Studies on the stabilization of poly(vinyl chloride) with epoxides. Transformation products and their migration from packaging to foods

Epoxidized glyceryl trioleate has been used as a model compound to extend previous studies on the mode of action of epoxides in the stabilization of poly(vinyl chloride) (PVC). Sheets of PVC containing 3% expoxidized glyceryl tri[1-¹⁴C]oleate were prepared on a hydraulic press and subsequently heated in an oven for various times to simulate heat processing. After separation of the polymer from the low molecular weight components by steric exclusion chromatography, there was only a negligible amount (max. 2%) of bonding to the polymer and progressive loss from 15 to 90% of epoxide function occurred with heat processing over the period from 0.2 to 40 min. The concentration of the chlorohydrin transformation product was estimated by high performance steric exclusion chromatography after formation of a suitable u.v. detectable derivative, but the levels found did not fully account for the overall loss of epoxide. To assess the potential of both epoxide and chlorohydrin for migration from plastic packaging into foods, sheets individually containing the epoxide and the corresponding chlorohydrin were placed in contact with a range of solvents, orange squash and edible oil. No migration was measurable at a limit of detection of 0.1 ppm (orange squash limit 0.5 ppm) after 10 days contact at 40, with the exception of edible oil where a level of 1.0 ppm was detectable.     

Right angle free subsets in the plane

In this paper we investigate the complexity of finding maximum right angle free subsets of a given set of points in the plane. For a set of rational pointsP in the plane, theright angle number (P) (respectivelyrectilinear right angle number _R (P)) ofP is the cardinality of a maximum subset ofP, no three members of which form a right angle triangle (respectively a right angle triangle with its side or base parallel to thex-axis). It is shown that both parameters areNP-hard to compute. The latter problem is also shown to be equivalent to finding a minimum dominating set in a bipartite graph. This is used to show that there is a polynomial algorithm for computing _R (P) whenP is a horizontally-convex subset of the lattice × (P ishorizontally-convex if for any pair of points inP which lie on a horizontal line, every lattice point between them is also inP). We then show that this algorithm yields a 1/2-approximate algorithm for the right angle number of a convex subregion of the lattice.     

Performance of a low-loss pulsed-laser-deposited Nd:Gd(3) Ga(5)O(12) waveguide laser at 1.06 and 0.94 mum

We report the laser performance of a low-propagation-loss neodymium-doped Gd(3)Ga(5)O(12) (Nd:GGG) waveguide fabricated by pulsed-laser deposition. An 8- mum -thick crystalline Nd:GGG film grown upon an undoped Y(3)Al(5)O(12) substrate lases at 1.060 and 1.062 microm when pumped by a Ti:sapphire laser operating at 740 or 808nm.Using a 2.2% output coupler, we observed a 1060-nm laser threshold of 4mW and a slope efficiency of 20%. Laser action was also achieved, for what we believe is the first time in Nd:GGG, on the quasi-three-level 937-nm transition. With a 2% output coupler at this wavelength a laser threshold of 17mW and a 20% slope efficiency were obtained. This demonstration of low propagation loss combined with the fact that these waveguides have a very high numerical aperture (0.75) makes pulsed-laser-deposited thin films attractive for high-power diode-pumped devices.     

Sauerstoffbestimmung

Ohne Zusammenfassung     

The circular chromatic number of hypergraphs

A generalization of the circular chromatic number to hypergraphs is discussed. In particular, it is indicated how the basic theory, and five equivalent formulations of the circular chromatic number of graphs, can be carried over to hypergraphs with essentially the same proofs.     

Crystal and molecular structures of some six‐coordinate tin(IV) halogeno complexes with phosphorus‐containing ligands

Six new complexes of tin(IV) halides with phosphorus‐containing ligands have been fully characterized by single‐crystal X‐ray diffraction at low temperature. Three of the compounds, derived from the diphosphanes bis‐(diphenylphosphino)methane or bis‐(dicyclohexylphosphino)methane, have a novel zwitterionic structure, with five Cl ligands and one unidentate phosphorus‐containing ligand on tin, together with a proton on the second phosphorus atom of the potentially bidentate ligand; these are Cl₅Sn⁻P(Ph₂)CH₂PPh₂H⁺ ( 1 ), Cl₅Sn⁻OP(Ph₂)CH₂‐PPh₂H⁺ ( 2 ), and Cl₅Sn⁻OP(cy₂)CH₂Pcy₂H⁺ ( 3 ). The other three complexes have a bidentate donor attached to the SnX₄ moiety; they comprise Cl₄SnOP(Ph₂)‐(CH₂)₂PPh₂O ( 4 ), a derivative of bis‐(diphenylphosphino)ethane dioxide, I₄SnOP(Ph₂)CH₂PPh₂O ( 5 ), a similar derivative of bis‐(diphenylphosphino)‐methane dioxide, and the very unusual Br₄SnAs‐(Ph₂)(CH₂)₂PPh₂O ( 6 ), with coordination to tin by As and O. Since the starting material for the last compound was Ph₂As(CH₂)₂PPh₂, this result illustrates well the more facile oxidation of P(III) than As(III). © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:136–143, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20525     

Single turn peptide alpha helices with exceptional stability in water

Cyclic pentapeptides are not known to exist in alpha-helical conformations. CD and NMR spectra show that specific 20-membered cyclic pentapeptides, Ac-(cyclo-1,5) [KxxxD]-NH(2) and Ac-(cyclo-2,6)-R[KxxxD]-NH(2), are highly alpha-helical structures in water and independent of concentration, TFE, denaturants, and proteases. These are the smallest alpha-helical peptides in water.     

Quadrupole moments of highly deformed structures in the A approximately 135 region: probing the single-particle motion in a rotating potential

The latest generation gamma-ray detection system, GAMMASPHERE, coupled with the Microball charged-particle detector, has made possible a new class of nuclear lifetime measurement. For the first time differential lifetime measurements free from common systematic errors for over 15 different nuclei ( >30 rotational bands in various isotopes of Ce, Pr, Nd, Pm, and Sm) have been extracted at high spin within a single experiment. This comprehensive study establishes the effective single-particle transition quadrupole moments in the A approximately 135 light rare-earth region. Detailed comparisons are made with theoretical calculations using the self-consistent cranked mean-field theory which convincingly demonstrates the validity of the additivity of single-particle quadrupole moments in this mass region.     

Extended operation of synchronously pumped optical parametric oscillators to longer idler wavelengths

A synchronously pumped optical parametric oscillator, based on periodically poled lithium niobate, has operated at idler wavelengths out to 7.3 microm . Directly measured idler output powers (average) are 4.2 mW at 6.1 microm, 0.5 mW at 7.0 microm, and 0.04 mW at 7.25 microm . Characterization of the idler output indicates essentially bandwidth-limited and diffraction-limited operation.