VOLTAMMETRY OF CYTOCHROME-C ENTRAPPED IN HYDROGEL MEMBRANE ON GRAPHITE ELECTRODE

The voltammetric behavior of cytochrome c entrapped in hydrogel membranes at paraffin wax-impregnated spectroscopic graphite electrodes (WISGE) was studied in this paper. A pair of well-defined peaks appeared at +70 mV (vs. Ag/AgCl). Beside these two peaks, another pair of peaks emerged at around +225 mV. Further investigations suggested that at least three states of cytochrome c existed in the membranes due to the special structure of the hydrogel. The native conformation of cytochrome c molecules was stabilized by the hydrophilic environment that was formed by the hydroxyl structure of the membranes and facilitated the cytochrome c electron transfer reaction at +70 mV. The molecules directly adsorbed on the surface of the graphite electrode were responsible for the redox peaks at around +225 mV. Whether the adsorption peaks were detectable or not was related to the thickness of membranes and the pre-retaining time before the formation of membranes.

CHEMICAL-IONIZATION MASS-SPECTROMETRY OF SOME NITRO-CONTAINING BIFUNCTIONAL AROMATIC-COMPOUNDS - LOCATION OF PROTONATION SITE

It is found that the nitro substituent of some aromatic bifunctional compounds shows unusual reactivity towards protonation. In the chemical ionization mass spectra of nitrobenzoic acids and their esters and amides, and of nitrophenols and their ethers, protonations on the carboxyl, ester, amide, hydroxyl or alkoxyl groups are highly suppressed by that on the nitro group. As a result, fragmentations based on protonation on these groups unexpectedly become negligible. Ortho effects were observed for all the ortho isomers where the initial protonation on the nitro group is followed by an intramolecular proton transfer reaction, which leads to the expected 'normal' fragmentations. Protonation on the nitro substituent is much more favourable in energy than on any of the other substituents. The interaction of the two substituents through the conjugating benzene ring is found to be responsible for this 'unfair' competitive protonation. The electron-attracting nitro group strongly destabilizes the MH+ ions formed through protonation on the other substituent; although the COR (R = OH, OMe, OEt, NH2) groups are also electron-withdrawing, their effects are weaker than that of NO2; thus protonation on the latter group produces more-stable MH+ ions. On the other hand, an electron-releasing group OR (R = H, Me, Et) stabilizes the nitro-protonated species; the stronger the electron-donating effect of this group the more stable the nitro-protonated ions.

COMPATIBILIZATION OF POLYPROPYLENE POLY(ETHYLENE OXIDE) BLENDS AND CRYSTALLIZATION BEHAVIOR OF THE BLENDS

The compatibilization of incompatible polypropylene (PP)/poly(ethylene oxide) (PEO) blends was studied. The experimental results showed that the graft copolymer [(PP-MA)-g-PEO] of maleated PP (PP-MA) and mono-hydroxyl PEO (PEO-OH) was a good compatibilize

SYNTHESIS AND CRYSTALLIZATION BEHAVIOR OF (PP-MA)-G-PEO

A new graft copolymer (PP-MA)-g-PEO was synthesized by means of the chemical reaction between maleated polypropylene (PP-MA) and mono hydroxyl poly(ethylene oxide) (PEO-OH). The effect of reaction conditions on the degree of grafting of PEO-OH was studied

MODIFIED POLYSULFONES .1. SYNTHESIS AND CHARACTERIZATION OF POLYSULFONES WITH UNSATURATED END-GROUPS

Chloro-terminated polysulfones with various molecular weights were modified with poly(ethylene oxide) and poly[(ethylene oxide)(propylene oxide)] macromers carrying alpha-hydroxyl and omega-allyl end groups via classical polycondensation reactions. The pr

SOME CHEMICAL-CHANGES IN CHITOSAN INDUCED BY GAMMA-RAY IRRADIATION

Chitosan was subjected to gamma-ray irradiation in air. It was found that the -NH2 group is more sensitive to irradiation than the -NHCOCH3 group, and moreover, the hydroxyl group increases with increasing radiation dose while the C-O-C group decreases, but no evidence for carbonyl formation was observed.

MISCIBILITY AND PHASE-BEHAVIOR IN BLENDS OF POLY(HYDROXYETHER OF BISPHENOL-A) WITH POLY(ETHYLENE OXIDE-CO-PROPYLENE OXIDE)

The miscibility of poly(hydroxyether of bisphenol A) (phenoxy) with a series of poly(ethylene oxide-co-propylene oxide) (EPO) has been studied. It was found that the critical copolymer composition for achieving miscibility with phenoxy around 60-degrees-C is about 22 mol % ethylene oxide (EO). Some blends undergo phase separation at elevated temperatures, but there is no maximum in the miscibility window. The mean-field approach has been used to describe this homopolymer/copolymer system. From the miscibility maps and the melting-point depression of the crystallizable component in the blends, the binary interaction energy densities, B(ij), have been calculated for all three pairs. The miscibility of phenoxy with EPO is considered to be caused mainly by the intermolecular hydrogen-bonding interactions between the hydroxyl groups of phenoxy and the ether oxygens of the EO units in the copolymers, while the intramolecular repulsion between EO and propylene oxide units in the copolymers contributes relatively little to the miscibility.

NORMAL COORDINATE TREATMENT OF LEU(5)-ENKEPHALIN IN THE CRYSTAL-STATE

Vibrational studies on the neuropentapeptide Leu5-enkephalin were performed for the crystal state where different specific conformations can arise. In the present case, the peptide adopts a double fused folded conformation (beta-turn), the presence of which in the crystal state is directly related to the nature of the solvent used for its crystallization. This study completes other work relating to similar conformations of isolated molecules. It can be seen that specific interactions in the crystal state perturb to a large extent the vibrational relationships between the amide frequencies and the specific sets of dihedral angles characteristic of the particular type of turn. The tyrosyl moiety and its frequency dependence on its hydrogen bond state was especially investigated both for the Fermi resonance and the hydroxyl bending modes.

THERMAL-DECOMPOSITION PROCESS OF SOME RARE-EARTH NITRILOTRIACETIC ACID SERINE MIXED COMPLEXES

Thermal decomposition processes of the mixed complexes of nitrilotriacetates of Pr, Sm, Tb, Ho and Tm with 2-amino-3-hydroxypropionic acid have been investigated. The results indicate that serine may coordinate to the rare earth ion via its hydroxyl group, not by means of its carboxyl group. From the thermogravimetric and the derivative thermogravimetric curves it can be deduced that there may be six or seven steps in the thermal decomposition process of these mixed complexes, and that not all thermal decomposition processes in these mixed complexes are the same. Some possible thermal decomposition reactions have been proposed, and the differences between the thermal decomposition processes of these complexes are also discussed.

EFFECT OF REPTATION ON FRACTURE-MECHANICS OF RUBBER NETWORKS

End-linked hydroxyl-terminated polybutadiene containing unattached linear polybutadiene was used to study the effect of reptating species on the fracture mechanics of rubber networks. The concentration of reptating species in the networks ranged from 0 to 100%. The fracture mechanics of the networks was described using the critical strain energy release rate in mode III testing, i.e. the tearing energy. The tearing energy was measured at room temperature using a 'trouser' specimen at a strain rate spanning five logarithmic decades. When the strain rate was as low as 10(-4) s-1, the tearing energy of the networks increased with reduction in reptating species. In this case the reptating species did not contribute to the tearing energy of the networks due to relaxation. Hence, the tearing energy increased with the number of crosslinked chains per unit volume in the networks. At a strain rate ranging from 10(-3) to 10(-1) s-1, the tearing energy of the networks was governed by local viscosity. The tearing energies of the networks containing various amounts of reptating species were superimposed to give a master curve based on the Williams-Landel-Ferry equation.

A potent anti-oxidant property: fluorescent recombinant alpha-phycocyanin of Spirulina

To express and product a fluorescent antioxidant holo-alpha-phycocyanin (PC) of Spirulina platensis (Sp) with His-tag (rHHPC; recombinant holo-alpha-phycocyaninof Spirulina platensis with His-tag) in 5-l bench scale. A vector harbouring two cassettes was constructed: cpcA along with cpcE-cpcF in one cassette; ho1-pcyA in the other cassette. Lyases CpcE/F of Synechocystis sp. PCC6803 (S6) could catalyse the 82 site Cys in apo-alpha-PC of Sp linking with bilin chromophores, and rHHPC was biosynthesized in Escherichia coli BL21. The constant feeding mode was adopted, and transformant reached the biomass of rHHPC up to 0.55 g l(-1) broth in 5-litre bench scale. rHHPC was purified by Ni2+ affinity column conveniently. The absorbance and the fluorescence emission spectra of rHHPC had lambda(max) at 621 and 650 nm, respectively. The IC50 values of rHHPC were 277.5 +/- 25.8 mu g ml(-1) against hydroxyl radicals and 20.8 +/- 2.2 mu g ml(-1) against peroxyl radicals. Combinational biosynthesis of rHHPC was feasible, and the constant feeding mode was adopted to produce good yields of rHHPC. Fluorescent rHHPC with several unique qualitative and quantitative features was effective on scavenging hydroxyl and peroxyl radicals. A potent antioxidant rHHPC was co-expressed, produced and characterized for nutritional and pharmacological values, which would help to develop phycobiliproteins' applications in their fluorescent and biological activities.

Antioxidative principals of Jussiaea repens: an edible medicinal plant

Jussiaea repens L. (JRL) is an edible medicinal plant and is also used as a vegetable by the local people in southwestern China. The crude extract and its four fractions derived from JRL were evaluated for the 1,1-diphenyl-2-picrylhydrazyl radical-scavenging ability, hydroxyl radical-scavenging capacity and the potassium ferricyanide reduction property. The ethyl acetate-soluble fraction (EAF) and EAF6 (a subfraction derived from EAF) were the most valuable fraction and subfraction, respectively. Furthermore, bioactivity-guided chromatographic fractionation revealed that three pure compounds greatly contributed to the antioxidant activities. Qualitative and quantitative analyses of the major antioxidant constituents in the extract were systematically conducted by NMR, mass spectral analyses and RP-HPLC. The result demonstrated that rosmarinic acid (2.00 mg g(-1) JRL dry weight) quercetin 3-O-beta-D-glucopyranoside (9.88 mg g(-1) JRL dry weight), and kaempferol 3-O-beta-D-glucopyranoside (1.85 mg g(-1) JRL dry weight) were the major antioxidative constituents in JRL. These compounds are reported for the first time from this plant.

The influence of the cation of quaternized chitosans on antioxidant activity

Various quaternized chitosans (QCSs) were synthesized according to previous method. Their reducing power and antioxidant potency against hydroxyl radicals ((OH)-O-center dot) and hydrogen peroxide (H2O2) were explored by the established systems in vitro. The QCSs exhibited markedly antioxidant activity, especially TCEDMCS, whose IC50 on hydroxyl radicals was 0.235 mg/mL. They showed 65-80% scavenging effect on hydrogen peroxide at a dose of 0.5 mg/mL. Generally, the antioxidant activity decreased in the order TCEDMCS > TBEDMCS > EDMCS > PDMCS > IBDMCS > Chitosan. Furthermore, the order of their (OH)-O-center dot and H2O2 scavenging activity was consistent with the electronegativity of different substituted groups in the QCSs. The QCSs showed much stronger antioxidant activity than that of chitosan may be due to the positive charge density of the nitrogen atoms in QCSs strengthened by the substituted groups. (C) 2009 Elsevier Ltd. All rights reserved.

Biosynthesis of fluorescent allophycocyanin alpha-subunits by autocatalysis in Escherichia coli

APC (allophycocyanin) is widely used for fluorescence tagging and may be a promising antioxidant agent for use within the food and pharmaceutical industries. Chromophore attachment to apo-ApcA (apo-APC alpha-subunit without chromophore) can be auto-catalysed both in vitro and in vivo. In the present study, a plasmid containing genes of apo-ApcA and chromophore synthetases (HOI (ferredoxin-dependent haem oxygenase) and PcyA (phycocyanobilin:ferredoxin oxidoreductase)] was constructed and expressed in Escherichia coli. The results show that holo-ApcA (APC alpha-subunit with chromophore) can be synthesized by autocatalysis in E. coli. Recombinant holo-ApcA showed the same spectral and fluorescent properties as PC (phycocyanin) and could serve as a good substitute for native PC for fluorescent tagging. Moreover, recombinant ApcA can inhibit hydroxyl and peroxyl radicals more strongly than holo-ApcA and native APC. The EC50 values were 296.4 +/- 22.4 mu g/ml against hydroxyl radicals and 38.5 +/- 2.6 mu g/ml against peroxyl radicals.

Factors that effect antioxidant activity of C-phycocyanins from Spirulina platensis

Currently, antioxidants are added in the human diet to prevent free radical-induced cell damage, and there has been an explosive interest in the use of antioxidant nutritional supplements. The effects of different factors on the antioxidant activity of phycocyanins (PCs) were studied. The results showed that PCs generated hydroxyl radicals in the light, while scavenging them in the dark. When PCs were denatured by sodium dodecyl sulfate, urea and in alkaline condition, their ability to generate hydroxyl radicals disappeared and that of scavenging them greatly increased. This showed that the phycobilin moiety is the main part of PC involved in scavenging hydroxyl radicals. Trypsin hydrolysis of PCs showed that the apoprotein portion of the molecule also made a significant contribution to the antioxidant activity.