Dynamic depolarization

Molecular Rotational Diffusion. Rotational diffusion is the dominant intrinsic cause of depolarization under conditions of low solution viscosity and low fluorophore concentration. Polarization measurements are accurate indicators of molecular size. Two types of measurements are used steady-state depolarization and time-dependent (dynamic) depolarization. 

Muon Spin Relaxation refers to the observation of incoherent motions of the muon spins which result in a loss of polarization with time. This will occur if the magnetic field sensed by the ensemble of implanted muons is broadly distributed. If the local field each muon sees in addition fluctuates randomly during a muon s life we observe what is called dynamic depolarization , but also a stationary distributed field causes depolarization by phase incoherence ( static depolarization ). These two cases must be clearly distinguished. The situation corresponds to the two relaxation times Ty (spin-lattice) and Ti (spin-spin) in NMR. Muon Spin Relaxation measurements can be carried out without observing spin rotation and thus are possible in zero applied field or with a longitudinally applied field (i.e., a field applied parallel to the muon spin direction at the moment of implantation). Longitudinal field measurements are the most appropriate way to obtain a clear distinction between static and dynamic muon spin depolarization. Muon Spin Relaxation hence mostly refers to zero or longitudinal field (iSR. 

The residual depolarization rate in the absence of spin correlations is contained in k2 of eq. (68) and determined by the RKKY (4f-4f) and Korringa (4f-ce) interactions. Starting from a treatment of the transverse NMR relaxation rate Tf by Moriya (1956) and the common Korringa formalism (Korringa 1950) it was shown that the dynamic depolarization rate at high temperatures (when contact coupling is neglected) can be written as... 

Badaire et al. reported the formation of liquid crystalline phase of CNTs by noncovalent functionalization with single strand DNA in water [74]. The nonco-valent functionalization in water is simpler and does not affect the intrinsic properties of the CNTs. They observed that a nematic-isotropic coexistence is observed for nanombes concentrations between 2 and 4 wt%. Above 4 wt%, the system forms a single nematic phase of unmodified and freely dispersed nanotubes. They investigated the boundaries of the phase diagram with respect to the aspect ratios of the nanombes determined by dynamic depolarized light scattering. Poulin et al. uniformly aligned the nematic aqueous suspensions of nanombes in... 

Analysis of the dynamic depolarized scattering from the rods shown in Figure 9.1 yielded a rod with a length near 2 pm and an axial ratio less than 0.02. 

Aoki, H., Kitamura, M. and Ito, S. (2008) Nanosecond dynamics of poly(methyl methacrylate) brushes in solvents studied by fluorescence depolarization method. Macromolecules, 41, 285-287. 

Horinaka, J., Ono, K. and Yamamoto, M. (1995) Local chain dynamics of syndiotactic poly(methyl methacrylate) studied by the fluorescence depolarization method. Polym. J., 27, 429-435. 

Presynaptic events during synaptic transmission are rapid, dynamic and interconnected. The time between Ca2+ influx and exocytosis in the nerve terminal is very short. At the frog NMJ at room temperature, 0.5-1 ms elapses between the depolarization of the nerve terminal and the beginning of the postsynaptic response. In the squid giant synapse, recordings can be made simultaneously in the presynaptic nerve terminal and in the postsynaptic cell. Voltage-sensitive Ca2+ channels open toward the end of the action potential. The time between Ca2+ influx and the postsynaptic response as measured by the postsynaptic membrane potential is 200 ps (Fig. 10-7). However, measurements made with optical methods to record presynaptic events indicate a delay of only 60 ps between Ca2+ influx and the postsynaptic response at 38°C [21]. 

T. Ichiye and M. Karplus, Fluorescence depolarization of tryptophan residues in proteins A molecular dynamics study, Biochemistry 22, 2884-2894 (1983). 

Figure 4.1. Time scales for rotational motions of long DNAs that contribute to the relaxation of the optical anisotropy r(t). Experimental methods used to study these motions in different time ranges are also indicated along with the authors and dates of some early work in each case. FPA, Fluorescence polarization anisotropy (Refs. 15, 18-20, and 87) TPD, transient photodichroism (Refs. 28 and 62) TEB, transient electric birefringence (Refs. 26 and 27) DDLS, depolarized dynamic light scattering (Ref. 116) TED, transient electric dichroism (Refs. 25, 115, and 130) Microscopy, time-resolved fluorescent microscopy (Ref. 176).

One would still like to examine the effect of ethidium on the torsional rigidity and dynamics at high binding ratios. One would also like to test the Forster theory for excitation transfer between bound ethidium molecules, since it has been questioned/65- This is possible in principle by deconvoluting the effects of depolarization by excitation transfer on the FPA, as will be shown subsequently. DLS also provides crucial information on this same question. 

Significantly smaller values of the hydrodynamic radius in the range a = 10.0 0.3 A were recently obtained for 8-, 12- and 20-bp synthetic DNAs by depolarized dynamic light scattering(225) (DDLS) and for 12- and 36-bp synthetic DNAs by FPA.(2 6) The origin of the difference in hydrodynamic radius between these short synthetic DNAs, which contain 83—100% GC, and the restriction fragments studied previously is not yet known, but is currently under investigation. 

R. E. Dale, Membrane structure and dynamics by fluorescence probe depolarization kinetics, in Time-Resolved Fluorescence Spectroscopy in Biochemistry and Biology (R. B. Cundall and R. E. Dale, eds.), pp. 555-612, Plenum, New York (1984). 

Allison, S.A. (1986) Brownian dynamics simulation of wormlike chains. Fluorescence depolarization and depolarized light scattering. Macromolecules 19, 118-124. 

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