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A new, triple resonance, pulse electron paramagnetic resonance (EPR) sequence is described. It provides spin links between forbidden electron spin transitions (ΔMS=±1, ΔMI≠0) and allowed nuclear spin transitions (ΔMI=±1), thus, facilitating the assignment of nuclear frequencies to their respective electron spin manifolds and paramagnetic centers. It also yields the relative signs of the hyperfine couplings of the different nuclei. The technique is based on the combination of electron-nuclear double resonance (ENDOR) and electron-electron double resonance (ELDOR)–detected NMR experiments in a way similar to the TRIPLE experiment. The feasibility and the information content of the method are demonstrated first on a single crystal of Cu-doped L-histidine and then on a frozen solution of a Cu-histidine complex. [ABSTRACT FROM AUTHOR]

The semiquninone radical anions B[Q.sup..-], N[Q.sup..-], V[K3.sup..-] and V[K1.sup..-] in frozen propanol solution is measured using pulsed Q-band electron nuclear double resonance spectroscopy. The hyperfine (hf) tensors study concluded that four solvent molecules are coordinated through hydrogen bonds to the quinone oxygens but in V[K3.sup..-] and V[K1.sup..-] some of these hydrogen bonds do not lie in the plane of the quinone.

Results reveal two types of manganese with zero-field splitting tensors at low temperatures in single crystals of concanavalin A. At room temperature, the crystals display one type of manganese. Temperature dependent electron paramagnetic resonance spectra suggest a two-state conformational equilibria at 200K absolute temperature.

The simulations of both strongly and weakly coupled protons, along with the known copper hyperfine couplings, were used to estimate and compare the spin density distribution in the various CuA centers. The largest sulfur spin density was found in M160T9, and the lowest was found in purpAz.

Copper histidine plays a pivotal role in biological systems, especially in the treatment of Menkes and Wilson diseases. W=-band (95 Ghz) pulsed EPR and electron nuclear double resonance (ENDOR) spectroscopic techniques are used to determine the hyperfine couplings of different protons of Cu(II)-histidine complexes in frozen solutions.

(super 55)MN pulse ENDOR spectra for the So and S2 states at Q-band frequency is reported. Numerical analysis of the spectra shows that all four Mn ions are magnetically coupled, allows a refinement of the hyperfine interaction (HFI) parameters for the S2 state and provides the first reliable HFI tensors for the S0 state.

In vivo oximetry by pulsed electron paramagnetic resonance is based on measurements of changes in electron spin relaxation rates of probe molecules, such as the triarylmethyl radicals. A series of experiments was performed at frequencies between 250 MHz and 1.5 GHz to assist in the selection of an optimum frequency for oximetry. Electron spin relaxation rates for the triarylmethyl radical OX063 as a function of radical concentration, salt concentration, and resonance frequency were measured by electron spin echo 2-pulse decay and 3-pulse inversion recovery in the frequency range of 250 MHz-1.5 GHz. At constant OX063 concentration, 1/T1 decreases with increasing frequency because the tumbling dependent processes that dominate relaxation at 250 MHz are less effective at higher frequency. 1/T2 also decreases with increasing frequency because 1/T1 is a significant contribution to 1/T2 for trityl radicals in fluid solution. 1/T2-1/T1, the incomplete motional averaging contribution to 1/T2, increases with increasing frequency. At constant frequency, relaxation rates increase with increasing radical concentration due to contributions from collisions that are more effective for 1/T2 than 1/T1. The collisional contribution to relaxation increases as the concentration of counter-ions in solution increases, which is attributed to interactions of cations with the negatively charged radicals that decrease repulsion between trityl radicals. The Signal-to-Noise ratio (S/N) of field-swept echo-detected spectra of OX063 were measured in the frequency range of 400 MHz-1 GHz. S/N values, normalized by √Q, increase as frequency increases. Adding salt to the radical solution decreased S/N because salt lowers the resonator Q. Changing the temperature from 19 to 37°C caused little change in S/N at 700 MHz. Both slower relaxation rates and higher S/N at higher frequencies are advantageous for oximetry. The potential disadvantage of higher frequencies is the decreased depth of penetration into tissue. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) Imaging (EPRI) is a robust method for measuring in vivo oxygen concentration (pO2). For 3D pulse EPRI, a commonly used reconstruction algorithm is the filtered backprojection (FBP) algorithm, in which the backprojection process is computationally intensive and may be time consuming when implemented on a CPU. A multistage implementation of the backprojection can be used for acceleration, however it is not flexible (requires equal linear angle projection distribution) and may still be time consuming. In this work, single-stage backprojection is implemented on a GPU (Graphics Processing Units) having 1152 cores to accelerate the process. The GPU implementation results in acceleration by over a factor of 200 overall and by over a factor of 3500 if only the computing time is considered. Some important experiences regarding the implementation of GPU-accelerated backprojection for EPRI are summarized. The resulting accelerated image reconstruction is useful for real-time image reconstruction monitoring and other time sensitive applications. [ABSTRACT FROM AUTHOR]