Polymorphic forms of lupane triterpenoid betulonic aldehyde (betulonal)

The lupane triterpenoid betulonic aldehyde [also known as betulonal; systematic name: lup‐20(29)‐en‐28‐al‐3‐one, C₃₀H₄₆O₂] is a product of betulin oxidation. Crystals were obtained from hexane [form (I)] and dimethyl sulfoxide [form (II)] solutions. Forms (I) and (II) are both orthorhombic. The molecular geometric parameters in the two forms are similar, but the structures are different with respect to the crystal packing. Polymorph (I) contains two independent molecules in the asymmetric unit, while polymorph (II) contains only one molecule, which has a disordered aldehyde group [the disorder ratio is 0.769 (4):0.231 (4)]. In each molecule, the six‐membered rings have chair conformations, whereas the cyclopentane ring in each molecule adopts an envelope conformation. All the rings in the lupane nucleus are trans‐fused. The extended structures of both polymorphs are stabilized by weak intermolecular C—H...O and van der Waals interactions. Weak intramolecular C—H...O interactions are also observed.     

Applications of Approximation Theory to thermographic images in earthquake engineering

In this paper we show some new applications of the approximation theory, by means of the multivariate sampling Kantorovich operators, to thermographic images in seismic engineering. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Covalent anionic copolymer coatings with tunable electroosmotic flow for optimization of capillary electrophoretic separations

We present a method for finely adjustable electroosmotic flow (EOF) velocity in cathodic direction for the optimization of separations in capillary electrophoresis. To this end, we use surface modification of the separation fused silica capillary by the covalently attached copolymer of acrylamide (AM) and 2-acrylamido-2-methyl-1-propanesulfonate (AMPS), that is, poly(AM-co-AMPS) or PAMAMPS. Coatings were formed by the in-capillary polymerization of a mixture of the neutral AM and anionic AMPS monomers premixed in various ratios in order to control the charge density of the copolymer. EOF mobility varies in the 0 to ∼40 × 10⁻⁹ m² V⁻¹ s⁻¹ interval for PAMAMPS coatings ranging from 0 to 60 mol.% of charged AMPS monomer. For EOF in PAMAMPS-treated capillaries, we observed (i) a negligible dependence on pH in the 2–10 interval, (ii) a minor variance among background electrolytes (BGEs) in function of their components and (iii) its standard decrease with increasing ionic strength of the BGE. Interest in variable cathodic EOF was demonstrated by the amelioration of separation of two kinds of isomeric anionic analytes, that is, monosaccharides phosphates and helquat enantiomers, in counter-EOF mode.     

Fingerprinting pre-historical symbolic artefacts by a non-destructive methodological approach

Journal of Radioanalytical and Nuclear Chemistry - A contribution to the discussion about Vila Nova de São Pedro (VNSP) as a production centre of symbolic lithic artefacts, the origin of raw...     

Synthesis,structural characterization and anticancer properties of p-cymene Ru(II) complexes with 2-(N-methyl-1H-1,2,4-triazol-3-yl)pyridines

Transition Metal Chemistry - The structures of new p-cymene Ru(II) complexes with 2-(1-methyl-1H-1,2,4-triazol-3-yl)pyridine and 2-(1-methyl-1H-1,2,4-triazol-5-yl)pyridine were established based on...     

Late-Stage Modification of Aminoglycoside Antibiotics Overcomes Bacterial Resistance Mediated by APH(3’) Kinases

The continuous emergence of antimicrobial resistance is causing a threat to patients infected by multidrug-resistant pathogens. In particular, the clinical use of aminoglycoside antibiotics, broad-spectrum antibacterials of last resort, is limited due to rising bacterial resistance. One of the major resistance mechanisms in Gram-positive and Gram-negative bacteria is phosphorylation of these amino sugars at the 3’-position by O-phosphotransferases [APH(3’)s]. Structural alteration of these antibiotics at the 3’-position would be an obvious strategy to tackle this resistance mechanism. However, the access to such derivatives requires cumbersome multi-step synthesis, which is not appealing for pharma industry in this low-return-on-investment market. To overcome this obstacle and combat bacterial resistance mediated by APH(3’)s, we introduce a novel regioselective modification of aminoglycosides in the 3’-position via palladium-catalyzed oxidation. To underline the effectiveness of our method for structural modification of aminoglycosides, we have developed two novel antibiotic candidates overcoming APH(3’)s-mediated resistance employing only four synthetic steps.     

Binding,Release and Functionalization of Intact Pnictogen Tetrahedra Coordinated to Dicopper Complexes

The bridging MeCN ligand in the dicopper(I) complexes [(DPFN)Cu₂(μ,η¹ : η¹-MeCN)][X]₂ (X=weakly coordinating anion, NTf₂ ( 1 a ), FAl[OC₆F₁₀(C₆F₅)]₃ ( 1 b ), Al[OC(CF₃)₃]₄ ( 1 c )) was replaced by white phosphorus (P₄) or yellow arsenic (As₄) to yield [(DPFN)Cu₂(μ,η² : η²-E₄)][X]₂ (E=P ( 2 a – c ), As ( 3 a – c )). The molecular structures in the solid state reveal novel coordination modes for E₄ tetrahedra bonded to coinage metal ions. Experimental data and quantum chemical computations provide information concerning perturbations to the bonding in coordinated E₄ tetrahedra. Reactions with N-heterocyclic carbenes (NHCs) led to replacement of the E₄ tetrahedra with release of P₄ or As₄ and formation of [(DPFN)Cu₂(μ,η¹ : η¹-^MeNHC)][X]₂ ( 4 a,b ) or to an opening of one E−E bond leading to an unusual E₄ butterfly structural motif in [(DPFN)Cu₂(μ,η¹ : η¹-E₄^DippNHC)][X]₂ (E=P ( 5 a,b ), E=As ( 6 )). With a cyclic alkyl amino carbene (^EtCAAC), cleavage of two As−As bonds was observed to give two isomers of [(DPFN)Cu₂(μ,η² : η²-As₄^EtCAAC)][X]₂ ( 7 a,b ) with an unusual As₄-triangle+1 unit.     

An Anionic Amido-Substituted Seven-Vertex Siliconoid Cluster

The silanide [Si₄{N(SiMe₃)Dipp}₃]⁻ ( 1 ) transforms into the anionic siliconoid cluster [Si₇{N(SiMe₃)Dipp}₃]⁻ ( 2 ) with four unsubstituted silicon atoms as a contact ion pair with [K([18]crown-6)] in C₆D₆ at room temperature within five weeks. Anion 2 was investigated by natural population analysis and visualization of intrinsic atomic orbitals. Magnetically induced current-density calculations of 2 revealed two distinct strong diatropic vortices that sum up in one direction and create a strongly shielded apical silicon atom in 2 .