Trace element concentrations from São Francisco River - PR analyzed with PIXE technique

Summary Kulcsszavak (angolul, ha nem azonos az elozovel)     

Copolymerization of ethylene and non-conjugated diene using homogenous catalyst

Ethylene and different amounts of 1,7-octadiene were copolymerized using the metallocene catalyst system ethylidene-bis(fluorenyl) zirconium dichloride and methylaluminoxane (MAO) at both 50 and 90 °C. The catalyst activity has slightly increased with the addition of low amounts of the diene in relation to the homopolymerization of ethylene. The obtained polymers were characterized according to their melting temperature (T_m) and crystallinity degree (x_c) by differential scanning calorimetry (DSC). Weight-average molecular weight (M_w) and polydispersity were determined by gel permeation chromatography (GPC). Diene contents in the copolymer were obtained through the FTIR spectroscopy. The results indicated that at polymerization temperature of 90 °C, crosslinking bonds in the obtained copolymers were low, differently from what was observed at 50 °C. The diene content in the copolymer achieved more than 3 mol% and the comonomer conversion was around 15%. Moreover, the obtained copolymers have M_w around 100,000 and large polydispersity.     

Polysaccharide differences between planktonic and biofilm-associated EPS from Pseudomonas fluorescens B52

The polysaccharides associated with free (planktonic) and surface-attached (biofilm) cells from cultures of Pseudomonas fluorescens strain B52 were compared. Variations in the attached matrix due to surface material (glass or stainless steel) were also analyzed. Two digestion methods were used to optimize the recoveries of sugars, uronic acids and acidic substituents. The yield of analyzable material after digestion reached 90% for the material associated to the biofilms, though only 20–30% for that bound to planktonic cells. The polysaccharide(s) in the biofilm had glucuronic and guluronic acids as main components, besides rhamnose, glucose and glucosamine. The proportion of glucuronic to guluronic acid was higher in the polysaccharide(s) found in biofilms formed on stainless steel than in those on glass.     

Effect of hydration of polyamide membranes on the surface electrokinetic parameters: surface characterization by x-ray photoelectronic spectroscopy and atomic force microscopy

The surface and the solid/liquid interface of two polyamide membranes, one experimental (B0) and one commercial (NF45), have been characterized by X-ray photoelectronic spectroscopy (XPS), atomic force microscopy (AFM), and zeta potential, respectively. The surface roughness, determined by AFM data analysis, is different for the two membranes, and results show that the commercial NF45 membrane presents a much lower roughness than the experimental B0 membrane. XPS data indicate that the surface of membrane NF45 is similar to that of pure polyamide, while membrane B0 contains a considerable amount of impurities. The homogeneity in depth of both membranes was also studied by determining the composition profile at different analysis angles. Streaming potential along the membrane surface or tangential streaming potential (TSP) measurements with NaCl solutions at different concentrations were carried out with both membranes to determine the zeta potential and the electrokinetic surface charge density, and a correlation between membrane surface and interface parameters is made. Some differences in atomic concentrations of membrane surface elements and X-ray photoelectronic spectra of the samples used in TSP measurements and after a drying process at 90 degrees C for 24 h can be observed when they are compared with those for fresh membranes. Electrokinetic parameters for membrane NF45 (TSP, zeta potential, and surface electrokinetic charge density) obtained from three different series of measurements strongly decrease as a result of membrane use, but for membrane B0 they are practically independent of the number of measurements. This difference in the electrokinetic behavior of the two membranes has been related to the hydration process of the surface for each sample studied by XPS and AFM.     

Total synthesis of 1-(Z)-atractylodinol

The total synthesis of 1-(Z)-atractylodinol, a natural polyacetylenic alcohol with several biological activities, has been achieved using a newly developed telluride synthon and a novel use for the Negishi type coupling reaction employing vinyl tellurides.     

Standard enthalpy of solution and formation of cesium chromate. Derived thermodynamic properties of the aqueous chromate,bichromate, and dichromate ions,alkali metal and alkaline earth chromates,and lead chromate

Calorimetric measurements of the enthalpy of solution of cesium chromate gave ΔH_soln = (7622 ± 24) cal_th mol^?1 for a dilution of Cs₂CrO₄·21128H₂O. This result, along with the enthalpy of dilution gave the standard enthalpy of solution, ΔH_soln^o = (7512 ± 31) cal_th mol^?1, whence the standard enthalpy of formation, ΔH_f⁰(Cs₂CrO₄, c, 298.15 K), was calculated to be ?(341.78 ± 0.46) kcal_th mol^?1. Recomputed thermodynamic data for the formation of the other alkali metal chromates have been tabulated. From their solubilities and enthalpies of solution, the standard entropies, S⁰(298 K), of BaCrO₄ and PbCrO₄ were estimated to be (38.9 ± 0.9) and (43.7 ± 1.2) cal_th K^?1 mol^?1, respectively. There is evidence that ΔH_f⁰(SrCrO₄, c, 298.15 K) may be in error. Thermochemical, solubility, and equilibrium data, have been combined to update the thermodynamic properties of the aqueous chromate (CrO₄^2?), bichromate (HCrO₄^?), and dichromate (Cr₂O₇^2?) ions. The new values at 298.15 K are as follows:

     

7.

Characterization of Sol-gel bioencapsulates for ester hydrolysis and synthesis     

Cleide M. F. Soares  Heizir F. de Castro  Juliana E. Itako  Flavio F. De Moraes  Gisella M. Zanin 《Applied biochemistry and biotechnology》2005,123(1-3):845-859

Candida rugosa lipase was entrapped in silica sol-gel particles prepared by hydrolysis of methyltrimethoxysilane and assayed by p-nitrophenyl palmitate hydrolysis, as a function of pH and temperature, giving pH optima of 7.8 (free enzyme) and 5.0–8.0 (immobilized enzyme). The optimum temperature for the immobilized enzyme (50–55°C) was 19°C higher than for the free enzyme. Thermal, operational, and storage stability were determined with n-butanol and bytyric acid, giving at 45°C a half-life 2.7 times greater for the immobilized enzyme; storage time was 21 d at room temperature. For ester synthesis, the optimum temperature was 47°C, and high esterification conversions were obtained under repeated batch cycles (half-life of 138 h).     

8.

Manganese(II) and copper(II) hexafluoroacetylacetonate 1:1 complexes with 5-(4-[N-tert-butyl-N-aminoxyl]phenyl)pyrimidine: regiochemical parity analysis for exchange behavior of complexes between radicals and paramagnetic cations     

Field LM  Lahti PM  Palacio F  Paduan-Filho A 《Journal of the American Chemical Society》2003,125(33):10110-10118

Mn(hfac)(2) and Cu(hfac)(2) form coordination complexes with 5-(4-[N-tert-butyl-N-aminoxyl]phenyl)pyrimidine, PyrimPh-NIT. (Mn[PyrimPh-NIT](hfac)(2))(2) and (Cu[PyrimPh-NIT](hfac)(2))(2), 1 and 2, respectively, are cyclic M(2)L(2) dimers that exhibit strong exchange coupling between the coordinated paramagnetic dication (M) and nitroxide (NIT) unit. The M-NIT exchange is strongly antiferromagnetic (AFM) in 1 and strongly ferromagnetic (FM) in 2. Magnetic susceptibility measurements for 1 were fitted to an AFM spin pairing model with J/k = -0.25 K between Mn-NIT spin sites units. Complex 2 also exhibits AFM spin pairing between S = 1 Cu-NIT spin units that is somewhat field dependent at low temperature. The fit of corrected paramagnetic susceptibility chi(T) to an AFM spin pairing model at 200 Oe yields J/k = (-)3.8 K, quite similar to earlier measurements at 1000 Oe yielding J/k = (-)5.0 K. At 1.40 K, the magnetization of 2 does not approach saturation until somewhat above 170 kOe, giving an S-shaped curve; at 0.55 K, the magnetization curve shows steps characteristic of field-induced crossover between the S = 0 ground state and excited spin states. From the steps in the 0.55 K data, we estimate J/k = (-)3.8-4.0 K for 2, in good agreement with the analysis of chi(T).     

9.

A new polyphenol modified electrode containing an anchored ruthenium complex and its use in electrocatalytic oxidation of organic substrates     

Juliana R. Steter  José O.S. PontólioM.I.C.F. Costa  J.R. Romero 《Polyhedron》2007

This work describes the preparation of a new modified electrode containing a ruthenium complex (cis-aquadimethylbipyridyltriphenylphosphineruthenium II), bonded to a stable polyphenol film. This modified electrode promotes the fast electrocatalytic oxidation of safrol (5-allyl-benzo[1,3]dioxole) and isosafrol (5-propenyl-benzo[1,3]dioxole), giving two interesting products benzo[1,3]dioxole-5-carbaldehyde (piperonal) and 3-benzo[1,3]dioxol-5-yl-propenal respectively, with good yields. The electrode preparation can be carried out at a potential range which does not interfere on the anchored electroactive ruthenium complex, but it allows for the phenol oxidation to occur and therefore polymerize forming the polyphenol film. The catalytic character of this modified electrode is showed by its high turnover numbers. The procedure to isolate the products is very simple.     

10.

Optimization of acid hydrolysis of sugarcane bagasse and investigations on its fermentability for the production of xylitol by Candida guilliermondii     

Rafael Fogel  Rafaela Rodrigues Garcia  Rebeca da Silva Oliveira  Denise Neves Menchero Palacio  Luciana da Silva Madeira  Nei Pereira Jr. 《Applied biochemistry and biotechnology》2005,122(1-3):741-752

The dilute-acid hydrolysis of sugarcane bagasse was optimized using a statistical experimental design resulting in hydrolysates containing 57.25 g/L of xylose, which were fermented with a high inoculum concentration (10 g/L of the yeast Candida guilliermondii IM/UFRJ 50088). The addition of urea reduced the time of conversion (t _C) to 75 h (without nitrogen source addition t _C>127 h), and, consequently, improving the rates of xylitol bioproduction. Fermentator experiments, using the optimized conditions, resulted in enhanced conversion rates, reducing t _C to 30 h. The stability of the yeast in the hydrolysate was also verified in a 480-h cultivation.     

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	$\text{S}{}^0\text{/}\text{cal}{}_{\mathrm{th}}\text{K}{}^{\mathrm{?1}}\text{mol}{}^{\mathrm{?1}}$	$\text{ΔH}{}_{\mathrm{f}}{}^0\text{/kcal}{}_{\mathrm{th}}\text{mol}{}^{\mathrm{?1}}$	$\text{ΔG}{}_{\mathrm{f}}{}^0\text{/kcal}{}_{\mathrm{th}}\text{mol}{}^{\mathrm{?1}}$
CrO42?(aq)	(13.8 ± 0.5)	?(210.93 ± 0.45)	?(174.8 ± 0.5)
HCrO4?(aq)	(46.6 ± 1.8)	?(210.0 ± 0.7)	?(183.7 ± 0.5)
Cr2O72?(aq)	(67.4 ± 3.9)	?(356.5 ± 1.5)	?(312.8 ± 1.0)

Characterization of Sol-gel bioencapsulates for ester hydrolysis and synthesis

Candida rugosa lipase was entrapped in silica sol-gel particles prepared by hydrolysis of methyltrimethoxysilane and assayed by p-nitrophenyl palmitate hydrolysis, as a function of pH and temperature, giving pH optima of 7.8 (free enzyme) and 5.0–8.0 (immobilized enzyme). The optimum temperature for the immobilized enzyme (50–55°C) was 19°C higher than for the free enzyme. Thermal, operational, and storage stability were determined with n-butanol and bytyric acid, giving at 45°C a half-life 2.7 times greater for the immobilized enzyme; storage time was 21 d at room temperature. For ester synthesis, the optimum temperature was 47°C, and high esterification conversions were obtained under repeated batch cycles (half-life of 138 h).     

Manganese(II) and copper(II) hexafluoroacetylacetonate 1:1 complexes with 5-(4-[N-tert-butyl-N-aminoxyl]phenyl)pyrimidine: regiochemical parity analysis for exchange behavior of complexes between radicals and paramagnetic cations

Mn(hfac)(2) and Cu(hfac)(2) form coordination complexes with 5-(4-[N-tert-butyl-N-aminoxyl]phenyl)pyrimidine, PyrimPh-NIT. (Mn[PyrimPh-NIT](hfac)(2))(2) and (Cu[PyrimPh-NIT](hfac)(2))(2), 1 and 2, respectively, are cyclic M(2)L(2) dimers that exhibit strong exchange coupling between the coordinated paramagnetic dication (M) and nitroxide (NIT) unit. The M-NIT exchange is strongly antiferromagnetic (AFM) in 1 and strongly ferromagnetic (FM) in 2. Magnetic susceptibility measurements for 1 were fitted to an AFM spin pairing model with J/k = -0.25 K between Mn-NIT spin sites units. Complex 2 also exhibits AFM spin pairing between S = 1 Cu-NIT spin units that is somewhat field dependent at low temperature. The fit of corrected paramagnetic susceptibility chi(T) to an AFM spin pairing model at 200 Oe yields J/k = (-)3.8 K, quite similar to earlier measurements at 1000 Oe yielding J/k = (-)5.0 K. At 1.40 K, the magnetization of 2 does not approach saturation until somewhat above 170 kOe, giving an S-shaped curve; at 0.55 K, the magnetization curve shows steps characteristic of field-induced crossover between the S = 0 ground state and excited spin states. From the steps in the 0.55 K data, we estimate J/k = (-)3.8-4.0 K for 2, in good agreement with the analysis of chi(T).     

A new polyphenol modified electrode containing an anchored ruthenium complex and its use in electrocatalytic oxidation of organic substrates

This work describes the preparation of a new modified electrode containing a ruthenium complex (cis-aquadimethylbipyridyltriphenylphosphineruthenium II), bonded to a stable polyphenol film. This modified electrode promotes the fast electrocatalytic oxidation of safrol (5-allyl-benzo[1,3]dioxole) and isosafrol (5-propenyl-benzo[1,3]dioxole), giving two interesting products benzo[1,3]dioxole-5-carbaldehyde (piperonal) and 3-benzo[1,3]dioxol-5-yl-propenal respectively, with good yields. The electrode preparation can be carried out at a potential range which does not interfere on the anchored electroactive ruthenium complex, but it allows for the phenol oxidation to occur and therefore polymerize forming the polyphenol film. The catalytic character of this modified electrode is showed by its high turnover numbers. The procedure to isolate the products is very simple.     

Optimization of acid hydrolysis of sugarcane bagasse and investigations on its fermentability for the production of xylitol by Candida guilliermondii

The dilute-acid hydrolysis of sugarcane bagasse was optimized using a statistical experimental design resulting in hydrolysates containing 57.25 g/L of xylose, which were fermented with a high inoculum concentration (10 g/L of the yeast Candida guilliermondii IM/UFRJ 50088). The addition of urea reduced the time of conversion (t _C) to 75 h (without nitrogen source addition t _C>127 h), and, consequently, improving the rates of xylitol bioproduction. Fermentator experiments, using the optimized conditions, resulted in enhanced conversion rates, reducing t _C to 30 h. The stability of the yeast in the hydrolysate was also verified in a 480-h cultivation.