Molecular recognition capabilities of a nucleolipid amphiphile (3′,5′-distearoyl)-2′-deoxythymidine to adenosine at the air/water interface and Langmuir-Blodgett films studied by molecular spectroscopy

Monolayer behavior of a nucleolipid amphiphile, (3',5'-distearoyl)-2'-deoxythymidine, on pure water, aqueous 1 mM and 5 mM adenosine solutions was investigated by means of surface pressure-molecular area (pi-A) isotherms, which indicate that both hydrogen-bonding and stacking interactions are present between the (3',5'-distearoyl)-2'-deoxythymidine monolayer and adenosine in subphase, and the recognition of this amphiphile to adenosine is more complete in higher subphase concentration. The ultraviolet-visible (UV-vis), Fourier transform infrared (FTIR)transmission FTIR-attenuated total reflection (ATR), and Fourier transform surface-enhanced Raman scattering (FT-SERS) spectroscopic results indicate that the adenosine molecules in the subphase can be transferred onto solid substrates by Langmuir-Blodgett (LB) technique as a result of the formation of Watson-Crick base-pairing at the air/water interface. The regular and closed packing of the constituent molecules facilitates the photodimerization of the thymine moieties in the headgroup under ultraviolet irradiation even at room temperature. FT-SERS technique, for the first time, was introduced into the research area of molecular recognition occurring at an interface system. High-quality FT-SERS spectra of single LB monolayers obtained in the 1750-500 cm(-1) region, together with the FTIR-ATR results in the NH-stretching high-frequency region, provide direct evidences for the formation of multiple complementary hydrogen bonds between the base pairs.