title: Solid-state Hadamard NMR spectroscopy: simultaneous measurements of multiple selective homonuclear scalar couplings.
abstract: Unambiguous measurement of homonuclear scalar couplings (J) in multi-spin scalar network systems is not straightforward. Further, the direct measurement of J-couplings is obscured in solid-state samples due to the dipolar and chemical shift anisotropy (CSA)-dominated line broadening, even under the magic angle spinning (MAS). We present a new multiple frequency selective spin-echo method based on Hadamard matrix encoding, for simultaneous measurement of multiple homonuclear scalar couplings (J) in the solid-state. In contrast to the Hadamard encoded selective excitation schemes known for the solution-state, herein the selectivity is achieved during refocusing period. The Hadamard encoded refocusing scheme concurrently allows to create the spin-spin commutation property between number of spin-pairs of choice in uniformly labelled molecules, which, therefore avoids (1) the repetition of the double selective refocusing experiments for each spin-pair and (2) the synthesis of expensive selective labelled molecules. The experimental scheme is exemplified for determining (1)JCC and (3)JCC values in (13)C6l-Histidine.HCl molecule, which are found to be in excellent agreement with those measured in conventional double frequency selective refocusing mode as well as in the solution-state. This method can be simply extended to 2D/3D pulse schemes and be applied to small bio-molecular solids.
authors.affiliation: Centre for NMR & Structural Chemistry, CSIR-Indian Institute of Chemical Technology, Hyderabad 500 007, India.
authors.forename: Veera Mohana Rao
authors.initials: VM
authors.lastname: Kakita
authors.affiliation: Bruker UK Limited, Banner Lane, Coventry CV4 9GH, UK.
authors.forename: Eriks
authors.initials: E
authors.lastname: Kupče
authors.affiliation: Centre for NMR & Structural Chemistry, CSIR-Indian Institute of Chemical Technology, Hyderabad 500 007, India. Electronic address: bj@iict.res.in.
authors.forename: Jagadeesh
authors.initials: J
authors.lastname: Bharatam
mesh_terms: D000465:Algorithms; D016880:Anisotropy; D006639:Histidine / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*
chemical_list: D006639:Histidine
keywords: Hadamard encoding; Magic angle spinning; Multiple-selective refocusing; Simultaneous spin–spin couplings; Solid-state NMR