Physical properties of anticancer drug 6-thioguanine

摘要

6-thioguanine has long been in use as an anticancer drug. In the recent years 6-thioguanine and its derivatives are coming into application as photosensibilizers, luminescence probes, targets for forming photo-crosslinks. To ascertain spectroscopic properties of 6-thioguanine, its UV absorption, low temperature (4.2K) luminescence and circular dichroism spectra were studied in solutions of different polarities. Spectrophotometric titration of 6-thioguanine was carried out in the pH 1-13 interval. The MP2 ab initio method was used to calculate the molecular structure, dipole moments, electronic density distribution, thermodynamic characteristics, UV and IR spectra of some 6-thioguanine tautomers. Based on theoretical calculations and experimental results, a diagram of electronic excited states of 6-thioguanine and a scheme of acid-base and tautomeric equilibrium of 6-thioguanine in the polar solvent were built. Migration of excitation in DNA with incorporated 6-thioguanine was investigated. As well, we used 6-thioguanine as a luminescent probe to study structural changes in cryoprotector and DNA solutions in the temperature range from 4.2 to 273K. In particular, glassification of the DNA hydrate shell in the range of 200K was revealed.