Co-extrusion of multilayer poly(m-xylylene adipimide) nanocomposite films for high oxygen barrier packaging applications

Multilayer packaging films incorporating a montmorillonite layered silicate (MLS)/poly(m-xylylene adipimide) (MXD6) nanocomposite as the oxygen barrier layer and low-density polyethylene (LDPE) as the moisture resistant layer were produced through the co-extrusion process at the laboratory and pilot scale level. Extrusion screw speeds were varied from 30 to 130 rpm in order to produce samples with varying layer thicknesses. The multilayer film structure was scaled up from the laboratory scale to the pilot-level scale based on oxygen transmission data obtained from the laboratory-scale process parameters. Laboratory-scale film results indicated that the film which demonstrated an optimal oxygen transmission rate (OTR) of 0.3 cm³/(m² day) at 60%RH and water vapor transmission rate (WvTR) of 1.4 g/(m² day) at 90%RH had a structure that contained a core barrier film layer of nanocomposite MXD6 that makes up roughly 34% of the total film thickness, with the remainder of the film material consisting of maleic anhydride grafted polyolefin tie layers and LDPE skin layers. The OTR of the films changed as the relative humidity of the test environment was varied from 0 to 90%. However, for the pilot-scale trial it was necessary to reduce the target thickness of the core nylon barrier layer to 22% due to layer-to-layer melt flow instabilities that occurred during processing. The barrier properties of the multi-layer co-extruded films were highly dependant on overall film thickness. The highest performing oxygen barrier pilot-scale film had an OTR of 0.3 cm³/(m² day) (60%RH) and a WvTR of 2.4 g/(m² day) (90%RH) with a core nylon layer of 1.5 mil and a total thickness of 7.7 mil. Correlation of the layer thicknesses to the barrier and mechanical properties of the pilot-scale multilayer films indicated that an increased nanocomposite core layer thickness improved the oxygen barrier performance and decreased film elongation while improving the tear resistance of the films.     

Intramolecular cyclization reactions of unsaturated amino Fischer chromium carbenes forming indoles and quinolines

A thermally induced intramolecular annulation reaction of N-(2-alkenylphenyl)amino substituted Fischer chromium carbenes has been extensively examined. The carbene complexes were prepared in moderate to good yields by reaction of 2-aminostyrenes with intermediately formed acyloxy substituted carbenes. Upon heating, the thermally labile carbenes decomposed producing indoles and quinolines as the major products. The product distribution was found to be highly dependent on the substitution pattern and electronic properties of the starting material, and on the solvent used.     

Supported diazonium salts--convenient reagents for the combinatorial synthesis of azo dye

Resin supported diazonium salts were synthesised. These were observed to be stable to storage and to provide a convenient means of compound handling and were employed in the solution synthesis of a 6 x 6 azo dye library.     

Structure/activity study of tris(2-aminoethyl)amine-derived translocases for phosphatidylcholine

Sulfonamide and amide derivatives of tris(aminoethyl)amine (TREN) are known to facilitate phospholipid translocation across vesicle and erythrocyte membranes; that is, they act as synthetic translocases. In this report, a number of new TREN-based translocases are evaluated for their abilities to bind phosphatidylcholine and translocate a fluorescent phosphatidylcholine probe. Association constants were determined from (1)H NMR titration experiments, and translocation half-lives were determined via 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD)/dithionite quenching assays. A rough correlation exists between translocase/phosphatidylcholine association constants and translocation half-lives. The tris-sulfonamide translocases are superior to the tris-amide versions because they associate more strongly with the phospholipid headgroup. The stronger association is due to the increased acidity of the sulfonamide NHs as well as a molecular geometry (as shown by X-ray crystallography) that is able to form tridentate complexes with one of the phosphate oxygens. Two fluorescent translocase analogues were synthesized and used to characterize membrane partitioning properties. The results indicate that the facilitated translocation of phospholipids by TREN-derived translocases is due to the formation of hydrogen-bonded complexes with the phospholipid headgroups. In the case of zwitterionic phosphatidylcholine, it is the neutral form of the translocases that rapidly associates with the phosphate portion of the phosphocholine headgroup. Complexation masks the headgroup polarity and promotes diffusion of the phospholipid-translocase complex across the lipophilic interior of the membrane.     

Protein prosthesis: a semisynthetic enzyme with a beta-peptide reverse turn

beta-Amino acids are incorporated into an enzyme by using the method of expressed protein ligation. In the resulting semisynthetic enzyme, an R-nipecotic acid-S-nipecotic acid module replaces Asn113 and Pro114 of ribonuclease A. The semisynthetic enzyme not only retains full catalytic activity but also gains conformational stability. Thus, structural elements can be replaced with foldameric equivalents to endow proteins with more desirable properties.     

Molecular recognition of alkylammonium contact ion-pairs using a ditopic receptor

A ditopic, macrobicyclic receptor with adjacent anion and cation binding sites is able to distinguish between various monoalkylammonium salts by binding them as contact ion-pairs. The affinity for linear n-propylammonium chloride is at least 2 orders of magnitude greater than that for n-propylammonium acetate, n-propylammonium p-toluenesulfonate, and branched isopropylammonium chloride. An X-ray structure of the receptor complexed with methylammonium chloride illuminates the basis of the molecular recognition.     

Loading amplification of radiation grafted polymers (crowns and lanterns) and their application in the solid-phase synthesis of hydantoin libraries

Solid-phase dendrimer chemistry using a symmetrical 13C-branched isocyanate monomer was used to prepareradiation-grafted polymers with enhanced loading. Afterevaluation of the physical and chemical properties of thesenew high-loading supports, they were tested in the multipleparallel synthesis of hydantoins.     

Application of Ugi reactions in synthesis of divalent neoglycoconjugates: evidence that the sugars are presented in restricted conformation

[reaction: see text]. The Ugi reaction has been used to prepare divalent galactose derivatives. NMR analysis shows that a divalent neoglycoconjugate, where the glycopeptides are bridged by a terephthaloyl group, is an 83:17 mixture of two conformers; the amide groups of the major isomer have E-anti conformations. The spatial relationship and the relative orientation of the sugars are restricted, which may have consequences for the recognition of this and related structures in biological systems.     

A Stationary Rho-Mixing Markov Chain Which Is Not “Interlaced” Rho-Mixing

A strictly stationary, countable-state Markov chain is constructed which is -mixing (with arbitrarily fast mixing rate) but fails to be *-mixing (interlaced-mixing).