Bordello Jorge, Reija Belén, Al-Soufi Wajih, Novo Mercedes
Grupo de Fotofísica e Fotoquímica Molecular, Departamento de Química Física, Facultade de Ciencias, Universidade de Santiago de Compostela, 27002 Lugo, Spain.
Chemphyschem. 2009 Apr 14;10(6):931-9. doi: 10.1002/cphc.200800776.
Buckle up! The dimerization of small fluorescent guests is strongly enhanced in presence of a cyclodextrin host. The host cavity acts like a belt to assist the self-assembly of guests (see picture). Small variations in the guest structure have significant influence on the stability and geometry of the aggregates.The role of small variations in the structural properties of host and guest molecules on the stoichiometry and strength of supramolecular associations is analyzed. Earlier we found that a change in substituents from pyronine B to pyronine Y has a dramatic effect on both the stability and the dynamics of the association of these guests with beta-cyclodextrin as host. Now we study the association between these two pyronines and a cyclodextrin with a bigger cavity (gamma-cyclodextrin) using UV/Vis absorption and fluorescence spectroscopy. The absorption spectra of the pyronines show complex variations with cyclodextrin concentration indicating that pyronine dimerization is strongly enhanced inside the cavity of the cyclodextrin. A full model is proposed and the equilibrium constants of the involved processes and the absorption and emission spectra of the different species are estimated. The equilibrium constants of the formation of complexed dimers are much higher than those for free dimerization or for the inclusion of a single guest. The gamma-cyclodextrin host acts like a belt to assist the guest self-assembly. The differences in the stability of pyronine B and pyronine Y dimers are explained on the basis of their structure and geometry.
系好安全带！在环糊精主体存在的情况下，小荧光客体的二聚化作用会大大增强。主体空腔就像一条腰带，有助于客体的自组装（见图）。客体结构的微小变化对聚集体的稳定性和几何形状有重大影响。分析了主体和客体分子结构性质的微小变化对超分子缔合的化学计量和强度的作用。此前我们发现，从吡啰红B到吡啰红Y的取代基变化对这些客体与β-环糊精主体缔合的稳定性和动力学都有显著影响。现在我们使用紫外/可见吸收光谱和荧光光谱研究这两种吡啰红与具有更大空腔的环糊精（γ-环糊精）之间的缔合。吡啰红的吸收光谱随环糊精浓度呈现出复杂的变化，这表明在环糊精空腔内吡啰红的二聚化作用大大增强。我们提出了一个完整的模型，并估算了相关过程的平衡常数以及不同物种的吸收光谱和发射光谱。形成复合二聚体的平衡常数远高于自由二聚化或单个客体包合的平衡常数。γ-环糊精主体就像一条腰带，有助于客体的自组装。基于吡啰红B和吡啰红Y二聚体的结构和几何形状解释了它们稳定性的差异。
