RHEOLOGICAL PROPERTIES FOR CONCENTRATED-SOLUTION OF CHITOSAN - DEPENDENCE OF SOLVENTS

Rheological properties for concentrated solution of chitosan were investigated in different solvents, such as HCOOH, CH3COOH, HCl and 0.2 mol.dm-3 CH3COOH+ 0.l mol.dm-3 CH3COONa aqueous solutions. It was shown that viscosities and flow behavior of the sol

Solution properties of doped polyaniline

Solution properties of polyaniline (PAn) doped by camphorsulfonic acid (CSA) were examined. PAn-CSA behaves like a polyelectrolyte to different extents depending on the solvent used. In an m-cresol/chloroform solution, PAn-CSA exhibits an expanded chain conformation because of its polyelectrolytic properties. Dilute and concentrated solution properties of PAn-CSA indicate that PAn-CSA is a semirigid polymer which has strong interchain interactions.

Electrophoretic migration behavior of DNA fragments in polymer solution

A newly developed polymer coil shrinking theory is described and compared with the existing entangled solution theory to explain electrophoretic migration behaviour of DNA in hydroxypropylmethylcellulose (HPMC) polymer solution in buffer containing 100 mM tris(hydroxymethyl)aminomethane 100 mM boric acid, 2 mm ethylenediaminetetraacetic acid at pH 8.3. The polymer coil shrinking theory gave a better model to explain the results obtained. The polymer coil shrinking concentration, C-s, was found to be 0.305% and the uniform entangled concentration, C+, 0.806%. The existence of three regions (the dilute, semidilute, and concentrated solution) at different polymer concentrations enables a better understanding of the system to guide the selection of the best conditions to separate DNA fragments. For separating large fragments (700/800 bp), dilute solutions (HPMC < 0.3%) should be used to achieve a short migration time (10 min). For small fragments (200/300 bp), concentrated solutions are preferred to obtain constant resolution and uniform separation. The best resolution is 0.6% HPMC due to a combined interaction of the polymer coils and the entangled structure. The possibility of DNA separation in semidilute solution is often neglected and the present results indicate that this region has a promising potential for analytical separation of DNA fragments.

New Modified Dipping Method Using 4-hexylresorcinol for Preventing Blackspot Formation in Prawns.

Industry acceptance of alternative sulphite treatments for preventing blackspot in prawns is limited. This study demonstrated that dipping prawns (Penaeus monodon and Fenneropenaeus merguiensis) in a less concentrated solution for longer times provides better control of blackspot formation than the recommended 2 minute dip in 50 mg/L 4-hexylresorcinol. Protection improved as modified dipping times and solution concentrations increased. Blackspot protection provided by most of the modified dip methods was more effective than a 1 minute dip in 1% sodium metabisulphite. The recommended 2 minute dip method should be limited to 125 kg when used on consecutive 25-kg batches of prawns. Yields increased by less than 10% even after 72-hour exposure in the modified dip. The new dipping method meets most international residue standards when applying the modified treatments evaluated.

Semimicro determination of selenium and tellurium by chloramine-T oxidation

Finely divided selenium and tellurium undergo oxidation to selenic and orthotelluric acids by a concentrated solution of chloramine-T in acid medium. An analytical procedure (accurate to <1 %) has been developed based on this reaction.

Distribution of transverse chain fluctuations in harmonically confined semiflexible polymers

Two different experimental studies of polymer dynamics based on single-molecule fluorescence imaging have recently found evidence of heterogeneities in the widths of the putative tubes that surround filaments of F-actin during their motion in concentrated solution. In one J. Glaser, D. Chakraborty, K. Kroy, I. Lauter, M. Degawa, N. Kirchesner, B. Hoffmann, R. Merkel, and M. Giesen, Phys. Rev. Lett. 105, 037801 (2010)], the observations were explained in terms of the statistics of a worm-like chain confined to a potential determined self-consistently by a binary collision approximation, and in the other B. Wang, J. Guan, S. M. Anthony, S. C. Bae, K. S. Schweizer, and S. Granick, Phys. Rev. Lett. 104, 118301 (2010)], they were explained in terms of the scaling properties of a random fluid of thin rods. In this paper, we show, using an exact path integral calculation, that the distribution of the length-averaged transverse fluctuations of a harmonically confined weakly bendable rod (one possible realization of a semiflexible chain in a tube), is in good qualitative agreement with the experimental data, although it is qualitatively different in analytic structure from the earlier theoretical predictions. We also show that similar path integral techniques can be used to obtain an exact expression for the time correlation function of fluctuations in the tube cross section. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4712306]

Biossorção de tório e urânio pela macroalga marinha sargassum filipendula

Por ser um material de baixo custo e apresentar propriedades ligantes, a macroalga marinha Sargassum filipendula vem sendo utilizada como material biossorvente no processo de biossorção de metais. No presente trabalho a alga marrom foi utilizada no estudo cinético e de equilíbrio dos íons de tório e urânio individuais e os resultados comparados à biossorção desses metais em sistema binário. Os testes foram realizados nas concentrações 1 e 10 mg/L e pH= 1,0 e 4,0 na temperatura de 25 1C. A melhor condição para biossorção de tório foi encontrada para 1 mg/L e pH= 1,0, enquanto que para urânio foi em 1 mg/L e pH= 4,0. O estudo cinético de biossorção de tório mostrou que o modelo de segunda ordem descreve melhor os dados experimentais em 1 mg/L (R2= 0,9987) e 10 mg/L (R2= 0,9919) em pH= 1,0 e 1 mg/L (R2= 0,9976) em pH= 4,0, enquanto em 10 mg/L (R2= 0,9787) pH= 4,0 a curva encontrada representou uma cinética de primeira ordem. Para a cinética de urânio os dois modelos se adequaram bem aos dados em ambas as condições experimentais. O estudo de equilíbrio mostrou um perfil crescente de captação de tório, com uma remoção de 96% e 54% do metal em pH= 1,0 e 4,0, respectivamente, a partir da Co= 1 mg/L. A melhor eficiência de captação dos íons de urânio foi de 33% para Co= 100 mg/L em pH= 1,0 e 71% para Co= 1 mg/L em pH= 4,0. Os dados experimentais da isoterma de tório mostraram-se mais adequados ao modelo de Freundlich para pH= 1,0, enquanto que para o pH= 4,0 esses foram melhor representados pelo modelo de Langmuir, com valores de coeficiente de determinação superiores. Em relação à isoterma do urânio, o modelo de Freundlich representou bem os dados experimentais. Os parâmetros de equilíbrio calculados a partir do modelo de Langmuir (kL, qmax ) e Freundlich (kF, n) indicaram uma maior afinidade da biomassa pelos íons de tório em ambas as condições experimentais. O estudo de equilíbrio do sistema binário mostrou que a biossorção dos íons de tório não é afetada pela presença do urânio em solução. Por outro lado, a sorção do urânio foi fortemente afetada pela coexistência com os íons de tório.

Efeito da temperatura de incubação na cinética e no equilíbrio da biossorção do cádmio por Sargassum filipendula

O uso de biomassas para biossorção de metais pesados é bem documentado na literatura e vários tipos de espécies de microrganismos e algas já foram testados. A maior parte destes trabalhos foi realizada com biomassa seca para prevenir qualquer resposta metabólica indesejável. Vários estudos na literatura sugerem o uso de biomassa seca sobre condições moderadas, tais como secagem ao sol; por outro lado, vários trabalhos recomendam a faixa de 313K a 353K para garantir completa inativação da biomassa. O efeito da biomassa seca ao sol a 303K e seca a 333K em estufa na remoção de Cd2+ é aqui reportado. A avaliação dos resultados foi baseada na cinética e capacidade de remoção do metal pela alga Sargassum filipendula. Os resultados indicam que a adsorção máxima de metal não foi notadamente reduzida quando a biomassa seca em estufa foi usada, para concentrações de cádmio na faixa de 10,0 a 500,0 mg L-1. O estudo cinético realizado indicou que o modelo de pseudo segunda ordem ajustou melhor os dados experimentais, tanto para uma solução diluída (10 mg L-1) quanto para a concentrada (100 mg L-1). Em ambos os casos, os efeitos da secagem em estufa, a 60C refletiu-se suavemente na remoção do metal. Os dados experimentais foram melhor ajustados pelo modelo de Langmuir em comparação com o modelo de Freundlich. Análises termogravimétricas mostraram que não havia dano estrutural no biossorvente devido à secagem em estufa. O espectro de infravermelho não indicou diferença entre a biomassa in natura e seca. O efeito da temperatura na biossorção do metal significativo na faixa de 303K a 328K, refletindo-se na capacidade de remoção do cádmio

"Sandglass"-shaped self-assembly of coil-rod-coil triblock copolymer containing rigid aniline-pentamer

The amphiphilic PEG1 500-b-EM AP-b-PEG1 500 (EM PAP) triblock copolymer of poly(ethylene glycol) (PEG) and emeraldine aniline-pentamer (EM AP) in its concentrated solution can self-assemble into a special shape like "sandglass", as observed by transmission electron microscopy (TEM), field emission scanning electron microscopy (ESEM) and atomic force microscopy (AFM). This "sandglass"- shaped assembly is composed of several "rods" aggregated in the middle, with every "rod" being about 8 VLrn in length and 300 nm in diameter.

Influence of intermolecular entanglements on the glass transition and structural relaxation behaviors of macromolecules. 2. Polystyrene and phenolphthalein poly(ether sulfone)

The effect of entanglements on the glass transition and structural relaxation behaviors has been studied for polystyrene (PS) and phenolphthalein poly(ether sulfone) (PES-C) samples by fast evaporation of the solution of concentrations varying from above the overlapping concentration to far below it, and compared to the results we have studied previously in PC. It has been found that for all the polymers we have studied, in the concentrated solution region, the T-g of the samples obtained from solution are independent of the change of concentration and are very close to that of normal bulk samples, whereas in the dilute solution region the T-g of the samples decrease with the logarithm of decreasing concentration. The critical concentrations that divide the two distinct regions for the three polymers are 0.9% g/mL for PC, 0.1% g/mL for PS, and 1% g/mL for PES-C. The decrease of T-g of the samples is interpreted by the decrease of intermolecular entanglements as the isolation of polymer chains, and the entanglement of polymer chains restrained the mobility of the segments. The structural relaxation behavior of the polymers is also found to be different from that of normal bulk samples. The enthalpies of single-chain samples are lower than that of the bulk ones, which correspond to the lower glass transition temperature; the peaks are lower and broader, and the relaxed enthalpy is much lower as compared to that of bulk samples. In the three polymers we have studied, the influence of change of entanglements on both the decrease in glass transition temperature and relaxed enthalpy is the most significant for PS and the least for PES-C. It is indicated that the interactions in the flexible polymers are weak; thus, the restraint of the entanglements on the mobility of the segments plays a more important role in the flexible polymers, and the change of entanglement in the flexible polymers has a more significant influence on the physical properties.

Effect of urea on synchronous fluorescence spectra and electrochemical behaviour of cytochrome c

The changes of the synchronous fluorescence spectra and the electrochemical behaviour of cytochrome c with the urea concentration are studied. It has been found that with the increase of urea concentration, there occur sequentially the deaggregation of cytochrome c molecules, the increase of exposure extent of the heme group to the solvent, the disruption of Fe-S bond of the heme group and the change in the electrochemical behaviour of cytochrome c. It is suggested that the reason why the electrochemical reaction of cytochrome c is irreversible is that cytochrome c molecules exist in the concentrated solution as oligomers which are electrochemically inactive.

Ring-chain interconversion in high-performance polymer systems. 3. Cyclodepolymerization of poly(m-phenylene isophthalamide) (Nomex) and entropically driven ring-opening polymerization of the macrocyclic oligomers so produced

A homologous series of macrocyclic oligoamides has been prepared in high yield by reaction of isophthaloyl chloride with m-phenylenediamine under pseudo-high-dilution conditions. The products were characterized by infrared and H-1 NMR spectroscopies, matrix assisted laser desorption-ionization time-of-flight mass spectrometry, and gel permeation chromatography (GPC). A series of linear oligomers was prepared for comparison. The macrocycles ranged in size from the cyclic trimer up to at least the cyclic nonamer (90 ring atoms). The same homologous series of macrocyclic oligomers was prepared in high yield by the cyclodepolymerization of poly(m-phenylene isophthalamide) (Nomex). Cyclodepolymerization was best achieved by treating a 1% w/v solution of the polymer in dimethyl sulfoxide containing calcium chloride or lithium chloride with 3-4 mol % of sodium hydride or the sodium salt of benzanilide at 150 degreesC for 70 h. Treatment of a concentrated solution of the macrocyclic oligomers (25% w/v) with 4 mol % of sodium hydride or the sodium salt of benzanilide in a solution of lithium chloride in dimethyl sulfoxide at 170 degreesC for 6 h resulted in efficient entropically driven ring-opening polymerizations to give poly(m-phenylene isophthalamide), characterized by infrared and H-1 NMR spectroscopies and by GPC. The molecular weights obtained were comparable with those of the commercial polymer.

Influence of the solvent on the self-assembly of a modified amyloid beta peptide fragment. II. NMR and computer simulation investigation

The conformation of a model peptide AAKLVFF based on a fragment of the amyloid beta peptide A beta 16-20, KLVFF, is investigated in methanol and water via solution NMR experiments and Molecular dynamics computer simulations. In previous work, we have shown that AAKLVFF forms peptide nanotubes in methanol and twisted fibrils in water. Chemical shift measurements were used to investigate the solubility of the peptide as a function of concentration in methanol and water. This enabled the determination of critical aggregation concentrations, The Solubility was lower in water. In dilute solution, diffusion coefficients revealed the presence of intermediate aggregates in concentrated solution, coexisting with NMR-silent larger aggregates, presumed to be beta-sheets. In water, diffusion coefficients did not change appreciably with concentration, indicating the presence mainly of monomers, coexisting with larger aggregates in more concentrated solution. Concentration-dependent chemical shift measurements indicated a folded conformation for the monomers/intermediate aggregates in dilute methanol, with unfolding at higher concentration. In water, an antiparallel arrangement of strands was indicated by certain ROESY peak correlations. The temperature-dependent solubility of AAKLVFF in methanol was well described by a van't Hoff analysis, providing a solubilization enthalpy and entropy. This pointed to the importance of solvophobic interactions in the self-assembly process. Molecular dynamics Simulations constrained by NOE values from NMR suggested disordered reverse turn structures for the monomer, with an antiparallel twisted conformation for dimers. To model the beta-sheet structures formed at higher concentration, possible model arrangements of strands into beta-sheets with parallel and antiparallel configurations and different stacking sequences were used as the basis for MD simulations; two particular arrangements of antiparallel beta-sheets were found to be stable, one being linear and twisted and the other twisted in two directions. These structures Were used to simulate Circular dichroism spectra. The roles of aromatic stacking interactions and charge transfer effects were also examined. Simulated spectra were found to be similar to those observed experimentally.(in water or methanol) which show a maximum at 215 or 218 nm due to pi-pi* interactions, when allowance is made for a 15-18 nm red-shift that may be due to light scattering effects.

DYNAMIC AND STEADY-SHEAR RHEOLOGICAL PROPERTIES OF XANTHAN AND GUAR GUMS DISPERSED IN YELLOW PASSION FRUIT PULP (Passiflora edulis f. flavicarpa)

Yellow passion fruit pulp is unstable, presenting phase separation that can be avoided by the addition of hydrocolloids. For this purpose, xanthan and guar gum [0.3, 0.7 and 1.0% (w/w)] were added to yellow passion fruit pulp and the changes in the dynamic and steady-shear rheological behavior evaluated. Xanthan dispersions showed a more pronounced pseudoplasticity and the presence of yield stress, which was not observed in the guar gum dispersions. Cross model fitting to flow curves showed that the xanthan suspensions also had higher zero shear viscosity than the guar suspensions, and, for both gums, an increase in temperature led to lower values for this parameter. The gums showed different behavior as a function of temperature in the range of 5-35 degrees C. The activation energy of the apparent viscosity was dependent on the shear rate and gum concentration for guar, whereas for xanthan these values only varied with the concentration. The mechanical spectra were well described by the generalized Maxwell model and the xanthan dispersions showed a more elastic character than the guar dispersions, with higher values for the relaxation time. Xanthan was characterized as a weak gel, while guar presented a concentrated solution behavior. The simultaneous evaluation of temperature and concentration showed a stronger influence of the polysaccharide concentration on the apparent viscosity and the G` and G `` moduli than the variation in temperature.

Extração, caracterização estrutural e atividades farmacológicas do olginato obtido da alga marrom Lobophora variegata (Lamouroux) Oliveira Filho, 1977

The alginic acid or alginates are acidic polysaccharides found in brown seaweed widely used in food, cosmetic, medical and pharmaceutical industry. This paper proposes the extraction, chemical characterization and verification of the pharmacological activities of brown seaweed variegata Lobophora . The alginate was extracted from the seaweed Lobophora variegata and part was sulphated for comparative purposes. The native extract showed 42% total sugar, 65% uronic acid, 0,36 % protein and 0% of sulfate, while the sulfate showed 39% , 60%, 0.36% and 27,92 % respectively. The presence of a sulfate group may be observed by the metachromasia with toluidine blue in electrophoresis system and characteristic vibration 1262,34 cm-1 in infrared spectroscopy connections assigned to S = O. We observed the formation of films and beads of native alginate, where more concentrated solution 6% resulted in a thicker and more consistent film. Native alginate showed proliferative activity at concentrations (25 and 50 mcg), (50 mg) and (100 mg) in 3T3 cell line in 24h, 48h and 72h, respectively , as the sulfated (100 mg) in 24 . Also showed antiproliferative or cytotoxic activity in HeLa cells of strain, (25 and 100 mg), (25 and 100 mg) and (25, 50 and 100 mg), to native, now for the sulfate concentrations (100 mg) in 24 (25, 50 and 100 mg) in 48 hours, and (50 and 100 mg ) 72h. For their antioxidant activity, the sulfated alginates have better total antioxidant activity reaching 29 % of the native activity while 7.5 % of activity . For the hydroxyl radical AS showed high inhibition ( between 77-83 % ) in concentrations, but the AN surpassed these numbers in the order of 78-92 % inhibition. The reducing power of AN and AS ranged between 39-82 % . In the method of ferric chelation NA reached 100 % chelating while the AS remained at a plateau oscillating 6.5%. However, in this study , we found alginates with promising pharmacological activities, to use in various industries as an antioxidant / anti-tumor compound