Pravdivtsev Andrey N, Yurkovskaya Alexandra V, Ivanov Konstantin L, Vieth Hans-Martin
International Tomography Center, Siberian Branch of the Russian Academy of Science, Institutskaya 3a, Novosibirsk 630090, Russia; Novosibirsk State University, Pirogova 2, Novosibirsk 630090, Russia.
International Tomography Center, Siberian Branch of the Russian Academy of Science, Institutskaya 3a, Novosibirsk 630090, Russia; Novosibirsk State University, Pirogova 2, Novosibirsk 630090, Russia.
J Magn Reson. 2015 May;254:35-47. doi: 10.1016/j.jmr.2015.02.008. Epub 2015 Mar 7.
The magnetic field dependence of Chemically Induced Dynamic Nuclear Polarization (CIDNP) was studied for the amino acids N-acetyl histidine, N-acetyl tryptophan and N-acetyl tyrosine. It is demonstrated that at low field CIDNP is strongly affected by polarization redistribution in the diamagnetic molecules. Such a polarization transfer is of coherent nature and is due to spin coherences formed together with non-equilibrium population of the spin states. These coherences clearly manifest themselves in an oscillatory time dependence of polarization. Polarization transfer effects are most pronounced at nuclear spin Level Anti-Crossings (LACs), which also result in sharp features in the CIDNP field dependence. Thus, polarization transfer is an important factor, which has to be taken into account in order to interpret low-field CIDNP data on both qualitative and quantitative level. Possible applications of polarization transfer phenomena are also discussed in the paper. In particular, the role of LACs in spin order transfer is highlighted: LACs provide a new tool for precise manipulation of spin hyperpolarization and NMR enhancement of selected target spins.
研究了化学诱导动态核极化（CIDNP）对氨基酸N - 乙酰组氨酸、N - 乙酰色氨酸和N - 乙酰酪氨酸的磁场依赖性。结果表明，在低场下，CIDNP受到抗磁性分子中极化重新分布的强烈影响。这种极化转移具有相干性质，是由于自旋相干与自旋态的非平衡布居共同形成的。这些相干性在极化的振荡时间依赖性中明显表现出来。极化转移效应在核自旋能级反交叉（LACs）处最为显著，这也导致了CIDNP场依赖性中的尖锐特征。因此，极化转移是一个重要因素，为了在定性和定量层面解释低场CIDNP数据都必须加以考虑。本文还讨论了极化转移现象的可能应用。特别强调了LACs在自旋序转移中的作用：LACs为精确操纵自旋超极化和选定目标自旋的NMR增强提供了一种新工具。
