title: Compensated second-order recoupling: application to third spin assisted recoupling.
abstract: We consider the effect of phase shifts in the context of second-order recoupling techniques in solid-state NMR. Notably we highlight conditions leading to significant improvements for the Third Spin Assisted Recoupling (TSAR) mechanism and demonstrate the benefits of resulting techniques for detecting long-distance transfer in biomolecular systems. The modified pulse sequences of PAR and PAIN-CP, Phase-Shifted Proton Assisted Recoupling (AH-PS-PAR) and Phase-Shifted Proton-Assisted Insensitive Nuclei Cross Polarization (ABH-PS-PAIN-CP), still rely on cross terms between heteronuclear dipolar couplings involving assisting protons that mediate zero-quantum polarization transfer between low-γ nuclei ((13)C-(13)C, (15)N-(15)N, (15)N-(13)C polarization transfer). Using Average Hamiltonian Theory we show that phase inversion compensates off-resonance contributions and yields improved polarization transfer as well as substantial broadening of the matching conditions. PS-TSAR greatly improves on the standard TSAR based methods because it alleviates their sensitivity to precise RF settings which significantly enhances robustness of the experiments. We demonstrate these new methods on a 19.6 kDa protein (U-[(15)N, (13)C]-YajG) at high magnetic fields (up to 900 MHz (1)H frequency) and fast sample spinning (up to 65 kHz MAS frequency).
authors.affiliation: Laboratoire de Chimie Inorganique et Biologique, UMR-E3 (CEA/UJF) and CNRS, CEA/DSM/INAC-38054, Grenoble, France.
authors.forename: Mathilde
authors.initials: M
authors.lastname: Giffard
authors.forename: Sabine
authors.initials: S
authors.lastname: Hediger
authors.forename: Józef R
authors.initials: JR
authors.lastname: Lewandowski
authors.forename: Michel
authors.initials: M
authors.lastname: Bardet
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Simorre
authors.forename: Robert G
authors.initials: RG
authors.lastname: Griffin
authors.forename: Gaël
authors.initials: G
authors.lastname: De Paëpe
mesh_terms: D000409:Alanine / Q000737:chemistry; D000465:Algorithms; D002247:Carbon Isotopes / Q000737:chemistry; D003198:Computer Simulation; D008956:Models, Chemical; D009587:Nitrogen Isotopes / Q000737:chemistry; D009590:Nitrogen Radioisotopes / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D011506:Proteins / Q000737:chemistry; D011522:Protons
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D009590:Nitrogen Radioisotopes; D011506:Proteins; D011522:Protons; D000409:Alanine