Cationic nitroxide spin probes

Electron spin resonance (ESR) is a useful technique for investigating the mobility and orientation of exchange cations at the surface of layer silicate clays in various states of hydration. Using Cu2+ and the charged nitroxide spin probe, TEMPAMINE+... 

The molecular motion of redox couples within polymer-coated electrodes has recently been investigated by making use of both nitroxide spin probes and various cationic spin probes [94-97]. Spin probes, such as the nitroxide probe TEMPO (see Sect. 2.1.2) and its derivatives, have well-defined electrochemistry and their ESR spectra in viscous media exhibit effects due to incomplete rotational averaging of the g and hyperfine coupling constant tensors. Analysis of the spectra [98] allows deductions to be made concerning the molecular rotation. Such analysis has been performed for spin probes incorporated into various polymer films. 

Pace. M.D. Snow. A.W. Nitroxide spin-probe label of hydrogen-bonding and probe size effects in a linear epoxy polymer. Macromolecules 1995. 28 (15), 5300-5305. Starodoubtsev. S.G. Ryabova. A.A. Dembo, A.T. Dembo. K.A. Aliev, I.I. Wasserman, A.M. Khokhlov, A.R. Composite gels of poly(acrylamide) with incorporated bentonite. Interaction with cationic surfactants. ESR and SAXS study. Macromolecules 2002. 35 (16). 6362-6369. 

Self-assembled hexaresorcinarene capsules 397 and 398 (Scheme 3.71) have been used in [70] as potent hosts for paramagnetic nitroxide spin probes (e.g., the derivatives of tempo). According to EPR data, they encapsulate cationic and amine nitroxide guests, which are complementary to the mostly aromatic inner cavities of these caging ligands, but discriminate 0x0- and hydroxyl-functionalized nitroxides [70]. 

Motyakin, M.V., Comet, N., Gebel, G., Schlick, S. (2000) Morphology of sulfonated polyimide ionomers from ESR spectra of paramagnetic transition metal cations and nitroxide spin probes. Bulletin of the Polish Academy of Sciences. Chemistry, 48, 273-292. 

For the characterization of acid sites on soUds such as silica-alumina, alumina, and zeolites, di-tert-butyl niffoxide (DTBN), a stable organic nitroxide radical, was employed as a spin probe molecule by Hoffman et al. [47,48] and others [49, 50]. Gutjahr et al. [50] studied the electron pair acceptor properties of the monovalent cations such as Li+, Na+, K", and Cs" in a faujacite (Y) type of zeolite by means of ESR using DTBN as a probe molecule. They reported a linear relationship between the nitrogen spin density estimated from the nitrogen /i/constants of DTBN and the electro-negativity of the zeolite cations. 

Spectroscopic techniques such as electron spin resonance (ESR) offer the possibility to "probe" the chemical environment of the interlayer regions. With the ESR technique, an appropriate paramagnetic ion or molecule is allowed to penetrate the interlayer, and chemical information is deduced from the ESR spectrum. Transition metal ions, such as Cu2+, and nitroxide radical cations, such as TEMPAMINE (4-amino-2,2,6,6-tetramethylpiperidine N-oxide) have been used as probes in this manner (6-14). Since ESR is a sensitive and non-destructive method, investigations of small quantities of cations on layer silicate clays at various stages... 

Electron Spin Resonance.—Nitroxide radicals of varying structiu-e have been employed in studies of micelle structure and mobility. The basic spectrum is a triplet due to N-electron coupling, which may show hyperfine coupling to 3-C-H in appropriate cases. On micelle formation or incorporation of the probe the spectrum normally broadens because of reduction in the rotational correlation time and shows enhanced broadening and change in positions of the high-field line. Cationic micelles incorporate the probe (10) with an association constant of 3 x 10 and at low surfactant concentrations there is... 

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