Clostridium scindens American Type Culture Collection 35704 is capable of converting primary bile acids to toxic secondary bile acids, as well as converting glucocorticoids to androgens by side-chain cleavage. The molecular structure of the side-chain cleavage product of cortisol produced by C. scindens was determined to be 11β-hydroxyandrost-4-ene-3,17-dione (11β-OHA) by high-resolution mass spectrometry, 1H and 13C NMR spectroscopy, and X-ray crystallography. Using RNA-Seq technology, we identified a cortisol-inducible (∼1,000-fold) operon (desABCD) encoding at least one enzyme involved in anaerobic side-chain cleavage. The desC gene was cloned, overexpressed, purified, and found to encode a 20α-hydroxysteroid dehydrogenase (HSDH). This operon also encodes a putative “transketolase” (desAB) hypothesized to have steroid-17,20-desmolase/oxidase activity, and a possible corticosteroid transporter (desD). RNA-Seq data suggests that the two-carbon side chain of glucocorticords may feed into the pentose-phosphate pathway and are used as a carbon source. The 20α-HSDH is hypothesized to function as a metabolic “rheostat” controlling rates of side-chain cleavage. Phylogenetic analysis suggests this operon is rare in nature and the desC gene evolved from a gene encoding threonine dehydrogenase. The physiological effect of 11β-OHAD on the host or other gut microbes is currently unknown.
Pucker up! Metal-organic perovskites containing azetidinium cations, [(CH(2))(3)NH(2)][M(HCOO)(3)] (M = Mn, Cu, Zn), all show a structural phase transition, coupled with the freezing of the ring-puckering molecular motion of azetidinium cations, and an extremely large dielectric anomaly near room temperature. Molecular dynamics simulations showed the freezing of ring-puckering motion of the four-membered-ring azetidinium cation near room temperature.
Ferroelectric materials with dielectric constants larger than 10 4 over a broad temperature range near room temperature have great potential for technological applications. Such highly polarizable materials have been found only in the perovskite-related metal oxides called relaxors. [1][2][3] Recently, the development of molecule-based highly polarizable materials has attracted increasing interest. For example, antiferroelectric and ferroelectric porous coordination polymer crystals with guest water molecules, a ferroelectric crystal consisting of single-component molecules with very large spontaneous polarization, and an exotic ferroelectric crystal based on supramolecular rotators have been reported. [4,5] However, there has been no report of molecule-based solids with broad dielectric peaks higher than 10 4 . High polarizability in a material is usually related to its structural freedom, such as the orientational motion of the permanent electric dipole and the freezing of the optical lattice vibration. Since molecules generally possess large structural freedom, the realization of molecule-based materials exhibiting giant polarizability will be a promising challenge. One of the structural freedom characteristics of the molecules is the ring-puckering motion of four-memberedring molecules. It has been known for over half a century that the four-membered-ring molecules, such as trimethylene sulfide, trimethylene oxide, and cyclobutane as well as fivemembered-ring molecules with one double bond, such as 2,5-dihydrofurane, have double minimum potentials for the outof-plane bending deformation of the molecule and therefore exhibit characteristic ring-puckering molecular vibrations (Figure 1 a). [6][7][8] If the energy barrier between the double minima is sufficiently high, the molecule will adopt a nonplanar structure even at high temperatures. However, if the magnitude of the energy barrier is thermally accessible, it may be possible that the molecule adopts a nonplanar structure at low temperatures and a planar structure at high temperatures. In such a case, it would be possible for the crystal to exhibit a large dielectric susceptibility coupled with a cooperative change of the molecular conformation. However, to our knowledge, studies to develop molecule-based dielectrics utilizing the conformational freedom characteristics of the four-membered-ring molecule have not been reported. Herein we report a metal-organic perovskite containing four-membered-ring ammonium cations, [(CH 2 ) 3 [9] which has been regarded as a metal-organic perovskite ABX 3 (A = ammonium cation, B = M 2+ (M = Zn, Mn), and X = HCOO À ) with three-dimensional CaTiO 3 -like structure. [10][11][12] Similar to well-known inorganic ferroelectric and antiferroelectric perovskites such as BaTiO 3 and PbZrO 3 , these metal-organic perovskites have been reported to exhibit dielectric transitions. [10, 11] With the aim of utilizing the ring-puckering molecular motion in inducing the dielectric transition of metal-organic perovskite, we have prepare...
Ice one: A porous molecular crystal with guest water molecules in the channels—[La2Cu3{NH(CH2COO)2}6](H2O)n (see picture)—exhibits a distinct peak for the dielectric constant at 180 K (εr≈150) with the electric field parallel to the channel direction. This crystalline compound also shows a large enhancement of εr above 250 K and a characteristic antiferroelectric hysteresis coupled with a liquid–solid transition of the guest water molecules at around 350 K.
Traditional molecular conductors are composed of more than two chemical species and are characterized by low-dimensional electronic band structures. By contrast, the single-component molecular metals [M(tmdt)(2)] (M = Ni, Pt, Au; tmdt = trimethylenetetrathiafulvalenedithiolate) possess three-dimensional electronic structures that can be widely tuned by exchanging the central transition metal atom (M). In this study, the Cu atom was used to realize a new magnetic single-component molecular conductor exhibiting strong pi-d interactions. The crystal structure of [Cu(tmdt)(2)] was found to be essentially the same as those of the Ni, Pt, or Au-based systems with metallic states down to low temperature, but different from the structure of [Cu(dmdt)(2)] (dmdt = dimethyltetrathiafulvalenedithiolate) with its tetrahedrally coordinated dmdt ligands. A compressed pellet of microcrystals exhibited fairly high room-temperature conductivity (sigma(RT) approximately 7 S.cm(-1)), which increased almost linearly with pressure, reaching 110 S.cm(-1) at 15 kbar. This strongly suggests that the single crystal of [Cu(tmdt)(2)] is metallic at high pressure. Magnetic susceptibility measurements indicated one-dimensional Heisenberg behavior with |J| = 117 cm(-1) and an antiferromagnetic transition at 13 K. Density functional theory molecular orbital calculations revealed that the alpha-spin orbital of pdsigma(-) is distributed at the central part of the complex (CuS(4)), and alpha- and beta-sym-Lpi orbitals have almost the same energies and their spins are distributed mainly in the pdsigma(-) orbital. This is in contrast to the first single-component molecular metal [Ni(tmdt)(2)], which has stable metal bands formed from an almost degenerated sym-Lpi orbital (the highest occupied molecular orbital) and asym-Lpi(d) orbital (the lowest unoccupied molecular orbital). These results suggest that the alpha-pdsigma(-) state of [Cu(tmdt)(2)] exists just around the Fermi energy of the virtual metal band formed from the asym-Lpi(d) and sym-Lpi states. Thus, as expected, [Cu(tmdt)(2)] is a non-trivial single-component molecular conductor with pi-d multifrontier orbitals. In addition, ((n)Bu(4)N)(2)[Cu(tmdt)(2)] was synthesized, and its crystal structure was determined. Its Curie behavior (chi(rt) = 1.2 x 10(-3) emu mol(-1); C = 0.36 emu.K mol(-1)) indicates the existence of an isolated S = 1/2 spin on each dianionic molecule.
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