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Photochromic probes

Due to the relatively long lifetime of the sensitiser triplet state and the possibility of integrating data on the stilbene photoisomerisation, the apparent characteristic time of the method can reach hundreds of seconds. This unique property of the cascade system and, therefor triplet-photochrome technique, allows the investigation of slow diffusion processes, including encounters of proteins in membranes using very low concentrations of both the triplet and photochrome probes. [Pg.13]

An additional step in the cascade reaction scheme is the quenching of the sensitizer triplet state with relatively low-concentration radicals (Fig. 1.5) (Papper et al 1999, 2000 Papper and Likhtenshtein, 2001). The entire investigated reaction that is shown in Fig. 1.5 is the sequence of the four kinetic processes and serves as a basis for the spin-triplet-photochrome labeling technique. This technique combines the three types of biophysical probes stilbene photochrome probe, triplet probe and stable nitroxide-radical spin probe, which depresses the sensitiser exited triplet state. [Pg.13]

The triplet-photochrome labeling method has been used to study very rare encounters in a system containing the Erythrosin B sensitiser and SITC photochrome probe (Mekler and Likhtenshtein, 1986). Both types of the molecules were covalently bound to a-chymotrypsin. The photoisomerisation kinetics was monitored by fluorescence decay of the frans-SITS. The rate constants of the triplet-triplet energy transfer between Erythrosin B and SITS (at room temperature and pH 7) were found k,r = 2 xlO7 NT s-1 and ktT = 107 M V. It should be emphasized that the concentration of the triplet sensitiser attached to the protein did not exceed 10 7 M in those experiments, and the collision frequencies were close to 10 s 1 which are 8-9 orders of magnitude less than those measured with the regular luminescence or ESR techniques. [Pg.14]

Papper, V., Likhtenshtein, G.I., Medvedeva N., and Khoudyakov, D.V. (1999) Quenching of cascade reaction between triplet and photochrome probes with nitroxide radicals, Photochem. Photobiol. A Chem. 122, 79-85. [Pg.215]

J. S. Royal, J. G. Victor, and J. M. Torkelson, Photochromic and fluorescent probe studies in glassy polymer matrices. 4. Effects ofphysical aging on poly(methyl methacrylate) as sensed by a size distribution of photochromic probes, Macromolecules 25, 729-734 (1992). [Pg.56]

Free Volume Distribution by Photochromic Probing and Vapour Transport Properties... [Pg.59]

The scope of this chapter is to determine the average free volume size and size distribution for Hyflon AD (Figure 4.1) by the photochromic probe method and to study the transport of organic vapours in membranes of this polymer. The final aim is to correlate the transport data in the polymer with the free volume element (FVE) size distribution and to gain a better understanding of structure-property relationships in perfluoropolymers. [Pg.60]

The photochromic probe method uses different probe molecules, usually substituted stilbenes and azobenzenes, and in this case the evaluation is based on the capacity of the probe molecules to undergo a trans-cis isomerization upon irradiation (Figure 4.2) [9]. This depends on the probe size and on the size of the FVE in which it is located. The probe molecules are dissolved in the polymer matrix, isomerization is induced by a strong UV lamp and the degree of isomerization is determined from the absorbance spectra before and after the isomerization. [Pg.61]

Figure 4.3 Illustration of the total volume required for the isomerization of the photochromic probe 4-(4-nitro-phenylazo)aniline (4-amino-4 -nitro-azobenzene, Disperse... Figure 4.3 Illustration of the total volume required for the isomerization of the photochromic probe 4-(4-nitro-phenylazo)aniline (4-amino-4 -nitro-azobenzene, Disperse...
A fundamental requirement for the system to be suitable for the application of the photochromic probe method is that the polymer is sufficiently transparent to UV or visible light in the spectral range of the photochromic probe molecules, first of all to induce the photo-isomerization reaction upon irradiation of the sample, and secondly to allow the determination of the absorption spectrum of the isomers before and after the irradiation, and thus to calculate the degree of isomerization. In this respect, Hyflon AD is an excellent polymer because it is highly transparent in the visible spectrum and in most of the UV spectrum, the reason for its original application in optical devices. [Pg.64]

These dependences may serve as calibration curves for microviscosity determination in the vicinity of the fluorescence-photochrome probe. Appropriate calibration would make possible the determination of the viscosity of a media (in the range 1-500 cP) as well as ascorbate content in the range (1-9) x 10 M. [Pg.295]

Spin probe Triplet probe Photochrome probe... [Pg.299]

In order to monitor the diffusion of the probe molecules the sample is illuminated for a short time interval gating the laser with a Kerr cell (Fig. 20.4). The length of the excitation pulse must be careMly matched to the intrinsic relaxation time of the photochromic probe. After terminatio of excitation the grating is washed out by diffusion of both, excited and unexcited dye molecules. Hence, the diffraction efficiency of the grating is diminished and the intensity I t) of the diffracted probe laser beam decreases according to the equation... [Pg.406]

This procedure is illustrated in Fig. 20.5, using as an example the diffusion of the hydro-phobic dye methyl red (2-carbohydroxy-4 -dimethylamino-azobenzene) in simple linear chain aliphatic alcohols. This photochromic probe molecule is transformed from the trans into the cis form by irradiation with the Ar" laser wavelength of 514.5 nm. The lifetime Tdye varies between about 20 ms and 1 s, depending on the medium and its viscosity. The dependence of the diffusion coefficient on the viscosity is clearly seen from the different slopes in Fig. 20.5. [Pg.406]


See other pages where Photochromic probes is mentioned: [Pg.226]    [Pg.233]    [Pg.391]    [Pg.62]    [Pg.62]    [Pg.65]    [Pg.66]    [Pg.71]    [Pg.80]    [Pg.80]    [Pg.299]    [Pg.301]    [Pg.336]    [Pg.209]    [Pg.225]   
See also in sourсe #XX -- [ Pg.7 , Pg.103 ]




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