Surface pressure-area isotherms for Langmuir monolayers and a docking molecular orientation of perylene tetracarboxylic derivatives on a water surface

The surface pressure-molecular area (pi-A) isotherms for Langmuir monolayers of four perylenetetracarboxylic (PTCD) derivatives, measured with varying subphase temperatures and compression speeds, are reported. The behavior of these PTCD derivatives at the water-air interface is modeled using the rigid docking method. This approach is the first attempt to model the molecular orientation of PTCD on the water surface to be compared with experimental Langmuir isotherms. Through this methodology, it would be possible to anticipate aggregation and determine if favorable spatial orientations of perylenes are generated on the water surface. The pi-A isotherm experiments show that these molecules can support high surface pressures, indicating strong packing on the water surface and that the isotherms are compression speed independent but temperature dependent. The molecular orientation and stacking was further examined in Langmuir-Blodgett (LB) monolayers deposited onto glass and glass coated with Ag island films using UV-visible absorption and surface-enhanced fluorescence (SEF) measurements.

Water sorption enthalpy-entropy compensation based on isotherms of plum skin and pulp

The net isosteric heat and entropy of water sorption were calculated for plum, based on sorption isotherms obtained by the static gravimetric method at different temperatures (20 to 70 degrees C). The Guggenheim-Anderson-deBoer model was applied to the experimental data giving a good agreement between experimental and calculated values. The net isosteric heat of water sorption, estimated by applying Claussius-Clapeyron equation to sorption isotherms, was found to be different for plum skin and pulp, mainly at low moisture contents, and could be well adjusted by an empirical exponential relationship. Plots of enthalpy in contrast to entropy provided the isokinetic temperatures for skin and pulp, indicating an enthalpy-controlled sorption process. Thermodynamic data on water sorption for plums are not found in literature, as opposed to prunes for which the data are abundant.

Isolation and sequence determination of peptides in the venom of the spider wasp (Cyphononyx dorsalis) guided by matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry

Micro-scale (sub-pmol) isolation and sequence determination of three peptides from the venom of the solitary spider wasp Cyphononyx dorsalis is described. We isolated two novel peptides Cd-125 and Cd-146 and a known peptide Thr(6)-bradykinin from only two venom sacs of solitary spider wasp Cyphononyx dorsalis without bioassay-guided fractionation. but instead guided by MALDI-TOF MS. The MALDI-TOF MS analysis of each fraction showed the purity and molecular weight of the components, which led to the isolation of the peptides virtually without loss of sample amount. The sequences of the novel peptides Cd-125 (Asp-Thr-Ala-Arg-Leu-Lys-Trp-His) and Cd-146 (Ser-Glu-Thr-Gly-Asn-Thr-Val-Thr-Val-Lys-Gly-Phe-Ser-Pro-Leu-Arg) were determined by Edman degradation together with mass spectrometry. and finally corroborated by solid-phase synthesis. The known peptide Thr(6)-bradykinin (Arg-Pro-Pro-Gly-Phe-Thr-Pro-Phe-Arg) was identified by comparison with the synthetic authentic specimen. This is the first example for any kinins to be found in Pompilidae wasp venoms. The procedure reported here can be applicable to studies on many other components of solitary wasp venoms with limited sample availability. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Thermodynamic models for water sorption by grape skin and pulp

The enthalpy-entropy compensation theory was applied to water sorption for grapes of Italy variety. The moisture sorption isotherms were analyzed using the static gravimetric method at 35, 40, 50, 60, 70 and 75 degrees C. For isotherms construction, the skin and pulp of the grape were used separately and it was possible to observe significant differences. The GAB equation was fitted to the experimental data, using direct nonlinear regression analysis; the agreement between experimental and calculated values was satisfactory. The net isosteric heat or enthalpy of water sorption, determined from the equilibrium sorption data, showed a different behavior when compared with other works, as it was obtained for skin and pulp separately. Plots of Delta h vs Delta S for skin and pulp provided the isokinetic temperatures T-Bs = 423.2 +/- 27.6 K and T-Bp = 424.5 +/- 25.3 K, respectively, indicating an enthalpy-controlled desorption process over the whole range of moisture content considered.

Effect of drying method on the sorption isotherms and isosteric heat of persimmon pulp powder

Moisture equilibrium data of persimmon pulp powders with 50% maltodextrin (dry basis) obtained with different drying methods were determined at 20, 30, 40 and 50 degrees C. The spray-dryer gave a dry product with a higher adsorption capacity than the other methods. The vacuum- and freeze-dried products had the same adsorption capacity. The highest isosteric heat of sorption was observed for powders produced by spray-drying. The isokinetic temperature (T(B)) calculated for persimmon pulp powder obtained by vacuum-, spray- and freeze-drying were 541.4 K, 616.3 K, 513.2 K, respectively. The sorption process was spontaneous and enthalpy controlled.

Sorption isotherms of alligator's meat (Caiman crocodilus yacare)

Sorption isotherms were determined for salted alligator's meat at four different temperatures (10degreesC, 15degreesC, 25degreesC and 35degreesC), using a standard gravimetric method. The goodness of fit of five sorption models to experimental data was determined. Five models, namely the GAB, the BET, the Halsey, the Henderson and the Hailwood and Horrobin, were evaluated to determine the best fit for the experimental data. The GAB was the best fitted model for the data of salted alligator's meat with an average error less than 10% for temperature of 10degreesC and less than 5% for the others temperatures. The coefficients of determination (r(2)) were 0.99 for all temperatures considered. The monolayer values decreased as temperature increased. The other four models were not appropriated to fit the data because of the high error values, although the r(2) were also similar to the GAB model. The net isosteric heat of sorption was estimated from equilibrium sorption data, using the Clausis-Clapeyron equation. Isosteric heats of sorption were found to increase with increasing temperature and could be well adjusted by an exponential relationship. (C) 2002 Elsevier B.V. Ltd. All rights reserved.

Reflux synthesis and hydrothermal processing of ZrO2 nanopowders at low temperature

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

First-order-like transition in salt-induced macroion-polyelectrolyte desorption

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Characterization of gallotannins from Astronium species by flow injection analysis-electrospray ionization-ion trap-tandem mass spectrometry and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Preconcentration and determination of metal ions from fuel ethanol with a new 2,2'-dipyridylamine bonded silica

A silica surface chemically modified with [3-(2,2'-dipyridylamine) propyl] groups was prepared, characterized, and evaluated for its metal ion preconcentration in fuel ethanol. To our knowledge, we are the first authors who have reported the present modification on silica gel surface. The material was characterized using infrared spectra, scanning electronic microscopy, and 13C and 29Si solid-state NMR spectra. Batch and column experiments were conducted to investigate for metal ion removal from fuel ethanol. The results showed that the Langmuir model describes the sorption equilibrium data of the metal ions in a satisfactory way. From the Langmuir isotherms, the following maximum adsorption capacities (in mmolg -1) were determined: 1.81 for Fe(III), 1.75 for Cr(III), 1.30 for Cu(II), 1.25 for Co(II), 1.15 for Pb(II), 0.95 for Ni(II), and 0.87 for Zn(II). Thermodynamic functions, the change of free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) showed that the adsorption of metal ions onto Si-Pr-DPA was feasible, spontaneous, and endothermic. The sorption-desorption of the metal ions made possible the development of a preconcentration and quantification method of metal ions in fuel ethanol. © 2012 Elsevier Inc.

Sorption and desorption of phosphate on biochar and biochar-soil mixtures

The term biochar refers to materials with diverse chemical, physical and physicochemical characteristics that have potential as a soil amendment. The purpose of this study was to investigate the P sorption/desorption properties of various slow biochars and one fast pyrolysis biochar and to determine how a fast pyrolysis biochar influences these properties in a degraded tropical soil. The fast pyrolysis biochar was a mixture of three separate biochars: sawdust, elephant grass and sugar cane leaves. Three other biochars were made by slow pyrolysis from three Amazonian tree species (Lacre, Ingá and Embaúba) at three temperatures of formation (400 °C, 500 °C, 600 °C). Inorganic P was added to develop sorption curves and then desorbed to develop desorption curves for all biochar situations. For the slow pyrolysis, the 600 oC biochar had a reduced capacity to sorb P (4-10 times less) relative to those biochars formed at 400 °C and 500 °C. Conversely, biochar from Ingá desorbed the most P. The fast pyrolysis biochar, when mixed with degraded tropical mineral soil, decreased the soil's P sorption capacity by 55% presumably because of the high soluble, inorganic P prevalent in this biochar (909 mg P/kg of biochar). Phosphorus desorption from the fast pyrolysis biochar/soil mixture not only exhibited a common desorption curve but also buffered the soil solution at a value of ca. 0.2 mg/L. This study shows the diversity in P chemistry that can be expected when biochar is a soil amendment and suggests the potential to develop biochars with properties to meet specific objectives. © 2013 British Society of Soil Science.

Biosorption of cadmium (II) and lead (II) from aqueous solution using exopolysaccharide and biomass produced by Colletotrichum sp.

The biosorption of Cd(II) and Pb(II) ions on biomass and exopolysaccharide (EPS) produced by Colletotrichum sp. fungus has been investigated as a function of contact time, initial pH, initial metal ion concentration, and initial adsorbent concentration in a batch system. Adsorption equilibrium was described by Freundlich and Langmuir isotherms. Adsorption was characterized through granulometry, SEM and EDX analysis. Then, studies were performed to regenerate the adsorbent. Biosorption of metals by biomass and EPS were best described by the Langmuir and Freundlich isotherm, respectively. Results of thermodynamic investigations showed that adsorption reactions were spontaneous (ΔG° < 0), exothermal, and mainly physical. The EPS was able to remove 79 and 98% of cadmium and lead, respectively, and the biomass removed 85 and 84% of cadmium and lead, respectively, in a solution with initial concentration 100 mg L-1, and the four adsorption-desorption cycles of all adsorbents showed up with great regenerative capacity and relative stability after these four cycles, the high potential of these biological materials in sorption has been shown. © 2013 Copyright Balaban Desalination Publications.

Propriedades físico-químicas de abacate submetido à secagem convectiva e desidratação osmótica

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)