Photo-responsive catalysis by thymine–cyclodextrin conjugates

Abstract

Primary hydroxy groups of β-cyclodextrin (β-CD) have been substituted with thymine (Thy) groups. By photo-irradiation with UV light at 280 nm, the introduced thymine groups adjacent to the CD cavity underwent reversible dimerization and the catalytic efficiency (k_cat/K_diss) of the modified CD in the hydrolyses of p-nitrophenyl acetate and m-nitrophenyl acetate increased. By further irradiation with light at 240 nm, the catalytic efficiency decreased to that of the CD–Thy conjugate due to the photo-cleavage of the thymine dimer. This phenomenon implies that the binding of guest molecules by the CD–Thy conjugate and subsequent change in the catalytic efficiency of the conjugate occurred photo-responsively. The steric effect on the acceleration or deceleration of the hydrolyses of phenyl esters by CD–Thy and its derivatives is also discussed.