Interaction of calf thymus DNA with a cationic tetrandrine derivative at the air-water interface

The interaction of the semi-synthetic dicationic cyclophane-type macrocycle (TC) with calf thymus DNA was investigated at the air-water interface. The macrocycle has been prepared by chemical modification of S,S-(+)-tetrandrine with acridinylmethyl groups. The macrocycle was mixed with arachidic acid in a chloroform solution (1:1, 3:1, 9:1 arachidic acid:macrocycle weight proportions) and spread on a DNA buffer solution in a Langmuir Balance. Results indicate isotherms shifts and phase modification of the arachidic acid/macrocycle mixture monolayers due to the DNA adsorption from the subphase after different times. The presence of the arachidic acid at the interface gives support to the macrocycle at the air-water interface, otherwise macrocycle molecules do not remain at the interface. Atomic force microscopy images of Langmuir-Blodgett monolayers obtained on mica demonstrate the DNA adhesion on the macrocycle domains. The DNA adsorption process was also monitored by Brewster Angle Microscopy images. Circular Dichroism spectra of different DNA:macrocycle proportions were performed and show secondary structure changes of DNA. UV spectrometric measurements indicated a strong DNA-macrocycle interaction and molecular mechanics simulations corroborate that the macrocycle interaction with DNA occurs mainly in the major groove of the DNA molecule.