Relative sublevel populations due to OSP and ZFS parameters of haloanthracenes determined through best fit simulations of the TR-EPR spectra shown in Fig 3.

<p>Relative sublevel populations due to OSP and ZFS parameters of haloanthracenes determined through best fit simulations of the TR-EPR spectra shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184239#pone.0184239.g003" target="_blank">Fig 3</a>.</p

SLR times of haloanthracenes obtained from best fit simulations of ESE EPR detected triplet kinetics, partially shown in Fig 4.

<p>For the full set of decay curves and their simulations, cf. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184239#pone.0184239.s001" target="_blank">S1</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184239#pone.0184239.s002" target="_blank">S2</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184239#pone.0184239.s003" target="_blank">S3</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184239#pone.0184239.s004" target="_blank">S4</a> Figs. Since in the case of 3, the signals of the canonical X and Y direction can not be distinguished spectrally, the mutual SLR times are given in the X columns. The numbers in braces indicate the width of the distributions of the parameters, described in terms of 2<i>σ</i> of corresponding normal distributions, as obtained from Monte Carlo simulations.</p

Excited triplet state sublevel scheme and transition rate constants.

<p>The dotted arrows indicate combined radiationless (ISC) and radiative (phosphorescence) decay.</p

TR-EPR spectra of haloanthracenes.

<p>The TR-EPR spectra (solid lines) and corresponding spectral simulations (dashed, shifted vertically for better visibility). Absorption and emission are indicated by arrows at the left ordinate. A: Anthracene (<b>1</b>), B: Bromoanthracene (<b>2</b>), C: Dibromoanthracene (<b>3</b>), D: Iodoanthracene (<b>4</b>). Recorded at 20 K in X band. Relative sublevel populations and ZFS parameters of the simulations can be found in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184239#pone.0184239.t001" target="_blank">Table 1</a>. For the full set of parameters, cf. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184239#pone.0184239.s013" target="_blank">S3 Table</a>.</p

Structural formula of haloanthracenes.

<p>Structural formula of haloanthracenes.</p

Triplet life times of haloanthracenes obtained from best fit simulations of ESE EPR detected triplet kinetics, as exemplary shown in Fig 4.

<p>For the full set of decay curves and their simulations, cf. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184239#pone.0184239.s001" target="_blank">S1</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184239#pone.0184239.s002" target="_blank">S2</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184239#pone.0184239.s003" target="_blank">S3</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184239#pone.0184239.s004" target="_blank">S4</a> Figs. Since in the case of 3, the signals of the canonical X and Y direction can not be distinguished spectrally, the mutual triplet life times are given in the X column. For 1, the triplet life time has been determined in a separate measurement (cf. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184239#pone.0184239.s005" target="_blank">S5 Fig</a>), in good agreement to the value found in the literature [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184239#pone.0184239.ref029" target="_blank">29</a>] (≈ 40 ms), and was held constant. In the cases of 1 and 2 no triplet decay anisotropy was found, meaning that <i>k</i>_X = <i>k</i>_Y = <i>k</i>_Z = <i>k</i>. The numbers in braces indicate the width of the distributions of the parameters, described in terms of 2<i>σ</i> of corresponding normal distributions, as obtained from Monte Carlo simulations.</p

Exemplary ESE detected triplet kinetics of two haloanthracenes.

<p>A: Anthracene (<b>1</b>). B: Dibromoanthracene (<b>3</b>). The Hahn spin echo amplitude (dots) is recorded at different temperatures (50 K, 30 K, and 10 K, from top to bottom) in X band as a function of the delay time <i>t</i>_DAF after photoexcitation for both allowed EPR transitions on the Z canonical orientation, 1Z being emissive and 2Z being absorptive as indicated with arrows at the left ordinate. The parameters obtained from the best fit simulations (solid lines) are given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184239#pone.0184239.t002" target="_blank">Table 2</a>. Note the different time scales.</p

A Genetically Encoded Spin Label for Electron Paramagnetic Resonance Distance Measurements

We report the genetic encoding of a noncanonical, spin-labeled amino acid in <i>Escherichia coli</i>. This enables the intracellular biosynthesis of spin-labeled proteins and obviates the need for any chemical labeling step usually required for protein electron paramagnetic resonance (EPR) studies. The amino acid can be introduced at multiple, user-defined sites of a protein and is stable in <i>E. coli</i> even for prolonged expression times. It can report intramolecular distance distributions in proteins by double-electron electron resonance measurements. Moreover, the signal of spin-labeled protein can be selectively detected in cells. This provides elegant new perspectives for in-cell EPR studies of endogenous proteins

Gd(III)-PyMTA Label Is Suitable for In-Cell EPR

Distance measurement in the nanometer range by electron paramagnetic resonance spectroscopy (EPR) in combination with site-directed spin labeling is a very powerful tool to monitor the structure and dynamics of biomacromolecules in their natural environment. However, in-cell application is hampered by the short lifetime of the commonly used nitroxide spin labels in the reducing milieu inside a cell. Here, we demonstrate that the Gd­(III) based spin label Gd-PyMTA is suitable for in-cell EPR. Gd-PyMTA turned out to be cell compatible and was proven to be inert in in-cell extracts of <i>Xenopus laevis</i> oocytes at 18 °C for more than 24 h. The proline rich peptide H-AP₁₀CP₁₀CP₁₀-NH₂ was site-directedly spin labeled with Gd-PyMTA at both cysteine moieties. The resulting peptide, H-AP₁₀C­(Gd-PyMTA)­P₁₀C­(Gd-PyMTA)­P₁₀-NH₂, as well as the model compound Gd-spacer-Gd, which consists of a spacer of well-known stiffness, were microinjected into <i>Xenopus laevis</i> oocytes, and the Gd­(III)–Gd­(III) distances were determined by double electron–electron resonance (DEER) spectroscopy. To analyze the intracellular peptide conformation, a rotamer library was set up to take the conformational flexibility of the tether between the Gd­(III) ion and the C_α of the cysteine moiety into account. The results suggest that the spin labeled peptide H-AP₁₀C­(Gd-PyMTA)­P₁₀C­(Gd-PyMTA)­P₁₀-NH₂ is inserted into cell membranes, coinciding with a conformational change of the oligoproline from a PPII into a PPI helix

Negative and Positive Confinement Effects in Chiral Separation Chromatography Monitored with Molecular-Scale Precision by In-Situ Electron Paramagnetic Resonance Techniques

Separation of compounds using liquid chromatography is a process of enormous technological importance. This is true in particular for chiral substances, when one enantiomer has the desired set of properties and the other one may be harmful. The degree of development in liquid chromatography is extremely high, but still there is a lack in understanding based on experimental data how selectivity works on a molecular level directly at the surfaces of a porous host material. We have prepared amino-acid containing organosilica as such host materials. Watching the rotational dynamics of chiral spin probes using electron paramagnetic resonance spectroscopy allows us to differentiate between surface adsorbed and free guest species. Diastereotopic selectivity factors were determined, and the influence of chiral surface group density, chemical character of the surface groups, pore-size, and temperature was investigated. We found higher selectivity values in macroporous solids with a rather rigid organosilica network and at lower temperature, indicating the significant effect of confinement effects. In mesoporous materials features are opposed with regards to the T-dependent behavior. From EPR imaging techniques and the resulting (macroscopic) diffusion coefficients, we could confirm that the correlations found on the microscopic level transform also to the macroscopic behavior. Thus, our study is of value for the development of future chromatography materials by design