Oxygen, Volume 1, Issue 1 (September 2021) – 7 articles

Epitaxial SrTiO₃ (STO) thin films were grown on (001)-oriented LaAlO₃ (LAO) substrates at 800 °C by an ion beam sputter deposition (IBSD). Oxygen partial pressure (PO₂) was varied at 1.5 × 10⁻⁵, 1.5 × 10⁻⁴, and 1.5 × 10⁻³ Torr during the growth. The effects of PO₂ on crystal structure, oxygen vacancy, and surface morphology of the STO films were investigated and are discussed to understand their correlation. It was found that PO₂ played a significant role in influencing the crystal structure, oxygen vacancy, and surface morphology of the STO films. All STO films grew on the LAO substrates under a compressive strain along an in-plane direction (a- and b-axes) and a tensile strain along the growth direction (c-axis). The crystalline quality of STO films was slightly improved at higher PO₂. Oxygen vacancy was favorably created in the STO lattice grown at low PO₂ due to a lack of oxygen during growth and became suppressed at high PO₂. The existence of oxygen vacancy could result in a lattice expansion in both out-of-plane and in-plane directions due to the presence of Ti³⁺ instead of Ti⁴⁺ ions. The surface roughness of the STO films gradually decreased and was nearly close to that of the bare LAO substrate at high PO₂, indicating a two-dimensional (2D) growth mode. The results presented in this work provide a correlation among crystal structure, oxygen vacancy, and surface morphology of the epitaxial STO films grown by IBSD, which form a useful guideline for further study. Full article

Many cells in the human body strongly react on decreased oxygen concentrations, generally defined as hypoxia. Therefore, inducing hypoxia in vitro is essential for research. Classically, hypoxia is induced using a hypoxia chamber, but alternative methods exist that do not require special equipment. Here, we compared three different methods to induce hypoxia without a hypoxia chamber: the chemical stabilization of HIF-1α by CoCl₂, the decrease in pericellular oxygen concentrations by increased media height, and the consumption of oxygen by an enzymatic system. Hypoxia induction was further analyzed within three different cell culture systems: 2D (adherent) osteoprogenitor cells, monocytic (suspension) cells, and in a 3D in vitro fracture hematoma model. The different methods were analyzed within the scope of fracture healing regarding inflammation and differentiation. We could show that all three induction methods were feasible for hypoxia induction within adherent cells. Increased media heights did not stimulate a hypoxic response within suspension cells and in the 3D system. Chemical stabilization of HIF-1α showed limitations when looking at the expression of cytokines in osteoprogenitors and monocytes. Enzymatic reduction of oxygen proofed to be most effective within all three systems inducing inflammation and differentiation. Full article

Sixteen years (July 2003–July 2019) of ground-based measurements of total ozone in the urban environment of Athens, Greece, are analyzed in this work. Measurements were acquired with a single Brewer monochromator operating on the roof of the Biomedical Research Foundation of the Academy of Athens since July 2003. We estimate a 16-year climatological mean of total ozone in Athens of about 322 DU, with no significant change since 2003. Ozone data from the Brewer spectrophotometer were compared with TOMS, OMI, and GOME-2A satellite retrievals. The results reveal excellent correlations between the ground-based and satellite ozone measurements greater than 0.9. The variability of total ozone over Athens related to the seasonal cycle, the quasi biennial oscillation (QBO), the El Nino Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), the 11-year solar cycle, and tropopause pressure variability is presented. Full article

Epigenetics contains various mechanisms by which cells employ to regulate the transcription of many DNAs. Histone acetylation is an obvious example of the epigenetic mechanism regulating the expression of several genes by changing chromatin accessibility. Histone deacetylases (HDACs) are a class of enzymes that play a critical role in the epigenetic regulation by deacetylation of histone proteins. Inhibitors of the histone deacetylase could result in hyperacetylation of histones, which eventually induce various cellular consequences such as generation of reactive oxygen species (ROS), activation of apoptotic pathways, and initiating autophagy. In particular, excessive levels of ROS have been proposed to contribute to the pathophysiology of various diseases including cancer. Cancers are, as it were, a class of redox diseases. Low levels of ROS are beneficial for cells, however, cancer cells generally have high levels of ROS, which makes them more susceptible than normal cells to the further increases of ROS levels. Cancer cells exhibit metabolic alterations for managing to sustain these oxidative stresses. There is a growing interest in the use of HDAC inhibitors as promising cancer therapeutics with potentiating the activity of established therapeutic applications. Therefore, it should be important to understand the underlying relationship between the regulation of HDACs, ROS production, and cancer cell biology. Full article

A lithium superionic conductor of Li₁₀GeP₂S₁₂ that exhibits the highest lithium ionic conductivity among the sulfide electrolytes and the most promising oxide electrolytes, namely, Li_6.6La₃Sr_0.06Zr_1.6Sb_0.4O₁₂ and Li_6.6La₃Zr_1.6Sb_0.4O₁₂, are successfully synthesized. Novel hybrid electrolytes with a weight ratio of Li_6.6La₃Zr_1.6Sb_0.4O₁₂ to Li₁₀GeP₂S₁₂ from 1/1 to 1/3 with the higher Li-ion conductivity than that of the pure Li₁₀GeP₂S₁₂ electrolyte are developed for the fabrication of the advanced all-solid-state Li batteries. Full article

Control of cellular function is extremely complex, being reliant on a wide range of components. Several of these are small oxygen-based molecules. Although reactive compounds containing oxygen are usually harmful to cells when accumulated to relatively high concentrations, they are also instrumental in the control of the activity of a myriad of proteins, and control both the upregulation and downregulation of gene expression. The formation of one oxygen-based molecule, such as the superoxide anion, can lead to a cascade of downstream generation of others, such as hydrogen peroxide (H₂O₂) and the hydroxyl radical (^∙OH), each with their own reactivity and effect. Nitrogen-based signaling molecules also contain oxygen, and include nitric oxide (NO) and peroxynitrite, both instrumental among the suite of cell signaling components. These molecules do not act alone, but form part of a complex interplay of reactions, including with several sulfur-based compounds, such as glutathione and hydrogen sulfide (H₂S). Overaccumulation of oxygen-based reactive compounds may alter the redox status of the cell and lead to programmed cell death, in processes referred to as oxidative stress, or nitrosative stress (for nitrogen-based molecules). Here, an overview of the main oxygen-based molecules involved, and the ramifications of their production, is given. Full article