Reaction fields and solvent dependence of the EPR parameters of nitroxides: The microenvironment of spin labels

Marsh, Derek

doi:10.1016/j.jmr.2007.10.004

Cited by 36 publications

(27 citation statements)

References 52 publications

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“…On the other hand, changes in experimental coupling constants, on titration of a dissociable group attached to the nitroxide ring, are consistent with a value of C 1 = 1.9 · 10 À11 V À1 m, for Q N À Q NO = 2.04 mT, when compared with classical electrostatic calculations of the change in local electric field [28]. In aprotic media, the reaction field at the nitroxide that arises from polarisation of the solvent by the (polarisable) N-O electric dipole, p, is given by [29,30]:…”

Section: Isotropic Hyperfine Couplingssupporting

confidence: 72%

Polarity dependence of EPR parameters for TOAC and MTSSL spin labels: Correlation with DOXYL spin labels for membrane studies

Marsh

Toniolo

2008

Journal of Magnetic Resonance

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TOAC (2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid) is a nitroxyl amino acid that can be incorporated in the backbone of peptides. DOXYL (4,4-dimethyl-oxazolidine-1-oxyl) is a nitroxyl ring that can be attached rigidly at specific C-atom positions in the acyl chains of phospholipids. Spin-labelled phosphatidylcholines of the DOXYL type have been used previously to establish the transmembrane polarity profile in biological lipid bilayers [D. Marsh, Polarity and permeation profiles in lipid membranes, Proc. Natl. Acad. Sci. USA 87 (2001) 7777-7782]. Here, we determine the polarity dependence of the isotropic (14)N-hyperfine couplings, a(o)(N), and g-values, g(o), in a wide range of protic and aprotic media, for a TOAC-containing dipeptide (Fmoc-TOAC-Aib-OMe) and for a DOXYL-containing fatty acid (12-DOXYL-stearic acid). The correlation between datasets for TOAC and DOXYL nitroxides in the various solvents is used to establish the polarity profile for isotropic hyperfine couplings of TOAC in a transmembrane peptide. This calibration can be used to determine the location of TOAC at selected residue positions in a transmembrane or surface-active peptide. A similar calibration procedure is also applied to a(o)(N) and g(o) for the pyrroline methanethiosulphonate nitroxide (MTSSL) that is used in site-directed spin-labelling studies of membrane proteins.

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Section: Isotropic Hyperfine Couplingssupporting

confidence: 72%

Polarity dependence of EPR parameters for TOAC and MTSSL spin labels: Correlation with DOXYL spin labels for membrane studies

Marsh

Toniolo

2008

Journal of Magnetic Resonance

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“…This finding with this solvent parameter is indeed expected as according to several reports in the literature, it is dependent on the class of solvent [31][32][33]. The dielectric constant varies when the solvent form or not hydrogen bonds and/or van der Waals interactions with the N-O moiety of the spin probes, inducing redistribution of the electrons in the medium.…”

Section: Resultssupporting

confidence: 85%

Application of Electron Paramagnetic Resonance Spectroscopy for Validation of the Novel (AN+DN) Solvent Polarity Scale

Malavolta

Poletti

Silva

et al. 2008

IJMS

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Abstract:Based on solvation studies of polymers, the sum (1:1) of the electron acceptor (AN) and electron donor (DN) values of solvents has been proposed as an alternative polarity scale. To test this, the electron paramagnetic resonance isotropic hyperfine splitting constant, a parameter known to be dependent on the polarity/proticity of the medium, was correlated with the (AN+DN) term using three paramagnetic probes. The linear regression coefficient calculated for 15 different solvents was approximately 0.9, quite similar to those of other well-known polarity parameters, attesting to the validity of the (AN+DN) term as a novel "two-parameter" solvent polarity scale.

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“…The 14 N-hyperfine splittings in the conventional CW EPR spectra are sensitive to environmental polarity, including the presence of nonbonded and hydrogen-bonded water (2,36). Fig.…”

Section: N-hyperfine Splittingsmentioning

confidence: 99%

Water Penetration Profile at the Protein-Lipid Interface in Na,K-ATPase Membranes

Bartucci

Guzzi

Esmann

et al. 2014

Biophysical Journal

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The affinity of ionized fatty acids for the Na,K-ATPase is used to determine the transmembrane profile of water penetration at the protein-lipid interface. The standardized intensity of the electron spin echo envelope modulation (ESEEM) from (2)H-hyperfine interaction with D2O is determined for stearic acid, n-SASL, spin-labeled systematically at the C-n atoms throughout the chain. In both native Na,K-ATPase membranes from shark salt gland and bilayers of the extracted membrane lipids, the D2O-ESEEM intensities of fully charged n-SASL decrease progressively with position down the fatty acid chain toward the terminal methyl group. Whereas the D2O intensities decrease sharply at the n = 9 position in the lipid bilayers, a much broader transition region in the range n = 6 to 10 is found with Na,K-ATPase membranes. Correction for the bilayer population in the membranes yields the intrinsic D2O-intensity profile at the protein-lipid interface. For positions at either end of the chains, the D2O concentrations at the protein interface are greater than in the lipid bilayer, and the positional profile is much broader. This reveals the higher polarity, and consequently higher intramembrane water concentration, at the protein-lipid interface. In particular, there is a significant water concentration adjacent to the protein at the membrane midplane, unlike the situation in the bilayer regions of this cholesterol-rich membrane. Experiments with protonated fatty acid and phosphatidylcholine spin labels, both of which have a considerably lower affinity for the Na,K-ATPase, confirm these results.

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Reaction fields and solvent dependence of the EPR parameters of nitroxides: The microenvironment of spin labels

Cited by 36 publications

References 52 publications

Polarity dependence of EPR parameters for TOAC and MTSSL spin labels: Correlation with DOXYL spin labels for membrane studies

Polarity dependence of EPR parameters for TOAC and MTSSL spin labels: Correlation with DOXYL spin labels for membrane studies

Application of Electron Paramagnetic Resonance Spectroscopy for Validation of the Novel (AN+DN) Solvent Polarity Scale

Water Penetration Profile at the Protein-Lipid Interface in Na,K-ATPase Membranes

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