Aggregation behavior of dabsylated poly(ε-L-lysine) in aqueous DMSO solution

Summary

Side chain amino groups of microbial Poly(ε-L-lysine) (ε-PL) were chemically modified with an amino labeling reagent, 4-dimethylaminoazobenzene-4’-sulfonyl chloride (dabsyl chloride) to give dabsylated ε-PL (Dabs-ε-PL). Aggregation behavior of Dabs-ε-PL in aqueous DMSO solution was studied through UV-Vis and CD spectra. In DMSO solution, Dabs-ε-PL shows a symmetric visible absorption at 450 nm, corresponding to the azobenzene chromophore in the monomeric state. Upon addition of water to the DMSO solution, the λ_max is shifted to around 400 nm. CD spectra were detected in the region of the blue shifted band: a pair of CD signals of opposite sign appears with a crossover point related to the shifted λ_max. Similar trends were also observed for UV-Vis and CD spectra of dabsylated oligo(ε-L-lysine)mers. These spectroscopic results indicate that side chain azo chromophores of Dabs-ε-PL form H-aggregates and are disposed according to a chiral arrangement with right handedness in aqueous DMSO solution.