RESUMO
An attempt is made to bypass spectral analysis and fit internal coordinates of radicals directly to experimental liquid- and solid-state electron spin resonance (ESR) spectra. We take advantage of the recently introduced large-scale spin dynamics simulation algorithms and of the fact that the accuracy of quantum mechanical calculations of ESR parameters has improved to the point of quantitative correctness. Partial solutions are offered to the local minimum problem in spectral fitting and to the problem of spin interaction parameters (hyperfine couplings, chemical shifts, etc.) being very sensitive to vibrational excursions from the equilibrium geometry.
Assuntos
Espectroscopia de Ressonância de Spin Eletrônica/métodos , Proteínas/química , Algoritmos , Simulação por Computador , Computadores , Espectroscopia de Ressonância de Spin Eletrônica/economia , Escherichia coli/enzimologia , Modelos Moleculares , Conformação Molecular , Distribuição Normal , Ribonucleotídeo Redutases/química , Salmonella typhimurium/química , Tirosina/química , Difração de Raios XRESUMO
This technical note reports a continuous-wave electron paramagnetic resonance (CW-EPR) imager that can visualize the distribution of free radicals with a half-life of subminutes in three-dimensional (3D) space. A total of 46 EPR spectra under magnetic field gradients, called projections, were obtained for image reconstruction at an interval of 3.6 s. A shortened data-acquisition time was achieved with the use of analog signals that drove field gradient coils in the imager. 3D mapping of the half-lives of nitroxyl radicals (4-hydroxyl-2,2,6,6-tetramethyl-piperidinyl-1-oxyl) was demonstrated in their reduction reaction with ascorbic acid. Inhomogeneous half-lives were clearly mapped pixel-by-pixel in a sample tube.
Assuntos
Espectroscopia de Ressonância de Spin Eletrônica/métodos , Imageamento Tridimensional/métodos , Óxidos de Nitrogênio/análise , Ácido Ascórbico/metabolismo , Espectroscopia de Ressonância de Spin Eletrônica/economia , Espectroscopia de Ressonância de Spin Eletrônica/instrumentação , Desenho de Equipamento , Meia-Vida , Imageamento Tridimensional/economia , Imageamento Tridimensional/instrumentação , Óxidos de Nitrogênio/metabolismo , Oxirredução , Sensibilidade e Especificidade , Fatores de TempoRESUMO
A new method has been developed for sample packing in rapid freeze-quench electron paramagnetic resonance spectroscopy (EPR) kinetic experiments. Sample particles freeze-quenched in chilled isopentane are filtered under pressure through a stainless steel funnel attached to an EPR tube fitted with a porous disk at its bottom. Isopentane exits through the porous disk and the sample particles can be transferred essentially quantitatively into the receiving EPR tube. This device provides a more predictable, reproducible, and time-saving method for sample packing, enables use of a wider range of flow velocity, and allows efficient use of valuable reactants.
