Hamed, Abdelaaty
Abdel-Razek, Ahmed S.
Frese, Marcel
Stammler, Hans Georg
El-Haddad, Atef F.
Ibrahim, Tarek M. A.
Sewald, Norbert
Shaaban, Mohamed
Terretonin N (1), a new highly oxygenated and unique tetracyclic 6-hydroxymeroterpenoid, was isolated together with seven known compounds from the ethyl acetate extract of a solid-state fermented culture of Nocardiopsis sp. Their structures were elucidated by spectroscopic analysis. The structure and absolute configuration of 1 were unambiguously determined by X-ray crystallography. The isolation and taxonomic characterization of Nocardiopsis sp. is reported. The antimicrobial activity and cytotoxicity of the strain extract and compound 1 were studied using different microorganisms and a cervix carcinoma cell line, respectively.
Bobev, Nikolay
Gautason, Fridrik Freyr
Niehoff, Benjamin E.
van Muiden, Jesse
We find a new supersymmetric solution of type IIB supergravity which is the uplift of the GPPZ solution of maximal SO(6) gauged supergravity in five dimensions. This background is expected to be holographically dual to an N =3D 1* supersymmetric mass deformation of four-dimensional N =3D 4 SYM. The ten-dimensional solution is singular in the region corresponding to the IR regime of the dual gauge theory and we discuss the physics of the singularity in some detail.
Michael Krasnopolskia
Rüdiger W. Seidelb
Richard Goddardc
Jürgen Breidungc
Manuela V. Wintera
Anjana Devia
Roland A. Fischera
The crystal and molecular structure of (E)-N,N?dicyclohexylacetamidine (1) is described. Crystalline material of 1 was obtained by sublimation. Single-crystal X-ray analysis revealed a centrosymmetric triclinic structure (space group ) with six molecules in the asymmetric unit (Z?#xA0;= 6). The six crystallographically distinct molecules all exhibit an E-syn structure, but differ in the orientation of the cyclohexyl groups about the central acetamidine moiety. In the crystal, the molecules form polymeric helices via NH?N hydrogen bonds. The crystal structure comprises two crystallographically distinct helices of opposite handedness (P and M form). The characterisation of 1 in the solid-state is augmented by powder X-ray diffraction, infrared spectroscopy and thermal analysis. Density functional theory (DFT) structure optimisation and frequency calculation were performed at the B3LYP/cc-pVTZ level. The DFT results for the isolated molecule are compared with the experimental results for the solid-state.
In 2002, Luca and Walsh (J. Number Theory96 (2002) 152-173) solved the diophantine equation for all pairs (a,b) such that 2 <=3D a4 with 2|n. Here, the equation is also solved for the pairs (a,b)=3D(2,50),(4,49),(12,45),(13,76),(20,77),(28,49),(45,100). Lastly, we show that when b is even, the equation (an-1)(b2nan-1)=3Dx2 has no solutions n,x.
Wiggins, Kelly M.
Moerdyk, Jonathan P.
Bielawski, Christopher W.
The activation of molecules possessing homonuclear bonds (i.e., X-X, where X Br, O, S, or C) using a stable N, N'-diamidocarbene (DAC) is described. Exposing bromine to the DAC at 25 degrees C afforded a substituted tetrahydropyrimidinium salt in good yield (70%). In contrast, treatment of the DAC with benzoyl peroxide or various disulfides afforded the corresponding diamidoketal or diamidothioketal products, respectively, under mild conditions (25 degrees C) and in good yield (60-80%). Mechanistic and kinetic studies of the latter reactions were consistent with a concerted process involving the nucleophilic attack of the DAC on the aforementioned substrates. While the diamidoketal decomposed to the corresponding urea (91% yield) at 25 degrees C, the diamidothioketals produced a thiolate which induced rearrangement to the corresponding ring-opened thioesters (78-90% yield) at elevated temperatures (60 degrees C). The DAC also inserted into the C(O)-C(O) bond of cyclic and acyclic diones as well as the C(O)-CR bond of a cyclopropenone under mild conditions (25-60 degrees C); the corresponding products were subsequently isolated in good yield (75-90%).
The hybrid HF/DFT method B3LYP has been employed to investigate the geometrical and electronic structures of AuC (n) (n = 1-11) clusters. The properties such as geometrical parameters and electronic energies are determined for open-chain and cyclic species. Our results indicate that the open-chain structures with low spin states (doublet) are more stable than the cyclic ones for the small sizes clusters (n a parts per thousand currency sign 9), as the cluster sizes increase (n = 10, 11), the cyclic species are more stable. The incremental binding energies show a smooth even-odd alternation phenomenon for open-chain species, n-even (n is the numbers of C atom in the clusters) species have the stronger stabilities relative to the adjacent odd-numbered ones. In addition, the most favorable dissociation channels are determined by calculating the fragmentation energies accompanying various possible pathways. The studied clusters incline to be dissociated to Au + C (n) and AuC (n-3) + C-3 fragments.
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