Phase relations in K_xFe_{2-y}Se_2 and the structure of superconducting K_xFe_2Se_2 via high-resolution synchrotron diffraction

Superconductivity in iron selenides has experienced a rapid growth, but not without major inconsistencies in the reported properties. For alkali-intercalated iron selenides, even the structure of the superconducting phase is a subject of debate, in part because the onset of superconductivity is affected much more delicately by stoichiometry and preparation than in cuprate or pnictide superconductors. If high-quality, pure, superconducting intercalated iron selenides are ever to be made, the intertwined physics and chemistry must be explained by systematic studies of how these materials form and by and identifying the many coexisting phases. To that end, we prepared pure K_2Fe_4Se_5 powder and superconductors in the K_xFe_{2-y}Se_2 system, and examined differences in their structures by high-resolution synchrotron and single-crystal x-ray diffraction. We found four distinct phases: semiconducting K_2Fe_4Se_5, a metallic superconducting phase K_xFe_2Se_2 with x ranging from 0.38 to 0.58, an insulator KFe_{1.6}Se_2 with no vacancy ordering, and an oxidized phase K_{0.51(5)}Fe_{0.70(2)}Se that forms the PbClF structure upon exposure to moisture. We find that the vacancy-ordered phase K_2Fe_4Se_5 does not become superconducting by doping, but the distinct iron-rich minority phase K_xFe_2Se_2 precipitates from single crystals upon cooling from above the vacancy ordering temperature. This coexistence of metallic and semiconducting phases explains a broad maximum in resistivity around 100 K. Further studies to understand the solubility of excess Fe in the K_xFe_{2-y}Se_2 structure will shed light on the maximum fraction of superconducting K_xFe_2Se_2 that can be obtained by solid state synthesis.Comment: 12 pages, 16 figures, supplemental materia

Ischemia modified albumin and thiol/disulfide balance in patients with Hashimoto’s thyroiditis

Hashimoto thyroiditis is a common cause of goiter and acquired hypothyroidism in individuals residing in areas of no iodine deficiency. The fact that the structure of serum albumin exhibits changes in ischemic conditions has paved the way for the discovery of a new serum cardiac ischemia marker, Ischemia Modified Albumin. The other one, thiol/disulphide homeostasis, plays an important part in antioxidative protection, detoxification, cell growth, and apoptosis. In this study, we aimed to investigate both the relationship between Thiol/Disulphide homeostasis and Ischemia Modified Albumin in patients diagnosed with Hashimoto’s Thyroiditis. A total of 70 Hashimoto’’s thyroiditis patients and 50 healthy ones were included in this study. Age, gender, thyroid-stimulating hormone (TSH), anti-thyroid peroxidase (TPO), anti-thyroglobulin (TG) levels were recorded. Ischemia Modified Albumin and thiol-disulphid homeostasis parameters were measured through automated spectrophotometric methods. The ages of individuals included in the study ranged from 35 to 58 years. The native thiol/total thiol were found to be significantly lower in Hashimoto patients when compared to those enrolled in the control group (P < 0.05), whereas the Ischemia Modified Albumin, disulphide, native thiol, total thiol, disulphide/native thiol, and disulphide/total thiol were found to be significantly higher in Hashimoto patients when compared to those in the control (P < 0.05). Increased Ischemia Modified Albumin, native and total thiol, and disulphide levels are related to increased oxidative stress. Although Ischemia Modified Albumin and Thiol-disulphide defense are important oxidative indicators in Hashimoto’s Thyroiditis, many determinants are known to be involved in this process

Human mesenchymal stromal cells from different sources diverge in their expression of cell surface proteins and display distinct differentiation patterns

When germ-free cell cultures became a laboratory routine, hopes were high for using this novel technology for treatment of diseases or replacement of cells in patients suffering from injury, inflammation, or cancer or even refreshing cells in the elderly. Today, more than 50 years after the first successful bone marrow transplantation, clinical application of hematopoietic stem cells is a routine procedure, saving the lives of many every day. However, transplanting other than hematopoietic stem and progenitor cells is still limited to a few applications, and it mainly applies to mesenchymal stromal cells (MSCs) isolated from bone marrow. But research progressed and different trials explore the clinical potential of human MSCs isolated from bone marrow but also from other tissues including adipose tissue. Recently, MSCs isolated from bone marrow (bmMSCs) were shown to be a blend of distinct cells and MSCs isolated from different tissues show besides some common features also some significant differences. This includes the expression of distinct antigens on subsets of MSCs, which was utilized recently to define and separate functionally different subsets from bulk MSCs. We therefore briefly discuss differences found in subsets of human bmMSCs and in MSCs isolated from some other sources and touch upon how this could be utilized for cell-based therapies