Developments in the Coordination Chemistry of Dicoordinate Phosphenium Ion Ligands

Abstract

Phosphenium ion ligands display synergic [sgrave]-donor, σ-acceptor properties which resemble other small molecules and the coordination chemistry of X₂P⁺ ligands is compared here with NO and SO₂.     

Rotating ellipses of varying shape

This article describes an investigation carried out while the second author was an undergraduate. The article gives an account of the way the work evolved, to give insight into the learning processes, as well as the mathematical issues encountered.     

A non‐natural dinucleotide containing an isomeric l‐related deoxy­nucleoside: dinucleotide inhibitors of anti‐HIV integrase activity

The first X‐ray crystal structure of a non‐natural dinucleotide, 5′‐O‐phosphoryl‐1′‐deoxy‐2′‐isoadenylyl‐(3′ → 5′)‐cytidine 6.5‐hydrate (pIsodApC), C₁₉H₂₆N₈O₁₃P₂·6.5H₂O, belonging to a family of dinucleotides that contain an isomeric nucleoside component, is described. A complex system of hydrogen bonds between water mol­ecules and various sites on the dinucleotide was found. All H atoms were located from electron‐density difference maps, which allowed identification of protonation sites. Compounds of this family have been found to bind at the active site of HIV integrase and to be inhibitors of this key viral enzyme. These dinucleotides are completely resistant to cleavage by exonucleases; an abnormal dihedral angle twist in an inter­nucleotide phosphate bond revealed in the X‐ray crystal structure may be contributing to this unusual stability towards nucleases.     

A numerical solution of the nonlinear wave resistance problem for simple shaped submerged bodies

Summary This paper presents a numerical method to compute the nonlinear wave resistance of a body, submerged in a free stream of infinite depth. The solution is given in the form of a potential of single layer and the nonlinear boundary conditions on the free surface are fulfilled by means of an iterative procedure. Results are shown for the 2-D case of an elliptical cylinder and for the 3-D case of prolate spheroids. All the presented results are discussed taking into account some experimental data and analytical solutions available in literature.

---

Sommario In questo lavoro viene sviluppato un metodo per il calcolo della resistenza ondosa di corpi immersi bidimensionali e tridimensionali, tenendo conto della non linearità delle condizioni sulla superficie libera. La soluzione cercata è posta nella forma di potenziale di strato semplice e la non linearità presente nelle condizioni al contorno viene trattata con un procedimento iterativo. Vengono presentati dei risultati numerici relativi al caso bidimensionale di un cilindro ellittico ed al caso tridimensionale di sferoidi prolati di diversa eccentricità. I risultati vengono discussi in relazione a soluzioni analitiche e dati sperimentali ottenuti dalla letteratura.

     

Exploring the interaction of ruthenium(II) polypyridyl complexes with DNA using single-molecule techniques

Here we explore DNA binding by a family of ruthenium(II) polypyridyl complexes using an atomic force microscope (AFM) and optical tweezers. We demonstrate using AFM that Ru(bpy)2dppz2+ intercalates into DNA (K(b) = 1.5 x 10(5) M(-1)), as does its close relative Ru(bpy)2dppx2+ (K(b) = 1.5 x 10(5) M(-1)). However, intercalation by Ru(phen)3(2+) and other Ru(II) complexes with K(b) values lower than that of Ru(bpy)2dppz2+ is difficult to determine using AFM because of competing aggregation and surface-binding phenomena. At the high Ru(II) concentrations required to evaluate intercalation, most of the DNA strands acquire a twisted, curled conformation that is impossible to measure accurately. The condensation of DNA on mica in the presence of polycations is well known, but it clearly precludes the accurate assessment by AFM of DNA intercalation by most Ru(II) complexes, though not by ethidium bromide and other monovalent intercalators. When stretching individual DNA molecules using optical tweezers, the same limitation on high metal concentration does not exist. Using optical tweezers, we show that Ru(phen)2dppz2+ intercalates avidly (K(b) = 3.2 x 10(6) M(-1)) whereas Ru(bpy)3(2+) does not intercalate, even at micromolar ruthenium concentrations. Ru(phen)3(2+) is shown to intercalate weakly (i.e., at micromolar concentrations (K(b) = 8.8 x 10(3) M(-1))). The distinct differences in DNA stretching behavior between Ru(phen)3(2+) and Ru(bpy)3(2+) clearly illustrate that intercalation can be distinguished from groove binding by pulling the DNA with optical tweezers. Our results demonstrate both the benefits and challenges of two single-molecule methods of exploring DNA binding and help to elucidate the mode of binding of Ru(phen)3(2+).     

Synthesis, structural and spectroscopic characterization, catalytic properties, and thermal transformations of new cyclic di- and trisiloxanediolato tantalum complexes

The reaction between Ta(OEt)5 and 1,1,3,3-tetramethyl-1,3-disiloxanediol, (HOSiMe2OSiMe2OH), leads to new siloxy complexes in which the dimeric nature of Ta(OEt)5 is maintained with both bridging ethoxide and disiloxanediolato bridges. With equal amounts of the reagents, two terminal OEt groups are replaced to form [Ta(OEt)2]2(mu-OEt)2(mu-OSiMe2OSiMe2O)2, 1, whereas with an excess of diol, the remaining terminal OEt groups are also replaced but with a trisiloxanediolato unit to form [Ta(OSiMe2OSiMe2OSiMe2O)]2(mu-OEt)2(mu-OSiMe2OSiMe2O)2, 2. Complexes 1 and 2 catalyze the transformation of HOSiMe2OSiMe2OH to polysiloxanes. Thermal treatment of 1 results in the formation of a 1:2 mixture of Ta2O5/SiO2; no new phases are observed. The molecular structures of 1 and 2 are confirmed by X-ray crystallography.     

Ni-GDC microtubular cermets

Ni-GDC cermet tubes (~ 3 mm inside diameter, 0.3–0.4 mm wall thickness and ～ 100 mm in length) with different amounts of porosity have been prepared by sintering of NiO-Ce_0.9Gd_0.1O_1.95 (NiO-GDC) nanopowders and further reduction. The NiO-GDC nanopowders were synthesized by chemical route and the different pore density was obtained by modifying the processing conditions (calcining and adjustment of carbonous remains).Ni-GDC cermets were obtained from the sintered NiO-GDC composites using reduction treatment at 700 °C for 3 h in reducing atmosphere (5 vol.% H₂–95 vol.% Ar). After the reduction process, tubes with 25–32% porosity were obtained. Gas permeability and Hg porosimetry studies were used to evaluate permeability, pore distribution and pore density. Electrical conductivity studies of the cermets were also performed.