title: Determination of transverse relaxation rates in systems with scalar-coupled spins: The role of antiphase coherences.
abstract: Homogeneous line-widths that arise from transverse relaxation tend to be masked by B0 field inhomogeneity and by multiplets due to homonuclear J-couplings. Besides well-known spin-locking sequences that lead to signals that decay with a rate R1ρ without any modulations, alternative experiments allow one to determine the transverse relaxation rates R2 in systems with scalar-coupled spins. We evaluate three recent strategies by experiment and simulation: (i) moderate-amplitude SITCOM-CPMG sequences (Dittmer and Bodenhausen, 2006), (ii) multiple-quantum filtered (MQF) sequences (Barrère et al., 2011) and (iii) PROJECT sequences (Aguilar et al., 2012). Experiments where the J-evolution is suppressed by spin-locking measure the pure relaxation rate R2(Ix) of an in-phase component. Experiments based on J-refocusing yield a mixture of in-phase rates R2(Ix) and antiphase rates R2(2IySz), where the latter are usually faster than the former. Moderate-amplitude SITCOM-CPMG and PROJECT methods can be applied to systems with many coupled spins, but applications of MQF sequences are limited to two-spin systems since modulations in larger systems can only partly be suppressed.
authors.affiliation: Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), Batochime, 1015 Lausanne, Switzerland.
authors.forename: Takuya F
authors.initials: TF
authors.lastname: Segawa
authors.affiliation: Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), Batochime, 1015 Lausanne, Switzerland; Département de Chimie, Ecole Normale Supérieure, 24 Rue Lhomond, 75231 Paris Cedex 05, France; Université Pierre-et-Marie Curie, Paris, France; UMR 7203 CNRS, Paris, France. Electronic address: geoffrey.bodenhausen@epfl.ch.
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Bodenhausen
keywords: Homonuclear J-coupling; Homonuclear decoupling; Relaxation of antiphase terms; Spin dynamics; Transverse relaxation