Nanostructuring of Watson–Crick type base‐paired (C60‐uracil):(2‐aminopurine) conjugates in Langmuir films

Abstract

AbstractLangmuir films of an uracil adduct of C60 (C60ur), spread on aqueous subphases of different pH and ionic strength in the presence and absence of 2‐aminopurine (2‐AP), were studied by simultaneous recording of the isotherms of surface pressure and surface potential vs. area per molecule. The film morphology was imaged by Brewster angle microscopy (BAM). C60ur forms “liquid‐expanded” Langmuir films on all studied subphase solutions. The dependence of area per molecule on the initial surface concentration of C60ur indicates substantial aggregation of the adduct molecules in films. Area per molecule for the C60ur film, prepared in the presence of 2‐AP in the subphase solution, is higher than that in its absence indicating that 2‐AP self assemble with C60ur via the Watson–Crick type base‐pairing. Accordingly, the BAM imaged surface of the former film is smoother than that of the latter. Charging of the C60ur film by either protonation or deprotonation of the uracil moiety of the adduct by using either the acidic or basic subphase solution, respectively, leads to formation of less aggregated films. This behavior is manifested by higher values of area per molecule as compared to that determined for the neutral subphase solution. The UV–vis spectra of the C60ur Langmuir‐Blodgett films, transferred from the subphase solutions containing 2‐AP, did not show the absorption band characteristic of 2‐AP as if the (C60ur):(2‐AP) conjugate was ruptured during the transfer. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)