Nitrile ylide dimerization: investigation of the carbene reactivity of nitrile ylides

A series of novel hexaaryl diazatrienes 5 ("nitrile ylide dimers") were synthesized directly from the corresponding diaryl ketimines 12 and dichlorotoluenes 13 in a facile one-pot synthesis. The carbene character of the nitrile ylides was investigated by varying the substituents on the aromatic ring adjacent to the carbene center. The isolation of the corresponding carbene dimers as stable crystalline materials with absorption maxima (lambda(max)) from 363 to 422 nm was shown to be promoted by the absence of strongly electron-withdrawing substituents. The crystal structures indicate that the E-isomers were isolated when phenyl, 3-methylphenyl, and 3-chlorophenyl substituents are present at the carbene carbon; the Z-isomer was isolated when the more sterically hindered 2,4,6-trimethylphenyl substituent (Mes) is present. The (1)H NMR spectra of the E-isomers demonstrate the nonequivalence of the aromatic rings, in which two of the aromatic rings of the imine moiety are pseudoaxial and the remaining aromatic rings are pseudoequatorial. The reactions proceed via the intermediate nitrile ylides 1 generated by the base-promoted 1,1-elimination of HCl from the intermediate chloroimine 14. The nitrile ylide was also generated by 1,3-elimination of HCl from the imidoyl chloride 18, confirming common pathways via the nitrile ylide as the dimer products obtained from these different routes were identical. The strongly electron-withdrawing 4-nitrophenyl substituent promotes the linear carbanion character of the 1,3-dipole and no dimer is formed.     

Understanding the factors controlling the photo-oxidation of natural DNA by enantiomerically pure intercalating ruthenium polypyridyl complexes through TA/TRIR studies with polydeoxynucleotides and mixed sequence oligodeoxynucleotides

Ruthenium polypyridyl complexes which can sensitise the photo-oxidation of nucleic acids and other biological molecules show potential for photo-therapeutic applications. In this article a combination of transient visible absorption (TrA) and time-resolved infra-red (TRIR) spectroscopy are used to compare the photo-oxidation of guanine by the enantiomers of [Ru(TAP)₂(dppz)]²⁺ in both polymeric {poly(dG-dC), poly(dA-dT) and natural DNA} and small mixed-sequence duplex-forming oligodeoxynucleotides. The products of electron transfer are readily monitored by the appearance of a characteristic TRIR band centred at ca. 1700 cm⁻¹ for the guanine radical cation and a band centered at ca. 515 nm in the TrA for the reduced ruthenium complex. It is found that efficient electron transfer requires that the complex be intercalated at a G-C base-pair containing site. Significantly, changes in the nucleobase vibrations of the TRIR spectra induced by the bound excited state before electron transfer takes place are used to identify preferred intercalation sites in mixed-sequence oligodeoxynucleotides and natural DNA. Interestingly, with natural DNA, while it is found that quenching is inefficient in the picosecond range, a slower electron transfer process occurs, which is not found with the mixed-sequence duplex-forming oligodeoxynucleotides studied.

Efficient electron transfer requires the complex to be intercalated at a G-C base-pair. Identification of preferred intercalation sites is achieved by TRIR monitoring of the nucleobase vibrations before electron transfer.     

Some generators for the algebra of n×n matrices

In this note, we show how the algebra of n×n matrices over a field can be generated by a pair of matrices A B, where A is an arbitrary nonscalar matrix and B can be chosen so that there is the maximum degree of linear independence between the higher commutators of B with A.     

Courtyard acoustics

The acoustic environment of courtyard housing has been studied and the ability of the courtyard to attenuate external noise examined. A scale-model was used to study the effect of the ground treatment, the source and the receiver locations, the depth of the courtyard and the position and arrangement of openings in the walls.Experimental results obtained from the model, together with a simple procedure for predicting the sound pressure levels inside the courtyard, are presented.     

Preparation of a clay-modified carbon paste electrode based on 2-thiazoline-2-thiol-hexadecylammonium sorption for the sensitive determination of mercury.

A montmorillonite from Wyoming-USA was used to prepare an organo-clay complex, named 2-thiazoline-2-thiol-hexadecyltrimethylammonium-clay (TZT-HDTA-clay), for the purpose of the selective adsorption of the heavy metals ions and possible use as a chemically modified carbon paste electrode (CMCPE). Adsorption isotherms of Hg2+, Pb2+, Cd2+, Cu2+, and Zn2+ from aqueous solutions as a function of the pH were studied at 298 K. Conditions for quantitative retention and elution were established for each metal by batch and column methods. The organo-clay complex was very selective to Hg(II) in aqueous solution in which other metals and ions were also present. The accumulation voltammetry of Hg(II) was studied at a carbon paste electrode chemically modified with this material. The mercury response was evaluated with respect to the pH, electrode composition, preconcentration time, mercury concentration, "cleaning" solution, possible interferences and other variables. A carbon paste electrode modified by TZT-HDTA-clay showed two peaks: one cathodic peak at about 0.0 V and an anodic peak at 0.25 V, scanning the potential from -0.2 to 0.8 V (0.05 M KNO3 vs. Ag/AgCl). The anodic peak at 0.25 V presents excellent selectivity for Hg(II) ions in the presence of foreign ions. The detection limit was estimated as 0.1 microg L(-1). The precision of determination was satisfactory for the respective concentration level.     

Synthesis and structural study of (8-phenylsulfanylnaphth-1-yl)diphenylphosphine metal complexes

A series of three platinum(II) halide complexes 2–4 [Pt(X)₂{Nap(PPh₂)(SPh)}] (Nap = naphthalene-1,8-diyl; X = Cl, Br, I) and a ruthenium(II) p-cymene complex 5 [Ru(η⁶-MeC₆H₄ⁱPr)(Cl){Nap(PPh₂)(SPh)}]⁺Cl^? of the sterically crowded peri-substituted naphthalene phosphine 1 have been prepared. The compounds were fully characterised by multinuclear NMR, IR and MS and X-ray data for 1–5 are compared. Molecular structures are analysed by naphthalene ring torsions, peri-atom displacement, splay angle magnitude, P···S interactions, aromatic ring orientations and geometry around the metal centre. Platinum adopts a strictly square planar geometry which increases the distortion of the naphthalene skeleton in 2–4. Conversely, the classical-piano stool conformation of 5 results in a pseudo-octahedral conformation around the ruthenium atom which influences the naphthalene geometry to a much lesser extent with distortion of a similar magnitude to the free ligand 1.     

Influence of the layer charge and clay particle size on the interactions between the cationic dye methylene blue and clays in an aqueous suspension

The spectroscopic behavior of the dye MB in suspensions of different clays have been used for evaluating layer charge density influence on the adsorption properties of the particles. The clays with higher charge density, like SAz-1 and SCa-3, promote a higher aggregation and do not show deaggregation at longer times, so that practically only the aggregate peak at approximately 570 nm is observed, without any change with time. This is due to, on one side, the larger particle size that decreases the surface area available for adsorption. Additionally, the clay layers will be held together more tightly, avoiding the migration of the dye to the interlamellar region. On the other hand, SWy-1, having a lower charge density, shows a completely different behavior. The dye molecules, initially adsorbed as aggregates on the outer surface of the clay, deaggregate to form monomers that migrate to the interlamellar spaces, giving rise to absorption bands at 670 and 760 nm. Experiments using Ca-exchanged SWy-1, variation of the ionic strength by addition of salt, and the use of different size fractions of the clays confirm the finding that the main factor ruling the adsorption behavior of the probe is the size of the clay particles.     

Inhibition of the MEK1/ERK pathway reduces arachidonic acid release independently of cPLA<Subscript>2</Subscript> phosphorylation and translocation

Background  

The 85-kDa cytosolic phospholipase A₂ (cPLA₂) mediates arachidonic acid (AA) release in MDCK cells. Although calcium and mitogen-activated protein kinases regulate cPLA₂, the correlation of cPLA₂ translocation and phosphorylation with MAPK activation and AA release is unclear.     

Some generators for the algebra of n×n matrices

In this note, we show how the algebra of n×n matrices over a field can be generated by a pair of matrices AB, where A is an arbitrary nonscalar matrix and B can be chosen so that there is the maximum degree of linear independence between the higher commutators of B with A.