Electron spin labeling

The solution structures, dynamics, and interactions of and between biological macromolecules are topics of widespread interest in biochemistry. The chapter on electron spin labels, by Millhauser et al. illustrates how the EPR spectra of the stable nitroxide free radical can be used to address such problems. The chemistry of the nitroxides and their modes of attachment to the host molecules are discussed first. The details of the EPR spectra and of the spin Hamiltonian are then presented, showing how the intrinsic tensorial nature of the EPR spectrum of the reporter group is affected by motion. Such dynamic information is then extracted from some small peptides. The interaction between pairs of nitroxides is used to extract structural information. Finally, an example of Fourier transform EPR is introduced. ... 

From the Electron Spin Labeling it was shown that ... 

This specfmm is dominated by ftmdamenfals, combinations and overtones of fofally symmefric vibrations. The intensify disfribufions among fhese bands are determined by fhe Franck-Condon factors (vibrational overlap integrals) between the state of the molecule and the ground state, Dq, of the ion. (The ground state of the ion has one unpaired electron spin and is, therefore, a doublet state, D, and the lowest doublet state is labelled Dq.) The... 

The structure of spin-labeled acetylenes includes 7r-electron-rich pyrazole and... 

The effectiveness of a crude oil demulsifier is correlated with the lowering of the shear viscosity and the dynamic tension gradient of the oil-water interface. The interfacial tension relaxation occurs faster with an effective demulsifier [1714]. Short relaxation times imply that interfacial tension gradients at slow film thinning are suppressed. Electron spin resonance experiments with labeled demulsifiers indicate that the demulsifiers form reverse micellelike clusters in the bulk oil [1275]. The slow unclustering of the demulsifier at the interface appears to be the rate-determining step in the tension relaxation process. 

Ligeza A, Tikhonov AN, Hyde JS, Subczynski WK. 1998. Oxygen permeability of thylakoid membranes Electron paramagnetic resonance spin labeling study. Biochim Biophys Acta 1365 453. 

A planar BLM cannot be investigated by means of the molecular spectroscopical methods because of the small amount of substance in an individual BLM. This disadvantage is removed for liposomes as they can form quite concentrated suspensions. For example, in the application of electron spin resonance (ESR) a spin-labelled phospholipid is incorporated into the liposome membrane this substance can be a phospholipid with, for example, a 2,2,6,6-tetramethylpiperidyl-A-oxide (TEMPO) group ... 

As with the nitroxalkylcobalamins (119) and cobinamides, the co-binamides in which nitroxide is coordinated show electron spin resonance spectra very similar to the spectrum of free nitroxide. The high field line is not broadened as much as in the spectrum of a nitroxalkyl-cobinamide. No hyperfine splitting from methyl protons in the 2 or 6 positions can be observed for the bound nitroxide. However, treatment of the coordinate spin labeled compounds with cyanide releases the nitroxide. When this happens, the proton hyperfine can be observed (Fig. 25). Thus treatment with cyanide simply displaces the nitroxide and a spectrum for free nitroxide is observed. 

Fig. 28. Routes of cobalt-carbon bond cleavage showing possible electronic arrangements of the resulting spin labeled derivative...

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