The noncovalent host–guest interactions of the cationic (AcH⁺) and neutral (Ac) forms of an acridine dye with macrocyclic hosts such as cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) have been investigated to evaluate the effect of cavity size on the photophysical properties and the protolytic equilibrium of the acridine dye. The cationic form undergoes significant complexation with CB7 (K_eq = 10⁶ M⁻¹), causing a sharp decrease in the fluorescence intensity, whereas the neutral Ac form of the dye undergoes weak complexation with CB7 (K_eq = 10³ M⁻¹) and the binding constant is lowered by three orders of magnitude compared to that of the CB7–AcH⁺ system. The Job plot revealed that both forms form a 1:1 complex with CB7. On the other hand, the AcH⁺ form shows strong emission quenching on interaction with CB8 and the formation of the 1:2 CB8:AcH⁺ complex has been confirmed from the Job plot. The strong affinity of CB7 and CB8 to the protonated form resulted in a large upward pK_a shift (ΔpK_a ∼ 3.4 units for CB7 and ∼1.3 units for CB8) in the dye. Taking advantage of the above modulations in the fluorescence and pK_a values, adamantylamine-induced fluorescence regeneration, controlled pK_a tuning and dye relocation from the CB7 cavity to cell lines have been established for the first time, which find potential applications in fluorescence off–on sensing and drug delivery.

中文翻译：

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调制与瓜环吖啶染料的酸度常数：刺激响应p ķ_一个调整和搬迁染料进入活细胞

已研究了（啶染料的阳离子（AcH ⁺）和中性（Ac）形式与大环基质（如葫芦[7] uril（CB7）和葫芦[8] uril（CB8））的非共价宿主-客体相互作用腔尺寸对a啶染料的光物理性质和蛋白水解平衡的影响。阳离子形式与CB7发生显着络合（K _eq = 10 ⁶ M ^-1），导致荧光强度急剧下降，而染料的中性Ac形式与CB7发生弱络合（K _eq = 10 ³ M ^-1）），与CB7–AcH ⁺系统相比，结合常数降低了三个数量级。乔布图显示两种形式都与CB7形成1 ：1的复合物。另一方面，AcH ⁺形式在与CB8相互作用时显示出强烈的发射猝灭，并且已从Job图中确认了1 ：2 CB8 ：AcH ^+配合物的形成。CB7 CB8和对质子化形式的强亲和力导致了大的向上p ķ_一个移位（ΔP ķ_一〜3.4单位CB7和〜1.3单位CB8）在染料。利用荧光和p K _a中的上述调制值，金刚烷基胺诱导的荧光再生，控制磷ķ_一个从CB7空腔细胞系已经建立了所述第一时间，这在发现荧光潜在应用调谐和染料迁移断-上感测和药物递送。