Spin-labelled molecules

In ref. 5, a method has been suggested of controlling the character of the spatial distribution of the additive in solid matrices, which is based on analyzing the EPR spectra of spin-labelled molecules introduced into the system under study. Due to the magnetic dipole dipole interactions of the paramagnetic spin-labelled molecules, the width of their EPR lines in the diluted (concentration N < 1 M) vitrified solutions changes in proportion to their concentration... 

In eqn. (2), AH°m is the EPR line width in the limit of such dilution that one can neglect the dipole-dipole interaction and A is a coefficient depending on the EPR line shape and on the character of the spatial distribution of the spin-labelled molecules. In the case of random spatial distribution according to theoretical calculations A = 35 GM 1 for the Gaussian EPR line shape and A = 56GM-1 for the Lorentzian EPR line shape. 

Spin-Label Methodology Applied to Hydrophobic Interaction Studies of Humic Substances. Many molecules have no intrinsic paramagnetic centers, but EPR can provide useful information about these molecules if a structurally sensitive spin label is attached (Knowles et al., 1976). Spin-label molecules are stable free... 

The anisotropy of the spin-label hyperfine splitting is a consequence of the particular charge distribution symmetry within the molecule. The analysis of spectral anisotropy provides the immobilization extent of the spin label and is sensitive to the molecular conformation. Moreover, the spin-label molecules have their charge distribution distorted by the polarity of their environment. The isotropic hyperfine splitting constant (a0) provides a relative polarity indicator (Knowles et al., 1976 Campbell and Dwek, 1984). 

ESR spectroscopy has also been used to study dynamics in more complex systems on oxide surfaces, i.e. self-assembled molecular (SAM) films [136, 137]. Fig. 28 shows ESR spectra taken for spin labeled stearic acid, namely n-doxyl-stearic acid (n-DXSA) immersed onto a thin alumina film. These nitrox-ides, with an oxazolidinyl ring as paramagnetic group connected to different positions of the aliphatic chain, are well known as paramagnetic probes in the study of natural and synthetic membranes. The spin labeled molecules are pres-... 

There is a striking contrast between our surface collision model in Ref. 7 and the formulas e.g. Ref. 22) used to relate t2 to the three-dimensional transport of spin label molecules. In the three-dimensional model, the spin labels are diffused by Brownian motion, in which case (18)... 

Depending on the labeling strategy, inter- and intramolecular distances are accessible. While for measuring intramolecular distance constraints doubly spin labeled molecules can be used, intermolecular distances can be determined between singly labeled molecules (Fig. 4). 

Here P(r,t) gives the concentration of spin labeled molecules at a point r away from the center of the circle at time t. The results lead to a lateral diffusion coefficient ... 

A typical ESR spectrum is shown in Fig. 2. As described, Xc can be calculated from the spectra. Shah and co-workers [35] used ESR to study the structure of microemulsion, and Rosen et al. [36] used ESR and found the microviscosity gradient in the middle phase of three-phase micellar systems. Shirhama et al. [37] and Witte et al. [38] have used ESR to study the interaction of SDS with PEO and PVP, yielding information on the structure of complex from the polymers and SDS. But the influence of the spin-label molecule on the microstructure should be considered. 

The measuring principle is based on the fact that hundreds of hapten molecules are incorporated into the cell membrane of liposomes, e.g.. by linkage of phosphatidylethanolamine (a functional part of the multilayer membrane). In the presence of an antibody for the formation of an immune complex, destabilization of the entire vesicle occurs. The contents of the liposome, e.g., fluorophores dyes, spin-labeled molecules, or... 

Molecular Dynamics of Small Spin-labeled Molecules in Simple FMds. 

More recently, a striking demonstration of the excellent resolution of HF EPR to orientations of spin labeled molecules was provided by a 250 GHz EPR study... 

ESEEM amplitudes of spin-labelled molecules can depend on the freezing protocol, and this can cause non-reproducibility in the data, as was shown for spin-labelled lipids in model membranes. This effect can be explained by exclusion of the spin-labelled lipids from the bilayer, and by the presence of U-shaped lipid conformations, which can occur during freezing of the sample. ... 

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