Stereoselective synthesis of tetracyclic indolines via gold-catalyzed cascade cyclization reactions

A reliable synthetic route to fused polycyclic indolines is documented by the development of a stereoselective gold catalyzed cascade cyclization of indole propargylic alcohols.     

Weak O‐Assistance Outcompeting Strong N,N‐Bidentate Directing Groups in Copper‐Catalyzed C−H Chalcogenation

A copper‐mediated C?H chalcogenation of triazoles has been achieved by weak coordination. The user‐friendly protocol showed high functional‐group tolerance and ample substrate scope, yielding fully substituted 1,2,3‐triazoles with complete positional site‐selectivity. The C?H selenylation could likewise be achieved by means of copper catalysis. Our findings highlight for the first time that weak O‐coordination can outcompete the strong N,N‐bidentate coordination mode in C?H functionalization technology.     

Interlaboratory comparison of melt flow rate testing of moisture sensitive plastics

The current standard for melt flow rate testing, ISO 1133, does not adequately cover the measurement of materials that degrade or further polymerise at the melt flow rate test conditions. Materials such as PET, PBT and PA tend to degrade, sometimes rapidly, at melt temperatures if they contain absorbed water. This results in poor repeatability and reproducibility of melt flow rate results. The ISO Plastics Melt Rheology Working Group (TC61/SC5/WG9) is currently developing a modified melt flow rate test method for reliable measurement of moisture sensitive materials, thereby providing an alternative to intrinsic viscosity measurements. The modified method controls more tightly the time–temperature history experienced by the material during testing and, thus, the resultant variability in measured properties due to degradation.The results of an intercomparison of testing of moisture sensitive polymers using the melt volume flow rate (MVR) and melt mass flow rate (MFR) methods are reported. A polypropylene (PP), used as a benchmark material, and five moisture sensitive materials were tested by a number of laboratories measuring either MVR or MFR, or both. For standard testing of the PP material, the repeatability and reproducibility of measurements of MVR were up to 5% and 11%, respectively, and for MFR were 7% and 21%, respectively (95% confidence level, outliers excluded). For the moisture sensitive materials the repeatability and reproducibility of measurements varied significantly, with repeatability values up to 26% and reproducibility values up to 114% being obtained. By imposing moisture and temperature control criteria in accordance with the proposed testing standard, the repeatability and reproducibility limits were significantly reduced to approximately 10% and 60%, respectively. The results suggest that both the moisture and temperature criteria were important for improving the repeatability of MVR measurements. However, the moisture content criterion was more important for improving the reproducibility of MVR measurements.The need to tightly control the sample preparation, in particular the drying and subsequent sample handing procedures, and the time–temperature history of the sample throughout the test is considered critical to further improve the precision of measurements of such materials.     

Elasticity of flexible and semiflexible polymers with extensible bonds in the Gibbs and Helmholtz ensembles

Stretching experiments on single molecules of arbitrary length opened the way for studying the statistical mechanics of small systems. In many cases in which the thermodynamic limit is not satisfied, different macroscopic boundary conditions, corresponding to different statistical mechanics ensembles, yield different force-displacement curves. We formulate analytical expressions and develop Monte Carlo simulations to quantitatively evaluate the difference between the Helmholtz and the Gibbs ensembles for a wide range of polymer models of biological relevance. We consider generalizations of the freely jointed chain and of the worm-like chain models with extensible bonds. In all cases we show that the convergence to the thermodynamic limit upon increasing contour length is described by a suitable power law and a specific scaling exponent, characteristic of each model.     

The study of electron energy distribution functions, Swarm parameters, and transition rates in N2+O2 plasma

Using the Boltzman equation electron energy distribution functions, swarm parameters (mean energy, characteristic energy, drift velocity and diffusion coefficient), and transition rates (one for vibrational and one for electronical excitation for each of the gases) for N₂+O₂ (80%+20%) mixture plasma have been calculated. The influence of the applied reduced electric field and the vibrational temperatures on these quantities is studied.     

Reaction of gold(III) oxo complexes with alkenes. Synthesis of unprecedented gold alkene complexes, [Au(N,N)(alkene)][PF6]. Crystal structure of [Au(bipy(ip))(eta2-CH2=CHPh)][PF6] (bipy(ip) = 6-isopropyl-2,2'-bipyridine)

Gold alkene complexes [Au(bipyR)(eta2-alkene)][PF6] (bipyR = 6-alkyl-2,2'-bipyridine) have been obtained by reaction of gold(III) oxo complexes [Au2(bipyR)2(mu-O)2][PF6]2 with alkenes. The crystal structure of the styrene adduct [Au(bipy(ip))(eta2-CH2=CHPh)][PF6] (bipy(ip) = 6-isopropyl-2,2'-bipyridine) has been solved by X-ray analysis.     

A chemometric survey of three sites in Muggia Bay (Northern Adriatic Sea): meteorological effects on heavy metal patterns in surface coastal waters

Within research on the quality of the waters of the Gulf of Trieste, this study on patterns of trace metal contents in the inner part of the gulf (Muggia Bay) discusses data of Cu, Pb, Cd and Zn, determined voltammetrically (DPASV), and collected in three sites with a 10-day frequency over the period of one year. Two of the sites lie inside the dam system which protects the harbour of Trieste, while the third one is situated outside for comparison purposes. Principal component analysis pointed out different metal patterns inside and outside the dam system; PC scores were related to meteorological information: rain plays a major role in conditioning the estuarine inner site: wind stirring action was detectable for the outer site. Both univariate graphics and canonical correlation analysis suggest a diffuse source for Pb, probably atmospheric deposition. Received: 1 August 1997 / Revised: 20 November 1997 / Accepted: 23 November 1997