Characterization of muoniated spin probes in cholesterol by avoided level crossing muon spin resonance

Avoided level crossing muon spin resonance (ALC-mu SR) has been used to characterize muoniated radicals formed by the reaction of muonium (Mu) with cholesterol in the solid state and in solution. Mu adds to the secondary carbon of the C=C bond and the observed radical has Mu in the 6 beta position. The isotropic hyperfine coupling constant (A(mu)) and dipolar muon hyperfine coupling constant (D-mu(parallel to)) were determined in solid cholesterol between 318 and 398 K from the position and shape of the Delta(1) resonance. A(mu) and D-mu(parallel to) decrease with increasing temperature; the former due to intramolecular motion and the latter due to both intramolecular motion and wobbling of the molecule. A Delta(0) resonance due to the proton in the 4 beta position was observed in the ALC-mu SR spectra of dilute solutions of cholesterol in tetrahydrofuran and methanol. The position of the Delta(0) resonance is sensitive to the polarity of the solvent and its width depends on the viscosity of the solution.

Automated summary

ALC-mu SR is used to characterize muoniated radicals formed by the reaction of Mu with cholesterol, showing that Mu adds to the secondary carbon of the C=C bond and the observed radical has Mu in the 6 beta position. A(μ) and D-μ(∥) decrease with increasing temperature due to intramolecular motion and both intramolecular motion and wobbling of the molecule, respectively. The Delta(0) resonance observed in dilute solutions of cholesterol is sensitive to the polarity of the solvent and its width depends on the viscosity of the solution.