New Explanation for Ligand Bending in Transition Metal Tris(dithiolate) Complexes

The results of Fenske-Hall molecular orbital calculations are reported for the trigonal prismatic complexes Mo(S(2)C(2)H(2))(3) and Mo(S(2)C(6)H(4))(3). Both complexes exhibit a bend of the S-C-C-S ligand plane away from the S-Mo-S plane. A series of calculations which systematically follow the changes in electronic structure as the bend angle alpha is varied between 0 and 30 degrees indicates that the bend can be attributed to a second order Jahn-Teller distortion. The driving force for this distortion, which allows mixing between a set of ligand pi orbitals and the metal d(z)()()2 orbital, should be greatest for d(0) systems. In these systems the bent geometry leads to the stabilization of the doubly occupied HOMO. The driving force for ligand bending should be lower in systems having more or fewer electrons (e.g. Re(S(2)C(2)Ph(2))(3) or V(S(2)C(2)Ph(2))(3), respectively). While the steric bulk of the dithiolate ligands in the latter complexes may also influence the degree of ligand bending, this is probably a secondary effect.     

The nonaqueous,potentiometric titration of free hydrochloric acid in chloride-containing polymers

The thermal and/or catalytic degradation of chloride-containing polymers causes dehydrohalogenation which produces hydrochloric acid. A nonaqueous method has been developed for the termination of hydrochloric acid. The sample is dissolved in tetrahydrofuran and titrated potentiometrically with a standard tetrabutylammonium hydroxide solution in a 7.5% (V/V) aqueous tetrahydrofuran solution with a combination glass-calomel electrode. The method has a relative precision of ±3.7% at the 95% confidence limit and a sensitivity of 25 ppm HCI.     

Synthesis of some 5,6,7,8-tetrahydro-4-cinnolone derivatives and 1-methyl-3-arylacetyl-4,5,6,7-tetrahydroindazoles

2-Arylidene-3-oxo-2,3,4,5,6,7-hexahydrobenzo[b]furans 2 react with hydrazine hydrate to afford 5,6,7,8-tetrahydro-4-cinnolones. By methylation, these compounds gave the corresponding N-1 and N-2 methyl derivatives. The mesoionic compounds are obtained, accompanied by 3-arylacetyl-4,5,6,7-tetrahydroindazoles upon reaction of 2 with methylhydrazine.     

Influence of the coordination number of nitrogen on the structure of 6aλ4-thia-1,3,4,6-tetraazapentalenic systems. Crystal structure analyses of 3-(2-pyridylimino)-3H-[1,2,4]thiadiazolo[4,3-a]pyridine and its 1-methylated salt

Structural data were obtained by X-ray crystallography for the title compounds which show that they are essentially planar and exhibit an approximately linear N2-S1-N8 arrangement. In compound 3 the separation between the sulfur atom and the pyridine nitrogen atom (2.61 Å) is larger than the Huggins constant energy distance (2.58 Å), suggesting that there is little or no bonding between them. The methylated salt 4 , on the contrary, has a closer S…N(pyridine) distance (2.19 Å) with an estimated bond dissociation energy of 6 kcal/mole.     

Hétérocycles à fonction quinone. 7. Benzo[f]quinazolinediones-7,10 à action antitumorale potentielle

Few benzo[f]quinazoline-7,10-diones 4a-c are prepared by oxidation, with potassium nitrosodisulfonate, of the corresponding benzo[f]quinazolinamines, made by reduction of the nitro analogues which were obtained from 8-methoxybenzo[f]quinazolin-1(2H)-one. The compound 4a shows an interesting cytotoxicity.     

CU(II) SENSITIZES pBR322 PLASMID DNA TO INACTIVATION BY UV-B(280–315 nm)

Abstract— Copper(II), in the presence of UV-B radiation(280–315 nm), can generate single-strand breaks in the sugar-phosphate backbone of pBR322 plasmid DNA. A low level of single-strand backbone breaks occurs in the presence of Cu(II) alone, but UV-B irradiation increases the rate by the more than 100-fold. Concomitant with the damage to the DNA backbone is a loss of transforming activity. Oxygen is required for generation of the single-strand breaks but not for the loss of transforming activity. A DNA glycosylase (Fpg), which participates in the repair of certain DNA nitrogenous base damage, does not repair plasmid DNA damaged by Cu(II). The hydroxyl radical scavenging compound DMSO is only somewhat effective at protecting the physical and biological properties of the DNA. These results with Cu(II) are compared to those obtained previously with pBR322 plasmid DNA in the presence of Fe(III) and UV-A.     

Quantification of tryptamine in brain using high-performance liquid chromatography

The concentration of endogenously formed tryptamine in central nervous system tissue was determined after extraction into ethyl acetate, purification on a weak cation-exchange resin and analysis using high-performance liquid chromatography with fluorometric detection. Final chromatographic separation of this indoleamine was achieved using a muBondapak C18 reversed-phase column under isocratic conditions. Using this method, the concentration of tryptamine in the whole brain of normal rats was found to be 0.60 +/- 0.06 ng/g of tissue, while pretreatment with dl-p-chlorophenylalanine, tranylcypromine and l-tryptophan increased the concentration to 96.7 +/- 21.9 ng/g.     

Short-chain reactive probes as tools to unravel the Pseudomonas aeruginosa quorum sensing regulon

In recent years, the world has seen a troubling increase in antibiotic resistance among bacterial pathogens. In order to provide alternative strategies to combat bacterial infections, it is crucial deepen our understanding into the mechanisms that pathogens use to thrive in complex environments. Most bacteria use sophisticated chemical communication systems to sense their population density and coordinate gene expression in a collective manner, a process that is termed “quorum sensing” (QS). The human pathogen Pseudomonas aeruginosa uses several small molecules to regulate QS, and one of them is N-butyryl-l-homoserine lactone (C₄-HSL). Using an activity-based protein profiling (ABPP) strategy, we designed biomimetic probes with a photoreactive group and a ‘click’ tag as an analytical handle. Using these probes, we have identified previously uncharacterized proteins that are part of the P. aeruginosa QS network, and we uncovered an additional role for this natural autoinducer in the virulence regulon of P. aeruginosa, through its interaction with PhzB1/2 that results in inhibition of pyocyanin production.

Short-chain reactive probes can be used as tools to shed new light on virulence mechanisms in bacterial pathogens.     

One-step preparation of highly monodisperse micron-size particles in organic solvents

In this communication, we report the first simple and fast one-step method for synthesizing highly monodisperse micron-size PMMA particles in organic media through dispersion polymerization in the presence of PHSA (a polyhydroxyl-stearic-acid graft PMMA copolymer) as a stabilizer. There are two significant advantages of our method over earlier methods. First, by optimizing the composition of a solvent mixture of hexane and dodecane, we were able to increase the concentration of monomer up to 50-56% and obtain unusually large (up to 10 mum in diameter) PMMA particles. Second, by strictly controlling the nucleation time, we were able to make PMMA particles with a low polydispersity of around 1%, much lower than has ever before been achieved for such large particles. We also report an unusual apparent metastable state in the nucleation stage.