Photo-stabilising performance of a hindered piperidine compound in polypropylene film: Anti-oxidant/light stabiliser effects

The effect of various primary and secondary anti-oxidants and light stabiliser systems on the photo-stabilising performance of a hindered piperidine compound bis[2,2,6,6-tetramethyl-4-piperidinyl]-sebacate, in polypropylene film has been examined. None of the anti-oxidants or light stabilisers gave an additive effect with the hindered piperidine compound. In many cases antagonistic effects were observed. The effects observed are discussed in relation to our current understanding of the mechanistic behaviour of these hindered piperidine systems.     

Rapid detection and characterization of minor reactive metabolites using stable-isotope trapping in combination with tandem mass spectrometry

Stable-isotope trapping combined with mass spectrometry (MS) neutral loss scanning has recently been developed as a high-throughput method for the in vitro screening of major reactive metabolites. In fact, detection and identification of minor reactive metabolites are equally important since the minor metabolites, even though at low levels, may be highly reactive and also play an important role in drug-induced adverse reactions. In this study, 2-acetylthiophene, clozapine, troglitazone and 7-methylindole were selected as model compounds to further validate the advantages of this method for rapid detection and structural characterization of minor glutathione (GSH) adducts derived from reactive metabolites. The utility of the current method was clearly demonstrated by successful identification of novel reactive metabolites at low levels and also minor ones either masked by non-specific responses or co-eluted with other conjugates. In comparison with existing methods, this method is sensitive, efficient, and suitable for rapid screening and more complete profiling of reactive metabolites.     

The photo-stabilisation of polypropylene: A review

The incorporation of antioxidants and light stabilisers in polymers is important in order to preserve their long-term use in the environment. The mechanisms of photo-stabilisation are complex and with continued research grow even more in complexity. The processes involved are further complicated by the effects of processing which can in many cases dramatically influence the performance of the additives. This review presents an in-depth account of the complex mechanisms involved in both thermal and photochemical oxidation of polyolefins, with particular emphasis on polypropylene and the interactions that take place thermally.     

Structural Studies on some Iodoantimonate and Iodobismuthate Anions

The reaction between BiI₃ and two equivalents of dmpu (dmpu = N,N′-dimethylpropylene urea) in thf (tetrahydrofuran) or toluene affords dark red crystals of the complex [Bi(dmpu)₆][Bi₃I₁₂] which was characterised by X-ray crystallography and consists of octahedral [Bi(dmpu)₆]³⁺ cations and [Bi₃I₁₂]^3? anions both with 3 symmetry. An analogous reaction between SbI₃ and dmpu afforded orange crystals of what is probably a hydrolysis product, [C₅NH₆]₂[H(dmpu)₂][Sb₂I₉], which was also characterised by X-ray crystallography and contains a face-shared bioctahedral [Sb₂I₉]^3? anion with two pyridinium cations and a hydrogen bonded [H(dmpu)₂]⁺ cation. [CH₂?C(C₆H₄-4-NO₂)CH₂NMe₃]I and one equivalent of SbI₃ afforded the orange crystalline complex [CH₂?C(C₆H₄-4-NO₂)CH₂NMe₃]₃[Sb₂I₉] an X-ray crystallographic study of which revealed a face-shared bioctahedral [Sb₂I₉]^3? anion similar to that present in [C₅NH₆]₂[H(dmpu)₂][Sb₂I₉]. Four equivalents of BiI₃ and [CH₂?C(C₆H₄-4-NO₂)CH₂NMe₃]I afforded the complex [CH₂?C(C₆H₄-4-NO₂)CH₂NMe₃]₃[Bi₃I₁₂], the [Bi₃I₁₂]^3? anion being essentially identical to that encountered in [Bi(dmpu)₆][Bi₃I₁₂]. [CH₃(CH₂)₂COS(CH₂)₂NMe₃]I and four equivalents of SbI₃ yielded orange crystals of the complex [CH₃(CH₂)₂COS(CH₂)₂NMe₃]₄[Sb₈I₂₈] which was also characterised by X-ray crystallography and shown to contain a new structural type of [E₈X₂₈]^4? anion (E = As, Sb, Bi; X = halide).     

Generation and absolute reactivity of an aryl enol radical cation in solution

Laser flash photolysis of 1-bromo-1-(4-methoxyphenyl)acetone in acetonitrile leads to the formation of the alpha-acyl 4-methoxybenzyl radical that under acidic conditions rapidly protonates to give detectable amounts of the radical cation of the enol of 4-methoxyphenylacetone. This enol radical cation is relatively long-lived in acidic acetonitrile (tau approximately equal to 200 micros), which is on the same order of magnitude as the radical cations of other 4-methoxystyrene derivatives. Rate constants for deprotonation of the radical cation and the acid dissociation constant for the enol radical cation were also determined using time-resolved absorption spectroscopy. Deprotonation is rapid, taking place with a rate constant of 3.9 x 10(6) s(-1), but the enol radical cation is found to be only moderately acidic in acetonitrile having a pK(a) = 3.2. The lifetime of the enol radical cation was also found to be sensitive to the presence of oxygen and chloride. The sensitivity toward oxygen is explained by oxygen trapping the vinyloxy radical component of the enol radical cation/vinyloxy equilibrium, while chloride acts as a nucleophile to trap the enol radical cation.     

Analysis of aminophospholipid molecular species by methyl-beta-cyclodextrin modified micellar electrokinetic capillary chromatography with laser-induced fluorescence detection

Micellar electrokinetic capillary chromatography (MEKC) with laser-induced fluorescence detection is used for the analysis of three classes of aminophospholipids: phosphatidylethanolamine (PE), phosphatidylserine (PS), and lysophosphatidylethanolamine (LPE) molecular species. 3-(2-Furoyl) quinoline-2-carboxaldehyde (FQ), a fluorogenic dye, was employed for labeling of these phospholipids. The FQ-labeled lipid species were then separated by sodium deoxycholate MEKC modified with methyl-beta-cyclodextrin. Baseline resolution of each class of phospholipids was achieved within 7 min. The migration time in each class increased with the carbon number of their side aliphatic chain. Separation efficiencies of approximately 3x10(5) plates were observed for most of these species. Concentration detection limits (3 sigma) were from 10(-9) to 10(-10) M for PE and LPE species and from 10(-8) to 10(-9) M for PS species. The relative standard deviations for migration time and peak area were less than 0.9% and 4.5%, respectively, for seven PE species. This method was applied to the separation of PE isolated from HT29 human colon cancer cells and roughly 30 PE species were resolved.     

Donor–acceptor complexes in copolymerization. LVIII. Alternating diene–dienophile copolymers. 12. Structure of furan–maleic anhydride copolymers prepared from the monomers and the diels-Alder adduct

The copolymerization of furan with maleic anhydride in the presence of a perester or azobisiso-butyronitrile at 50 or 70°C yields an unsaturated equimolar, alternating copolymer in which the furan units have 3,4 unsaturation and 2,5 linkages. The furan–maleic anhydride Diels-Alder adduct undergoes retrograde dissociation in solution at 70°C and, in the presence of radical catalysts, yields the same unsaturated alternating copolymer as is obtained from the monomers. The adduct undergoes homopolymerization in the presence of a rapidly decomposing perester at 50°C to yield a saturated polymer having a rearranged structure containing 3-oxabicyclo[2.2.1]heptane-5,6-dicarboxylic anhydride repeating units with 2,7 linkages.     

Spectrophotometric assay of chloramine-T using sulfanilamide

A new spectrophotometric method for the assay of very small amounts of chloramine-T has been developed using sulfanilamide. This method is simple and accurate within the limits described.     

Microwave-assisted decarboxylation of bicyclic 2-pyridone scaffolds and identification of Abeta-peptide aggregation inhibitors

A reagent-free microwave-assisted decarboxylation procedure for carboxylic acid functionalized bicyclic 2-pyridones has been developed. This new method, based on microwave heating at 220 degrees C for 600 seconds in N-methyl pyrrolidone (NMP), proved to be practical and very efficient, resulting in decarboxylated 2-pyridones in near-quantitative yields. The decarboxylated products and the intermediate 2-pyridones in the form of carboxylic acid methyl esters and carboxylic acids were screened for their effect on Abeta-peptide aggregation. Two out of the 21 2-pyridones described in this study inhibited amyloid formation of the Alzheimer Abeta(1-40) peptide. The effect was seen even at a 4 : 1 ratio of 2-pyridone and monomeric Abeta-peptide.     

Radical-catalyzed homopolymerization of maleic anhydride in presence of polar organic compounds

Polar organic compounds either (1) inhibit the peroxide-catalyzed bulk homopolymerizations of both MAH and MMA at 80°C, (2) do not inhibit the polymerization of either MAH or MMA, or (3) inhibit the polymerization of MAH but not that of MMA. Compounds generally used as polymerization inhibitors or antioxidants inhibit the polymerizations of both MAH and MMA, presumably by interaction with peroxide decomposition products. Ketones, ethers, acids, esters, nitriles, imides, sulfones, sulfonates, sulfonamides, and acyl disulfides do not inhibit either MAH or MMA polymerization. However, amides, lactams, carbamates, amine oxides, phosphites, phosphates, phosphonates, phosphoramides, phosphine oxides, monosulfides, sulfoxides, aryl disulfides, and thiazyl disulfides inhibit the polymerization of MAH but not that of MMA. Inhibition presumably occurs as a result of electron transfer from the nitrogen-, phosphorous- or sulfur-containing electron donor compound to the MAH carbocation which is an intermediate in the polymerization of MAH.