title: Dynamic nuclear polarization-enhanced ¹H-¹³C double resonance NMR in static samples below 20 K.
abstract: We demonstrate the feasibility of one-dimensional and two-dimensional ¹H-¹³C double resonance NMR experiments with dynamic nuclear polarization (DNP) at 9.4 T and temperatures below 20 K, including both ¹H-¹³C cross-polarization and ¹H decoupling, and discuss the effects of polarizing agent type, polarizing agent concentration, temperature, and solvent deuteration. We describe a two-channel low-temperature DNP/NMR probe, capable of carrying the radio-frequency power load required for ¹H-¹³C cross-polarization and high-power proton decoupling. Experiments at 8 K and 16 K reveal a significant T₂ relaxation of ¹³C, induced by electron spin flips. Carr-Purcell experiments and numerical simulations of Carr-Purcell dephasing curves allow us to determine the effective correlation time of electron flips under our experimental conditions. The dependence of the DNP signal enhancement on electron spin concentration shows a maximum near 80 mM. Although no significant difference in the absolute DNP enhancements for triradical (DOTOPA-TEMPO) and biradical (TOTAPOL) dopants was found, the triradical produced greater DNP build-up rates, which are advantageous for DNP experiments. Additionally the feasibility of structural measurements on ¹³C-labeled biomolecules was demonstrated with a two-dimensional ¹³C-¹³C exchange spectrum of selectively ¹³C-labeled β-amyloid fibrils.
authors: Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institute of Health, Bethesda, MD 20892-0520, USA. potapovai@niddk.nih.gov
authors: Alexey
authors: A
authors: Potapov
authors: Kent R
authors: KR
authors: Thurber
authors: Wai-Ming
authors: WM
authors: Yau
authors: Robert
authors: R
authors: Tycko
mesh_terms: D000409:Alanine / Q000737:chemistry; D000465:Algorithms; D016229:Amyloid beta-Peptides / Q000737:chemistry; D002138:Calibration; D002247:Carbon Isotopes; D003080:Cold Temperature; D003903:Deuterium; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008872:Microwaves; D010446:Peptide Fragments / Q000737:chemistry; D011846:Radio Waves
chemical_list: D016229:Amyloid beta-Peptides; D002247:Carbon Isotopes; D010446:Peptide Fragments; C075222:amyloid beta-protein (1-42); D003903:Deuterium; D000409:Alanine