Phosphorescence depolarization

The rotational mobility of human low-density (LDL) and very-low-density (VLDL) lipoproteins was studied as a function of viscosity and temperature in the range of —90 to — 50°C.(86)The rotational behavior for LDL is represented by a single correlation time, consistent with the overall rotation of a spherical rigid particle as the source of the phosphorescence depolarization. For VLDL, internal peptide motions dominate the depolarization profile. 

In the current paper we extend previous work on poly(methyl acrylate) (9 - 10) and poly(methyl methacrylate) (9 - 11) in which the phosphorescence depolarization technique was shown to provide data which were consistent with reported dielectric and mechanical relaxation experiments, to the study of the molecular behaviour of poly(n-butyl methacrylate). This polymer, whilst of technological application, has received much lesser attention using conventional dynamic relaxation techniques than has been devoted to PMA and PMMA. In addition, fluorescence depolarization measurements have been employed in an attempt to provide complementary information regarding the higher frequency behaviour of the polymer. 

Figure 1. Temperature dependence of relaxation times derived from phosphorescence depolarization data.

The acenaphthylene label, being incapable of motion independent of the polymer chain, is expected to monitor segmental relaxation of the macromolecule. The relaxation data adhere well to an Arrhenius relationship over the relatively restricted frequency-temperature range sampled. This behaviour is similar to that observed for the PMA relaxation as determined by phosphorescence depolarization(9,10) but contrasts with that of PMMA in which backbone motion of lesser activation energy was sensible at temperatures inferior to T (11),... 

Triplet state emission in solid phase (10 phosphorescence quenching phosphorescence depolarization... 

Room temperature phosphorescence can be observed from dried proteins. Sheep wool keratin(47) has a phosphorescence lifetime of 1.4 s. Six lyophilized proteins were shown to exhibit phosphorescence at room temperature.(48) The spectra were diffuse, and the lifetime was non-single-exponential, which the authors interpreted as due to inhomogeneous distribution of tryptophans. As the protein was hydrated, the phosphorescence lifetime decreased. This decrease occurred over the same range of hydration where the tryptophan fluorescence becomes depolarized. Hence, these results are consistent with the idea that rigidity of the site contributes to the lifetimes. 

Strambini and Galley have used tryptophan anisotropy to measure the rotation of proteins in glassy solvents as a function of temperature. They found that the anisotropy of tryptophan phosphorescence reflected the size of globular proteins in glycerol buffer in the temperature range -90 to -70°C.(84 85) Tryptophan phosphorescence of erythrocyte ghosts depolarized discontinuously as a function of temperature. These authors interpreted the complex temperature dependence to indicate protein-protein interactions in the membrane. 

Berger and Vanderkooi(88) studied the depolarization of tryptophan from tobacco mosaic virus. The major subunit of the coat protein contains three tryptophans. The phosphorescence decay is non-single-exponential. At 22°C the lifetime of the long component decays with a time constant of 22 ms, and at 3°C the lifetime is 61 ms. The anisotropy decay is clearly not singleexponential and was consistent with the known geometry of the virus. 

The fluorescence polarization excitation spectrum has been measured for thymine in aqueous solution. " The depolarization at the red edge is attributed to the hidden n, ir transition. Ionization of the lowest excited singlet and triplet states have been determined by the effect of pH on the absorption, fluorescence, and phosphorescence spectra of purines and pyrimidines. " Spectral, polarization, and quantum yield studies of cytidylyl-(3, 5 )-adenosine have also been published. Intermediates in the room-temperature flash photolysis of adenine and some of its derivatives have been identified hydrated electron, radical cations and anions, and neutral radicals resulting from their reactions have been assigned. Photoionization occurs via the triplet state. FMN encapsulated in surfactant-entrapped water pools interacts with polar head groups, entrapped water molecules, and outer apolar solvent. ... 

Phosphorescence Polarization Measurements. The degree of polarization was determined as a function of temperature for the systems P/ACE, P/VN and P-Np (dispersed naphthalene probe). The excitation wavelength was 310 nm and that of analysis, 490 nm. The onset of depolarization was observed at ca. 210, 195 and 180K for P/ACE,... 

Both absorption and emissirm processes may be intramolecular, localized in a single molecule. On the other hand, they can also involve whole crystals that may act as absorbers and emitters. Such energy transfers can manifest themselves in different ways that include sensitized fluorescence or phosphorescence, concentration depolarization of fluorescence, photo-conduction, and formation of triplet acceptor molecules. 

Rutherford H, Soutar I (1980) Phosphorescence studies of relaxation effects in bulk polymers. 2. Emission depolarization study of relaxation mechanisms in polyfmethyl methacrylate). J Polym Sci Part B Polym Phys 18(5) 1021-1034. doi 10.1002/pol.l980.180180509... 

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