We present the results of Monitor of All-sky X-ray Image (MAXI) monitoring and two Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the recently discovered faint X-ray transient MAXI J1848015. Analysis of the MAXI light curve shows that the source underwent a rapid flux increase beginning on 2020 December 20, followed by a rapid decrease in flux after only ∼5 days. NuSTAR observations reveal that the source transitioned from a bright soft state with unabsorbed, bolometric (0.1–100 keV) flux F = 6.9 ± 0.1 × 10−10 erg cm−2 s−1, to a low hard state with flux F = 2.85 ± 0.04 × 10−10 erg cm−2 s−1. Given a distance of 3.3 kpc, inferred via association of the source with the GLIMPSE-C01 cluster, these fluxes correspond to an Eddington fraction of the order of 10−3 for an accreting neutron star (NS) of mass M = 1.4M ⊙, or even lower for a more massive accretor. However, the source spectra exhibit strong relativistic reflection features, indicating the presence of an accretion disk that extends close to the accretor, for which we measure a high spin, a = 0.967 ± 0.013. In addition to a change in flux and spectral shape, we find evidence for other changes between the soft and hard states, including moderate disk truncation with the inner disk radius increasing from R in ≈ 3 R g to R in ≈ 8 R g, narrow Fe emission whose centroid decreases from 6.8 ± 0.1 keV to 6.3 ± 0.1 keV, and an increase in low-frequency (10−3–10−1 Hz) variability. Due to the high spin, we conclude that the source is likely to be a black hole rather than an NS, and we discuss physical interpretations of the low apparent luminosity as well as the narrow Fe emission.

Electron transfer kinetics between donor and acceptor molecules in electrolytes has been described by Marcus theory using reorganization energy (λ), electronic coupling (H), and free energy difference (ΔG°). In solution, the molecules can collide freely, while collision occurs only at the exposed area of the molecules when the donors or the acceptors are anchored onto an electrode, altering the values of λ and H. To date, these structural effects of electrode-bound molecules have not been considered in detail. To study geometrical effects, we fabricate TiO2 electrodes with nine different donor-(π-bridge)-acceptor type molecules and measure the kinetics of electron transfer from five different Co complexes in electrolytes. For densely adsorbed electrodes, the molecules with larger donor moieties have faster reduction kinetics and the kinetics are independent of the length of the π-bridge. When the amount of the adsorbed molecules is reduced, the kinetics become faster and the kinetics depend on the π-bridge length. These phenomena can be partially correlated to the increased exposed area of the molecules to the electrolyte. By fitting the data, we obtain lower λ values for lower dye-loading conditions, which is not expected if only the effect of solvent molecules is considered. Obtained H values with various geometries suggest that it is important not only to increase the exposed area but also to expose the point giving high H values to increase the kinetics. One example found is designing molecules with small molecular orbitals to increase H values, though this would also give large λ values.

Growth differentiation factor-9 (GDF-9), a member of the transforming growth factor-β (TGF-β) superfamily, is expressed exclusively in the oocyte within the ovary and plays essential roles in the ovarian function in mammals. However, a possible involvement of GDF-9 in canine ovarian physiology that has a unique ovulation process among mammals has not been studied. Interestingly, we have isolated two types of cDNA clones generated by an alternative splicing from a canine ovarian total RNA. The predominant long form cDNA shares a common precursor structure with GDF-9s in other species whereas the minor short form cDNA has a 172 amino acid truncation in the proregion. Using a transient expression system, we found that the long form cDNA has a defect in mature protein production whereas the short form cDNA readily produces mature protein. However, mutations at one or two N-glycosylation sites in the mature domain of the short form GDF-9 caused a loss in mature protein production. These results suggest that the prodomain and N-linked glycosylation of the mature domain regulate proper processing and secretion of canine GDF-9. Based on the biological functions of GDF-9, these characteristics of canine GDF-9 could be causatively linked to the unique ovulation process in the Canidae.

No abstract

The first enantioselective total synthesis of a bioactive lignanamide was achieved with high enantiomeric excess. Key synthetic steps include an organocatalytic enantioselective cyclopropanation and a Lewis-acid-mediated chirality-transferring 5-endo-tet-type cyclization that proceeds with a very high degree of stereoinduction. The proposed mechanism of the key reaction is supported by the experimental results. Based on these experimental results, the 5-endo-tet-type cyclization of a cyclopropylcarbinol proceeds predominantly via an S N 1 mechanism with high trans-selectivity, which arises from the steric hindrance of the neighboring substituent. Minor pathways include the anchimeric participation of (i) the oxygen atom of the benzoyl group in an S N 2 mechanism and/or (ii) a benzenecoordinated transition state in an S N 1-like mechanism.