Orientational disorder and phase transitions in ammonium oxofluorovanadates, (NH4)3VOF5 and (NH4)3VO2F4

Single crystals of (NH4)3VOF5 and (NH4)3VO2F4 were obtained from aqueous fluoride solutions and phase transitions in these compounds were investigated using X-ray diffraction, differential scanning microcalorimetry (DSM) and vibrational spectroscopy. The room-temperature (RT) phases of these compounds belong to orthorhombic symmetry [Immm and I222, Z = 6, for (NH4)3VOF5 and (NH4)3VO2F4, respectively] with similar unit-cell parameters and two independent vanadium atoms. Above RT [at 350 and 440 K for (NH4)3VOF5 and (NH4)3VO2F4, respectively], the compounds undergo reversible phase transitions into high-symmetry dynamically disordered elpasolite-like (Fm{\bar 3}m, Z = 4) structures with six and 12 spatial orientations of the vanadium octahedron for (NH4)3VOF5 and (NH4)3VO2F4, respectively. The ligand atoms are distributed in a mixed (split) position of 24e + 96j, one of the ammonium groups is disordered on the tetrahedron 32f site, but another one forms eight spatial orientations due to disorder of its hydrogen atoms in the 96j position. DSM and spectroscopic data enable the phase transition from high temperature to room temperature to be connected with the transition from isotropic orientations of the octahedron to its two different dynamic states.

Exploring the Balance between DNA Pressure and Capsid Stability in Herpesviruses and Phages

ABSTRACTWe have recently shown in both herpesviruses and phages that packaged viral DNA creates a pressure of tens of atmospheres pushing against the interior capsid wall. For the first time, using differential scanning microcalorimetry, we directly measured the energy powering the release of pressurized DNA from the capsid. Furthermore, using a new calorimetric assay to accurately determine the temperature inducing DNA release, we found a direct influence of internal DNA pressure on the stability of the viral particle. We show that the balance of forces between the DNA pressure and capsid strength, required for DNA retention between rounds of infection, is conserved between evolutionarily diverse bacterial viruses (phages λ and P22), as well as a eukaryotic virus, human herpes simplex 1 (HSV-1). Our data also suggest that the portal vertex in these viruses is the weakest point in the overall capsid structure and presents the Achilles heel of the virus's stability. Comparison between these viral systems shows that viruses with higher DNA packing density (resulting in higher capsid pressure) have inherently stronger capsid structures, preventing spontaneous genome release prior to infection. This force balance is of key importance for viral survival and replication. Investigating the ways to disrupt this balance can lead to development of new mutation-resistant antivirals.IMPORTANCEA virus can generally be described as a nucleic acid genome contained within a protective protein shell, called the capsid. For many double-stranded DNA viruses, confinement of the large DNA molecule within the small protein capsid results in an energetically stressed DNA state exerting tens of atmospheres of pressures on the inner capsid wall. We show that stability of viral particles (which directly relates to infectivity) is strongly influenced by the state of the packaged genome. Using scanning calorimetry on a bacterial virus (phage λ) as an experimental model system, we investigated the thermodynamics of genome release associated with destabilizing the viral particle. Furthermore, we compare the influence of tight genome confinement on the relative stability for diverse bacterial and eukaryotic viruses. These comparisons reveal an evolutionarily conserved force balance between the capsid stability and the density of the packaged genome.

DNA damage and anti-tumor activity induced by Zn, Ag and Co containing meso- tetra(4-N-oxyethylpyridyl)porphyrins in vivo

In the present study, the activity of the new water-soluble cationic meso-tetra(4-N-oxyethylpyridyl)porphyrin and its Zn , Ag and Co metal derivatives as anti-tumor agents was explored. The tumor was induced by 7,12-dimethylbenz[a]antracene (DMBA) on rats of Wistar strain. The levels of DNA damage induced by porphyrins T4OEPyP , AgT4OEPyP , ZnT4OEPyP and CoT4OEPyP in tumor tissue were analyzed. Thermodynamic parameters of DNA were investigated by thermal melting method and differential scanning microcalorimetry to understand the differences in DNA structure of three types of rat: normal, dieseased with tumor, and treated by porphyrins. Agarose gel electrophoresis method was used to detect porphyrin-induced apoptosis or necroses. Based on the data obtained, we concluded that the investigated ZnTOEPyP and AgTOEPyP porphyrins have more anti-tumor activity than CoTOEPyP and TOEPyP .