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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Sensitization of an Endogenous Photosensitizer: Electronic Spectroscopy of Riboflavin in the Proximity of Semiconductor, Insulator, and Metal Nanoparticles
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Sensitization of an Endogenous Photosensitizer: Electronic Spectroscopy of Riboflavin in the Proximity of Semiconductor, Insulator, and Metal Nanoparticles

机译：内源性光敏剂的敏化：核黄素在半导体，绝缘体和金属纳米粒子附近的电子光谱

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摘要

Riboflavin (Rf) is a class of important vitamins (Vitamin B2) and a well-known antioxidant. Here we have synthesized nanohybrids of Rf with a number of inorganic nanoparticles (NPs); namely zinc oxide (ZnO), titanium oxide (TiO2), aluminum oxide (Al2O3) and gold NPs of similar sizes. While high resolution transmission electron microscopy (HRTEM) confirms integrity and sizes of the NPs, intactness of the molecular structure of the drug Rf is revealed from absorption and steady-state emission spectra of the drug in the nanohybrid. Raman spectroscopy on the nanohybrids shows the nature of molecular complexation of the drug with the inorganic NPs. For the semiconductor and insulator NPs, the complexation is found to be noncovalent, however, a covalent attachment of the drug with the dangling bonds of metal atoms at the surface is observed. In order to investigate antioxidant activity of the nanohybrids, we have performed 2, 2-diphenyl-1-picrylhydrazyl (DPPH) assay of the nanohybrids in dark as well as under blue light irradiation. Whereas change of the antioxidant activity of the nanohybrids with respect to free riboflavin in the absence of light is observed to be insignificant, a drastic change in the activity in the case of TiO2 and ZnO in the presence of light is evident. No change in the case of Al2O3 and a significant decrease in the antioxidant activity for gold nanohybrids are also remarkable. Picosecond-resolved fluorescence studies on the nanohybrids reveal a molecular picture of the differential antioxidant activities. An ultrafast photoinduced electron transfer from Rf to ZnO and TiO2 are clearly evident from the corresponding fluorescence transients. We have compared the picosecond-resolved transients with that of Rf in the presence of a well-known electron acceptor benzoquinone (BQ) and found similar time scales. No temporal change in the fluorescence transient of riboflavin in Al2O3 nanohybrids compared to that of free Rf is observed indicating uneventful excited state relaxation of the nanohybrids. Nanosurface energy transfer (NSET) over Forster resonance energy transfer (FRET) is found to be the prevailing de-excitation mechanism in the case of gold nanohybrids, because of the strong spectral overlap between Rf emission and surface plasmon absorption of the gold NPs. Different excited state mechanisms as revealed from our studies are expected to be useful for the design of NP-sensitized drugs, which are reported sparsely in the literature.
机译：核黄素（Rf）是一类重要的维生素（维生素B2）和众所周知的抗氧化剂。在这里，我们合成了Rf的纳米杂化物和许多无机纳米粒子（NPs）。即氧化锌（ZnO），氧化钛（TiO2），氧化铝（Al2O3）和大小相似的金纳米颗粒。尽管高分辨率透射电子显微镜（HRTEM）证实了NP的完整性和大小，但从纳米杂合物中药物的吸收和稳态发射光谱揭示了药物Rf分子结构的完整性。纳米杂化物的拉曼光谱显示了药物与无机NP分子分子复合的性质。对于半导体和绝缘体NP，发现络合物是非共价的，但是，观察到药物与表面金属原子的悬挂键共价结合。为了研究纳米杂化物的抗氧化活性，我们在黑暗中以及在蓝光照射下对纳米杂化物进行了2，2-二苯基-1-吡啶并肼基（DPPH）测定。尽管观察到在不存在光的情况下纳米杂化物相对于游离核黄素的抗氧化活性的变化是微不足道的，但是在存在光的情况下，在TiO 2和ZnO的情况下，活性的急剧变化是明显的。 Al 2 O 3的情况没有改变，并且对于金纳米杂化物的抗氧化剂活性显着降低。皮秒分辨的纳米杂化荧光研究揭示了不同抗氧化剂活性的分子图。从相应的荧光瞬变中可以清楚地看到从Rf到ZnO和TiO2的超快光诱导电子转移。我们在已知的电子受体苯醌（BQ）的存在下，将皮秒分辨的瞬变与Rf的瞬变进行了比较，并发现了类似的时标。与游离Rf相比，在Al2O3纳米杂化物中未观察到核黄素荧光瞬变的瞬时变化，表明纳米杂化物的激发态松弛不均匀。在金纳米杂化物的情况下，发现相对于福斯特共振能量转移（FRET）而言，纳米表面能量转移（NSET）是主要的去激励机制，这是因为Rf发射与金NP的表面等离激元吸收之间存在很强的光谱重叠。我们的研究揭示了不同的激发态机制，有望用于NP敏化药物的设计，这在文献中很少报道。

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