Spin probes TEMPOL

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. 

An additional probe of the system is the spin label that we have examined by using ESR. The experimental sequence employed is shown in Figure 4. It is well known that coals contain significant amounts of kinetically stable carbon radicals, which yield an ESR spectrum of the type shown in Figure 4(a). In this particular sample of Wyodak coal, weighing about 200 mg, 3.6 x 10 spins were observed. Immediately after, a hexane solution containing the spin label TEMPOL (2,2,6,6-... 

Marinovic et al. have examined the effect of temperature on the ESR signals of TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidin-l-yl)oxyl) spin probe embedded NR. The temperature dependence of ESR spectra is due to change in rotational motion of the nitroxide radicals, characterized by the rotational correlation time (tr). " The representative ESR spectra of spin probed NR measured over a wide range of temperature are given in Figure 25.4(a). The separation of the outer maxima (2A f) is maximum for the spectrum of immobilized spin probe molecules at —120 °C and is slightly decreased with the increase in temperature. The shape of the spectral lines are separated when temperature approaches the glass transition temperature (Tg) (—20 °C) and above it, referred as Ts mT (the temperature at which the separation between the lAzz attains 5 mT). 

Figure 25.6 displays the ESR spectra of four different types of nitroxide spin probes (TEMPO (I), TEMPOL (II), EGONO (4-ethylene glycoloxy-TEMPO) (III) and BZONO (4-benzyloxy-TEMPO) (IV)) dispersed in NR matrix. The molecular weights and molecular volume are different for different types of spin probes. The spin probes (I, II and III) in the NR matrix show composite spectrum but the only difference between them is the intensity of the broad component, which increases with increasing molecular volume of the probes. Alternatively, the largest spin probe (IV) exhibits only one component in... 

Valic applied TEMPOL spin probe ESR technique to nano-sihca and nanoclay particles filled NR nanocomposites. Figure 25.34 shows the ESR spectra of 10 phr nano-silica filled NR nanocomposites doped with spin probe obtained at the temperature range of —100 to 80 °C. The shape and width of the spectral lines significantly changed with test temperatures. The spectra obtained at temperature below glass transition temperature (TgX — 57 °C from dilferential scanning calorimetry (DSC) analysis) of NR are composed of three... 

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... 

Figure 6.1 (a) Example of a commonly used spin probe 4-hydroxy-2,2,6,6-tetramethyl pipiridinyl-l-oxy (TEMPOL). (b) Example of spin-labeled Fe(III) tetraphenylporphyrin (TPP) complexes (see also Section 5). 

Figure 1.2 shows the experimental and theoretical EPR spectra of spin probes in dry and water-saturated of both isotropic and textured morphology. A comparison shows that the theoretieal spectra of both Tempo and Tempol spin probes qualitatively deseribe the main features observed in the corresponding experimental speetra. This coincidence indicates that the spectra actually represent a superposition of the EPR signals from radi-eal molecules with different rotation correlation times. 

An analysis of these data leads to the following conclusions. First, the correlation times of rotation of the Tempol spin probes located in the dense regions are virtually the same for isotropic and textured PHB samples. At the same time, the mobility of this radical in the loose regions is somewhat higher in textured matrices than in the isotropic ones. Second, the distribution of spin probes between dense and loose regions is virtually the same in both textured and isotropic PHB samples. 

Fig. 14. Behavior of spin probes during film drying and lewetting. (a) Schematic plot of immo-bihzation of different spin probes as a function of water content during drying of PBMA dispersion. Sobd line TEMPO-4-carboxylate. Dashed Une 4-hydroxy-TEMPO. Dash-dot-dot line 5-DOXYL-stearate. Dash-dot line 16-DOXYL-stearate. Dotted Une TEMPO, (jb) RemobiUzation of TEMPOL in rewetted PBMA films (1% acryUc add comonomer) as a function of time after immersing the film in water. The film samples were obtained by mere drying of the dispersion at ambient temperature (filled circles) or by 4 h of annealing of the dried dispersion at T/Tg = 1.13 (open circles).

Spin Probes. There have been many ESR studies on spin probes in colloidal and biological systems. One of the stable spin probes often used is 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-l-oxy (TEMPOL Fig. 20-9). The spin probe has two ofnoteworthy advantages (1) nitrogen hyperfine coupling constant An is sensitive to solvent polarity, and (2) the rotational correlation times (tc) are functions of the solvent viscosity. Therefore, the ESR spectrum of TEMPOL provides information on the local polarity and viscosity of the microenvironment surrounding the TEMPOL probe. 

X PS 2-27) blended in a 1 1 ratio by weight with PPC [75]. Tempo, Tempol and Tempamine were each used as spin probes, but only the functionalized radicals could provide information on microphase separation or miscibility in these blends. The EPR spectra of Tempo in all examined samples did not disclose two components through the temperature range 100 to 400 K (Figure 23.13). 

Figure 23.14 Selected EPR spectra of Tempol corresponding to slow- and fast-motional spin probe in pure STMAA-12 copolymer (a), component signals (s and/ respectively), its linear blend with PBMA (b), and the respec- Reprinted with permission from Ref. [76] tives-IPN at the copolymer crosslinking density 2005, John Wiley, Sons.

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 relaxation of molecular probes (such as tempol)... 

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