Bakhmutov Vladimir I
Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, TX 77842-3012, USA.
Solid State Nucl Magn Reson. 2008 Nov;34(4):197-201. doi: 10.1016/j.ssnmr.2008.09.002. Epub 2008 Oct 11.
The (29)Si spin-lattice relaxation in porous silica-based material 1, doped by ions Mn(2+) at a Si/Mn ratio of 3.5, is non-exponential, independent of magic-angle spinning (MAS) rates and governed by direct dipolar coupling between electron and nucleus where an electron relaxation time is estimated to be about 10(-8)s. In the absence of mutual energy-conserving spin flips (spin diffusion) in 1, the (29)Si T(2) time increases linearly with spinning rates. None was observed in diamagnetic porous system 2. The unexpected (29)Si T(2) dependence has been interpreted in terms of the large bulk magnetic susceptibility (BMS) effects. It has been shown that editing the (29)Si Hahn-echo MAS NMR spectra eliminates wide lines, belonging to (29)Si nuclei in the proximity of paramagnetic centers, and reduces the BMS broadenings in sideband patterns for nuclei remote from these centers.
在硅/锰比为3.5的情况下，由Mn(2+)离子掺杂的多孔二氧化硅基材料1中的(29)Si自旋晶格弛豫是非指数性的，与魔角旋转（MAS）速率无关，并且由电子与原子核之间的直接偶极耦合控制，其中电子弛豫时间估计约为10(-8)s。在1中不存在相互能量守恒的自旋翻转（自旋扩散）的情况下，(29)Si T(2)时间随旋转速率线性增加。在抗磁性多孔系统2中未观察到这种情况。这种意外的(29)Si T(2)依赖性已根据大的体磁导率（BMS）效应进行了解释。结果表明，编辑(29)Si哈恩回波MAS NMR谱可以消除属于顺磁中心附近(29)Si核的宽线，并减少远离这些中心的核在边带模式中的BMS展宽。
