Departamento de Química/Instituto de Tecnología Química UPV-CSIC, Universitat Politècnica de València, Camino de Vera s/n, Apdo 22012, E-46071 Valencia, Spain.
Chem Soc Rev. 2014 Jun 21;43(12):4102-22. doi: 10.1039/c3cs60413f.
The properties of singlet and triplet excited states are strongly medium-dependent. Hence, these species constitute valuable tools as reporters to probe compartmentalised microenvironments, including drug@protein supramolecular systems. In the present review, the attention is focused on the photophysical properties of the probe drugs (rather than those of the protein chromophores) using transport proteins (serum albumins and α1-acid glycoproteins) as hosts. Specifically, fluorescence measurements allow investigation of the structural and dynamic properties of biomolecules or their complexes. Thus, the emission quantum yields and the decay kinetics of the drug singlet excited states provide key information to determine important parameters such as the stoichiometry of the complex, the binding constant, the relative degrees of occupancy of the different compartments, etc. Application of the FRET concept allows determination of donor-acceptor interchromophoric distances. In addition, anisotropy measurements can be related to the orientation of the drug within the binding sites, where the degrees of freedom for conformational relaxation are restricted. Transient absorption spectroscopy is also a potentially powerful tool to investigate the binding of drugs to proteins, where formation of encapsulated triplet excited states is favoured over other possible processes leading to ionic species (i.e. radical ions), and their photophysical properties are markedly sensitive to the microenvironment experienced within the protein binding sites. Even under aerobic conditions, the triplet lifetimes of protein-complexed drugs are remarkably long, which provides a broad dynamic range for identification of distinct triplet populations or for chiral discrimination. Specific applications of the laser flash photolysis technique include the determination of drug distribution among the bulk solution and the protein binding sites, competition of two types of proteins to bind a drug, occurrence of drug-drug interactions within protein binding sites, enzymatic-like activity of the protein or determination of enantiomeric compositions. The use of proteins as supramolecular hosts modifies the photoreactivity of encapsulated substrates by providing protection against oxygen or other external reagents, by imposing conformational restrictions in the binding pockets, or by influencing the stereochemical outcome. In this review, a selected group of examples is presented including decarboxylation, dehalogenation, nucleophilic addition, dimerisation, oxidation, Norrish type II reaction, photo-Fries rearrangement and 6π electrocyclisation.
单重态和三重态激发态的性质强烈依赖于介质。因此，这些物种是探测分隔微环境的有价值的工具，包括药物@蛋白质超分子系统。在本综述中，重点关注探针药物的光物理性质（而不是蛋白质发色团的性质），使用转运蛋白（血清白蛋白和α1-酸性糖蛋白）作为宿主。具体而言，荧光测量可用于研究生物分子或其复合物的结构和动态性质。因此，药物单重态激发态的发射量子产率和衰减动力学为确定重要参数提供了关键信息，例如复合物的化学计量、结合常数、不同隔室的相对占有率等。应用 FRET 概念可以确定供体-受体发色团间的距离。此外，各向异性测量可与药物在结合部位的取向相关联，其中构象弛豫的自由度受到限制。瞬态吸收光谱也是研究药物与蛋白质结合的一种潜在强大工具，其中封装的三重态激发态的形成有利于其他可能导致离子物种（即自由基离子）的过程，并且它们的光物理性质对蛋白质结合部位内经历的微环境非常敏感。即使在有氧条件下，蛋白质复合药物的三重态寿命也非常长，这为识别不同的三重态群体或手性区分提供了广泛的动态范围。激光闪光光解技术的特定应用包括确定药物在本体溶液和蛋白质结合部位之间的分布、两种类型的蛋白质竞争结合药物、蛋白质结合部位内药物-药物相互作用的发生、蛋白质的酶样活性或对映体组成的确定。蛋白质作为超分子宿主的使用通过提供对氧或其他外部试剂的保护、在结合口袋中施加构象限制、或影响立体化学结果来改变包封底物的光反应性。在本综述中，呈现了一组选定的示例，包括脱羧、脱卤、亲核加成、二聚化、氧化、Norrish 型 II 反应、光-Fries 重排和 6π 电环化。
