Structures and infrared spectra of 5-chlorouracil molecules in the low-temperature inert Ar, Ne matrices and composite films with oxide graphene

Abstract

The structures and vibrational spectra of biologically active molecules of 5-chlorouracil (5CU) in various states were studied. The IR Fourier spectra of 5CU molecules isolated in the low-temperature Ar and Ne matrices were obtained in the infrared range of 3800–500 cm–1. The populations of 5CU tautomers were estimated, and vibrational spectra were calculated using the DFT/B3LYP method with a basis of 6-311++G(df,pd). In the Ar matrix, 7 Raman modes of 5CU amplified by Fermi resonance were detected in the spectral range of 1900–500 cm–1. In the region of fundamental vibrations νCO and in the vibration region of the ring, triple Fermi resonances were observed. Thin 5CU films on the surface of graphene oxide (GO) and composite films 5CU/GO obtained from an aqueous solution were grown and investigated at cryogenic temperatures. It was shown that, as the temperature rises from the helium temperature to room temperature, the 5CU film crystallizes on the GO surface. Comparison of the spectra of the 5CU films obtained enabled identification of vibrations whose absorption bands were most sensitive to changes in the crystal structure of the film. Most of these fundamental modes were associated with vibrations of the NH group. With an increase in the concentration of 5CU in the 5CU/GO composite films, a nonuniform distribution of the 5CU micro-crystals over the sample area was observed.