p-Sulfonatocalix[8]arene and vitamin C complexation: assessment of photophysical, pKa and antioxidant property

Abstract Mode of inclusion complexation of p-sulfonatocalix[8]arene and ascorbic acid in aqueous solution has been investigated in acidic pH based by UV–visible, fluorescence, FT-IR, 1H-NMR and HR-MS spectroscopic studies. Addition of ascorbic acid solution to p-sulfonatocalix[8]arene enhances the fluorescence intensity of p-Sulfonatocalix[8]arene with blue shift in absorption spectra. Hypsochromic shift in absorbance maxima and hyperchromic shift in emission maxima indicates that ascorbic acid experiences less polar microenvironment when bind with SCX8. Binding site and stoichiometry are examined by 1H-NMR and HR-MS techniques. Binding constant (K = 0.42 × 102 M−1) for the inclusion complex is calculated. For complexation, forces like electrostatic attraction, hydrogen bonding and hydrophobic environment of p-sulfonatocalix[8]arene cavity play important role. p-sulfonatocalix[8]arene shows upward pKa shift after binding with Ascorbic acid. The antioxidant property of ascorbic acid has been investigated which shows enhancement by 57% upon complexation with p-sulfonatocalix[8]arene. Graphical Abstract

摘要 通过紫外-可见（UV–visible）、荧光、傅里叶变换红外（FT-IR）、氢核磁共振（1H-NMR）及高分辨质谱（HR-MS）光谱学研究，在酸性pH条件下探究了对磺酸钠杯[8]芳烃（p-sulfonatocalix[8]arene）与抗坏血酸在水溶液中的包合络合模式。向对磺酸钠杯[8]芳烃溶液中加入抗坏血酸溶液，可增强其荧光强度，且吸收光谱发生蓝移。吸收最大值的蓝移（Hypsochromic shift）和发射最大值的增色效应（hyperchromic shift）表明，抗坏血酸与SCX8结合时处于极性更低的微环境中。结合位点及化学计量比通过1H-NMR和HR-MS技术进行了测定。计算得到该包合络合物的结合常数（K = 0.42×10² M⁻¹）。络合过程中，静电引力、氢键及对磺酸钠杯[8]芳烃空腔的疏水环境等作用力发挥重要作用。对磺酸钠杯[8]芳烃与抗坏血酸结合后，其pKa值发生正向偏移。对抗坏血酸的抗氧化性能进行了研究，结果显示其与对磺酸钠杯[8]芳烃络合后抗氧化性能提升57%。图形摘要