Mechanism of thermal renaturation and hybridization of nucleic acids: Kramers' process and universality in Watson-Crick base pairing.

Renaturation and hybridization reactions lead to the pairing of complementary single-stranded nucleic acids. We present here a theoretical investigation of the mechanism of these reactions in vitro under thermal conditions (dilute solutions of single-stranded chains, in the presence of molar concentrations of monovalent salts and at elevated temperatures). The mechanism follows a Kramers' process, whereby the complementary chains overcome a potential barrier through Brownian motion.

DNA adsorption at liquid/solid interfaces.

DNA adsorption on solid or liquid surfaces is a topic of broad fundamental and applied interest. Here, we study by X-ray reflectivity the adsorption of monodisperse double-stranded DNA molecules on a positively charged surface, obtained through chemical grafting of a homogeneous organic monomolecular layer of N-(2-aminoethyl) dodecanamide on an oxide-free monocrystalline Si(111) wafer. The adsorbed dsDNA is found to embed into the soft monolayer, which is deformed in the process.

DNA adsorption at functionalized Si/buffer interfaces studied by x-ray reflectivity.

The adsorption of DNA on chemically homogeneous, functionalized, oxide-free single-crystal silicon surfaces is studied by x-ray reflectivity. The adsorption of monodisperse, 294 base-pair double-stranded DNA on a positively charged surface is detected through the deformation of the molecular monolayer of aminated alkyl-chain molecules covalently bonded to the surface. The adsorption of single-stranded DNA does not lead to the same deformation.

Structure and fluctuations of a single floating lipid bilayer.

A single lipid molecular bilayer of 17 or 18 carbon chain phosphocholines, floating in water near a flat wall, is prepared in the bilayer gel phase and then heated to the fluid phase. Its structure (electron density profile) and height fluctuations are determined by using x-ray reflectivity and non-specular scattering. By fitting the off-specular signal to that calculated for a two-dimensional membrane using a Helfrich Hamiltonian, we determine the three main physical quantities that govern the bilayer height fluctuations: The wall attraction potential is unexpectedly low; the surface tension, roughly independent on chain length and temperature, is moderate (approximately 5 x 10(-4) J.