title: Phase-modulated LA-REDOR: a robust, accurate and efficient solid-state NMR technique for distance measurements between a spin-1/2 and a quadrupole spin.
abstract: Distances between a spin-1/2 and a spin>1/2 can be efficiently measured by a variety of magic-angle spinning solid state NMR methods such as Rotational Echo Adiabatic Passage Double Resonance (REAPDOR), Low-Alpha/Low-Amplitude REDOR (LA-REDOR) and Rotational-Echo Saturation-Pulse Double-Resonance (R/S-RESPDOR). In this manuscript we show that the incorporation of a phase modulation into a long quadrupolar recoupling pulse, lasting 10 rotor periods that are sandwiched between rotor-synchronized pairs of dipolar recoupling π pulses, extends significantly the range of the values of the quadrupole moments that can be accessed by the experiment. We show by a combination of simulations and experiments that the new method, phase-modulated LA-REDOR, is very weakly dependent on the actual value of the radio-frequency field, and is highly robust with respect to off-resonance irradiation. The experimental results can be fitted by numerical simulations or using a universal formula corresponding to an equal-transition-probability model. Phase-modulated LA-REDOR (13)C{(11)B} and (15)N{(51)V} dipolar recoupling experiments confirm the accuracy and applicability of this new method.
authors.affiliation: School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel.
authors.forename: Evgeny
authors.initials: E
authors.lastname: Nimerovsky
authors.affiliation: Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA.
authors.forename: Rupal
authors.initials: R
authors.lastname: Gupta
authors.affiliation: Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA.
authors.forename: Jenna
authors.initials: J
authors.lastname: Yehl
authors.affiliation: Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA.
authors.forename: Mingyue
authors.initials: M
authors.lastname: Li
authors.affiliation: Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA.
authors.forename: Tatyana
authors.initials: T
authors.lastname: Polenova
authors.affiliation: School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel. Electronic address: amirgo@post.tau.ac.il.
authors.forename: Amir
authors.initials: A
authors.lastname: Goldbourt
keywords: Dipolar interaction; Distance measurement; Magic angle spinning; Quadrupolar coupling; REDOR; Solid state NMR; Universal curve