Spin probing

B1.13.4.1 SMALL MOLECULES THE DUAL SPIN PROBE TECHNIQUE... 

Another application of the knowledge of is to employ it for the interpretation of another relaxation measurement in the same system, an approach referred to as the dual spin probe teclmique. A rather old, but... 

The simplest system exliibiting a nuclear hyperfme interaction is the hydrogen atom with a coupling constant of 1420 MHz. If different isotopes of the same element exhibit hyperfme couplings, their ratio is detemiined by the ratio of the nuclear g-values. Small deviations from this ratio may occur for the Femii contact interaction, since the electron spin probes the inner stmcture of the nucleus if it is in an s orbital. However, this so-called hyperfme anomaly is usually smaller than 1 %. 

ESR provides useful indirect information on the nanoscale porosity of CFPs, after their swelling in a medium in which a suitable spin probe is dissolved. According to the investigation by Corain and associates, the rotational mobility of the spin probe can be nicely correlated to the nanoporosity of the examined CFP, in a quantitative fashion [14,25]. 

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). 

A review of the application of ESR to the study of free radical polymerisation is given by Yamada and co-workers [146]. A survey of the application ESR spectroscopy spin label/probe methods in heterogeneous polymer systems is provided by Veksli and co-workers [147]. Spin probe methods allow the study of the MD of the polymer, its free volume, phase separation and phase morphology. 

Chasteen, N.D. and Theil, E.C. 1982. Iron binding by horse spleen apoferritin a vanadyl(IV) EPR spin probe study. Journal of Biological Chemistry 257 7672-7677. 

McNeill SA, Gor kov PL, Shetty K, Brey WW, Long JR (2009) A low-E magic angle spinning probe for biological solid state NMR at 750 MHz. J Magn Reson 197 135-144... 

Method involves measuring the change in rotational correlation time for a free radical probe (e.g., nitroxide spin probes) introduced into a sample being studied. The temperature associated with a decrease in the rotational correlation time of a spin probe is assigned as Tg... 

Spin on glass (SOG) technique, 24 750 Spin-orbit split-off band, in compound semiconductors, 22 148-151 Spinosad, 14 346 Spinplates, rectilinear, 17 470 Spin probe testing, of plastics, 19 589 Spin welding, of ethylene-... 

Dendrimers have precise compositional and constitutional aspects, but they can exhibit many possible conformations. Thus, they lack long-range order in the condensed phase, which makes it inappropriate to characterize the molecular-level structure of dendrimers by X-ray diffraction analysis. However, there have been many studies performed using indirect spectroscopic methods to characterize dendrimer structures, such as studies using photophysical and photochemical probes by UV-Vis and fluorescence spectroscopy, as well as studies using spin probes by EPR spectroscopy. 

The stability of nitroxides will be well known to readers acquainted with the spin-labelling technique (Berliner, 1976), but it must be recognized that nitroxides employed as spin labels or spin probes are almost invariably di-t-alkyl nitroxides. Diaryl and many aryl t-alkyl nitroxides are also sufficiently persistent to be isolated, and it has recently been shown that several acyl t-alkyl nitroxides can also be obtained pure (Perkins and Ward, 1973 Alewood et al., 1978). However, other nitroxides are less persistent. Monosubstituted nitroxides, RN(H)Q-, rapidly disproportionate to nitroso-... 

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 exact value of g depends on the magnitude of local magnetic fields induced in the atom by the applied external field, H. Nitroxide spin probes possess an unpaired electron which is largely localized on the 2px orbital of the N atom (16), as is shown in the molecular structure of TEMPAMINE" " below ... 

Figure 4. First-derivative ESR spectra of a nitroxide spin probe with the x-axis (a), y-axis (b), and z-axis (c) aligned parallel to H. The rigid-limit "powder" spectrum (d) is also shown. The dashed line marks the free electron field position (g = 2.0027). Reproduced from Ref. (jl) with permission of D. Reidel Publishing Co.

For the relatively rapid anisotropic motion (tc < 3 x 10" s) of spin probes observed on fully hydrated smectites such as montmoril-lonite, hectorite, and beidellite, an external fixed axis system (x1, y, z ) can be defined in addition to the molecule-fixed axes (x, y, z). The angle, 0, between the z and z axes is given by ... 

Wright, P.B., Lamb, E., Dorsey, J.G, and Kooser, R.G., Microscopic order as a function of surface coverage in alkyl-modified silicas—spin probe studies. Anal. Chem., 64, 785, 1992. 

Ottaviani, M.F., Cangiotti, M., Famiglini, G., and CappieUo, A., Adsorption of pure and mixed solvent solutions of spin probes onto stationary phases, J. Phys. Chem. B, 110, 10421, 2006. 

EPR spectroscopy. Molecules can also be derivatised by stable nitroxides used as spin probes [64] which allows one to draw conclusions on the microenvironment of the interacting molecule, thus on its binding. 

Less frequently used at present is electron spin resonance spectroscopy, which is based on the use of spin probes as model componnds or covalent spin labeling of drugs. Microviscosity and micropolarity of the molecnlar environment of the probe can be derived from electron spin resonance spectra. Moreover, the spectra allow us to differentiate isotropic and anisotropic movements, which result from the incorporation of the probe into liposomal structures. Quantitative distribution of the spin probes between the internal lipid layer, the snrfactant, and the external water phase is to be determined noninvasively. On the basis of the chemical degradation of drugs released from the lipid compartment, agents with reductive features (e.g., ascorbic acid) allow us to measure the exchange rate of the drugs between lipophilic compartments and the water phase [27,28]. 

A stable paramagnetic group that has been attached to a molecular entity. Experiments with ESR measurements can reveal aspects of the microenvironment of the spin label. If the paramagnetic group is not covalently attached to the molecular entity of interest, the term spin probe is usually applied. See also Electron Spin Resonance... 

L. H. Sutcliffe, The design of spin probes for electron magnetic resonance spectroscopy and imaging, Phys. Med. Biol., 43 (1998) 1987-1993. 

Stearic acid with doxyl spin probe positions... 

The name spin trapping was coined by Janzen, and derives from analogy with the use of stable nitroxyls as spin labels (or spin probes ) that provide spectroscopic information regarding their microscopic environment, a procedure pioneered by McConnell et alP ... 

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