Ligand discrimination in the reaction of nitrones with [PtCl2(PhCN)2]. Selective formation of mono-oxadiazoline and mixed bis-oxadiazoline complexes under thermal and microwave conditions

[2+3] Cycloaddition of nitrones to the nitrile ligands in the complexes cis- or trans-[PtCl2(PhCN)2] occurs under ligand differentiation and allows for selective synthesis of complexes of the type cis- or trans-[PtCl2(oxadiazoline)(PhCN)]. Microwave irradiation enhances the reaction rates of the cycloaddition considerably and further favours the selectivity towards the mono-cycloadduct with respect to thermal conditions, because the first cycloaddition is accelerated to a higher extent than the second one. Reaction of the trans-substituted mono-oxadiazoline complexes with a nitrone different from the one used for the first cycloaddition step gives access to mixed bis-oxadiazoline compounds of the composition trans-[PtCl2(oxadiazoline-a)(oxadiazoline-b)]. The corresponding cis-configured complexes, however, do not undergo further cycloaddition. All reactions described occur without isomerisation of the stereochemistry around the platinum center, independently of whether thermal or microwave heating is applied.     

Characterization of SiO2 protective coatings on polycarbonate

SiO₂ protective coatings have been deposited on polycarbonate substrates by plasma ion assisted deposition. The influence of ion energy on the water permeability and the surface topography of the coatings was studied by infrared spectroscopy and atomic force microscopy. Coatings deposited at sufficiently high ion energies show a barrier effect against moisture uptake and considerably reduced film roughness. Both effects are attributed to an increase of the packing densities of the coatings.     

The alpha-helix folds more rapidly at the C-terminus than at the N-terminus

The helix-coil dynamics of different sections of an alpha-helical model peptide were observed separately by nanosecond temperature jump experiments with IR detection on a series of isotopically labeled peptides. The results show that the helix-coil dynamics of the alpha-helical C-terminus are faster than those of the N-terminus.     

Estimation of effective diffusion coefficients of model solutes through gastric mucus: assessment of a diffusion chamber technique based on spectrophotometric analysis.

A diffusion chamber technique based on spectrophotometric analysis to determine effective diffusion coefficients for solutes with various relative molecular mass (Mr) values and properties, passing through native mucus gel, is reported. For all solutes studied, a reduction in effective diffusion coefficients is observed with a retardation of solute flux by a factor of at least two. For the solutes investigated (with Mr values ranging from 126-14,400 u), no consistent effect of solutes of low Mr was evident with regard to the retarding effect of mucus; however, at high Mr values (greater than 4000 u) the retardation was greatly enhanced. A possible relationship between charged solutes of low Mr and the degree of retardation was observed, which possibly suggests the presence of ionic interactions of the solutes with the largely negatively charged mucus gel. The results provide further evidence for the suggestion that mucus is acting more than simply as a gel support for an unstirred water layer and is perhaps a more potent diffusion barrier to specific solutes.     

Preformulation compatibility studies of etamsylate and fluconazole drugs with lactose by DSC

Chemical compatibility of two drugs, namely, etamsylate and fluconazole was studied with lactose as excipient, employing differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques. The DSC patterns recorded for the mixtures of both the drugs with the common excipient (lactose) indicated that fluconazole as well as etamsylate were incompatible with lactose at high temperatures. X-ray diffraction patterns recorded for pure drugs and lactose and the mixtures of individual drugs with lactose prepared at room temperature by intimate grinding of the components revealed incompatibility of both the drugs with lactose also at room temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

A preliminary observation of additive thermodynamic contribution of pendant arms to the complexation of calixarene derivatives with mercury(II)

An additive thermodynamic contribution of pendant arms to the complexation of calixarene derivatives with mercury(II) in acetonitrile is for the first time demonstrated.     

Raney nickel reductions—VIII A synthesis of 1:2-benzanthracene and its 3′-methyl and 4-methyl derivatives

1:2-Benzanthracene and the 3′-methyl derivative have been prepared by Raney nickel reduction of the sulphuric esters of the leuco derivatives of 1:2-benzanthraquinone and 4′-chloro-3′-methyl-1:2-benzanthraquinone, followed by dehydrogenation. 3-Hydroxy-1:2-benzanthraquinone was methylated in the 4-position by formaldehyde, sodium hydrosulphite and sodium hydroxide solution (the Marschalk reaction). Simultaneous reduction of the nuclear hydroxyl and quinone groups was effected by Raney nickel reduction of the trisulphuric ester of 3:9:10-trihydroxy-4-methyl-1:2-benzanthracene, and the resultant hexahydro-4-methyl-1:2-benzanthracene was dehydrogenated to 4-methyl-1:2-benzanthracene. The preparation of 3:4:9:10-dibenzopyrene from Mayvat brilliant red AF by Raney nickel reduction of the sulphuric ester of the leuco derivative and subsequent dehydrogenation is described.     

Central polynomials and matrix invariants

LetK be a field, charK=0 andM _n (K) the algebra ofn×n matrices overK. If λ=(λ₁,…,λ _m ) andμ=(μ ₁,…,μ _m ) are partitions ofn ² let wherex ₁,…,x _n ²,y ₁,…,y _n ² are noncommuting indeterminates andS _n ² is the symmetric group of degreen ². The polynomialsF ^{λ, μ} , when evaluated inM _n (K), take central values and we study the problem of classifying those partitions λ,μ for whichF ^{λ, μ} is a central polynomial (not a polynomial identity) forM _n (K). We give a formula that allows us to evaluateF ^{λ, μ} inM(K) in general and we prove that if λ andμ are not both derived in a suitable way from the partition δ=(1, 3,…, 2n−3, 2n−1), thenF ^{λ, μ} is a polynomial identity forM _n (K). As an application, we exhibit a new class of central polynomials forM _n (K). In memory of Shimshon Amitsur Research supported by a grant from MURST of Italy.     

Thermal decomposition of lignocellulosic materials: comparison of the results obtained in different experimental systems

An experimental system that allows the use of large particle sizes and the simulation of different operating conditions was built to study the thermal decomposition of lignocellulosic materials. The values of solid conversion and of temperature obtained at different points using spherical particles of pine wood 2 cm in diameter are shown. The conversion values are compared with those calculated from the equations obtained in a thermobalance for small particle sizes.     

A sequential multielement separation scheme for determination of As,Mn, Mo,Cu and Zn in human milk by neutron activation analysis

A simple separation scheme for the analysis of As, Mn, Mo, Cu and Zn using neutron activation is described. It has been checked using three standard reference materials, A-11 milk powder (IAEA) and bovine liver and orchard leaves (USNBS) and found to give acceptable results. This scheme was applied for determination of these trace elements in mature human milk samples. The concentrations of As, Mn, Mo, Cu in samples obtained from two socio-economic groups—low and middle incomes—were not significantly different. However, Zn levels in samples obtained from the poor income group were significantly lower than in those obtained from the other group. Work carried out under Research Contract No. 2598/RB of International Atomic Energy, Vienna. Health Physics Division. Analytical Chemistry Division.