RESUMO
We describe a spectrometer for pulsed ENDOR at 140 GHz, which is based on microwave IMPATT diode amplifiers and a probe consisting of a TE011 cavity with a high-quality resonance circuit for variable radiofrequency irradiation. For pulsed EPR we obtain an absolute sensitivity of 3x10(9) spins/Gauss at 20 K. The performance of the spectrometer is demonstrated with pulsed ENDOR spectra of a standard bis-diphenylene-phenyl-allyl (BDPA) doped into polystyrene and of the tyrosyl radical from E. coli ribonucleotide reductase (RNR). The EPR spectrum of the RNR tyrosyl radical displays substantial g-anisotropy at 5 T and is used to demonstrate orientation-selective Davies-ENDOR.
Assuntos
Espectroscopia de Ressonância de Spin Eletrônica/métodos , Ribonucleotídeo Redutases/química , Compostos Alílicos/química , Anisotropia , Derivados de Benzeno/química , Simulação por Computador , Espectroscopia de Ressonância de Spin Eletrônica/instrumentação , Escherichia coli/enzimologia , Radicais Livres , Magnetismo , Poliestirenos , Prótons , Ondas de Rádio , Sensibilidade e Especificidade , Análise Espectral , Marcadores de Spin , Transdutores , TirosinaRESUMO
Large dynamic nuclear polarization signal enhancements (up to a factor of 100) were obtained in the solid-state magic-angle spinning nuclear magnetic resonance (NMR) spectra of arginine and the protein T4 lysozyme in frozen glycerol-water solutions with the use of dynamic nuclear polarization. Polarization was transferred from the unpaired electrons of nitroxide free radicals to nuclear spins through microwave irradiation near the electron paramagnetic resonance frequency. This approach may be a generally applicable signal enhancement scheme for the high-resolution solid-state NMR spectroscopy of biomolecules.
