Blends of starch with ethylene vinyl alcohol copolymers: effect of water,glycerol, and amino acids as plasticizers

Blends of thermoplastic starch with poly(ethylene‐co‐vinyl alcohol) copolymer (EVOH) were melt extruded with water/glycerol as plasticizer and a series of amino acid additives. The biggest factor in end‐use mechanical properties proved to be the relative humidity (RH) during storage. Plasticized starch‐EVOH blends stored at 0 and 50% RH changed significantly over time, with, for example, the tensile strength (TS) of the glycerol‐plasticized blend increasing from 4.7 to 26.3 MPa over 8 weeks when maintained at 0% RH. In contrast, the TS of this same sample stored at 75% RH remained unchanged for 8 weeks. Amino acids provided relatively minor, but significant changes in mechanical properties with time. Based on TS, elongation‐to‐break, and modulus, it may be concluded that β‐alanine, sarcosine, and L ‐proline were more effective than glycerol at maintaining strong flexible blends. Increases in crystallinity and changes in morphology with time, as described by modulated DSC were correlated to these changes in mechanical properties. Published in 2007 by John Wiley & Sons, Ltd.     

Electrochemistry of 6-methyl-5,6,7,8-tetrahydropterin

The electrochemical oxidation of 6-methyl-5,6,7,8-tetrahydropterin (6-MTHP), the most effective of the synthetic aromatic amino acid hydroxylase pseudo cofactors, has been studied in aqueous solution over a wide pH range at a pyrolytic graphite electrode. The first electrooxidation of 6-WTHP occurs by a quasi-reversible 2e-2H⁺ reaction giving an unstable quinonoid-dihydropterin. The latter undergoes a first order chemical follow-up reaction yielding 6-methyl-7,8-dihydropterin (6-MDHP). At pH values ?5.6 6-MDHP forms an equilibrium mixture of a covalently hydrated species and non-hydrated species. The covalently hydrated form of 6-MDHP is electrooxidized in a 2e-2H⁺ quasi-reversible reaction to another unstable quinonoid that appears to undergo a two-step rearrangement to 6-methylpterin. Non-hydrated 6-MDHP is electrooxidized at the most positive potential in an irreversible 2e-2H⁺ reaction giving 6-methylpterin.     

Rapid intramolecular interactions between organic isocyanates and hexafluorobut-2-yne on a dirhodium centre; X-ray crystal structure of (η-C5H5)2Rh2 {μ2(η3-C(CF3)C(CF3)C(O)N(Ph)}

Complexes of formula (η-C₅H₅₂Rh₂{CF₃C₂CF₃ · RNCO} have been prepared by three methods, from reactions between organic isocyanates and (η-C₅H₅)₂Rh₂(CO)(CF₃C₂CF₃) or (η-C₅H₅)₂Rh₂(CO)₂(CF₃C₂CF₃); by treatment of (η-C₅H₅)₂Rh₂(CO)(CF₃C₂CF₃) with organic azides; and by oxidation with Me₃NO of the organic isocyanide in (η-C₅H₅)₂Rh₂(CO)(CNR)(CF₃C₂CF₃). The crystal and molecular structure of the complex (η-C₅H₅)₂Rh₂{CF₃C₂CF₃ · RNCO} with R = Ph has been determined from single crystal X-ray diffraction data. This reveals that the isocyanate has condensed with the hexafluorobut-2-yne to form an amide ligand of the form C(CF₃)C(CF₃)C(=O)N(R); this bridges the two rhodium atoms in a μ₂η³-manner.     

A chromatographic determination of nitrate with amperometric detection at a copperized cadmium electrode

A copperized cadmium flow-through electrode is applied for cathodic detection of nitrate in the effluent stream of a liquid chromatograph. The nitrate is separated from dissolved oxygen in a small (10 cm) column of strong-base, anion-exchange resin (Dowex 1-X8) with 5 mM perchloric acid as the eluent. The effluent stream is buffered to pH 8 by mixing with a stream of buffer prior to detection. A large excess of chloride added to the sample dramatically improves the separation of nitrate from dissolved oxygen in the sample.     

Photochemically modulated endothelial cell thrombogenicity via the thrombomodulin-tissue factor pathways

Photodynamic therapy (PDT) is based on a photochemical reaction using a photosensitizer and light to produce reactive oxygen species that have biological effects. Although its application in some fields is largely based on thrombosis, in the vascular setting thrombosis must be prevented. In this study we examined the effects of PDT on the changes in activity of thrombomodulin (TM) and tissue factor (TF) as important regulators of the coagulation process of endothelial cells. Human umbilical vein endothelial cells were treated with PDT (chloro-aluminum-sulfonated phthalocyanine, lambda = 630 nm) at different light-energy doses, and TM and TF levels were measured using fluorescence spectroscopy. Microparticles (MP) were analyzed using flow cytometry analysis. PDT alters the thrombogenic state of endothelial cells by causing decreased expression of TM and increased expression of functional TF in a light-energy dose-dependent way. PDT-treated endothelial cells shed large numbers of MP containing high levels of TF. TF functionality of PDT-treated cells, measured by a Factor Xa-generating assay, was high. TF was located mostly intracellularly and in MP. The disturbed anticoagulant balance described in this study may explain the occurrence of thrombosis induced by PDT and, if not contained, dispute the suitability of PDT as an adjuvant modality to treat vascular restenosis.     

Aldol reactions of a cyclobutanone enolate

Addition of an aldehyde and zinc chloride to a cyclobutanone enolate, prepared by the reaction of an α-chlorocyclobutanone with dimethylcopperlithium, gave an aldol adduct in good yield.     

Regioselective synthesis of antiparallel loops on a macrocyclic scaffold constrained by oxazoles and thiazoles

The regioselective syntheses and structures are reported for two tris-macrocylic compounds, each possessing two antiparallel loops on a macrocyclic scaffold constrained by two oxazoles and two thiazoles. NMR solution structures show the loops projecting from the same face of the macrocycle. Such molecules are shown to be prototypes for mimicking multiple loops of proteins.[structure: see text]     

A diatropic ring current in a fluorofullerene trannulene

Ipsocentric current-density maps for a fluorofullerene derivative, C60F15H3, modelling the addition pattern of the experimentally characterised C60F15[CBr(CO2Et)2]3 which contains an [18]trans-annulene system, reveal a diamagnetic ring current dominated by the contribution of the four HOMO electrons, as in a classical (4n + 2) aromatic annulene.     

An evaporation-based microfluidic sample concentration method

We present a method for sample concentration within microfluidic devices using evaporation-induced flow. Evaporation-induced flow is easy to incorporate into microfluidic designs and can be used to concentrate a wide variety of molecules. The practicality of this method was demonstrated with 0.2 microm fluorescent spheres and FITC-labeled BSA. Thirty two percent of the 0.6 microL fluorescent sphere suspension was concentrated into a well within a microfluidic device. In the same amount of time, 93% of the 0.6 microL FITC-labeled BSA solution was concentrated.     

Asymmetric conjugate addition of thioglycolate to a range of chalcones using tetrahydroisoquinoline (TIQ) N,N′-dioxide ligands

A series of novel TIQ based N,N′-oxide ligands were synthesised and screened for their catalytic activity in the enantioselective conjugate addition of thioglycolate to chalcones. Bulky groups on the side chain of the TIQ backbone provided the highest enantioselectivity of up to 88% with 10 mol % catalyst loading. It was also observed that these reactions proceeded optimally in the presence of dichloromethane as a solvent. Screening of various metals emphasized La(OTf)₃ as the ideal pre-catalyst for this particular reaction.