Water vapour adsorption on DNA

Abstract

DNA is a molecule which is present in the nucleus of each living cell. It is the molecule which synthesizes proteins. DNA conformation [1], electrical conductivity [2] and density [3] depend on the amount of water it contains. The phosphate groups, nitrogen and oxygen atoms of the base pairs in DNA bind to water molecules by hydrogen bonding. DNA adsorbs moisture from atmosphere and it is a water soluble macromolecule. The state of water in DNA has been investigated by X-ray diffraction, by inelastic neutron scattering [4] and melting of frozen water in DNA [5] by previous workers. The bound water in frozen DNA does not show ice melting endotherm. This is due to distribution of electric charges around phosphate groups. Dielectric study on hydration of DNA in water-ethanol solutions showed that 19 and 13 molecules of water per nucleotide are required for B-DNA and A-DNA respectively to keep the double helix. Studies of water vapour adsorption of DNA films by IR spectroscopy have shown that the hydrogen bonded water peak maxima shifted from 3473 to 3583 cm -1 as moisture content increases. This was attributed to the formation of a thin liquid water film on the surface of DNA [6].The interaction between DNA and water were described by quantum mechanical methods [2] and by molecular dynamics [7]. Water network around simulated duplexes was more conformation specific rather than sequence specific [7]. Water influences DNA stability and the contribution of water molecules to the energy of DNA helical structure was found from the energy spectrum of the bound water and enthalpy of helix-coil transformation [8]. Energy change was inversely proportional to amount of bound water per nucleotide.In studying DNA by IR spectroscopy diffuse reflectance The state of the sample could change during sample preparation, handling and measurement stages using these techniques.This research aims studying water vapour adsorption of DNA in situ. Outgassing the samples in vacuum and sending water vapour at controlled rate and pressure prevented any change in state of the sample between outgassing and measuring stages. No change in state of the sample occurs since the sample was not transferred from preparation environment to measuring environment. While water vapour was sent continuously at a low rate in gravimetric system, water vapour at different pressures was sent in steps in FTIR Drift cell and microcalorimeter cell. ExperimentalIn the present study sodium salt DNA obtained from calf tymus (Sigma) was used.The morphology of the fibres was investigated by scanning electron microscopy using Philips VL30 SFEG SEM.Equilibrium and kinetics of water vapour adsorption on calf thymus DNA was studied by Cahn gravimetric adsorption system described in a previous paper [11]. The system has Edwards ultra high vacuum system and all vacuum glass valves were from Scientific Glass Company. Adsorption isotherm of water vapour on DNA at 25°C was determined after Analysis and Calorimetry, Vol. 94 (2008)

Nanoscale Growth and Patterning of Inorganic Oxides Using DNA Nanostructure Templates

“…This observation is consistent with the chemical inertness of gold, which does not allow water and ammonia to adsorb strongly on its surface . For a mica substrate, the contrast of the negative-tone pattern was very small, presumably because of the very small difference in the adsorption isotherms of water on DNA and mica. , …”

DNA Origami: Scaffolds for Creating Higher Order Structures

“…If the humidity is relatively high, DNA can absorb more than 100% (w/w) of water. 503 Furthermore, when present on the substrate surface, DNA nanostructures can inhibit the diffusion of the HF to the SiO 2 . Therefore, DNA nanostructures can manipulate the etching kinetics.…”

“…A DNA backbone is made up of phosphates that can bind water molecules, and a DNA origami can absorb a massive amount of water. If the humidity is relatively high, DNA can absorb more than 100% (w/w) of water . Furthermore, when present on the substrate surface, DNA nanostructures can inhibit the diffusion of the HF to the SiO 2 .…”

DNA nanostructure meets nanofabrication

“…It is known that at high relative humidity, DNA can absorb more than 100% (w/w) of water. 43 In the meantime, when deposited onto a SiO 2 substrate, DNA also serves as a diffusion barrier that blocks the access of HF to the underlying SiO 2 . Thus the effect of DNA on the HF etching of SiO 2 will depend on the relative magnitude of the two effects.…”

“…Thus the effect of DNA on the HF etching of SiO 2 will depend on the relative magnitude of the two effects. Based on the adsorption isotherms of water vapor on DNA 43 and on SiO 2 , 44 a qualitative prediction can be made that at high relative humidity, DNA will enhance the SiO 2 etching while at low relative humidity DNA will slow down the etching.…”