Search Results (4)

DNA gyrase is a bacterial type IIA topoisomerase that can create temporary double-stranded DNA breaks to regulate DNA topology and an archetypical target of antibiotics. The widely used quinolone class of drugs use a water–metal ion bridge in interacting with the GyrA subunit of DNA gyrase. Zoliflodacin sits in the same pocket as quinolones but interacts with the GyrB subunit and also stabilizes lethal double-stranded DNA breaks. Gepotidacin has been observed to sit on the twofold axis of the complex, midway between the two four-base-pair separated DNA-cleavage sites and has been observed to stabilize singe-stranded DNA breaks. Here, we use information from three crystal structures of complexes of Staphlococcus aureus DNA gyrase (one with a precursor of gepotidacin and one with the progenitor of zoliflodacin) to propose a simple single moving metal-ion-catalyzed DNA-cleavage mechanism. Our model explains why the catalytic tyrosine is in the tyrosinate (negatively charged) form for DNA cleavage. Movement of a single catalytic metal-ion (Mg²⁺ or Mn²⁺) guides water-mediated protonation and cleavage of the scissile phosphate, which is then accepted by the catalytic tyrosinate. Type IIA topoisomerases need to be able to rapidly cut the DNA when it becomes positively supercoiled (in front of replication forks and transcription bubbles) and we propose that the original purpose of the small Greek Key domain, common to all type IIA topoisomerases, was to allow access of the catalytic metal to the DNA-cleavage site. Although the proposed mechanism is consistent with published data, it is not proven and other mechanisms have been proposed. Finally, how such mechanisms can be experimentally distinguished is considered. Full article

Germanate-pyroxenes often are used as model systems to study the stability and phase relationships of analog silicate systems. Based on such analyses, it is assumed that silicates and germanates behave ideally in terms of mixing. A systematic study was performed to monitor in detail the changes introduced by a Si⁴⁺ through Ge⁴⁺ replacement in the important rock-forming pyroxene enstatite MgSiO₃. Well-shaped, idiomorphic singe crystals of a MgSi_1−xGe_xO₃ pyroxene solid solution were grown at ambient pressure from a high-temperature flux-assisted synthesis. Structural analysis using single-crystal X-ray diffraction methods revealed orthorhombic symmetry, Pbca, Z = 8, for the complete solid-solution series. Long-term storage over a period of 8 years at ambient conditions or annealing at 525 °C over a period of 10 weeks did not change the symmetry of the proposed thermodynamically stable monoclinic polymorph. Within the solid-solution series, lattice parameters increased almost linearly with increasing Si⁴⁺ by Ge⁴⁺ substitution. The main changes occurred on the tetrahedral sites, which showed an almost linear increase in individual and average bond lengths but also in distortion parameters. The refined site occupancy of Si⁴⁺ and Ge⁴⁺ showed a distinct preference of Ge⁴⁺ for the TB site. The altered topology and kinking state in the tetrahedral chains also imposed significant changes to the bonding topology and geometry of the neighboring M1 and M2 sites. Full article

In this work, we study the effect of substituents in cobalt(II) and iron(II) phthalocyanines (CoPcR₄ and FePcR₄ with R = H, F, Cl, tBu) on the structural features of their films, and their chemi-resistive sensor response to a low concentration of nitric oxide. For the correct interpretation of diffractograms of phthalocyanine films, structures of CoPcCl₄ and FePcCl₄ single crystals were determined for the first time. Films were tested as active layers for the determination of low concentrations of NO (10–1000 ppb). It was found that the best sensor response to NO was observed for the films of chlorinated derivatives MPcCl₄ (M = Co, Fe), while the lowest response was in the case of MPc(tBu)₄ films. FePcCl₄ films exhibited the maximal response to NO, with a calculated limit of detection (LOD) of 3 ppb; the response and recovery times determined at 30 ppb of NO were 30 s and 80 s, respectively. The LOD of a CoPcCl₄ film was 7 ppb. However, iron phthalocyanine films had low stability and their sensitivity to NO decreased rapidly over time, while the response of cobalt phthalocyanine films remained stable for at least several months. In order to explain the obtained regularities, quantum chemical calculations of the binding parameters between NO and phthalocyanine molecules were carried out. It was shown that the binding of NO to the side atoms of phthalocyanines occurred through van der Waals forces, and the values of the binding energies were in direct correlation with the values of the sensor response to NO. Full article

This study aimed to retrospectively investigate the effect of bone graft after extraction of wisdom teeth impacting with the distal aspect of the second molar, on soft tissue wound healing, bone loss, and periodontal parameters. Sixteen patients treated an for impacted mandibular wisdom tooth at least one year ago were re-called (18 teeth). Dental panoramic tomography and periodontal parameters were assessed. A graft material was used to fill the post-extractive sockets in the test group (GUIDOR easy-graft CRYSTAL), whereas in the control group, the socket was filled using a collagen sponge and blood clot (Hemocollagene, Septodont, Matarò, Spain). The radiographic bone loss was measured at the distal aspect of the second molar. The Wilcoxon singed-rank test for paired data was performed to evaluate statistical differences. In the test group, only two cases out of nine showed bone loss, with an average of 0.55 ± 1.30 mm. Conversely, in the control group, five teeth out of nine showed bone resorption with an average of 1.22 ± 1.30 mm. However, the differences were not statistically significant. Periodontal parameters at the second molar demonstrated similar behavior between the test and control groups. Soft tissue healing complications were lower in the grafted compared to the comparator sites without reaching statistical significance. Within the limitations of the present study, no difference was found between the two groups. Full article