were compared with sihcon diodes in exposure to kradiation with fast neutrons (59), an increase in forward resistance was noted only at a flux about 10 times that at which the increase occurs in a sihcon diode. In general, it appears that sihcon carbide, having the more tightly bound lattice, is less damaged by radiation than sihcon. 

We finish this section by comparing our results with NMR and incoherent neutron scattering experiments on water dynamics. Self-diffusion constants on the millisecond time scale have been measured by NMR with the pulsed field gradient spin echo (PFGSE) method. Applying this technique to oriented egg phosphatidylcholine bilayers, Wassail [68] demonstrated that the water motion was highly anisotropic, with diffusion in the plane of the bilayers hundreds of times greater than out of the plane. The anisotropy of... 

Figure 2.28 shows the anisotropy of the rotation of the pyridine ring in nicotine (46). The main axis passes through C-3 and C-6 C-6 relaxes correspondingly more rapidly (3.5 s) than the three other CH atoms (5.5 s) of the pyridine ring in nicotine, as can be seen from the times at which the appropriate signals pass through zero. 

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