A Koszul complex over skew polynomial rings

We construct a Koszul complex in the category of left skew polynomial rings associated with a flat endomorphism that provides a finite free resolution of an ideal generated by a Koszul regular sequence.     

Indefinite Abstract Splines with a Quadratic Constraint

We study an extension to Krein spaces of the abstract interpolating spline problem in Hilbert spaces, introduced by M. Atteia. This is a quadratically constrained quadratic programming problem, where the objective function is not convex, while the equality constraint is sign indefinite. We characterize the existence of solutions and, if there are any, we describe the set of solutions as the union of a family of affine manifolds parallel to a fixed subspace, which depend on the original data.

     

Co-sensitized cells from Antarctic resources using Ag nanoparticles

In the present work, we explore in photoanodes of dye-sensitized solar cell (DSSC) the co-sensitization of the red protein phycoerythrin extracted from Antarctic algae with spherical silver nanoparticles between 10 and 200 nm and triangular nanoparticles of ~100 nm. We found that the order of addition of the sensitizers matters. Best results achieved for a sequential approach was phycoerythrin used as a dipping solution at the first step and nanoparticles at the second. We found that cell efficiency depends on the protein concentration, although no main differences detected with the nanoparticle shape or size. Our results show an average increase of 25% in the conversion efficiency values in the presence of nanoparticles.     

Double Insertion of Coordinated Phosphanylalkyne Ligands into a Pt−C6F5 Bond

Enhanced reactivity is shown by uncoordinated C≡C bonds in the proximity of a metal in phosphanylacetylene complexes. cis-[Pt(C₆F₅)₂(thf)₂] reacts with [M(C₆F₅)₂(PPh₂C≡CPh)₂] (M=Pt, Pd) to form binuclear complexes containing the novel 2,3-bis(diphenylphosphanyl)-1,3-butadien-1-yl bridging ligand. Substitution of the solvent ligands with, for example, PPh₂H (see picture) provides species that could be characterized by X-ray crystallography.     

Theoretical calculations on C30H12 bowl-shaped hydrocarbons: NMR shielding constants,stability, and aromaticity

Density Functional Theory (DFT) calculations at the B3LYP/6-31G* level have been performed on four bowl-shaped polyaromatic hydrocarbons of C₃₀H₁₂ molecular formula ( 1 – 4 ) showing C₃ ( 1 ), C_2v ( 2 and 4 ), and C_2h ( 3 ) symmetries. The geometrical and electronic properties of the compounds studied have been analyzed to explain their relative stability. NMR chemical shifts parameters for the atoms and Nucleus Independent Chemical Shifts (NICSs) for the rings were calculated using the GIAO method. The ¹³C and ¹H chemical shifts calculated are in very good agreement with the experimental data. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1412–1421, 1999     

Kinetic study of ruthenium(VI)‐catalyzed oxidation of 2‐butanol by alkaline hexacyanoferrate(III)

The oxidation kinetics of 2‐butanol by alkaline hexacyanoferrate(III) catalyzed by sodium ruthenate has been studied spectrophotometrically. The initial rates method was used for kinetic analysis. The reaction rate shows a fractional‐order in [hexacyanoferrate(III)] and [substrate] and a first‐order dependence on [Ru(VI)]. The dependence on [OH⁻] is rather more complicated. The kinetic data suggest a reaction mechanism involving two active catalytic species. Each one of these species forms an intermediate complex with the substrate. The attack of these complexes by hexacyanoferrate(III), in a slow step, produces ruthenium(V) complexes which are oxidized in subsequent steps to regenerate the catalyst species. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 1–9, 1999     

A Novel Domino Reaction: Cyclization of Alkynyl Sulfides by Reaction with IPy2BF4

Formation of polycyclic structures within a few minutes: The intramolecular cyclization of diynes, activated by a benzenesulfenyl substituent, upon reaction with IPy₂BF₄ proceeds as an efficient exo–endo coupling. A subsequent novel Friedel–Crafts-like ring closure provides the product [Eq. (1)]. Thus, intra- and intermolecular cyclizations can be carried out.