Ito, Jun-ichi
Crestani, Marco G.
Bailey, Brad C.
Gao, Xinfeng
Mindiola, Daniel J.
The titanium alkylidene-triflate complex (PNP)Ti=(CHBu)-Bu-t(OTf) was found to promote N-N bond cleavage of 9-diazofluorene and ditolyldiazomethane to give the imido complexes, (PNP)Ti=N[C13H9](OTf) (1) and (PNP)Ti=N[CHtolyl(2)](OTF) (2), respectively. The molecular structure of 2 was determined by single-crystal X-ray diffraction studies. Along with imido formation leading to 1 and 2, the alkylidene Ti=(CHBu)-Bu-t ligand in (PNP)Ti=(CHBu)-Bu-t(OTf) was found to eliminate with the alpha-N atom of the diazoalkane to form the nitrile (NCBu)-Bu-t, which was confirmed by a combination of H-1 NMR spectroscopy and GC-MS. The reaction mechanism of the N-N bond cleavage promoted by the reactive Ti=(CHBu)-Bu-t ligand is also discussed. (C) 2014 Elsevier Ltd. All rights reserved.
Cilleruelo, Javier
Kumchev, Angel
Luca, Florian
Rue, Juanjo
Shparlinski, Igor E.
We give various results about the distribution of the sequence {a(n)/n}(n >= 1) modulo 1, where a >= 2 is a fixed integer. In particular, we find an explicit infinite subsequence A such that {a(n)/n}(n is an element of A) is uniformly distributed modulo 1. Also we show that for any constant c > 0 and a sufficiently large N, the fractional parts of the first N terms of this sequence hit every interval subset of [0, 1] of length vertical bar vertical bar >= c N-0.475.
O'Donovan, Daniel H.
Kelly, Brendan
Diez-Cecilia, Elena
Kitson, Martin
Rozas, Isabel
The N-aryl- and N-acylguanidine structural motifs are essential for the function of several important classes of molecules, including pharmaceuticals, catalysts and natural products. Compounds combining both motifs can exist as different isomers due to tautomerism within the guanidine subunit, E/Z isomerism with reference to the guanidine double bond, and conformational isomerism. This complex phenomenon results in unresolved broad signal NMR spectra that strongly complicate the characterisation of these derivatives. Hence, the present study examines isomerism in N,N'-bis-aryl-N ''-acylguanidines using low temperature NMR spectroscopy in tandem with Density Functional Theory (DFT), Natural Bond Analysis (NBO) and the Gauge-Invariant Atomic Orbital (GIAO) approach for calculating the NMR chemical shifts associated with each isomer. It was found that the structural preference of these compounds is strongly influenced by intramolecular hydrogen bond (IMHB) effects.
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.