An Exceptionally Stable and Scalable Sugar–Polyolefin Frank–Kasper A15 Phase

“One-component” soft material Frank–Kasper (FK) phases are an intriguing structural form of matter that possess periodically ordered structures arising from the self-reconfiguration and close packing of an initial assembly of identical “deformable” spheres into two or more size- or shape-distinct sets of particles. Significant challenges that must still be addressed to advance the field of soft matter FK phases further, however, include their rare and unpredictable occurrence, uncertain mechanisms of solid-state assembly, and low thermodynamic stability. Here we show that a readily-accessible sugar–polyolefin conjugate quantitatively produces an exceptionally stable solid-state FK A15 phase through a rapid and irreversible thermotropic order–order transition, which contrary to other prevailing proposed mechanisms, does not require mass transfer between particles or large structural reorganization in the bulk to establish unit cell non-equivalency. Our results provide the basis for a realistic strategy for obtaining practical and scalable quantities of a diverse range of sugar–polyolefin FK A15 phases with unique intrinsic physical properties and chemical reactivities not previously seen in such systems.     

Chemoselective Hydrogenation of 6-Alkynyl-3-fluoro-2-pyridinaldoximes: Access to First-in-Class 6-Alkyl-3-Fluoro-2-pyridinaldoxime Scaffolds as New Reactivators of Sarin-Inhibited Human Acetylcholinesterase with Increased Blood–Brain Barrier Permeability

Novel 6-alkyl- and 6-alkenyl-3-fluoro-2-pyridinaldoximes have been synthesised by using a mild and efficient chemoselective hydrogenation of 6-alkynyl-3-fluoro-2-pyridinaldoxime scaffolds, without altering the reducible, unprotected, sensitive oxime functionality and the C−F bond. These novel 6-alkyl-3-fluoro-2-pyridinaldoximes may find medicinal application as antidotes to organophosphate poisoning. Indeed, one low-molecular-weight compound exhibited increased affinity for sarin-inhibited acetylcholinesterase (hAChE) and greater reactivation efficiency or resurrection for sarin-inhibited hAChE, compared with those of 2-pyridinaldoxime (2-PAM) and 1-({[4-(aminocarbonyl)pyridinio]methoxy}methyl)-2-[(hydroxyimino)methyl]pyridinium chloride (HI-6), two pyridinium salts currently used as antidote by several countries. In addition, the uncharged 3-fluorinated bifunctional hybrid showed increased in vitro blood–brain barrier permeability compared with those of 2-PAM, HI-6 and obidoxime. These promising features of novel low-molecular-weight alkylfluoropyridinaldoxime open up a new era for the design, synthesis and discovery of central non-quaternary broad spectrum reactivators for organophosphate-inhibited cholinesterases.     

Switching the Switch: Ligand Induced Disulfide Formation in HDAC8

Human histone deacetylase 8 is a well-recognized target for T-cell lymphoma and particularly childhood neuroblastoma. PD-404,182 was shown to be a selective covalent inhibitor of HDAC8 that forms mixed disulfides with several cysteine residues and is also able to transform thiol groups to thiocyanates. Moreover, HDAC8 was shown to be regulated by a redox switch based on the reversible formation of a disulfide bond between cysteines Cys₁₀₂ and Cys₁₅₃. This study on the distinct effects of PD-404,182 on HDAC8 reveals that this compound induces the dose-dependent formation of intramolecular disulfide bridges. Therefore, the inhibition mechanism of HDAC8 by PD-404,182 involves both, covalent modification of thiols as well as ligand mediated disulfide formation. Moreover, this study provides a deep molecular insight into the regulation mechanism of HDAC8 involving several cysteines with graduated capability to form reversible disulfide bridges.     

Tuning of Supramolecular Architectures of l‐Valine‐Containing Dicyanoplatinum(II) 2,2′‐Bipyridine Complexes by Metal–Metal, π–π Stacking,and Hydrogen‐Bonding Interactions

A series of newly synthesized dicyanoplatinum(II) 2,2′‐bipyridine complexes exhibits self‐assembly properties in solution after the incorporation of the l ‐valine amino units appended with various hydrophobic motifs. These l ‐valine‐derived substituents were found to have critical control over the aggregation behaviors of the complexes in the solution state. On one hand, one of the complexes was found to exhibit interesting circularly polarized luminescence (CPL) signals at low temperature due to the formation of chiral spherical aggregates in the temperature‐dependent studies. On the other hand, systematic transformation from less uniform aggregates to well‐defined fibrous and rod‐like structures via Pt???Pt and π–π stacking interactions has also been observed in the mixed‐solvent studies. These changes were monitored by UV/Vis absorption, emission, circular dichroism (CD), and CPL spectroscopies, and morphologies were studied by electron microscopy.     

Stem cell survival is severely compromised by the thymidineanalog EdU (5-ethynyl-2′-deoxyuridine), an alternative to BrdU for proliferation assays and stem cell tracing

Stem cell therapy has opened up the possibility of treating numerous degenerating diseases. However, we are still merely at the stage of identifying appropriate sources of stem cells and exploring their full differentiation potential. Thus, tracking the stem cells upon in vivo engraftment and during in vitro co-culture is very important and is an area of research embracing many pitfalls. 5-Ethynyl-2′-deoxyuridine (EdU), a rather new thymidine analog incorporated into DNA, has recently been suggested to be a novel highly valid alternative to other dyes for labeling of stem cells and subsequent tracing of their proliferation and differentiation ability. However, our results herein do not at any stage support this recommendation, since EdU severely reduces the viability of stem cells. Accordingly, we found that transplanted EdU-labeled stem cells hardly survive upon in vivo transplantation into regenerating muscle, whereas stem cells labeled in parallel with another dye survived very well and also participated in myofiber formation. Similar data were obtained upon in vitro myogenic culture, and further analysis showed that EdU reduced cell numbers by up to 88 % and increased the cell volume of remaining cells by as much as 91 %. Even at low EdU concentrations, cell survival and phenotype were substantially compromised, and the myogenic differentiation potential was inhibited. Since we examined both primary derived cells and cell lines from several species with the same result, this appears to be a common trait of EdU. We therefore suggest that EdU labeling should be avoided (or used with precaution) for stem cell tracing purposes.