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Spectroscopy Tools and Techniques
Published in Jay L. Nadeau, Introduction to Experimental Biophysics, 2017
A spin probe is a stable radical that can be conjugated to a specific part of a biomolecule in order to measure motility. The most common spin probes in biology are nitroxide radicals (Figure 16.36a). Spin-labeling was used to demonstrate for the first time that the interiors of lipid membranes are highly fluid, and is also used to measure association kinetics of biomolecules. Both of these types of experiments make use of the fact that electron exchange between radicals leads to spectral broadening (Figure 16.36b).
A case study of density functional theory and domain-based local pair natural orbital coupled cluster for vibrational effects on EPR hyperfine coupling constants: vibrational perturbation theory versus ab initio molecular dynamics
Published in Molecular Physics, 2020
Alexander A. Auer, Van Anh Tran, Bikramjit Sharma, Georgi L. Stoychev, Dominik Marx, Frank Neese
We focus the application of the different schemes on the 2,2,3,4,5,5-hexamethylperhydroimidazol-1-oxyl molecule, which we will simply denote as HMI in the following (see Figure 1). HMI provides a perfect test case with well characterised properties, high relevance for the experiment, and a size which renders the computations challenging for benchmarking. HMI belongs to a class of nitroxide radical spin labels which are widely used in EPR spectroscopic studies [37–42]. HMI itself is a pH-sensitive imidazole nitroxyl radical-based spin probe that has a variety of interesting properties and has been proposed, for example, for pH-monitoring inside chloroplasts [43,44]. It is well-known, that in such systems, the unpaired electron is mostly localised in a π* orbital involving the nitrogen in the 1 position and the adjacent oxygen with various degrees of delocalisation into the ring system depending on its chemical nature, in particular on the presence of conjugated double bonds.
EPR study of the polydomain structure of the twist-bend nematic phase of CB9CB in the bulk
Published in Liquid Crystals, 2018
Corrado Bacchiocchi, Maria-Gabriela Tamba, Georg H. Mehl, Alberto Arcioni, Isabella Miglioli, Claudio Zannoni
The nitroxide spin probe used for doping the CB9CB LC was the 3-doxyl-5-cholestane free radical (Aldrich, hereafter, referred to as CSL). This was employed in a number of previous studies [26,28,33–35] where it proved to be a reliable probe to monitor the order and the dynamics of the LC system due to its size, morphology and rigidity, which results in a strong orientation by the LC host. The CSL structure is shown in Figure 2 together with the chosen ordering (x,y,z, solid line) and magnetic (x′,y′,z′, dashed line) molecular frames and the indication of its two main reorientational motions, tumbling and spinning, with the corresponding components of the rotational diffusion tensor: (reorientation of the molecular long axis) and (rotation around the long axis), respectively.