Chirality-Induced Electron Spin Polarization and Enantiospecific Response in Solid-State Cross-Polarization Nuclear Magnetic Resonance,ACS Nano

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Chirality-Induced Electron Spin Polarization and Enantiospecific Response in Solid-State Cross-Polarization Nuclear Magnetic Resonance
ACS Nano ( IF 15.8 ) Pub Date : 2018-11-08 00:00:00 , DOI: 10.1021/acsnano.8b06467
Jose I. Santos ₁ , Iván Rivilla _{2,

3} , Fernando P. Cossío _{2,

3} , Jon M. Matxain _{3,

4} , Marek Grzelczak _{3,

5} , Shobeir K. S. Mazinani ₆ , Jesus M. Ugalde _{3,

4} , Vladimiro Mujica ₆

Affiliation

NMR-based techniques are supposed to be incapable of distinguishing pure crystalline chemical enantiomers. However, through systematic studies of cross-polarization magic angle spinning (CP-MAS) NMR in a series of amino acids, we have found a rather unexpected behavior in the intensity pattern of optical isomers in hydrogen/nitrogen nuclear polarization transfer that would allow the use of CP NMR as a nondestructive enantioselective detection technique. In all molecules considered, the d isomer yields higher intensity than the l form, while the chemical shift for all nuclei involved remains unchanged. We attribute this striking result to the onset of electron spin polarization, accompanying bond charge polarization through a chiral center, a secondary mechanism for polarization transfer that is triggered only in the CP experimental setup. Electron spin polarization is due to the chiral-induced spin selectivity effect (CISS), which creates an enantioselective response, analogous to the one involved in molecular recognition and enantiospecific separation with achiral magnetic substrates. This polarization influences the molecular magnetic environment, modifying the longitudinal relaxation time T₁ of ¹H, and ultimately provoking the observed asymmetry in the enantiomeric response.

中文翻译：

固态交叉极化核磁共振中的手性诱导电子自旋极化和对映体特异性响应

据认为，基于NMR的技术无法区分纯结晶化学对映体。但是，通过对一系列氨基酸中交叉极化魔角旋转（CP-MAS）NMR的系统研究，我们发现了氢/氮核极化转移中光学异构体的强度模式中存在相当意外的行为，这将允许CP NMR作为非破坏性对映选择性检测技术的应用。在所有考虑的分子中，d异构体的强度均高于l形式，而所有涉及的原子核的化学位移保持不变。我们将此惊人的结果归因于电子自旋极化的发生，伴随着通过手性中心的键电荷极化，这是仅在CP实验装置中触发的极化转移的次级机制。电子自旋极化归因于手性诱导的自旋选择性效应（CISS），可产生对映选择性响应，类似于涉及与非手性磁性底物进行分子识别和对映特异性分离的反应。这种极化影响分子磁性环境，改变纵向弛豫时间T ₁为¹ H，并最终在对映体响应中引起观察到的不对称性。

更新日期：2018-11-08

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