International Tomography Center, Institutskaya 3a, Novosibirsk 630090, Russia.
Langmuir. 2010 Jun 1;26(11):8971-80. doi: 10.1021/la904788t.
A systematic investigation of the photochemistry and ensuing radical chemistry of three guest ketones encapsulated in randomly methylated beta-cyclodextrin (beta-CD) hosts is reported. Dibenzyl ketone (DBK), deoxybenzoin (DOB), and benzophenone (BP) triplet states are rapidly formed after photolysis at 308 nm. Time-resolved electron paramagnetic resonance (TREPR) spectroscopy, steady-state NMR spectroscopy, and time-resolved chemically induced nuclear polarization (TR-CIDNP) experiments were performed on the ketone/CD complexes and on the ketones in free solution for comparison. The major reactivity pathways available from these excited states are either Norrish I alpha-cleavage or H-atom abstraction from the interior of the CD capsule or the solvent. The DOB triplet state undergoes both reactions, whereas the DBK triplet shows exclusively alpha-cleavage and the BP triplet shows exclusively H-atom abstraction. Radical pairs are observed in beta-CDs by TREPR, consisting of either DOB or BP ketyl radicals with sugar radicals from the CD interior. The TREPR spectra acquired in CDs are substantially broadened due to strong spin exchange. The electron spin polarization mechanism is mostly due to S-T(0) radical pair mechanism (RPM) in solution but changes to S-T(-) RPM in the CDs due to the large exchange interaction. The TR-CIDNP results confirm the reactivity patterns of all three ketones, and DOB shows strong nuclear spin polarization from a novel rearrangement product resulting from the alpha-cleavage reaction.
本文报道了三种客体酮分子在随机甲基化的β-环糊精（β-CD）主体中包合后的光化学和后续自由基化学的系统研究。在 308nm 光解后，二苄基酮（DBK）、脱氧安息香（DOB）和二苯甲酮（BP）的三重态迅速形成。我们对酮/CD 配合物以及游离溶液中的酮进行了时间分辨电子顺磁共振（TREPR）光谱、稳态 NMR 光谱和时间分辨化学诱导核极化（TR-CIDNP）实验，以进行比较。这些激发态下的主要反应途径要么是 Norrish I α 裂解，要么是从 CD 胶囊内部或溶剂中提取 H 原子。DOB 三重态发生这两种反应，而 DBK 三重态仅发生 α 裂解，BP 三重态仅发生 H 原子提取。TREPR 通过观察到β-CDs 中的自由基对，由 CD 内部的 DOB 或 BP 酮基自由基和糖自由基组成。由于强自旋交换，TREPR 光谱在 CDs 中大大展宽。电子自旋极化机制主要是由于溶液中的 S-T(0)自由基对机制（RPM），但由于交换相互作用较大，在 CDs 中变为 S-T(-)RPM。TR-CIDNP 结果证实了所有三种酮的反应模式，并且 DOB 显示出强烈的核自旋极化，这是由于α裂解反应导致的新型重排产物所致。
