Hydrogen bonded supramolecular elastomers : correlating hydrogen bonding strength with morphology and rheology

A series of six low molecular weight elastomers with hydrogen bonding end-groups have been designed, synthesised and studied. The poly(urethane) based elastomers all contained essentially the same hard block content (ca. 11%) and differ only in the nature of their end-groups. Solution state 1H NMR spectroscopic analysis of model compounds featuring the end-groups demonstrate that they all exhibit very low binding constants, in the range 1.4 to 45.0 M-1 in CDCl3, yet the corresponding elastomers each possess a markedly different nanoscale morphology and rheology in the bulk. We are able to correlate small variations of the binding constant of the end-groups with dramatic changes in the bulk properties of the elastomers. These results provide an important insight into the way in which weak non-covalent interactions can be utilized to afford a range of self-assembled polyurethane based materials that feature different morphologies.

Perylene as an electron-rich moiety in healable, complementary π–π stacked, supramolecular polymer systems

A two-component, supramolecular polymer blend has been designed using a novel π-electron rich bisperylene- terminated polyether. This polymer is able to self-assemble through electronically complementary π–π stacking interactions with a π-electron-deficient chain-folding polydiimide to afford thermally healable polymer blends. Model compounds were developed to assess the suitability of the deep green complexes formed between perylene residues and chain-folding bis-diimides for use in polymer blends. The polymer blends thus synthesised were elastomeric in nature and demonstrated healable properties as demonstrated by scanning electron microscopy. Healing was observed to occur rapidly at ca. 75 degC, and excellent healing efficiencies were found by tensometric and rheometric analyses. These tuneable, stimuli-responsive, supramolecular polymer blends are compared to related healable blends featuring pyrene-terminated oligomers.

Simple general method of generating non-oxo, non-amavadine model octacoordinated vanadium(IV) complexes of some tetradentate ONNO chelating ligands from various oxovanadium(IV/V) compounds and structural characterization of one of them

A simple general route of obtaining very stable octacoordinated non-oxovanadium( IV) complexes of the general formula VL2 (where H2L is a tetradentate ONNO donor) is presented. Six such complexes (1-6) are adequately characterized by elemental analysis, mass spectrometry, and various spectroscopic techniques. One of these compounds (1) has been structurally characterized. The molecule has crystallographic 4 symmetry and has a dodecahedral structure existing in a tetragonal space group P4n2. The non-oxo character and VL2 stoichiometry for all of the complexes are established from analytical and mass spectrometric data. In addition, the non-oxo character is clearly indicated by the complete absence of the strong nu(v=o) band in the 925-1025 cm(-1) region, which is a signature of all oxovanadium species. The complexes are quite stable in open air in the solid state and in solution, a phenomenon rarely observed in non-oxovanadium(IV) or bare vanadium(IV) complexes.

Interaction of sulphur-containing aroma compounds with proteins in both model systems and real food systems

Irreversible binding of key flavour disulphides to ovalbumin has been shown previously to occur in model systems. The extent of binding is determined by the availability of the sulphydryl groups to participate in disulphide exchange, influenced either by pH, or the state of the protein (native or heat-denatured). In this study, two further proteins, one with sulphydryl groups available in the native state (beta-lactoglobulin) and one with no sulphydryl groups in the native state (lysozyme) were used to confirm this hypothesis. When the investigation was extended to real food systems, a similar effect was shown when a commercial meat flavouring containing disulphides was added to heat-denatured ovalbumin. Furthermore, comparison of the volatiles generated from onions, cooked either alone, or in the presence of meat, showed a significant reduction of key onion-derived disulphides when cooked in the presence of meat, and an even greater reduction of trisulphides. These findings may have implications for consumer acceptance of food products; where these compounds are used as flavourings or where they occur naturally.

Pyrene-functionalised, alternating copolyimide for sensing nitroaromatic compounds

A novel, pyrene-functionalised copolymer has been synthesised in a single step via imidisation of poly(maleic anhydride-alt-1-octadecene) with 1-pyrenemethylamine, and its potential for the detection of volatile nitro aromatic compounds (NACs) evaluated. The new copolymer forms complexes in solution with NACs such as 2,5-dinitrobenzonitrile, as shown by H-1 NMR, UV-vis and fluorescence spectroscopy. Moreover, thin films of this copolymer, cast from THF solution, undergo almost instantaneous fluorescence quenching when exposed to the vapour of 2,5-dinitrobenzonitrile (a model for TNT) at ambient temperatures and pressures.

A DFT study of free radicals formed from artemisinin and related compounds

Ab initio calculations using density functional theory have shown that the reactions that occur between artemisinin, 1, a cyclic trioxane active against malaria, and some metal ions and complexes lead to a series of radicals which are probably responsible for its therapeutic activity. In particular it has been shown that the interaction of Fe(H) with artemisinin causes the O-O bond to be broken as indeed does Fe(III) and Cu(I), while Zn(II) does not. Calculations were carried out with Fe(II) in several different forms including the bare ion, [Fe(H2O)(5)](2+) and [FeP(Im)] (P, porphyrin; Im, imadazole) and similar results were obtained. The resulting oxygen-based radicals are readily converted to more stable carbon-based radicals and/or. stable products. Similar radicals and products are also formed from two simple model trioxanes 2 and 3 that show little or no therapeutic action against malaria although some subtle differences were obtained. This suggests that the scaffold surrounding the pharmacophore may be involved in molecular recognition events allowing efficient uptake of this trioxane warhead into the parasite. (C) 2004 Elsevier B.V. All rights reserved.

DNA cleavage and antitumour activity of platinum(II) and copper(II) compounds derived from 4-methyl-2-N-(2-pyridylmethyl)aminophenol: spectroscopic, electrochemical and biological investigation

The reaction of the redox-active ligand, Hpyramol (4-methyl-2-N-(2-pyridylmethyl)aminophenol) with K2PtCl4 yields monofunctional square-planar [Pt(pyrimol)Cl], PtL-Cl, which was structurally characterised by single-crystal X-ray diffraction and NMR spectroscopy. This compound unexpectedly cleaves supercoiled double-stranded DNA stoichiometrically and oxidatively, in a non-specific manner without any external reductant added, under physiological conditions. Spectro-electrochemical investigations of PtL-Cl were carried out in comparison with the analogue CuL-Cl as a reference compound. The results support a phenolate oxidation, generating a phenoxyl radical responsible for the ligand-based DNA cleavage property of the title compounds. Time-dependent in vitro cytotoxicity assays were performed with both PtL-Cl and CuL-Cl in various cancer cell lines. The compound CuL-Cl overcomes cisplatin-resistance in ovarian carcinoma and mouse leukaemia cell lines, with additional activity in some other cells. The platinum analogue, PtL-Cl also inhibits cell-proliferation selectively. Additionally, cellular-uptake studies performed for both compounds in ovarian carcinoma cell lines showed that significant amounts of Pt and Cu were accumulated in the A2780 and A2780R cancer cells. The conformational and structural changes induced by PtL-Cl and CuL-Cl on calf thymus DNA and phi X174 supercoiled phage DNA at ambient conditions were followed by electrophoretic mobility assay and circular dichroism spectroscopy. The compounds induce extensive DNA degradation and unwinding, along with formation of a monoadduct at the DNA minor groove. Thus, hybrid effects of metal-centre variation, multiple DNA-binding modes and ligand-based redox activity towards cancer cell-growth inhibition have been demonstrated. Finally, reactions of PtL-Cl with DNA model bases (9-Ethylguanine and 5'-GMP) followed by NMR and MS showed slow binding at Guanine-N7 and for the double stranded self complimentary oligonucleotide d(GTCGAC)(2) in the minor groove.

Effect of citric acid and glycine addition on acrylamide and flavor in a potato model system

Acrylamide levels in cooked/processed food can be reduced by treatment with citric acid or glycine. In a potato model system cooked at 180 degrees C for 10-60 min, these treatments affected the volatile profiles. Strecker aldehydes and alkylpyrazines, key flavor compounds of cooked potato, were monitored. Citric acid limited the generation of volatiles, particularly the alkylpyrazines. Glycine increased the total volatile yield by promoting the formation of certain alkylpyrazines, namely, 2,3-dimethylpyrazine, trimethylpyrazine, 2-ethyl-3,5-dimethylpyrazine, tetramethylpyrazine, and 2,5-diethyl-3- methylpyrazine. However, the formation of other pyrazines and Strecker aldehydes was suppressed. It was proposed that the opposing effects of these treatments on total volatile yield may be used to best advantage by employing a combined treatment at lower concentrations, especially as both treatments were found to have an additive effect in reducing acrylamide. This would minimize the impact on flavor but still achieve the desired reduction in acrylamide levels.

Sugars and related compounds as flavour precursors in meat

Sugars and related substances, namely sugar phosphates and ribonucleotides, are important meat flavour precursors. In particular, ribose and ribose 5-phosphate have been shown to be important in aroma development in heated model systems. There are few quantitative data on the concentrations and the variations of sugars and related substances in meat. This paper will report on the analysis of glucose, fructose, ribose, ribose 5-phosphate, fructose 6-phosphate, glucose 6-phosphate and inosine 5'-monophosphate (IMP) in aged beef. Sugars and related compounds were extracted from lean meat and derivatised to the corresponding TMS ethers. Analysis and quantitation of the sugars and sugar phosphates were performed using GC and GC/MS, while IMP analysis was performed using capillary electrophoresis (CE).

Evaluation by volatile profile of the synergistic antioxidant effect between bovine serum albumin and virgin olive oil phenolic compounds in an oil-in-water emulsion

THE OXIDATIVE STABILITY OF OIL-IN-WATER EMULSIONS, CONTAINING BOVINE SERUM ALBUMIN (BSA) AND VIRGIN OLIVE OIL PHENOLIC COMPOUNDS, WAS STUDIED BY THE DETERMINATION OF THE FORMATION OF VOLATILE OXIDATION PRODUCTS. FOUR OIL-IN-WATER EMULSIONS WITH AND WITHOUT PHENOLS ISOLATED FROM VIRGIN OLIVE OIL AND BSA WERE PREPARED. THESE MODEL SYSTEMS WERE STORED AT 60 degrees C TO ACCELERATE LIPID OXIDATION. VOLATILE OXIDATION PRODUCTS WERE MONITORED EVERY THREE DAYS BY HEADSPACE SOLID-PHASE MICROEXTRACTION COUPLED WITH GAS CHROMATOGRAPHY. ALTHOUGH INDIVIDUALLY OLIVE OIL PHENOLIC COMPOUNDS AND BSA SHOWED A SIGNIFICANT ANTIOXIDANT ACTIVITY, THE COMBINATION OF THESE COMPONENTS SHOWED A VERY GOOD SYNERGY, QUANTIFIED AS 127%. IN FACT, THE EMULSION CONTAINING BOTH PHENOLIC COMPOUNDS AND BSA SHOWED A VERY LOW LEVEL OF OXIDATIVE DETERIORATION AFTER 45 DAYS STORAGE.

Bovine serum albumin produces a synergistic increase in the antioxidant activity of virgin olive oil phenolic compounds in oil-in-water emulsions

Virgin olive oil is valued for its flavor, but unacceptable off-flavors may develop on storage in food products containing this oil due to oxidation. The oxidative stability of oil-in-water emulsions containing bovine serum albumin (BSA) and virgin olive oil phenolic compounds was studied. Four oil-in-water emulsions with and without BSA and phenols isolated from virgin olive oil were prepared. These model systems were stored at 60 degrees C to speed up lipid oxidation. Primary and secondary oxidation products were monitored every three days. Peroxide values and conjugated diene contents were determined as measures of the primary oxidation products. p-Anisidine values and volatile compounds were determined as measures of the secondary oxidation products. This latter determination was carried out by headspace solid-phase microextraction coupled with gas chromatography. Although olive oil phenolic compounds and BSA contributed some antioxidant activity when present as individual additives, the combination of BSA with phenols in an emulsion showed 58-127% synergy, depending on which analytical method was used in the calculation. The emulsion containing phenolic compounds and BSA showed a low level of deterioration after 45 days of storage at 60 degrees C.

Liposomes and skin: From drug delivery to model membranes

The early eighties saw the introduction of liposomes as skin drug delivery systems, initially promoted primarily for localised effects with minimal systemic delivery. Subsequently, a novel ultradeformable vesicular system (termed "Transfersomes" by the inventors) was reported for transdermal delivery with an efficiency similar to subcutaneous injection. Further research illustrated that the mechanisms of liposome action depended on the application regime and the vesicle composition and morphology. Ethical, health and supply problems with human skin have encouraged researchers to use skin models. 'IYaditional models involved polymer membranes and animal tissue, but whilst of value for release studies, such models are not always good mimics for the complex human skin barrier, particularly with respect to the stratum corneal intercellular lipid domains. These lipids have a multiply bilayered organization, a composition and organization somewhat similar to liposomes, Consequently researchers have used vesicles as skin model membranes. Early work first employed phospholipid liposomes and tested their interactions with skin penetration enhancers, typically using thermal analysis and spectroscopic analyses. Another approach probed how incorporation of compounds into liposomes led to the loss of entrapped markers, analogous to "fluidization" of stratum corneum lipids on treatment with a penetration enhancer. Subsequently scientists employed liposomes formulated with skin lipids in these types of studies. Following a brief description of the nature of the skin barrier to transdermal drug delivery and the use of liposomes in drug delivery through skin, this article critically reviews the relevance of using different types of vesicles as a model for human skin in permeation enhancement studies, concentrating primarily on liposomes after briefly surveying older models. The validity of different types of liposome is considered and traditional skin models are compared to vesicular model membranes for their precision and accuracy as skin membrane mimics. (c) 2008 Elsevier B.V. All rights reserved.

Rifaximin modulates the colonic microbiota of patients with Crohn's disease: an in vitro approach using a continuous culture colonic model system.

Rifaximin, a rifamycin derivative, has been reported to induce clinical remission of active Crohn's disease (CD), a chronic inflammatory bowel disorder. In order to understand how rifaximin affects the colonic microbiota and its metabolism, an in vitro human colonic model system was used in this study. We investigated the impact of the administration of 1800 mg/day of rifaximin on the faecal microbiota of four patients affected by colonic active CD [Crohn's disease activity index (CDAI > 200)] using a continuous culture colonic model system. We studied the effect of rifaximin on the human gut microbiota using fluorescence in situ hybridization, quantitative PCR and PCR–denaturing gradient gel electrophoresis. Furthermore, we investigated the effect of the antibiotic on microbial metabolic profiles, using 1H-NMR and solid phase microextraction coupled with gas chromatography/mass spectrometry, and its potential genotoxicity and cytotoxicity, using Comet and growth curve assays. Rifaximin did not affect the overall composition of the gut microbiota, whereas it caused an increase in concentration of Bifidobacterium, Atopobium and Faecalibacterium prausnitzii. A shift in microbial metabolism was observed, as shown by increases in short-chain fatty acids, propanol, decanol, nonanone and aromatic organic compounds, and decreases in ethanol, methanol and glutamate. No genotoxicity or cytotoxicity was attributed to rifaximin, and conversely rifaximin was shown to have a chemopreventive role by protecting against hydrogen peroxide-induced DNA damage. We demonstrated that rifaximin, while not altering the overall structure of the human colonic microbiota, increased bifidobacteria and led to variation of metabolic profiles associated with potential beneficial effects on the host.