  $TiO_{2}$ nanoparticles (NPs) are widely used in the environmental
engineering, medicine, chemical and food industries due to their unique
photocatalytic and biocidal properties. NPs may generate reactive oxygen
species and, hence, have the toxic effect on the living cells via oxidative
stress. An external UV irradiation may magnify the photocatalytic properties of
$TiO_{2}$ NPs. In this regard, we have analyzed the influence of $TiO_{2}$ NPs
on the conformation and thermal stability of native DNA in a buffer solution
without and under UV irradiation exploiting absorption spectroscopy with DNA
thermal denaturation in the range of 20-94 degrees Celsius. Upon DNA heating
from about 25 to 44 degrees Celsius, we have observed the stabilization of DNA
duplex in the presence of $TiO_{2}$ NPs. This additional biopolymer
stabilization indicates that partial DNA unwinding appears as a result of the
direct binding of the biopolymer to NPs. We showed that the performed UV
treatment of DNA during 3 hours leads to partial unwinding of the biopolymer
structure. The NPs injection to the biopolymer solution induced the additional
effect on the DNA thermal stability under UV irradiation. The performed
analysis of the experimental data suggests that the nature of the impact of NPs
on the biopolymer is complex.
