Synthesis and characterization of fluorescent poly(aromatic amide) dendrimers

The synthesis of a series of poly(aromatic amide) dendrimers up to the second generation is described herein. The AB, building block used throughout the synthesis of the dendrimers was the allyl ester of 3,5-diaminocinnamic acid, which has been synthesized from 3,5-dinitrobenzoic acid in good yield with use of a four-step procedure. Dendron synthesis was achieved via a convergent approach with use of a sequence of deprotection/coupling steps. Two commercially available alcohols, L-menthol and citronellol, were coupled to the AB(2) monomer by using an alkyl diacid spacer and two core units; 1,7-diaminoheptane and tris(2-aminoethyl)amine have been used to produce the final dendrimers. Characterization was carried out by NMR and IR spectroscopies, MALDI-TOF mass spectrometry, GPC, and DSC. The novel monomer and dendritic derivatives exhibited a strong fluorescence emission in the visible region (lambda approximate to 500 nm) of the spectrum and a weak emission in the near-infrared (lambda approximate to 850 nm) upon excitation in the near-UV region. The fluorescence emission characteristics were found to be solvent and dendrimer generation dependent.

Relative proportions of polycyclic aromatic hydrocarbons differ between accumulation bioassays and chemical methods to predict bioavailability

Chemical methods to predict the bioavailable fraction of organic contaminants are usually validated in the literature by comparison with established bioassays. A soil spiked with polycyclic aromatic hydrocarbons (PAHs) was aged over six months and subjected to butanol, cyclodextrin and tenax extractions as well as an exhaustive extraction to determine total PAH concentrations at several time points. Earthworm (Eisenia fetida) and rye grass root (Lolium multiflorum) accumulation bioassays were conducted in parallel. Butanol extractions gave the best relationship with earthworm accumulation (r2 ≤ 0.54, p ≤ 0.01); cyclodextrin, butanol and acetone–hexane extractions all gave good predictions of accumulation in rye grass roots (r2 ≤ 0.86, p ≤ 0.01). However, the profile of the PAHs extracted by the different chemical methods was significantly different (p < 0.01) to that accumulated in the organisms. Biota accumulated a higher proportion of the heavier 4-ringed PAHs. It is concluded that bioaccumulation is a complex process that cannot be predicted by measuring the bioavailable fraction alone. The ability of chemical methods to predict PAH accumulation in Eisenia fetida and Lolium multiflorum was hindered by the varied metabolic fate of the different PAHs within the organisms.

Uptake Pathways of Polycyclic Aromatic Hydrocarbons in White Clover

An understanding of the primary pathways of plant uptake of organic pollutants is important to enable the risks from crops grown on contaminated soils to be assessed. A series of experiments were undertaken to quantify the importance of the pathways of contamination and the Subsequent transport within the plant using white clover plants grown in solution culture. Root uptake was primarily an absorption process, but a component of the contamination was a result of the transpiration flux to the shoot for higher Solubility compounds. The root contamination can be easily predicted using a simple relationship with K-OW, although if a composition model was used based on lipid content, a significant under prediction of the contamination was observed. Shoot uptake was driven by the transpiration stream flux which was related to the solubility of the individual PAH rather than the K-OW. However, the experiment was over a short duration, 6 days, and models based on K-OW may be better for crops grown in the field where the vegetation will approach equilibrium and transpiration cannot easily be measured, A significant fraction of the shoot contamination resulted from aerial deposition derived from volatilized PAH. This pathway was more significant for compounds approaching log K-OA > 9 and log K-AW < -3. The shoot uptake pathways need further investigation to enable them to be modeled separately, There was no evidence of significant systemic transport of the PAR so transfer outside the transpiration stream is likely to be limited.

Bile metabolites of polycyclic aromatic hydrocarbons (PAHs) in European eels Anguilla anguilla from United Kingdom estuaries

A total of 94 European eels (Anguilla anguilla) were collected from five estuaries in the UK. The deconjugated metabolites of polycyclic aromatic hydrocarbons (PAHs) in the bile of the eels were separated using HPLC. Six PAH metabolites were identified: 1-hydroxy (1-OH) metabolites of phenanthrene, pyrene and chrysene; and the 1-OH, 3-OH and 7,8 dihydrodiol metabolites of benzo[a]pyrene (BaP). The mean concentration of the six metabolites was greatest in eels from the Tyne (49 muM) followed by the Wear (33 muM), Tees (19 muM), Thames (4 muM) and Severn (2 muM) estuaries. Although 1-OH pyrene was always the dominant compound, there were significant differences (P<0.05) between sites and between estuaries for some metabolites. Normalising the molar concentration of the bile metabolites to the bile biliverdin absorbance reduced sample variation. When the metabolites identified were-each expressed as a percentage of the total detected, the metabolite profile was characteristic for each estuary. (C) 2002 Elsevier Science B.V. All rights reserved.

A healable supramolecular polymer blend based on aromatic π-π stacking and hydrogen bonding interactions

An elastomeric, supramolecular healable polymer blend, comprising a chain-folding polyimide and a telechelic polyurethane with pyrenyl endgroups, is compatibilised by aromatic π−π stacking between the π-electron-deficient diimide groups and the π-electron-rich pyrenyl units. This inter-polymer interaction is key to forming a tough, healable, elastomeric material. Variable temperature FTIR analysis of the bulk material also conclusively demonstrates the presence of hydrogen bonding, which complements the π–π stacking interactions. Variable temperature SAXS analysis shows that the healable polymeric blend has a nanophase-separated morphology, and that the X-ray contrast between the two types of domain increases with increasing temperature, a feature that is repeatable over several heating and cooling cycles. A fractured sample of this material reproducibly regains more than 95% of the tensile modulus, 91% of the elongation to break, and 77% of the modulus of toughness of the pristine material.

Macrocyclic aromatic polysulfones and sulfide-sulfones: synthesis and structural characterisation of molecular pentagons and rectangles

Cyclo-condensation of arylenedithiols with bis(4-chlorophenylenesulfone)s under pseudo-high-dilution conditions affords macrocyclic aromatic sulfide-sulfones which are readily oxidised to all-sulfone-linked macrocycles. The cyclic pentamer of poly(1,4-phenylenesulfone) and cyclic dimer of poly(1,4-phenylenesulfonyl-4,4'-biphenylenesulfone) have been isolated and characterised.

Aromatic-aromatic interaction between metallacycle and phenyl ring

The X-ray crystal structure of [CuL2]ClO4 where L is the 1:1 condensate of benzil-monohydrazone and 2-pyridinecarboxalde-hyde, reveals unprecedented pi - pi interaction between the metallacycles and phenyl rings. The interaction is intramolecular. (C) 2003 Elsevier Science B.V. All rights reserved.

Reversible, nondegradative conversion of crystalline aromatic poly(ether ketone)s into organo-soluble poly(ether dithioketal)s

Crystalline aromatic poly(ether ketone)s Such as PEEK and PEK may be cleanly and reversibly derivatized by dithioketalization of the carbonyl groups With 1,2-ethanedithiol or 1,3-propanedithiol under strong acid conditions. The resulting 1,3-dithiolane and 1,3-dithiane polymers are hydrolytically stable, amorphous, and readily soluble in organic solvents such as chloroform and THF and are thus (unlike their parent polymers) easily characterized by gel permeation chromatography (GPC). GPC analysis of a range of derivatized PEEK samples using light-scattering detection revealed, in some instances, a bimodal molecular weight distribution with a small but potentially significant (and previously undetected) very high-molecular-weight fraction.

Dithioacetalisation of PEEK: a general technique for the solubilisation and characterisation of semi-crystalline aromatic polyketones

The family of semi-crystalline, aromatic, high-temperature thermoplastics known as poly(ether-ketone)s are insoluble in conventional organic solvents, but undergo completely general and quantitatively reversible reactions with alkanedithiols in strong acid media, to give soluble poly(dithioacetal)s, which are readily characterisable by GPC and light scattering techniques.

Principles of sequence-recognition in aromatic polyimides

Pyrene-based molecular tweezers show sequence-specific binding to aromatic polyimides through sterically-controlled donor-acceptor pi-stacking and hydrogen bonding; H-1 NMR spectra of tweezer-complexes with polyimides having different sequence-restrictions show conclusively that the detection of long range sequence-information results from multiple tweezer-binding at adjacent imide residues.

Microfabrication of high-performance aromatic polymers as nanotubes or fibrils by in situ ring-opening polymerisation of macrocyclic precursors

Melt-phase nucleophilic ring-opening polymerisation of macrocyclic aromatic ethers and thioethers at high temperatures within the cylindrical pores of an anodic-alumina membrane, followed by dissolution of the template, enables replication of the membrane's internal pore structure and so affords high-performance aromatic polymers with well-defined fibrillar or tubular morphologies.

Spontaneous ring-opening polymerization of macrocyclic aromatic thioether ketones under transient high-temperature conditions

Spontaneous ring-opening polymerization of macrocyclic aromatic thioether ketones [-1,4-SC6H4CO-C6H4-](n) (n = 3 and 4), in which the thioether linkages are para to the ketone, occurs during rapid, transient heating to 480degreesC, to afford a soluble, semi-crystalline poly(thioether ketone) of high molar mass (eta(inh) > 1.0 dL . g(-1)). Corresponding macrocyclic ether ketone, and a macrocyclic thioether ether ketone in which the thioether linkage is para to the ether rather than to the ketone, show no evidence of polymerization under analogous conditions.

Polymer-supported nitroxyl catalysts for selective oxidation of alcohols

Novel non-toxic poly(ethylene glycol)-supported 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) moieties are demonstrated to give an excellent interfacial catalysis for the selective oxidation of alcohols to the corresponding carbonyl species in biphasic media and investigation for the recovery of these new macromolecular catalysts via precipitation with diethyl ether after catalysis has also been briefly studied.