title: Satellite and central transitions selective1H/{27Al} D-HMQC experiments at very fast MAS for quadrupolar couplings determination.
abstract: Recent study has demonstrated the application of the proton-detected heteronuclear multi-quantum coherence (HMQC) at ultrafast Magic Angle Spinning (MAS) to probe quadrupolar nuclei including14N and35Cl. In addition, for half-integer quadrupolar nucleus like35Cl, the quadrupolar product can be calculated based on the shift difference between the center band of satellite transition (ST) and the central transition (CT) peaks. The applicability of this technique is further investigated on spin I=5/2, namely27Al nucleus, and kaolin is chosen as the testing sample. However this study is not straightforward owing to a spin quantum number I=5/2 of27Al nucleus and a small quadrupolar coupling of kaolin. Furthermore, very fast MAS, which is mandatory for proton-detected experiment to suppress1H-1H homonuclear dipolar interactions, introduces additional complexities. It induces the partial overlap of CT and the center band of inner ST (ST1) resonance in addition to the insufficiency of CT-selective excitation by soft-pulse irradiation. In the current work, we employ the constant-time D-HMQC experiment, in which the duration between two recoupling blocks is fixed to a constant value and the arbitrary t1increment can be used within this duration. This constant-time D-HMQC enables the precise determination of CT and ST resonance shifts through CT- and ST-selective observations by the indirect spectral width (i) with asynchronized sampling to the top of rotational-echoes for STs and (ii) three times larger than the spinning frequency, respectively. We also numerically and experimentally develop a satellite-selective excitation technique, in which the radio frequency field is applied to the first spinning sideband of ST1 resonance. The satellite-selective 1D single pulse and 2D conventional D-HMQC experiments are demonstrated. The quadrupolar product of27Al nucleus extracted from the resulting spectra is in good agreement with the literature.
authors.affiliation: RIKEN CLST-JEOL collaboration center, RIKEN, Yokohama, Kanagawa 230-0045, Japan.
authors.forename: Nghia Tuan
authors.initials: NT
authors.lastname: Duong
authors.affiliation: RIKEN CLST-JEOL collaboration center, RIKEN, Yokohama, Kanagawa 230-0045, Japan; JEOL RESONANCE Inc., Musashino, Akishima, Tokyo 196-8558, Japan. Electronic address: yunishiy@jeol.co.jp.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Nishiyama
keywords: Constant-time D-HMQC; Quadrupolar product determination; Satellite-selective excitation experiment; Spin I=5/2 nuclei ((27)Al); Very fast MAS