Sorting tryptophan containing peptide and protein by β-cyclodextrin appended magnetic nanoparticles

Recognition and sorting of molecules play significant roles in pharmaceutical, material, biological and medical sciences. This study reports the molecular recognition and sorting of tryptophan-containing peptides and proteins by β-cyclodextrin through host-guest complex formation. The FTIR and NMR spectra demonstrate that the peptides 1 and 2 adopt similar helical conformations. The L-Tyr-containing tripeptide 1 exhibits an emission band at 310 nm, but with increasing concentration, the emission band decreases. However, the L-Trp-containing tripeptide 2 exhibits an emission band at 340 nm, and with increasing concentration of tripeptide 2, the emission band increases, and the band at 340 nm shifts to 360 nm, indicating persistence of J-type aggregation. Moreover, on the addition of β-cyclodextrin-appended magnetic nanoparticles, the emission band of tripeptide 2 reduced gradually due to host-guest complex formation. From a mixture of peptides, the host-guest complex of tripeptide 2 and β-CD-appended magnetic nanoparticles was easily separated using an external magnet. The β-cyclodextrin-appended magnetic nanoparticles also recognize ovalbumin, a 385-residue, 45-Da hen egg-white protein having three Trp residues. The study could provide an effective method for the recognition and sorting of Trp-containing macromolecules.