Urea Derivatives as Functional Molecules: Supramolecular Capsules,Supramolecular Polymers,Supramolecular Gels,Artificial Hosts,and Catalysts

Urea, which has both hydrogen bond acceptor and donor moieties, is an ideal structure for a supramolecular synthon. Various supramolecules having ureido group(s) have been widely developed. This article summarizes recent developments of urea derivatives that exhibit various functions: i) supramolecular capsules that form discrete urea–urea intermolecular hydrogen bonds, ii) supramolecular polymers that form continuous urea–urea intermolecular hydrogen bonds, iii) supramolecular gels that form continuous urea–urea intermolecular hydrogen bonds, iv) artificial host molecules based on the molecular recognition ability of the ureido group, and v) catalytic reactions developed by utilizing the molecular recognition ability of the ureido group.     

Bioreduction of Acetophenone Derivatives by Red Marine Algae Bostrychia radicans and B. tenella,and Marine Bacteria Associated

The biocatalytic reduction of acetophenone derivatives was exploited by using algal biomass from Bostrychia radicans and B. tenella producing exclusively (S)‐2‐phenylethanols with high enantiomeric excess (>99% ee). Bacterial populations associated with algal biomass were identified as the Bacillus genus. This report deals with the first investigations involving the use of marine bacteria associated with B. radicans and B. tenella marine algae for the biocatalytic reduction of acetophenone derivatives.     

Chemistry of renieramycins. Part 13: Isolation and structure of stabilized renieramycin type derivatives,renieramycins W–Y,from Philippine blue sponge Xestospongia sp., pretreated with potassium cyanide

Three new bistetrahydroisoquinoline marine natural products, renieramycins W (1w), X (1x), and Y (1y), along with two known renieramycins M (1m) and T (1t), were isolated from the pretreated Philippine blue sponge Xestospongia sp. with KCN and their structures were elucidated by comparing their spectral data with those of 1m, 1t, and N-acetylsafracin B (11). Renieramycins W (1w) and X (1x) are the first examples of tiglic acid ester derivatives at the C-1 side chain. Renieramycin Y (1y) possesses a characteristic substitution pattern in A-ring and isolation of it from marine organism strongly evidences to link the possible precursor 3-hydroxy-5-methyl-O-methyltyrosine with both renieramycin and ecteinascidin marine natural products.     

Total synthesis of ent-dihydrocorynantheol by using a proline-catalyzed asymmetric addition reaction

[reaction: see text] 9-Tosyl-3,4-dihydro-beta-carboline reacted with 3-ethyl-3-buten-2-one in the presence of (S)-proline to give (3R,12bR)-3-ethyl-12-tosyl-3,4,6,7,8,9,10,11,12,12b-decahydro-1H-indolo[2,3-a]quinolizin-2-one in complete enantio- and diastereoselectivity. The compound thus obtained was readily transformed to ent-dihydrocorynantheol in three steps.     

Chemical profile and biological potential of non-polar fractions from Centroceras clavulatum (C. Agardh) Montagne (Ceramiales, Rhodophyta)

The present study reports the Gas Chromatography-Mass Spectrometry (GC-MS) evaluation of the hexanes and dichloromethane fractions from extracts of the red alga Centroceras clavulatum (C. Agardh) Montagne. Twenty three compounds were identified, totaling ca. 42% of both fractions (0.18 g mass extract). The main constituents of the fractions were hexadecanoic acid (17.6%) and pentadecanoic acid (15.9%). Several secondary metabolites with interesting biological activity, such as (-)-loliolide, neophytadiene, phytol were identified. In addition, several classes of secondary metabolites, including phenolic compounds (e.g., phenylacetic acid), terpene derivatives, fatty acids, halogenated compound (e.g., 2-chlorocyclohexenol), lignoids, steroids, esters, amides (e.g., hexadecanamide), ketones, carboxylic acids, aldehydes and alcohols were observed. The occurrence of several of these structural classes is described for the first time in this species. The same fractions analyzed by GC-MS, and a separate set of polar fractions, were evaluated against two life cycle stages (epimastigote and trypomastigote forms) of the protozoan Trypanosoma cruzi and against phytopatogenic fungi Cladosporium cladosporiodes and C. sphaerospermum. The dichloromethane fraction was active against both T. cruzi forms (epimastigote IC(50) = 19.1 μg.mL-1 and trypomastigote IC(50) = 76.2 μg.mL-1). The hexanes and ethyl acetate fractions also displayed activity against both fungi species (200 μg) by TLC-bioautography.     

Ultrahigh-resolution laser photoemission study of URu2Si2 across the hidden-order transition

We have studied the electronic structures of URu₂Si₂ employing ultrahigh-resolution laser angle-resolved photoemission spectroscopy. The change of photoemission spectra is investigated across the hidden-order transition, and the emergence of a narrow band is clearly observed near the Fermi level for both (π,0) and (π,π) directions. In addition, it is shown that tuning of light's polarization allows the signal of a hole-like dispersive feature to enhance. These observations prove that laser angle-resolved photoemission spectroscopy is an effective tool for studying the evolution of electronic structures across the hidden-order transition in URu₂Si₂.     

Angle-resolved photoemission study of the cobalt oxide superconductor Na(x)CoO(2) x yH(2)O: observation of the Fermi surface

The cobalt oxide superconductor Na(x)CoO(2) x yH(2)O is studied by angle-resolved photoemission spectroscopy. We report the Fermi surface (FS) topology and electronic structure near the Fermi level (E(F)) in the normal state of Na(x)CoO(2) x yH(2)O. Our result indicates the presence of the hexagonal FS centered at the Gamma point, while the small pocket FSs along Gamma-K direction are absent, similar to Na(x)CoO(2). The top of the e(g)(') band, which is expected in band calculations to form the small pocket FSs, extends to within approximately 30 meV below E(F), closer to E(F) than in Na(x)CoO(2). We discuss its possible role in superconductivity, comparing with other experimental and theoretical results.     

Definitive experimental evidence for two-band superconductivity in MgB2

The superconducting-gap of MgB2 has been studied by high-resolution angle-resolved photoemission spectroscopy. The results show that superconducting gaps with values of 5.5 and 2.2 meV open on the sigma band and the pi band, respectively, but both the gaps close at the bulk transition temperature, providing a definitive experimental evidence for the two-band superconductivity with strong interband pairing interaction in MgB2. The experiments validate the role of k-dependent electron-phonon coupling as the origin of multiple-gap superconductivity as well as the high transition temperature of MgB2.     

Distribution of suprofen in rats of both sexes

The tissue distribution of 3H-labeled DL-2-(4-(2-thienylcarbonyl) phenyl) propionic acid (suprofen) after po administration was studied in male, female, and pregnant rats by radiometry. The only tissues with concentrations comparable to plasma levels were those involved in metabolism and excretion (liver and kidney), except for the gastrointestinal tract, and all other tissue levels were very low. In pregnant rats, radioactivity crossed the blood-placenta barrier to a moderate extent and low concentrations were found in fetuses. Radioactivity disappeared from most tissues of male, female, and pregnant rats at rates similar to that from plasma and no appreciable radioactivity was found in rat tissues 24 h after dosing.     

Ultrahigh-resolution photoemission spectroscopy of Ni borocarbides: direct observation of the superconducting gap and a change in gap anisotropy by impurity

We have performed ultrahigh-resolution photoemission spectroscopy of Y(Ni1-xPtx)2B2C ( x = 0.0 and 0.2) in order to study the changes in the density of states across the superconducting transition. Because of a drastic increase in energy resolution, we clearly observe the opening of superconducting gaps across T(c) in both compounds. Furthermore, we find a small but significant difference in the superconducting-state spectral shape. This can be explained in terms of reduction in gap anisotropy by introducing impurities and provides spectroscopic evidence for an anisotropic s-wave gap in YNi2B2C.