The use of the Rx spin label in orientation measurement on proteins, by EPR

M.A.S. & J.E.M. would like to acknowledge funding from the EPSRC as part of the iMR-CDT. The Authors would like to acknowledge funding from The MRC UK, Grant G1100021, EPSRC Basic Technology EP/F039034/1, and from the Wellcome Trust 099149/Z/12/Z.The bipedal spin label Rx is more restricted in its conformation and dynamics than its monopodal counterpart R1. To systematically investigate the utility of the Rx label, we have attempted to comprehensively survey the attachment of Rx to protein secondary structures. We have examined the formation, structure and dynamics of the spin label in relation to the underlying protein in order to determine feasibility and optimum conditions for distance and orientation measurement by pulsed EPR. The labeled proteins have been studied using molecular dynamics, CW EPR, pulsed EPR distance measurement at X-band and orientation measurement at W-band. The utility of different modes and positions of attachment have been compared and contrasted.Publisher PDFPeer reviewe

Kinetic study of UV-irradiated amorphous sulfur by EPR spectroscopy

Electron paramagnetic resonance (EPR) spectroscopy is used to investigate UV-irradiation damage in amorphous sulfur by examining post-irradiation kinetics as a function of UV-exposure time. The kinetic study is described by first-order concurrent reactions where the sulfur, as reactant, undergoes two parallel processes leading to the formation of two distinct defects called S-1(center dot), and S-2(center dot). The temperature dependence of the EPR intensities of the signals, related to these defects, is used in the kinetic study. (c) 2005 Elsevier B.V. All rights reserved.</p

EPR investigation of two types of Syrian's natural zeolites

Two different samples of natural zeolite have been investigated by X-band electron paramagnetic resonance (EPR) spectroscopy. The observed EPR spectra are typical to those observed for Fe3+ and Mn2+ ions. The lines, related to the iron, are observed, respectively at g approximate to 4.3 and g approximate to 2. The observed six lines, at g approximate to 2, are the hyperfine structure due to the Mn2+ ions. The simulation of the experimental EPR spectra suggests that both of the manganese and the iron are present in more one site. The temperature dependence of the EPR spectra has been also investigated. The nature of the different sites involved in the EPR absorption is discussed. (C) 2004 Elsevier Ltd. All rights reserved.</p

Antiferromagnetic resonance studies in molecular magnetic materials

EPR spectroscopy has become an increasingly powerful tool to examine the spin states and dynamics of single-molecule magnets, but has not been exploited to probe bulk magnetically ordered phases of molecular magnets. In this article, we review the EPR spectra of antiferromagnets and canted antiferromagnets below T-N with particular reference to our own studies on the canted antiferromagnet, p-NCC6F4CNSSN (T-N = 36 K). The antiferromagnetic resonance experiment allows the saturation of the sublattice magnetisation to be probed. In addition, the exchange and anisotropy fields (H-e and H-a), the spin-flop field (H-sf) and for canted antiferromagnets, the Dzyaloshinskii-Moriya field (H-DM), which gives rise to the spontaneous moment, can be determined. (C) 2003 Elsevier Ltd. All rights reserved.</p

Paramagnetic defects in solid sulphur and glasses of the system Ge-S

Ge-S glasses are synthesised by melting pure S and Ge elements. Electron paramagnetic resonance (EPR) spectroscopy is used to analyse the paramagnetic defects in these glasses. Paramagnetic defects are also observed in amorphous and polycrystalline S samples after UV irradiation at T=77 K. The simulation of the EPR spectra leads to spectroscopic parameters of the sulphur centres which are similar in S samples and in S-rich Ge-S glasses, at the liquid nitrogen temperature. In Ge-S glasses, the paramagnetic sites remain stable at room temperature and the spectroscopic parameters are modified. The nature of the sites involved in these absorptions is discussed.</p

Electron paramagnetic resonance study of Mn²⁺ and Cu²⁺ spin probes in (Ag₂S) _x(GeS₂)_1-x glasses

Mn2+ and Cu2+ spin probes have been introduced in glassy (Ag2S)x(GeS2)1-x (0 ≤ x ≤ 0.8). The electron paramagnetic resonance spectra related to Mn2+ show a poorly resolved hyperfine structure at g = 2 and a characteristic line at g = 4.3 ascribed to the presence of Mn2+ in the center of GeS4 tetrahedra. For small contents of Mn2+, hyperfine structure is resolved as x increases to the limit x = 0.55 and not resolved when x ≥ 0.6. The Cu2+ probe leads to a well resolved signal when x = 0.4. No signal is observed for x &lt; 0.3. These results seem to confirm the presence of a phase separation domain for x &lt; 0.3 and the changes of the local structure of the probes with the appearance of micro-crystallinity due to the Ag8GeS6 phase when x ≥ 0.55.</p

Dc and ac Conductivities of (V₂O₅)_x(B₂O₃) _1-X oxide glasses

Glasses of composition (V2O5)x(B2O3) 1-x with x = 0.1, 0.3, 0.5, 0.7 and 0.9 were obtained by a quenching technique. Conductivity measurements using σac were performed on compact pellets of these materials. The conductivity behavior in direct regime, σdc, is described by the "small polaron" model. The room temperature variation of log σdc with the activation energy of each composition, suggests an adiabatic hopping character to the conduction. Application of Hunt's model to describe the ac conductivity behavior shows that the relaxation process has a local character and can be described by hops between each pair of sites.</p