Applied Magnetic Resonance 

About: Applied Magnetic Resonance is an academic journal published by Springer Science+Business Media. The journal publishes majorly in the area(s): Electron paramagnetic resonance & Relaxation (NMR). It has an ISSN identifier of 0937-9347. Over the lifetime, 3087 publications have been published receiving 30361 citations. The journal is also known as: AMR. Applied magnetic resonance & Applied magnetic resonance (Print).

DeerAnalysis2006 - a comprehensive software package for analyzing pulsed ELDOR data

Abstract: Pulsed electron-electron double resonance techniques such as the four-pulse double electron-electron resonance experiment measure a dipolar evolution function of the sample. For a sample consisting of spin-carrying nanoobjects, this function is the product of a form factor, corresponding to the internal structure of the nanoobject, and a background factor, corresponding to the distribution of nanoobjects in space. The form factor contains information on the spin-to-spin distance distribution within the nanoobject and on the average number of spins per nanoobject, while the background factor depends on constraints, such as a confinement of the nanoobjects to a two-dimensional layer. Separation of the dipolar evolution function into these two contributions and extraction of the spin-to-spin distance distribution require numerically stable mathematical algorithms that can handle data for different classes of samples, e.g., spin-labelled biomacromolecules and synthetic materials. Furthermore, experimental imperfections such as the limited excitation bandwidth of microwave pulses need to be considered. The software package DeerAnalysis2006 provides access to a comprehensive set of tools for such data analysis within a common user interface. This interface allows for several tests of the reliability and precision of the extracted information. User-supplied models for the spin-to-spin distance distribution within a certain class of nanoobjects can be added to an existing library and be fitted with a universal algorithm.

Automatic computer simulations of ESR spectra

Abstract: A versatility of automatic ESR simulation procedures has been developed to obtain high quality of fitting and produce additional information. The following examples are treated: derivation of long-range proton hyperfine coupling constants from unresolved lines; determination of13C hf couplings from the naturally abundant isotope satellites; analyzing chemical exchange phenomena with two-sites model; decomposition of superimposed spectra consisting of poorly resolved components. In order to achieve best agreement between calculated and experimental spectra within a reasonable number of iteration cycles, we combined various approaches, like consecutive independent parameter optimization, least-square approach, optimization on “serpentines” and optimization of compound parameters. The spectra can be computed both for liquid and solid state samples, for non-oriented, partially oriented and single crystal samples. Second order perturbation formulas are used for the spin Hamiltonian includingg- and hyperfine tensors that have isotropic, axial and rhombic symmetry. For chemical exchange the modified Bloch equation for two-site model is used. Various lineshapes, including Lorentzian, Gaussian, mixed, modulation and dispersion distorted forms are applied. Third order parabolic interpolations are used for building up spectra from individual lines. In order to correct sweep non-linearity a third order interpolation converts the spectrum to become equidistant. This procedure can occasionally improve square deviation by an order of magnitudes for well resolved spectra. In the analysis of strongly overlapping superimposed spectra, simultaneous adjustment of two independent experimental spectra can give an exact decomposition. The inclusion of long-range couplings offers highly perfect fitting and allows one to resolve contributions of naturally abundant13C isotopes.

High-Field Dynamic Nuclear Polarization for Solid and Solution Biological NMR

Abstract: Dynamic nuclear polarization (DNP) results in a substantial nuclear polarization enhancement through a transfer of the magnetization from electrons to nuclei. Recent years have seen considerable progress in the development of DNP experiments directed towards enhancing sensitivity in biological nuclear magnetic resonance (NMR). This review covers the applications, hardware, polarizing agents, and theoretical descriptions that were developed at the Francis Bitter Magnet Laboratory at Massachusetts Institute of Technology for high-field DNP experiments. In frozen dielectrics, the enhanced nuclear polarization developed in the vicinity of the polarizing agent can be efficiently dispersed to the bulk of the sample via 1H spin diffusion. This strategy has been proven effective in polarizing biologically interesting systems, such as nanocrystalline peptides and membrane proteins, without leading to paramagnetic broadening of the NMR signals. Gyrotrons have been used as a source of high-power (5–10 W) microwaves up to 460 GHz as required for the DNP experiments. Other hardware has also been developed allowing in situ microwave irradiation integrated with cryogenic magic-angle-spinning solid-state NMR. Advances in the quantum mechanical treatment are successful in describing the mechanism by which new biradical polarizing agents yield larger enhancements at higher magnetic fields. Finally, pulsed methods and solution experiments should play a prominent role in the future of DNP.

Pulsed electron double resonance (PELDOR) and its applications in free-radicals research

Abstract: The papers related to the theoretical background and experimental investigations by pulsed electron double resonance (PELDOR) are reviewed. The main aim of this pulsed ESR application is to study the dipole-dipole spin interaction. In PELDOR the ESR spectrum is excited by two ESE pulses at frequencyω a and additional pumping pulse atω b. Decay functionV(T) of the ESE signal, when the time intervalT between the first ESE pulse and pumping pulse is varied, contains the information on dipole-dipole couplings in the spin system. The kinetics ofV(T) decay strongly depends upon distance, mutual orientation inside interacting spin pairs and space distribution of radicals throughout the sample. The distances between spins which were measured or estimated using PELDOR in the papers reviewed are in the range of 15 ÷ 130 A. This pulsed ESR technique turns now to be a powerful supplement to conventional ESE in studying the free radicals space distribution..

Data analysis procedures for pulse ELDOR measurements of broad distance distributions

Abstract: The reliability of procedures for extracting the distance distribution between spins from the dipolar evolution function is studied with particular emphasis on broad distributions. A new numerically stable procedure for fitting distance distributions with polynomial interpolation between sampling points is introduced and compared to Tikhonov regularization in the dipolar frequency and distance domains and to approximate Pake transformation. Distance distribution with only narrow peaks are most reliably extracted by distance-domain Tikhonov regularization, while frequency-domain Tikhonov regularization is favorable for distributions with only broad peaks. For the quantification of distributions by their mean distance and variance, Hermite polynomial interpolation provides the best results. Distributions that contain both broad and narrow peaks are most difficult to analyze. In this case a high signal-to-noise ratio is strictly required and approximate Pake transformation should be applied. A procedure is given for renormalizing primary experimental data from protein preparations with slightly different degrees of spin labelling, so that they can be compared directly. Performance of all the data analysis procedures is demonstrated on experimental data for a shape-persistent biradical with a label-to-label distance of 5 nm, for a [2]catenane with a broad distance distribution, and for a doubly spin-labelled double mutant of plant light harvesting complex II