REDOR dephasing by multiple spins in the presence of molecular motion.
Closed-form, numerical algorithms are presented for calculating REDOR dephasing for three general cases: (i) collections of isolated I-S spin pairs; (ii) many S spins coupled to an I spin; and (iii) an I-S spin pair in relative motion. For the case when more than one S spin is dipolar coupled to an I spin, the calculation assumes that the S-S homonuclear interaction does not affect REDOR dephasing. Full numerical simulations show that this assumption is true if the S-spin lineshapes are inhomogeneously broadened, the S-spin chemical shifts are far from rotational resonance, and a version of REDOR is used which minimizes the number of S-spin pi pulses. For the rapidly rotating -CF3 group of poly(trifluoroethyl methacrylate), the formalisms of (ii) and (iii) are combined to calculate the dephasing. The experimentally measured dephasing matches theory when the wiggling motion of the -OCH2CF3 moiety of the polymer is taken into account.
Goetz
J M
JM
Department of Chemistry, Washington University, St. Louis, Missouri 63130, USA.
Schaefer
J
J
D000465:Algorithms; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008689:Methacrylates / Q000737:chemistry
D008689:Methacrylates