Discotic Mesogen – DNA Complex Films at Interfaces

Abstract

In this article, we review our studies on discotic mesogen – DNA complex films at interfaces. Discotic molecules are known to form highly anisotropic structures at the air-water (A-W) interface. We have studied films of a novel ionic discotic mesogenic molecule, pyridinium salt tethered with hexaalkoxytriphenylene (PyTp) and its complex with DNA (PyTp-DNA) at A-W and air-solid interfaces. The PyTp monolayer was formed on the aqueous subphase containing small amount of DNA. The electrostatic interaction between PyTp and DNA molecules results in a PyTp-DNA complex monolayer. Compared to the pure PyTp monolayer, the PyTp-DNA complex monolayer exhibits higher collapse pressure and lower limiting area. Surface manometry and Brewster angle microscope studies of the PyTp-DNA complex monolayer film indicate the molecules to be in the edge-on configuration. With increase in surface pressure, the complex monolayer undergoes a transition from a loosely packed monolayer phase to a compactly packed monolayer phase. The PyTp-DNA complex films on silicon wafers were prepared using Langmuir-Blodgett (LB) technique. We find that several tens of layers of PyTp-DNA complex monolayer can be transferred with good efficiency. We have carried out nanoscale electrical conductivity measurements for the pure PyTp and PyTp-DNA complex LB films using current sensing atomic force microscope. We have studied the current-voltage (I-V) characteristics for the metal-LB film-metal junction and our analysis shows that the I-V curves followed the Fowler-Nordheim tunneling model.