Spin probes concentration

Figure 4.3. Spin relaxation rate of charged molecules as a function of nitroxide spin probe concentration. Neutral, negative, and positive charged probes denoted are respectively denoted as 0, -, and + (Likhtenshtein et al., 1999). Reproduced with permission.

Okazaki and Toriyama studied the dynamics of liquid molecules 2 propanol and water confined to nanochannels (pore size 3 4 nm) of the mesoporous mate rial MCM-41 as a function of temperature using spin probe ESR [37]. They used DTBN and TEMPOL as the spin probes (concentration 0.2 mM). Both the spin probes were freely soluble in the two liquid hosts and did not have any strong inter action with the channel walls of MCM-41. It was seen that in both the liquids, the ESR spectra were characteristic of immobilized spin probes at temperatures even as high as 40° above their respective melting points. In addition, the 2 propanol... 

At amorphous glassy polymers as natural nanocomposites treatment the estimation of filling degree or nanoclusters relative fraction (p j has an important significance. Therefore, the authors of Ref. [27] carried out the comparison of the indicated parameter estimation different methods, one of which is EPR-spectroscopy (the method of spin probes). The indicated method allows to study amorphous polymer structural heterogeneity, using radicals distribution character. As it is known [28], the method, based on the parameter - the ratio of spectrum extreme components total intensity to central component intensity-measurement is the simplest and most suitable method of nitroxyl radicals local concentrations determination. The value of dipole-dipole interaction is directly proportional to spin probes concentration C [29] ... 

Additional investigations in [omim][BF4] using TEMPOL have been reported to get insights into the structural and dynamic microheterogeneity of that IL. ° Spectra were recorded at 77 K and additionally between 128 K and 330 K. Three different spin probe concentrations, Ci = (3.0 0.5) x 10 M, C2 = (4.6 0.5) X 10 M and C3 = (5.3 0.5) x 10 M were determined by double integration of the EPR-spectra. At concentrations Cj and Cj no dipole-dipole line broadening effects occur. The temperature dependent different line shapes recorded for concentration C2 and C3 are explained by the different temperature dependence of the solubility of the spin probe in relatively more polar or more unpolar domains of the IL. 

Spin probes are quite readily metabolized reductively by cells and have been utilized to monitor metabolic activity (lannore etal., 1990) The line widths of the e.s.r. signals are also sensitive to the presence of O2 in both intracellular and extracellular environments and hence O2 concentrations may be determined with TBN or alternative spin probes (Glockner and Swartz, 1991). 

Figure 12. EPR spin probe of the concentration dependence of the diffusion of (n6-C6H6)2V/pentane into NasgY (see text).

Abstract. The relationship of hydration properties of carbon nanoparticles in aqueous dispersions and stability of these dispersions with respect to aggregation have been studied using EPR spin probing of frozen dispersions. Aqueous dispersions of shungite carbon nanoparticles at different concentrations and aqueous colloids of fullerenes C60/C70 have been compared. Characteristic features of the bounded water have been shown to correlate with a decrease of aqueous dispersions stability to aggregation. 

Hydrophilic spin probe 4-Oxo- TEMPO (Sigma) of 0.1 mM concentration was introduced in water dispersions of ShC nanoparticles of different concentrations (0.1, 1.0 and 10 mg/ml). Paramagnetic spin probe like TEMPOL effectively dissolves in hydration water [7,8] owing to capability of polar and paramagnetic NO group of probe to form hydrogen bonds with water molecules. 

Figure 1 shows Arrenius plots of the spin probe effective rotational frequency (log x 1 vs. 1/T) in liquid and frozen colloid solutions and dispersions of carbon nanoparticles. The plots are presented for different concentrations of nanoparticles and for water. Linearization of individual segments of the plots (T< 250 K) allowed calculating the thermodynamic parameters of the spin probe motional activation. No significant difference in the spin probe motional activation parameters has been... 

Figure 1. Arrenius plots of the spin probe effective rotation frequency (log r"1 vs. 1/T) for water and frozen colloid solutions and carbon nanoparticles dispersions of different concentrations (1) - liquid water including supercooled water at -13°C and frozen water (experimental points within the temperature range of supercooling were taken on rising temperature) (2)- 0.1 mg/ml C6o/C7o (3) - 0.1 mg/ml C6o/C7o + 0.015 M NaCl (4) -1 mg/ml ShC (5) - 10 mg/ml ShC (unstable dispersion) (6) - 0.1 mg/ml ShC.

Figure 3. Temperature dependence of spin-probe EPR spectrum non-dimensional parameter for water and dispersions of silica, and carbon nanoparticles of different concentrations ...

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. 

According to the experimental data on rate constants of spin exchange at encounters between heme groups and nitroxides presented in Table 4.2., the accessibility of the heme group of cytochrome c to the encounters with neutral spin-probes IV is -31-33 times lower than that observed for free hemin. At present, it is difficult to separate the effect of heme group immersion into the protein globular structure from that of association in the relatively concentrated solutions (2-10mM) utilized in these studies. 

The mobility of low molecular weight additives in the presence of fillers is important for the same reasons. Recent studies show that UV stabilizers are immobilized on the surfaces of filler particles. Nitroxyl radicals were used as spin probes in silica filled polymers. Experimental work confirms that absorption occurs on the OH groups of silica but it was shown that a certain minimum concentration of filler is required to trigger this absorption effect. 

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