van Wüllen L, Züchner L, Müller-Warmuth W, Eckert H
Department of Chemistry, University of California, Santa Barbara 93106, USA.
Solid State Nucl Magn Reson. 1996 Jun;6(3):203-12. doi: 10.1016/0926-2040(96)01228-3.
Cross-polarization/magic-angle spinning (CP/MAS) and rotational echo double resonance (REDOR) experiments involving two half-integer quadrupolar nuclei, 11B and 27Al, are reported, to demonstrate boron-aluminum connectivities in a model aluminoborate glass. A detailed study of the spin-lock behavior of 11B and 27Al proves to be a prerequisite for successful CP/MAS experiments. Under MAS conditions, two distinct boron sites are observed, corresponding to tetrahedral BO4/2- sites (nuclear electric quadrupole coupling constant near 0.3 MHz) and trigonal BO3/2 sites (nuclear electric quadrupole coupling constant near 2.7 MHz). The BO4/2- sites are most successfully spin-locked in the adiabatic regime at high radio frequency (RF) field strengths, whereas for the BO3/2 sites optimum spin-lock conditions are achieved in the sudden regime (low RF field strengths). These differences can be exploited for spectral editing purposes in REDOR experiments. Using corresponding T1p filters, it becomes possible to measure individual REDOR dephasing curves for both types of boron sites. The results illustrate the possible utility of heteronuclear X-Y double resonance techniques in unravelling the intermediate range order in amorphous systems containing quadrupolar nuclei.
报道了涉及两个半整数四极核（11B和27Al）的交叉极化/魔角旋转（CP/MAS）和旋转回波双共振（REDOR）实验，以证明在一种模型铝硼酸盐玻璃中硼与铝的连接性。事实证明，对11B和27Al的自旋锁定行为进行详细研究是成功进行CP/MAS实验的先决条件。在MAS条件下，观察到两个不同的硼位点，分别对应于四面体BO4/2-位点（核电四极耦合常数接近0.3 MHz）和三角BO3/2位点（核电四极耦合常数接近2.7 MHz）。BO4/2-位点在高射频（RF）场强的绝热区域最成功地实现了自旋锁定，而对于BO3/2位点，在突变区域（低RF场强）实现了最佳自旋锁定条件。这些差异可用于REDOR实验中的光谱编辑。使用相应的T1p滤波器，可以测量两种硼位点各自的REDOR去相位曲线。结果说明了异核X-Y双共振技术在揭示含四极核的非晶系统中的中程有序方面的潜在用途。
