The dominant usage in NIH-funded grants is in the field of site-directed spin-labeling (SDSL) using nitroxide radical spin labels to probe molecular structure. The Technology Research and Development (TR&D) component of this application for continued support of the National Biomedical EPR Center, a P41 Research Resource, focuses on technology enhancement for SDSL applications of EPR. The TR&D component is tightly linked to the Collaborative component, with most collaborations falling in the SDSL classification. Applications involving metal ions are next among NlH-supported grants using EPR, and in this submission, special emphasis is placed in the Service component on making EPR capabilities available to this community. Training and Dissemination components are broadly based and vigorous. We introduced the technology of non-adiabatic rapid sweep (NARS) spectroscopy in the current funding period as a general purpose replacement for phase-sensitive detection (PSD) in EPR spectroscopy. NARS capabilities will be built at L-, X-, Q-, W-, and D-band. Extension to adiabatic rapid sweep (ARS) was demonstrated at W-band during the current funding period, establishing feasibility for Fourier transform EPR using ARS technology with arbitrary waveform generator (AWG) sweep, which is proposed. The intermediate "passage" range of magnetic field sweep will be used to probe very slow motions. Microwave frequency sweep will be developed at Q-, W-, and D-band. TR&D Project 1 focuses on development of the new technology at L,- X-, and Q-band;Project 3 carries the technology to W- and D-band;and Project 2 focuses on two L-band applications: distance determination at room temperature to 40 A and L-band electron-electron double resonance (ELDOR) for measurement of protein and membrane electrostatic potentials. The M = 0 line of perdeutero 14N spin labels is narrow and very nearly isotropic, making it an ideal probe for these two experiments. New resonators tailored for NARS detection are proposed. The ten collaborations are very tightly linked to the three TR&D projects. The strong support letter for this project from Prof. Wayne L. Hubbell, UCLA, who is also chairman of the External Advisory Committee for the Center, is notable. Collaborations demonstrate widespread interest in the SDSL community. The TR&D theme in this submission is non-adiabatic, adiabatic, and rapid passage technology development across a wide range of microwave frequencies for SDSL research. The NIH RePORTER database reveals 124 R0I research grants that use EPR. We serve the holders of these grants to enhance the nation's biomedical research. Progress in the current funding period includes 220 papers.
Molecular dynamics occur in all biological molecules across a wide range of motional frequencies, some of which are central to biological function. The nitroxide radical spin-label method, based on EPR, is suitable for the study of molecular dynamics, including dynamics with characteristic motional periods of a millisecond to a microsecond that are biologically relevant. The proposal applies new EPR spectrometer technology with many innovative features to characterize protein and membrane dynamics.
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