XPS investigation of the thymine thin film on polycrystalline titanium oxide surfaces


Purpose. Information biomolecules have attracted increasing attention as interest in nanoscience and nanotechnology of biomaterials has appeared. Recent studies have demonstrated that nano-TiO2 induces DNA damage and increase the risk of cancer and the mechanism might relate to oxidative stress. To our knowledge, no detailed spectroscopic study is reported on thymine on TiOx surface. Therefore, the aim of this work is study of the thymine biomolecules interaction with the polycrystalline titanium oxide by X-Ray photoelectron spectroscopy (XPS).
Methods. Titanium oxide TiOx on the surface of polycrystalline titanium foil was prepared according to the method described in [3]. The thermal evaporation of thymine at 385 K took place in the preparation chamber (pressure 1.4×10−5 Pa). Al Kα radiation (1486.6 eV) was used to measure the XPS core levels spectra of O1s, C1s, N1s and Ti 2p3/2 with total resolution of 1 eV. Curve fitting was performed after a Shirley background subtraction by a Lorenzian–Gaussian method.
Results. The thymine layer (d=13.66 Å) on the surface of titanium oxide was obtained by thermal deposition in vacuum. Analysis of the measured XPS spectra shows that the N 1s spectra can be divided into two regions above 400 eV and around 398–399 eV. A higher energy peak is attributed to amino –N- sites that connect with single bonds. A peak at the lower binding energy can be attributed to imino species that include a double N═C bond. C 1s core level spectra contains components that can be uniquely assigned to the hydrocarbons C─C, C─H, carbon bound to nitrogen C─N, N─C─N, amide carbon N─C═O, and urea carbon N─C(═O)─N with characteristic binding energies of approximately 285, 286–287, 288, and 289 eV, respectively. The heating in vacuum at T=50, 75, 100, 125, 150 and 200°C does not effect on the structure of the sample and the film thickness of thymine film.
Conclusions. The polycrystalline titanium oxide layer on the Ti foil was obtained. The thin film of thymine on the titanium oxide surface has was obtained by thermal evaporation in vacuum. XPS investigation of influence of thermal treatment on X-Ray photoelectron spectra of thymine thin film showed that the thickness of the film to 200˚C does not almost change. This indicates the formation of stable chemical bonds between the molecules C5H6N2O2 and the titanium oxide surface

Keywords: thymine, titanium oxide, biomolecule – surface interaction, X-ray photoelectron spectroscopy