Guest Rotations within a Capsuleplex Probed by NMR and EPR Techniques
Guest Rotations within a Capsuleplex Probed by NMR and EPR Techniques
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DOI：
10.1021/la904196g
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发表时间：
2010-05-18
期刊：
影响因子：
3.9
通讯作者：
Ramamurthy, V.
中科院分区：
文献类型：
--
作者：
Kulasekharan, Revathy;Jayaraj, Nithyanandhan;Ramamurthy, V.
借助 H-1 NMR 和 EPR 技术，我们探测了水溶性深腔腔内客体分子的动力学，该客体分子的俗名是八酸。这里研究的所有客体分子在水中形成 2:1（主体/客体）复合物，并且两个主体分子通过形成封闭的胶囊来封装客体分子。我们通过 H-1 NMR 和 EPR 技术探测了这个密闭容器内的古老客体分子的动力学。这两种技术提供的时间尺度完全不同，分别为毫秒和纳秒。对于 EPR 研究，使用了顺磁性硝基氧客体分子；对于 H-1 NMR 研究，使用了多种结构多样的中性有机客体分子。客体分子在 NMR 时间尺度上沿其 x 轴（分子长轴和磁轴）自由旋转；然而，在 EPR 时间尺度上，它们的旋转速度比水中的旋转速度慢。沿 x 轴的旋转取决于连接至硝基氧探针的烷基链的长度。沿 y 或 z 轴的整体旋转很大程度上取决于客体分子的结构。被调查的客人可分为三组：(a) 在室温和高温（55 摄氏度）下不沿 y 或 z 轴旋转的客人，(b) 在室温下自由旋转的客人，以及 (c) 在室温下不旋转但在较高温度下旋转的客人。应该注意的是，这里的旋转是指核磁共振时间尺度，所有分子很可能以比这里探测的时间尺度长得多的时间尺度旋转。结构的轻微变化会改变客体分子的旋转迁移率。
With the help of H-1 NMR and EPR techniques, we have probed the dynamics of guest molecules included within a water-soluble deep cavity cavil and known by the trivial name octa acid. All guest molecules investigated here form 2: 1(host/guest) complexes in water, and two host molecules encapsulate the guest molecule by forming a closed capsule. We have probed the dynamics oldie guest molecule within this closed container through H-1 NMR and EPR techniques. The timescales offered by these two techniques are quite different, millisecond and nanosecond, respectively. For EPR studies, paramagnetic nitroxide guest molecules and for H-1 NMR studies, a wide variety of structurally diverse neutral organic guest molecules were employed. The guest molecules freely rotate along their x axis (long molecular axis and magnetic axis) on the NM R timescale; however, their rotation is slowed with respect to that in water on the EPR timescale. Rotation along the x axis is dependent on the length of the alkyl chain attached to the nitroxide probe. Overall rotation along the y or z axis was very much dependent on the structure of the guest molecule. The guests investigated could be classified into three groups: (a) those that do not rotate along the y or z axis both at room and elevated (55 degrees C) temperatures, (b) those that rotate freely at room temperature, and (c) those that do not rotate at room temperature but do so at higher temperatures. One should note that rotation here refers to the NMR timescale and it is quite possible that all molecules may rotate at much longer timescales than the one probed here. A slight variation in structure alters the rotational mobility of the guest molecules.