Effects of ligand tuning on dinuclear indium catalysts for lactide polymerization

Functionalized diaminophenols, H(N(R1R2)N(R3)O), were investigated as ligands for indium catalysts in the ring-opening polymerization of racemic lactide. Precursor complexes (N(Me2)N(Me)O)InCl(2) (1), (N(Pr2)NO)InCl(2) (2), and (N(Mes)NO)InCl(2) (3) were synthesized and fully characterized by (1)H and (13)C NMR spectroscopy, elemental analysis, and single-crystal X-ray crystallography. Complexes 1 and 2 were used to synthesize alkoxy-bridged complexes [(N(Me2)N(Me)O)InCl](2)(μ-Cl)(μ-OEt) (4) and [(N(Pr2)NO)InCl](2)(μ-Cl)(μ-OEt) (5). These complexes catalysed the polymerization of racemic lactide at different rates, with complex 5 being substantially more active than complex 4. The dissociation behaviour of these catalysts in the presence of lactide was also studied and used to make comparisons with previously reported catalyst systems.     

On the approach to the critical solution in leading order thin-film coating and rimming flow

The approach to the critical solution in leading order coating and rimming flow of a thin fluid film on a uniformly rotating horizontal cylinder is investigated. In particular, it is shown that the weight of the leading order “full film” solution approaches its critical maximum value with logarithmically infinite slope as the volume flux approaches its critical value.     

Light induced fading in the OSL response of Al2O3:C

We are reporting the results of an investigation designed to determine the magnitude of the light induced fading associated with the OSL response of Al₂O₃:C. Unlike previous studies where bare, radiation sensitive OSL elements were exposed directly to light, most of the experiments described here were conducted using sealed commercially available OSL dosimeters. During light exposure the OSL sensitive elements were kept inside a standard commercially available plastic badge. A commercial OSL system was used for these experiments in an attempt to simulate typical field use conditions. Both light induced signal and light induced fading were considered, however no measurable light induced signal could be identified. Light induced fading effects, however, were significant, up to 55% loss of OSL signal following daylight exposure of 45 days. The possibility that dose information may be easily erased, intentionally or accidentally, could impose significant restrictions on the ability of the US Navy to defend, if needed, the reported personnel dose levels.     

A novel and highly stereoselective route for the synthesis of non-racemic 3-substituted isoindolin-1-one targets

A new, versatile and highly stereoselective approach for the synthesis of non-racemic 3-substituted isoindolin-1-ones is described from a readily available chiral template. The potential of this new protocol is demonstrated through the synthesis of an enantiomerically enriched 3-alkyl N-H isoindolin-1-one target with an e.e. of 98%.     

Does observation of others affect learning in strategic environments? An experimental study

This paper presents experimental results from an analysis of two similar games, the repeated ultimatum game and the repeated best-shot game. The experiment examines whether the amount and content of information given to players affects the evolution of play in the two games. In one experimental treatment, subjects in both games observe not only their own actions and payoffs, but also those of one randomly chosen pair of players in the just-completed round of play. In the other treatment, subjects in both games observe only their own actions and payoffs. We present evidence suggesting that observation of other players' actions and payoffs may affect the evolution of play relative to the case of no observation. Received February 1996/Final version April 1998     

A molecular orbital treatment of the basicity of oxyanion units

The basicity of the oxidic groups AlO₄^5?, SiO₄^4?, PO₄^3?, SO₄^2?, ClO₄^?, can be regarded in terms of electron donor power and expressed numerically as the optical basicity, λ. The λ value depends upon the oxidation number of the central atom and its basicity moderating parameter, γ. The results of (modified) self-consistent field CNDO calculations, presented and discussed in this paper, indicate the simple relationship that the optical basicity value is directly proportional to the negative charge borne by the oxygen atoms of the oxyanion. It is apparent that the basicity moderating parameter is a measure of the ability of the central atom to withdraw charge from the oxygen atoms. The results also indicate that the electron density at the “surface” of the oxyanion originates not only from the oxygens but also from the central atom, this effect increasing with decreasing oxidation number of the central atom.     

Structural characterization and preliminary decomposition study of four unsymmetrically substituted nickel dithiocarbamate complexes

Single-crystal X-ray structures of four nickel dithiocarbamate complexes, the homoleptic mixed-organic bis-dithiocarbamates Ni[S₂CN(isopropyl)(benzyl)]₂, Ni[S₂CN(ethyl)(n-butyl)]₂, and Ni[S₂CN(phenyl)(benzyl)]₂, as well as the heteroleptic mixed-ligand complex NiCl[P(phenyl)₃][(S₂CN(phenyl)(benzyl)], were determined. A slightly distorted square-planar nickel coordination environment was observed for all four complexes. The organic residues adopt conformations to minimize steric interactions. Steric effects also may determine puckering, if any, about the nickel and nitrogen atoms, both of which are planar or nearly so. A trans-influence affects the Ni-S bond distances. Nitrogens interact with the CS₂ carbons with a bond order near two; the other substituents on nitrogen display transoid conformations. There are no strong intermolecular interactions, consistent with prior observations of the volatility of nickel dithiocarbamate complexes. A preliminary thermolysis study of the homoleptic species results in production of 1?:?1 nickel sulfide phases, indicating the potential utility of these species as “single-source” precursors.     

Reactions of transition metal σ-acetylide complexes: III. Synthesis of some aryldiazovinylidene and cycloheptatrienylvinylidene complexes. X-ray structures of [Ru(CCPhNNC6H3Me2-3,4)(PPh3)2(η-C5H5)][BF4] · 0.67CH2Cl2 and [Ru{CCPh(C7H7)}(DPPE)(η-C5H5)][PF6] · 0.63CH2Cl2

Addition of arenediazonium or tropylium salts to Ru(C₂Ph)(L)₂(η-C₅H₅) (L₂ = (PPh₃)₂ or DPPE) gives the corresponding cationic aryldiazovinylidene and cycloheptatrienylvinylidene complexes, respectively; the X-ray structures of the title complexes confirm the presence of the new ligands. The RuC and CC distances are 1.823(9) and 1.34(1) Å for the aryldiazo complex, and 1.848(9) and 1.32(1) Å for the cycloheptatrienyl derivative.     

A simple high-performance liquid chromatography assay for the major cisapride metabolite, norcisapride, in human urine

A simple high-performance liquid chromatography assay using fluorescence detection for the major metabolite of the gastric prokinetic drug cisapride, norcisapride, is presented. Analysis is performed using an Alltech Platinum EPS C8 column with a mobile phase made up of methanol and 0.02M sodium dihygrogen phosphate (45:55, v/v) containing triethylamine (1 g/L). Complete resolution is achieved among norcisapride, the internal standard (metoclopramide), and endogenous urinary components. The assay is linear over the range 50-2000 ng/mL with a mean recovery of 71.2% across the analytical range following solvent extraction with toluene-isoamyl alcohol (95:5, v/v). Intraday coefficients of variation (precision) determined at 200 and 1000 ng/mL are 6.0 and 9.8%, respectively, and interday coefficients of variation are 8.8 and 6.6%, respectively. Intra- and interassay accuracy (as mean relative error) determined at the same concentrations is within 10% in all cases. An analysis of urine samples from a healthy volunteer following the administration of a single 10-mg oral dose of cisapride is shown.