Pinto da Silva Luís, Esteves da Silva Joaquim C G
Centro de Investigação em Química (CIQ-UP), Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, R. Campo Alegre 697, 4169-007 Porto (Portugal).
Chemphyschem. 2014 Dec 1;15(17):3761-7. doi: 10.1002/cphc.201402558. Epub 2014 Sep 18.
Firefly oxyluciferin is a photoacid that presents a pH-sensitive fluorescence, which results from pH-dependent changes on the conformation of self-aggregated π-π stacking complexes. Luciferin is a derivative of oxyluciferin with very similar fluorescence and photoacidic properties. This similarity indicates that luciferin is also expected to be able to form π-π stacking complexes, but no pH-sensitive fluorescence is found for this compound. Here, a theoretical approach is used to rationalize this finding. We have found that luciferin only forms π-π stacking complexes in the ground state at acidic pH. At basic pH and in the excited state, luciferin is present as a dianion. This species is not able to self-aggregate, owing to repulsive electrostatic interactions. Thus, this emissive species is not subject to π-π stacking interactions; this explains its pH-insensitive fluorescence.
萤火虫氧化荧光素是一种光酸，具有pH敏感的荧光，这是由自聚集的π-π堆积复合物构象的pH依赖性变化引起的。荧光素是氧化荧光素的衍生物，具有非常相似的荧光和光酸性性质。这种相似性表明荧光素也有望能够形成π-π堆积复合物，但该化合物未发现pH敏感的荧光。在此，采用理论方法来解释这一发现。我们发现荧光素仅在酸性pH的基态下形成π-π堆积复合物。在碱性pH和激发态下，荧光素以二价阴离子形式存在。由于排斥性静电相互作用，该物种无法自聚集。因此，这种发光物种不受π-π堆积相互作用的影响；这解释了其pH不敏感的荧光。
