Structural studies of new chiral nickel (II) complexes of cyclams: The influence of a systematically varied number of amide groups

The synthesis and structures of nickel (II) complexes of chiral cyclams originating from l-proline are presented. Upon addition of nickel acteate, oxocyclams having amide groups underwent deprotonation forming distorted square-planar complexes. In the case of the all-amine analogue a six-coordinate octahedral complex is formed.     

Complexes of heteroscorpionate trispyrazolylborate ligands. Part VI. Carboxylate induced conversion of mono-ligand Tp′M(L) into bis-ligand Tp′2M complexes (M=Co(II) and Cu(II))

A series of homoleptic complexes of hexacoordinate cobalt(II) and copper(II) complexes with 3,5-disubstituted homo- and heteroscorpionate tris(pyrazolyl)borate anionic ligands (Tp′) were synthesized, i.e. bis[hydrotris(3-phenyl,5-methylpyrazol-1-yl)borato]cobalt(II), bis[hydrobis(3-phenyl,5-methylpyrazol-1-yl)(3-methyl,5-phenylpyrazol-1-yl)borato]cobalt(II) and bis[hydrobis(3-phenyl,5-methylpyrazol-1-yl)(3-methyl,5-phenylpyrazol-1-yl)borato]copper(II) and their structures were elucidated crystallographically. The complexes were also formed spontaneously during attempted metathesis of the corresponding Tp′M(NCS) complexes into Tp′M(OOCCH(OH)CH₃) complexes. In the case of the analogous conversion applied for the thiocyanato [hydrobis(3-phenyl,5-methylpyrazol-1-yl)(3,5-dimethylpyrazol-1-yl)boratocobalt(II) complex with sodium carboxylates (lactate, pyruvate and 2-hydroxybutyrate), the cross-transfer of pyrazolyl residues between starting anionic ligands was observed resulting in formation of bis-ligand homo- and heteroleptic Tp′CoTp″ complexes, where Tp′, Tp″ were tris(pyrazolyl)borates composed of n 3(5)-phenyl,5(3)-methylpyrazolyl and (3−n) 3,5-dimethylpyrazolyl residues (n=0–3) identified by mass spectrometry. Metathesis of thiocyanate in thiocyanato hydrotris(3-phenyl,5-methylpyrazol-1-yl)boratocobalt(II) into pyruvate led to the isolation of stable the pyruvato hydrotris(3-phenyl,5-methylpyrazol-1-yl)boratocobalt(II) complex, the structure of which was determined crystallographically. The Tp′ ligands are η³ coordinated to metal ions in every case, whereas the pyruvate anion is coordinated through carboxylate and carbonyl oxygen atoms to the cobalt center. Two rotational isomers distinguishable by ¹H NMR spectroscopy for the hexacoordinate bis[hydrobis(3-phenyl,5-methylpyrazol-1-yl)(3-methyl,5-phenylpyrazol-1-yl)borato]cobalt(II) complex were detected in solution.     

Two Intercalation Mechanisms of Oxazole Yellow Dimer (YOYO-1) into DNA

The oxazole yellow dye, YOYO-1 (a symmetric homodimer), is a commonly used molecule for staining DNA. We applied the brightness analysis to study the intercalation of YOYO-1 into the DNA. We distinguished two binding modes of the dye to dsDNA: mono-intercalation and bis-intercalation. Bis-intercalation consists of two consecutive mono-intercalation steps, characterised by two distinct equilibrium constants (with the average number of base pair per binding site equals 3.5): K1=3.36±0.43×107M−1 and K2=1.90±0.61×105M−1, respectively. Mono-intercalation dominates at high concentrations of YOYO-1. Bis-intercalation occurs at low concentrations.     

Luminescent cellulose fibers activated by Eu3+-doped nanoparticles

UV- active cellulose fibers were obtained by dry-wet method spinning an 8?% by weight α-cellulose solution in N-methylomorpholine-N-oxide (NMMO) modified by europium-doped gadolinium oxyfluoride Gd₄O₃F₆:Eu³⁺ containing 5?mol (%) of the dopant. Photoluminescent nanoparticles were introduced in the in powder form into a polymer matrix during the process of cellulose dissolution in NMMO. The dependencies of emission intensity on excitation energy and the concentration of Gd₄O₃F₆:Eu³⁺ nanoparticles in the final cellulosic products were examined by photoluminescence spectroscopy (excitation and emission). The fiber structure was studied by X-ray powder diffraction analysis. The size and dispersity of the nanoparticles in the polymer matrix were evaluated using scanning electron microscopy and X-ray microanalysis. The influence of different concentration particles (in the range from 0.5 to 5?% by weight) on the mechanical properties of the fibers, such as tenacity and elongation at break, were determined.     

Inequalities for convex functions via Stieltjes integral

We present a method of proving inequalities for convex functions with use of Stieltjes integral. First, we show how some well-known inequalities can be obtained, and then we show how new inequalities and stronger versions of some existing results can be obtained.     

Absolute configurations of C34 and C35 of antibiotic niphimycin A

The relative configurations of four stereogenic centers of the C33‐C42 fragment of niphimycin A were assigned as 2S*, 3R*, 4S* and 6S*, based upon ¹H NMR analysis with double‐quantum filtered COSY and nuclear Overhauser spectroscopy experiments. These data were then correlated with absolute configurations at C36 and C38 of niphimycin A, which were declared previously as 36S and 38S [3]. This allowed for the assignment of the absolute configurations at C34 and C35 of niphimycin A as 34S and 35R. Copyright © 2012 John Wiley & Sons, Ltd.     

Oxidation properties of β-substituted pyrroles

Pyrroles represent building blocks of conjugated poly(heterocycles) which, as organic conductors, are potential materials for organic electronics. Oxidation of β-substituted pyrroles constitutes an important first step in the process of electropolymerization. Ionization energy and the electron spin density distribution are two the most important properties regarding monomers. These properties are studied as a function of electron-withdrawing and electron-donating substituents of pyrrole ring. Evolution of molecular structure, nature of bonding, and electronic density are studied as an effect of ionization process.