Survey on the complexation character of p-sulfonatocalix[n]arenes and Caffeic acid

• The inclusion interaction of SCXn with Caffeic acid was studied.
• Fluorescence, DSC, SEM, FT-IR, NMR were applied to characterize the complex.
• CA is able to form inclusion complexes with SCXn in a molar ratio of 1:1.
• The thermal stability and photostability of CA were increased.
• The antioxidant activity of CA on complexation with SCXn was increased.

In this work the inclusion complex formation of Caffeic acid (CA) with p-sulfonatocalix[n]arenes (SCXn, n = 4, 6, 8) is reported aiming to improve the antioxidant activity, thermal stability and photostability properties of CA. Evidence for the formation was obtained using fluorescence spectroscopy, nuclear magnetic resonance spectroscopy (NMR), pulsed field gradient NMR (PFG-NMR), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and scanning electron microphotographs (SEM). Experimental conditions including concentrations of SCXn and pH were investigated for the inclusion formation in detail. The results showed that CA was able to form inclusion complexes with SCXn in a molar ratio of 1:1, and the formation constants were varied with the pH conditions. NMR spectroscopy indicated that both the aromatic ring and the vinyl group of CA were partially covered by SCXn.

SCX4 was more suitable than any other SCXn for inclusion of the CA molecule in acidic media, whereas SCX8 had a higher capacity to form an inclusion complex with CA in basic media. The antioxidant activity of CA on complexation with SCXn and the thermal stability and photostability of the system were increased.Figure optionsDownload as PowerPoint slide