Abstract  An improved spectrophotometric determination of uranium(VI) is proposed using 4-(2-pyridylazo)resorcinol(PAR) in the presence of benzyldimethylstearyltrimethylammonium chloride(BSTAC) as a cationic surfactant. The calibration graph is linear in the range of 0.3-60 microg/10 ml uranium(VI), measuring the absorbance at 550 nm. The reproducibility for 19.0 microg/10 ml uranium(VI) is 0.57%. The third-derivative method using the third-derivative distance (d(3)A/dlambda(3)) among lambda(1) 530 nm, lambda(3) 594 nm and lambda(2) 565 nm was also investigated.

Abstract  The absorption of resorcinol di(phenyl phosphate) (RDP) oligomers on clay surfaces has been studied in detail and is being proposed as an alternative method for producing functionalized clays for nanocomposite polymers. The ability of these clays to be exfoliated or intercalated in different homopolymers was investigated using both transmission electron microscopy and small-angle X-ray scattering results, compared with contact angle measurements on Langmuir−Blodgett clay monolayers, where the interfacial energies were used as predictors of the polymer/clay interactions. We found that the contact angle between PS/RDP clay monolayer substrates was 2.5°, whereas the angle for polystyrene (PS)/Cloisite 20A clays substrates was 32°, consistent with the large degree of exfoliation observed in PS for the RDP-coated clays. The interfacial activity of these clays was also measured, and we found that the RDP-coated clays segregated to the interfaces of PC/poly(styrene-co-acrylonitrile) blends, while they segregated into the poly(methyl methacrylate) (PMMA) domain of PS/PMMA blends. This morphology was explained in terms of the relative energy advantage in placing the RDP versus the Cloisite clays at the interfaces. Finally, we demonstrated the effects of the relative surface energies of the clays in segregating to the blend air interface when heated to high temperatures. The segregation was shown to affect the composition and mechanical properties of the resulting chars, which in turn could determine their flame retardant response.

Abstract  The chronic toxicity of 2,4-toluenediamine (2,4-TDA) alone or in conbination with a hair dye complex (2,5-toluenediamine, p-phenylenediamine, and resorcinol) was studied in Swiss-Webster mice of both sexes by a skin-painting technique. The predominant neoplasms seen in these mice were primary pulmonary adenomas and adenocarcinomas. Skin neoplasms were seen in most groups of mice, including untreated control mice. Statistical analysis of the incidences of skin neoplasms among the various groups of mice did not show any significant differences. The 2,4-TDA alone or mixed with the hair dye complex did not produce any abnormal proliferation and maturation of the squamous epithelium of the skin. The 2,4-TDA under our experimental conditions was found to be nontoxic and noncarcinogenic to the skin of mice.

Abstract  Flavonoids are widely distributed in plant-derived foods and possess a variety of biological activities including antithyroid effects in experimental animals and humans. A structure-activity study of 13 commonly consumed flavonoids was conducted to evaluate inhibition of thyroid peroxidase (TPO), the enzyme that catalyzes thyroid hormone biosynthesis. Most flavonoids tested were potent inhibitors of TPO, with IC50 values ranging from 0.6 to 41 microM. Inhibition by the more potent compounds, fisetin, kaempferol, naringenin, and quercetin, which contain a resorcinol moiety, was consistent with mechanism-based inactivation of TPO as previously observed for resorcinol and derivatives. Other flavonoids inhibited TPO by different mechanisms, such as myricetin and naringin, showed noncompetitive inhibition of tyrosine iodination with respect to iodine ion and linear mixed-type inhibition with respect to hydrogen peroxide. In contrast, biochanin A was found to be an alternate substrate for iodination. The major product, 6,8-diiodo-biochanin A, was characterized by electrospray mass spectrometry and 1H-NMR. These inhibitory mechanisms for flavonoids are consistent with the antithyroid effects observed in experimental animals and, further, predict differences in hazards for antithyroid effects in humans consuming dietary flavonoids. In vivo, suicide substrate inhibition, which could be reversed only by de novo protein synthesis, would be long-lasting. However, the effects of reversible binding inhibitors and alternate substrates would be temporary due to attenuation by metabolism and excretion. The central role of hormonal regulation in growth and proliferation of thyroid tissue suggests that chronic consumption of flavonoids, especially suicide substrates, could play a role in the etiology of thyroid cancer.

Abstract  Vertical replication for TEM is ideal for studying non-periodic specimens from 0.7 to 3 nm, a resolution mid-range difficult to attain by any other technique. This paper discusses the importance of vertical replication, its methods and hardware for high-resolution TEM. Evidence from diverse published research will demonstrate vertical replication's versatility in imaging the molecular level normally unattainable in freeze-dried polymers, polyethylene tribological wear on surfaces, low-density polymer networks or biological gels. Vertical platinum-carbon (Pt-C) replication minimizes the horizontal movement of Pt-C on a surface. Surface objects are symmetrically enlarged by a vertically deposited Pt-C film. To estimate real size in replicas, 16-25 particles or filaments need to be measured in calibrated transmission electron microscopy (TEM) images and reduced by a value less than the Pt-C film thickness measured with a quartz monitor. Continuous, vertically deposited Pt-C films are formed on mica at a deposition thickness of around 1.0 nm and on silver at a thickness of 0.4-0.5 nm. The distance between helical turns in poly(1-tetradecene sulfone) of 0.7 nm is the highest resolution achieved with vertical replication. Two polysulfones freeze-dried and vertically replicated on mica contained structures are predicted by indirect physical chemical methods to be present in solution. Polymer chains are fully Pt-C coated, with no uncoated gaps along chains. Some side-chains on the extended non-helical poly(1-tetradecene sulfone) are also detected. To estimate the real chain width, polymer chains measured in images are reduced by the Pt-C film thickness minus 0.5 nm. The polymer chain widths estimated from molecular models are in the same range of widths as those measured using the image size correction method. Also, it is possible to distinguish random coil proteins (chain width of around 0.5 nm) from an alpha-helix (chain diameter of about 1 nm) in vertically replicated samples on silver substrates. In the future, subnanometer resolutions below 0.7 nm should be possible. The resolution of vertical replication depends on the thickness of a continuous, amorphous Pt-C film. That thin, continuous 0.4-0.5 nm Pt-C films on silver substrates can be made suggests that a point-to-point resolution limit of around 0.28 nm in TEM may ultimately be approachable with replication.

Abstract  Iridium-carbon (Ir-C) xerogels were synthesized via a one-pot sol-gel polycondensation of hexachloroiridic acid, resorcinol and formaldehyde, followed by carbonization in a nitrogen atmosphere at 500-1000 degrees C. The samples were characterized by various techniques including N-2 adsorption, XRD and TEM. The N-2 adsorption showed that the Ir-C samples were of microporous structures, and their specific surface areas increased with the pyrolysis temperature. Both the XRD and TEM revealed that the It particles in the Ir-C samples were highly dispersed in the carbon matrix, in contrast with the large Ir particles in the Ir/C sample which was obtained by impregnation. The Ir-C xerogels exhibited high activities and selectivities towards N-2 in the reduction of NO with carbon or CO. In particular, the Ir-C samples behaved much stably than the Ir/C, demonstrating the superiority of the one-pot synthesis method. (C) 2008 Elsevier B.V. All rights reserved.

Abstract  A new micelle-mediated separation and preconcentration method was developed for ultra-trace quantities of mercury ions prior to spectrophotometric determination. The method is based on cloud point extraction (CPE) of Hg(II) ions with polyethylene glycol tert-octylphenyl ether (Triton X-114) in the presence of chelating agents such as 1-(2-pyridylazo)-2-naphthol (PAN) and 4-(2-thiazolylazo) resorcinol (TAR). Hg(II) ions react with both PAN and TAR in a surfactant solution yielding a hydrophobic complex at pH 9.0 and 8.0, respectively. The phase separation was accomplished by centrifugation for 5 min at 3500 rpm. The calibration graphs obtained from Hg(II)-PAN and Hg(II)-TAR complexes were linear in the concentration ranges of 10-1000 μg L(-1) and 50-2500 μg L(-1) with detection limits of 1.65 and 14.5 μg L(-1), respectively. The relative standard deviations (RSDs) were 1.85% and 2.35% in determinations of 25 and 250 μg L(-1) Hg(II), respectively. The interference effect of several ions were studied and seen commonly present ions in water samples had no significantly effect on determination of Hg(II). The developed methods were successfully applied to determine mercury concentrations in environmental water samples. The accuracy and validity of the proposed methods were tested by means of five replicate analyses of the certified standard materials such as QC Metal LL3 (VWR, drinking water) and IAEA W-4 (NIST, simulated fresh water).

Abstract  A sensitive spectrophotometric method for the determination of nitrogen dioxide in air, nitrate and nitrite in water, soil, radiator coolant and some analytical grade chemicals is described. The method is based on diazo coupling reaction, where 4-amino azobenzene: is treated with nitrite under acidic condition in the presence of bromide ion and the formed diazonium salt couples with resorcinol in acid medium. The formed bisazo dye has an absorption maxims at 550 nm under alkaline condition and obeys Beer's law over the range 0-16 mug of nitrite in overall aqueous volume of 25 mL. The system obeys Beer's law over the range 0-3 mug nitrite, when extracted into toluene under ammoniacal condition (pH 9.0 +/- 0.5) and stripped to aqueous phase with 5 mt of 0.35 molar NaOH. The molar absorptivity of the colour system is 4.8 x 10(4) L. moL(-1). cm(-1).

Abstract  Resorcinol-formaldehyde (RF) aerogel chemistry has been used with encapsulation techniques to fabricate low-density, transparent, foam shells. To accomplish this, the gelation time was reduced from several hours to several minutes by the addition of acid following base-catalyzed RF particle growth. However, additional ''annealing'' of the gel for at least 20 h was needed to maximize crosslinking and minimize swelling in exchange solvents. Increasing the molar ratio of formaldehyde to resorcinol from 2 to 3 also helped to increase crosslinking. Densification of the foam shells due to dehydration during curing was greatly reduced by judicious choice of immiscible oil phases and by saturating the exterior oil phase during the annealing stage. Shells have been produced with diameters of about 2 mm, wall thicknesses ranging from 100 to 200 mu m and foam densities approaching 50 mg/cc. (C) 1997 John Wiley & Sons, Inc.

Abstract  We report a one-step method for the synthesis of M(Fe, Co, Ni) nanocrystals supported by ordered mesoporous carbon (OMC) materials. M/OMC composites were obtained by the soft templating route under acidic conditions using resorcinol and formaldehyde as carbon precursors, triblock copolymer Pluronic F127 as a template and Fe, Co, Ni nitrates as metal precursors. The as-synthesized materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and N-2 adsorption. Characterization revealed that the as-synthesized materials possessed an ordered hexagonal mesoporous structure similar to SBA-15. The specific surface areas of the Fe/OMC, Co/OMC, and Ni/OMC composites were found to be 586, 626, and 698 m(2) . g(-1), respectively. The fact that the metal species were present as highly dispersed nanocrystals in the OMC matrix was confirmed by XRD and high-resolution TEM.

Abstract  Medical case reports published in the 20th century over the course of several decades show that resorcinol caused reversible adverse effects on the human thyroid gland (TG) manifested as hypothyroidism. Affected patients had ulcerating leg varicosities and underwent prolonged treatment with ointments containing high concentrations of resorcinol. In animal studies resorcinol failed to induce TG toxicity, unless pharmacokinetic/toxicokinetic (PK/TK) conditions were manipulated (e.g., injection of resorcinol in oil or application in a slow release formulation). A recently completed two-generation reproductive toxicity study in rats did not detect any adverse effects on either reproductive or TG end points (Welsch, Nemec, and Lawrence, 2008, Int. J. Toxicol. 37, this issue). Resorcinol intake via drinking water up to the palatability limit had resulted in average daily intakes (mg/kg) of 233 in F0 and F1 males and 304 (premating/gestation) or 660 (lactation) in females. Free resorcinol in blood plasma was barely detectable in a few parental animals, indicating rapid metabolism. This short review communication offers a perspective on compromised human skin barrier function as a likely cause of drastic increases in resorcinol absorption. In conjunction with multiple daily applications over many months to hyperemic, inflamed, and lesioned human skin much higher absorption was likely responsible for the reported human TG toxicity.

Abstract  Ordered mesoporous carbons (OMCs) with embedded metallic nickel (Ni) nanoparticles have been directly synthesized by a simple and low temperature (50 degrees C) hydrothermal method. The synthesis involved the use of a triblock copolymer Pluronic F127 as the mesostructure directing agent, resorcinol (R) and formaldehyde (F) as carbon precursors, and Ni(NO3)(2)center dot 6N(2)O as nickel source. It consisted in the self-assembly of F127, Ni2+ salt and RF polymer in an acidic medium and further carbonization, where the Ni2+ was captured by the network of F127/RF and further reduced into metallic Ni nanoparticles. The resultant Ni/carbon materials were characterised by X-ray diffraction, thermogravimetric analysis, transmission electron microscopy and nitrogen sorption. Ni/carbon materials with a highly ordered mesostructure were obtained using equal moles of resorcinol and formaldehyde molar ratio (R/F = 1/1), whereas an excess amount of formaldehyde (R/F = 1/2) was found to not form an ordered carbon structure. The results showed that nickel particles, with sizes of similar to 10-50 nm, were homogeneously dispersed in the carbon matrices, while the pore mesostructure remained intact. The homogeneous Ni/carbon composites synthesized by this easy hydrothermal route have been demonstrated to be effective molecular adsorbents for magnetic separation. (C) 2012 Elsevier Ltd. All rights reserved.

Abstract  The formation and liquid-liquid extraction of ion-associated complexes between the vanadium(V) - 4-(2-pyridylazo)-resorcinol (PAR) anionic chelate and the cations of some methoxybis(tetrazolium) salts (MT2+), which contain different number of nitro groups {3,3'-(3,3'-dimethoxy-4,4'-biphenylene)bis[2,5-di(4-nitrophenyl)-2H-tetrazolium] chloride (Tetranitrotetrazolium Blue chloride, TNBT), 3,3'-(3,3'-dimethoxy-4,4'-biphenylene)bis[2-(4nitrophenyl)-5-phenyl-2H-tetrazolium] chloride (Nitro Blue Tetrazolium chloride, NBT) and 3,3'-(3,3'-dirnethoxy-4,4'-biphenylene)-bis(2,5-diphenyl-2H-tetrazolium) chloride (Tetrazolium Blue chloride, BTC)} have been studied. The optimal conditions for extraction in chloroform (pH, concentrations of the reagents, extraction time) and the composition of the complexes (V:PAR:MT=2:4:3) have been found. The equilibrium constants (the constants of extraction - K-Ex, the constants of distribution - K-D, the constants of formation - beta), and the recovery factors have been determined. The results show that a linear relationship exists between LogK(Ex) and the number of nitro groups included in MT2+ (N-NO2): the higher N-NO2, the lower LogK(Ex). A similar relationship has been established between Log beta and N-NO2. These relationships have been used to predict the values of LogK(Ex) and Log beta for new (uninvestigated) methoxybis(tetrazolium) ion-associated complexes.

Abstract  Planar triazinium cationic species from vanadyl-assisted cyclization of 1-(2-thiazolylazo)-2-naphthol (H-TAN, ), 1-(2-pyridylazo)-2-naphthol (H-PAN, ), 2-(2'-thiazolylazo)-p-cresol (H-TAC, ) and 6-(2'-thiazolylazo)-resorcinol (H-TAR, ) were prepared and characterized. A dioxovanadium(v) species [VO(TAR)] () was also isolated. Compounds , and were structurally characterized. Both and have planar structures. Complex has VON coordination geometry. The cyclised triazinium compound forms a radical species within -0.06 to -0.29 V vs. SCE in DMF-0.1 M tetrabutylammonium perchlorate with a second response due to formation of an anionic species. A confocal microscopic study showed higher nuclear uptake for having a fused thiazole moiety than with a fused pyridine ring. The compounds showed a partial intercalative mode of binding to calf thymus DNA. Compound showed plasmid DNA photo-cleavage activity under argon and photocytotoxicity in HeLa and MCF-7 cells with IC values of 15.1 and 3.4 μM respectively in visible light of 400-700 nm, while being essentially non-toxic in the dark with IC values of 90.4 and 21.9 μM. A TDDFT study was done to rationalize the experimental data.

Abstract  The chelidamic acid (CDA) is proposed as a new eluent reagent in high performance chelation ion chromatography for the simultaneous isocratic separation of Fe2+ and Fe3+, Mn2+, Pb2+, Cd2+, Zn2+, Co2+ and Cu2+ on an iminodiacetic acid functionalized silica column 150 x 4.0 mm i.d., with an optimized eluent composed of 2 mmol L-1 CDA, 3 mmol L-1 triethanolamine, 12 mmol L-1 HCl, and 50 % v/v of methanol at flow rate of 0.5 mL min(-1). Post-column reaction with 4-(2-Pyridylazo)resorcinol (PAR) was used for sensitive spectrophotometric detection at 510 nm. The developed method is suitable for the quantitative speciation of iron as well as for the determination of other metals. The applicability of this method to the direct analysis of fuel ethanol was demonstrated.

Abstract  Platinum nanocatalysts on two tungsten based supports have been synthesized and characterized as catalysts for oxygen reduction reaction in 0.5 mol dm(-3) HClO4 solution, at 25 degrees C. Tungsten based support assigned WCctabr has been synthesized by polycondensation of resorcinol and formaldehyde in the presence of CTABr surfactant. Support assigned WCwo(3) was synthesized from resorcinol/formaldehyde gel, using WO3 nanoparticles as starting material. Supporting materials have been characterized by BET (Brunauer, Emmett and Teller) technique and determined values of surface area were 80 m(2) g(-1) for WCctabr and 175 m (2) g(-1) for WCWO3. Platinum nanocatalysts (10% Pt) at tungsten based supports have been prepared by borohydride reduction method. Both synthesized supports and catalysts have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) techniques. Cyclic voltammetry was applied for determination of electrochemically active surface area (40 m2 g(-1) for Pt/WCWO3 and 55 m(2) g(-1) for Pt/WCctabr). Oxygen reduction reaction has been studied by cyclic voltammetry and linear sweep voltammetry at rotating disc electrode (RDE). These catalysts exhibited better catalytic activity, expressed in terms of kinetic current density per real surface area at the constant potential and better stability, in comparison with Pt/C catalyst, as well as with already reported catalytic activity values for Pt catalysts on tungsten based supports. (C) 2012 Elsevier B.V. All rights reserved.

Abstract  Highly mesoporous carbon xerogels (CXs) were synthesized using two different resorcinol to catalyst, R/C, molar ratios and functionalized with different oxidation treatments. The synthesized carbon materials were used as supports for Pt particles, deposited by impregnation and reduction in formic acid. Both carbon supports and the catalysts prepared were characterized by means of N-2 physisorption, scanning and transmission electron microscopy, temperature programmed desorption and X-ray diffraction. The electrochemical activity of the catalysts towards the oxidation of carbon monoxide and methanol was assayed by means of cyclic voltammetry and chronoamperometry. Textural characterization of the materials prepared evidenced more developed and mesopore-enriched porous structure for the carbon xerogel prepared using the highest R/C molar ratio. Enhanced textural properties of this material led to the preparation of highly active Pt-catalysts, which showed increased tolerance to CO and higher activity in methanol electro-oxidation, in comparison to Pt-E-TEK and the catalysts prepared in an analogous way using Vulcan XC-72R carbon black as support. Functionalization treatments resulted in enhanced dispersion, lower Pt crystal size and improved catalytic performance in the case of the catalysts prepared using the carbon xerogel possessing a less developed porous structure. Pt agglomeration was found to strongly determine the activity of the catalysts prepared. At high potentials, i.e. 1 V vs. RHE, the catalyst prepared using the carbon xerogel submitted to the most stringent oxidation treatment showed the highest specific peak activity towards methanol electro-oxidation, probably due to the positive influence of the presence of oxygen surface groups in Pt-carbon interaction, in spite of the higher agglomeration extent confirmed by TEM. On the other hand, at 0.60 V vs. RHE, highest activity towards methanol electro-oxidation was determined for the catalysts prepared using the non-functionalized carbon xerogel which can be explained in terms of enhanced reactant/product diffusion together with intrinsic higher catalytic activity due to lower Pt crystal size. In any case, the activity of this catalyst prepared using a carbon xerogel as support was found to be more than 2 times higher than the one determined for Pt/E-TEK, confirming the considerable improvement of the electrocatalytic system by means of optimization of the carbon support employed. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Abstract  BIOSIS COPYRIGHT: BIOL ABS. A method for the on-line preconcentration and chromatography of trace metals, e.g., Co, Ni, Cu, Zn, Cd and Pb, on N,N,N',N'-tera(2-aminoethyl)ethylenediamine-bonded silica is described. The preconcentrated metals were desorbed with 0.13 M tartrate, which allows direct separation on a cation-exchange chromatographic column. The metals separated were detected by postcolumn reaction with 4-(2-pyridylazo)resorcinol and measuring the absorbances at 500 nm. Linear calibrations graphs were obtained ove the range 1ynthesis and characteristics of the chelated silica are described. The method was applied to the analysis of river and interstitial sediment waters.