Study on inclusion complexes of meso-tetrakis(2-thienyl)porphyrin and Cu-meso-tetrakis(2-thienyl)porphyrin with cyclodextrins by spectroscopy method

In phosphate buffer solution of pH5.4, the interaction of meso-tetrakis(2-thienyl)porphyrin(H₂TTP) and Cu-meso-tetrakis(2-thienyl)porphyrin(Cu-TTP) with α-cyclodextrin(α-CD), β-CD, γ-CD, heptakis(2,3,6-tri-O-methyl)-β-CD(TM-β-CD) has been studied by means of UV-vis, fluorescence and ¹HNMR spectroscopy, respectively. The H₂TTP and Cu-TTP can form 1:2 inclusion complexes with TM-β-CD and 1:1 inclusion complexes with the other three cyclodextrins. In this paper, the inclusion constants (K) of H₂TTP and Cu-TTP for the formation of the inclusion complexes have been estimated from the changes of absorbance and fluorescence intensity in phosphate buffer solution. The inclusive capabilities of different kinds of cyclodextrins are compared. The result shows that the inclusion ability of α-CD with H₂TTP and Cu-TTP is the strongest among the three native CDs. The inclusion ability of modified β-CD with H₂TTP and Cu-TTP is stronger, compared to the native β-CD, which indicates that the capacity matching plays a crucial role in the inclusion procedure except for the hydrophobic effect. In addition ¹HNMR spectra supports the inclusion conformation of the TM-β-CD-Cu-TTP inclusion complex, indicating the interaction mechanism of inclusion processes.