Jadhav Ankita, Kalyani Vrashali S, Barooah Nilotpal, Malkhede Dipalee D, Mohanty Jyotirmayee
Department of Chemistry, University of Pune, Pune 411 007 (India).
Chemphyschem. 2015 Feb 2;16(2):420-7. doi: 10.1002/cphc.201402591. Epub 2014 Nov 17.
The host-guest interactions of cationic (AcH(+) ) and neutral (Ac) forms of the dye acridine with the macrocyclic host p-sulfonatocalix[6]arene (SCX6) were investigated by using ground-state absorption, steady-state and time-resolved fluorescence, and NMR measurements. The cationic form undergoes significant complexation with SCX6 (Keq =2.5×10(4) M(-1) ), causing a sharp decrease in the fluorescence intensity and severe quenching in the excited-state lifetime of the dye. The strong binding of the AcH(+) form of the dye with SCX6 is attributed to ion-ion interactions involving the sulfonato groups (SO3 (-) ) of SCX6 and the positively charged AcH(+) at pH of approximately 4.3. Whereas, the neutral Ac form of the dye undergoes weak complexation with SCX6 (Keq =0.9×10(3) M(-1) ) and the binding constant is lowered by one order of magnitude compared with that of the SCX6-AcH(+) system. The strong affinity of SCX6 to the protonated form leads to a large upward pKa shift (≈2 units) in the dye. In contrast, strong emission quenching upon SCX6 interaction and the regeneration of fluorescence intensity of the dye in the presence of Gd(3+) through competitive binding have also been demonstrated.
通过基态吸收、稳态和时间分辨荧光以及核磁共振测量，研究了染料吖啶的阳离子形式（AcH⁺）和中性形式（Ac）与大环主体对磺酸钠杯[6]芳烃（SCX6）的主客体相互作用。阳离子形式与SCX6发生显著络合（Keq = 2.5×10⁴ M⁻¹），导致荧光强度急剧下降，并使染料的激发态寿命严重猝灭。染料的AcH⁺形式与SCX6的强结合归因于在约4.3的pH值下，涉及SCX6的磺酸根基团（SO₃⁻）和带正电荷的AcH⁺的离子-离子相互作用。然而，染料的中性Ac形式与SCX6发生弱络合（Keq = 0.9×10³ M⁻¹），与SCX6-AcH⁺体系相比，结合常数降低了一个数量级。SCX6对质子化形式的强亲和力导致染料的pKa大幅上移（约2个单位）。相比之下，还证明了SCX6相互作用时的强发射猝灭以及在Gd³⁺存在下通过竞争性结合使染料荧光强度再生。
