Página 21 dos resultados de 7330 itens digitais encontrados em 0.011 segundos

## Diffusion coefficients of sodium dodecylsulfate in aqueous solutions of sucrose and in aqueous solutions

Ribeiro, Ana C. F.; Lobo, Victor M. M.; Azevedo, Eduarda F. G.; Miguel, M. da G.; Burrows, H. D.
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
Relevância na Pesquisa
366.00633%
Differential diffusion coefficients of sodium dodecylsulfate (SDS) in aqueous solutions of sucrose and in aqueous solutions at 298.15 K, over the concentration range 0.0018 M to 0.0817 M, have been measured using a conductimetric cell and an automatic apparatus to follow the diffusion. The results are discussed on the basis of the Onsager-Fuoss model. The cell uses an open ended capillary method, while a conductimetric technique is used to follow the diffusion process by measuring the resistance of a solution inside the capillaries, at recorded times. The influence of molecules of sucrose on the diffusion of this electrolyte was investigated. The presence of sucrose increases the diffusion coefficients of sodium dodecylsulfate both above and below the critical micelle concentration (cmc) of the surfactant.; http://www.sciencedirect.com/science/article/B6TGR-44WR41H-2/1/b113791c08559f77627bfc0ced653999

## Caracterização físico-química e fotodinâmica de fotossensibilizadores: efeito da modificação química para aumentar a solubilidade em meio aquoso; Physical-Chemistry and photodynamic characterization of photosensitizers: effect of chemical modification to increase the solubility in aqueous medium

Gonçalves, Joyce Laura da Silva
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Relevância na Pesquisa
366.00633%

## Estudo do extrato de Bauhinia forficata L. sobre o diabete em ratas prenhes

Volpato, Gustavo Tadeu; Damasceno, Débora Cristina; Calderon, Iracema de Mattos Paranhos; Rudge, Marilza Vieira Cunha
Tipo: Artigo de Revista Científica Formato: 49-55
POR
Relevância na Pesquisa
366.00633%
The objective of this paper was to study the aqueous extract of Bauhinia forficata L. (pata-de-vaca) effects on streptozotocin-induced diabete pregnant rats. We used Wistar pregnant rats, dividided in 3 experimental groups: control (C, n=7), non-treated diabetics (DNT, n=7) and streptozotocin induced-diabetics treated with an aqueous extract of pata-de-vaca leaves, 200 mg/kg dose (DT, n=7). The animals received the extract through a gastric tube (gavage). The blood glucose level were verified on day 0, 5, 14 and 20 of pregnancy. During pregnancy, the daily mean water intake, food intake and average maternal weight gains of rats were measured. The results demonstrated that plant extract reduced the postimplantation loss porcentage, increasing the number of live fetuses likely to the control group. We found increased food and water intake of the DT and DNT pregnant rats compared to control due to hyperglycemic state. We also observed average maternal weight gains was likely to the DT and control groups on different pregnant periods, suggesting treatment with the plant contributed for the rat weight gains. The blood glucose level of dams did not present significative differences between DT and DNT groups. Thus, the B. forficata aqueous extract...

## Aqueous biphasic system based on cholinium ionic liquids: extraction of biologically active phenolic acids

Branco, Sónia Isabel Pereira
Relevância na Pesquisa
366.00633%
Phenolic acids are aromatic secondary plant metabolites, widely spread throughout the plant kingdom. Due to their biological and pharmacological properties, they have been playing an important role in phytotherapy and consequently techniques for their separation and purification are in need. This thesis aims at exploring new sustainable separation processes based on ionic liquids (ILs) in the extraction of biologically active phenolic acids. For that purpose, three phenolic acids with similar chemical structures were selected: cinnamic acid, p-coumaric acid and caffeic acid. In the last years, it has been shown that ionic liquids-based aqueous biphasic systems (ABSs) are valid alternatives for the extraction, recovery and purification of biomolecules when compared to conventional ABS or extractions carried out with organic solvents. In particular, cholinium-based ILs represent a clear step towards a greener chemistry, while providing means for the implementation of efficient techniques for the separation and purification of biomolecules. In this work, ABSs were implemented using cholinium carboxylate ILs using either high charge density inorganic salt (K3PO4) or polyethylene glycol (PEG) to promote the phase separation of aqueous solutions containing three different phenolic acids. These systems allow for the evaluation of effect of chemical structure of the anion on the extraction efficiency. Only one imidazolium-based IL was used in order to establish the effect of the cation chemical structure. The selective extraction of one single acid was also researched. Overall...

## Experiences with dual protein bound aqueous vitamin B12 absorption test in subjects with low serum vitamin B12 concentrations.

Gozzard, D I; Dawson, D W; Lewis, M J
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
366.00633%
A dual isotope vitamin B12 absorption test in which vitamin B12 is given both in aqueous solution and bound to protein (chicken serum), was evaluated in 26 controls and 68 patients with subnormal serum vitamin B12 concentrations (19 with pernicious anaemia, 13 with iron deficiency, seven after partial gastrectomy, seven with malabsorptive states, five with folate deficiency, four with chronic alcoholism and 13 in whom no cause was apparent). In control patients protein bound absorption decreased with age; isotope excretion was 1.0% or over in those aged under 60 and 0.5% or over in those aged 60 and above. Malabsorption of protein bound vitamin B12 with normal aqueous absorption occurred in five patients with iron deficiency, three with alcoholism, two after partial gastrectomy, two with folate deficiency and in one with a malabsorptive state. In alcoholics abstinence produced an improvement in protein bound absorption. All patients in the group for whom no cause could be found for the subnormal serum vitamin B12 concentration had normal aqueous absorption but four had malabsorption of protein bound vitamin. Although the dual isotope test gave reproducible results and was consistent with the standard Schilling test some anomalies were detected; nine patients had reduced aqueous absorption with normal protein bound absorption. Despite this the dual test may prove useful in determining the importance of a subnormal vitamin B12 concentration where the cause is not clinically apparent. Further development is needed before it can be considered for routine use.

## Observation of Pyridine Aggregation in Aqueous Solution Using Neutron Scattering Experiments and MD Simulations

Mason, Philip E.; Neilson, George W.; Dempsey, Christopher E.; Price, David L.; Saboungi, Marie-Louise; Brady, John W.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
367.45566%
Neutron Diffraction with Isotopic Substitution (NDIS) experiments have been used to examine the structuring of aqueous solutions of pyridine. A new method is described for extracting the structure factors relating to intermolecular correlations from neutron scattering experiments on liquid solutions of complex molecular species. This approach performs experiments at different concentrations and exploits the intramolecular coordination number concentration invariance (ICNCI) to separate the internal and intermolecular contributions to the total intensities. The ability of this method to deconvolute molecular and intermolecular correlations is tested and demonstrated using simulated neutron scattering results predicted from molecular dynamics simulations of aqueous solutions of the polyatomic solute pyridine in which the inter- and intramolecular terms are known. The method is then implemented using neutron scattering measurements on solutions of pyridine. The results confirm that pyridine shows a significant propensity to aggregate in solution and demonstrate the prospects for the future application of the ICNCI approach to the study of large polyatomic solutes using next-generation neutron sources and detectors.

## Ammonium Removal from Aqueous Solutions by Clinoptilolite: Determination of Isotherm and Thermodynamic Parameters and Comparison of Kinetics by the Double Exponential Model and Conventional Kinetic Models

Tosun, İsmail
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
367.45566%
The adsorption isotherm, the adsorption kinetics, and the thermodynamic parameters of ammonium removal from aqueous solution by using clinoptilolite in aqueous solution was investigated in this study. Experimental data obtained from batch equilibrium tests have been analyzed by four two-parameter (Freundlich, Langmuir, Tempkin and Dubinin-Radushkevich (D-R)) and four three-parameter (Redlich-Peterson (R-P), Sips, Toth and Khan) isotherm models. D-R and R-P isotherms were the models that best fitted to experimental data over the other two- and three-parameter models applied. The adsorption energy (E) from the D-R isotherm was found to be approximately 7 kJ/mol for the ammonium-clinoptilolite system, thereby indicating that ammonium is adsorbed on clinoptilolite by physisorption. Kinetic parameters were determined by analyzing the nth-order kinetic model, the modified second-order model and the double exponential model, and each model resulted in a coefficient of determination (R2) of above 0.989 with an average relative error lower than 5%. A Double Exponential Model (DEM) showed that the adsorption process develops in two stages as rapid and slow phase. Changes in standard free energy (∆G°), enthalpy (∆H°) and entropy (∆S°) of ammonium-clinoptilolite system were estimated by using the thermodynamic equilibrium coefficients.

## Investigation of Homeodomain Membrane Translocation Properties: Insights from the Structure Determination of Engrailed-2 Homeodomain in Aqueous and Membrane-Mimetic Environments

Carlier, Ludovic; Balayssac, Stéphane; Cantrelle, François-Xavier; Khemtémourian, Lucie; Chassaing, Gérard; Joliot, Alain; Lequin, Olivier
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
367.45566%
In addition to their well-known DNA-binding properties, homeodomains have the ability to efficiently translocate across biological membranes through still poorly-characterized mechanisms. To date, most biophysical studies addressing the mechanisms of internalization have focused on small synthetic peptides rather than full-length globular homeodomains. In this work, we characterized the conformational properties of chicken Engrailed 2 homeodomain (En2HD) in aqueous solution and in membrane mimetic environments using circular dichroism, Trp fluorescence, and NMR spectroscopy. En2HD adopts a well-defined three-helical bundle fold in aqueous solution. The Trp-48 residue, which is critical for internalization, is fully buried in the hydrophobic core. Circular dichroism and fluorescence reveal that a conformational transition occurs in anionic lipid vesicles and in micelles. En2HD loses its native three-dimensional structure in micellar environments but, remarkably, near-native helical secondary structures are maintained. Long-range interactions could be detected using site-directed spin labels, indicating that the three helices do not adopt extended orientations. Noncovalent paramagnetic probes yielded information about helix positioning and unveiled the burial of critical aromatic and basic residues within the micelles. Our results suggest that electrostatic interactions with membranes may be determinant in inducing a conformational change enabling Trp-48 to insert into membranes.

## Removal of Cholera Toxin from Aqueous Solution by Probiotic Bacteria

Heikkilä, Jari E.; Nybom, Sonja M. K.; Salminen, Seppo J.; Meriluoto, Jussi A. O.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
367.45566%
Cholera remains a serious health problem, especially in developing countries where basic hygiene standards are not met. The symptoms of cholera are caused by cholera toxin, an enterotoxin, which is produced by the bacterium Vibrio cholerae. We have recently shown that human probiotic bacteria are capable of removing cyanobacterial toxins from aqueous solutions. In the present study we investigate the ability of the human probiotic bacteria, Lactobacillus rhamnosus strain GG (ATCC 53103) and Bifidobacteriumlongum 46 (DSM 14583), to remove cholera toxin from solution in vitro. Lactobacillus rhamnosus strain GG and Bifidobacteriumlongum 46 were able to remove 68% and 59% of cholera toxin from aqueous solutions during 18 h of incubation at 37 °C, respectively. The effect was dependent on bacterial concentration and L. rhamnosus GG was more effective at lower bacterial concentrations. No significant effect on cholera toxin concentration was observed when nonviable bacteria or bacterial supernatant was used.

## Environmentally friendly system for the degradation of multipesticide residues in aqueous media by the fenton’s reaction

Guimarães, Bruno de Souza; Kleemann, Natiele; Caldas, Sergiane; Costa, Fabiane Pinho; Silveira, Maria Angelis Kisner; Duarte, Fabio Andrei; Primel, Ednei Gilberto
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
367.45566%
A Fenton oxidation system employing zero-valent iron (whose source was swarf, a residue of metallurgical industries, in powder form) and hydrogen peroxide for the treatment of an aqueous solution with six pesticides was developed, and the effect of the iron metal content, pH, and hydrogen peroxide concentration was evaluated. The characterization of the aqueous solution resulted in: pH 5.6, 105 mg L−1 of dissolved organic carbon, and 44.6 NTU turbidity. In addition, the characterization of the swarf by FAAS and ICP-MS showed 98.43±7.40 % of zero-valent iron. The removal was strongly affected by the content of iron metal, pH, and hydrogen peroxide concentration. The best degradation conditions were 2.0 g swarf, pH 2.0, and 5 mmol L−1 H2O2. At the end of the treatment, the pesticide degradation ranged from 60 to 100 %, leading to 55 % mineralization. Besides, all hydrogen peroxide was consumed and the determination of total dissolved iron resulted in2mgL−1. Thus, the advantages of this system are rapid degradation (up to 20 min), high-degradation rates, simple handling, and low cost.

## Nanonization of megestrol acetate by laser fragmentation in aqueous milieu

Sylvestre, Jean-Philippe; Tang, Marie-Christine; Furtos, Alexandra; Leclair, Grégoire; Meunier, Michel; Leroux, Jean-Christophe
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
367.45566%
Nanonization is a simple and effective method to improve dissolution rate and oral bioavailability of drugs with poor water solubility. There is growing interest to downscale the nanocrystal production to enable early preclinical evaluation of new drug candidates when compound availability is scarce. The purpose of the present study was to investigate laser fragmentation to form nanosuspensions in aqueous solution of the insoluble model drug megestrol acetate (MA) using very little quantities of the drug. Laser fragmentation was obtained by focusing a femtosecond (fs) or nanosecond (ns) laser radiation on a magnetically stirred MA suspension in water or aqueous solution of a stabilizing agent. The size distribution and physicochemical properties of the drug nanoparticles were characterized, and the in vitro dissolution and in vivo oral pharmacokinetics of a laser fragmented formulation were evaluated. A MA nanosuspension was also prepared by media milling for comparison purpose. For both laser radiations, smaller particles were obtained as the laser power was increased, but at a cost of higher degradation. Significant nanonization was achieved after a 30-min fs laser treatment at 250 mW and a 1-h ns laser treatment at 2500 mW. The degradation induced by the laser process of the drug was primarily oxidative in nature. The crystal phase of the drug was maintained...

## Adsorption of tetracycline from aqueous solutions onto multi-walled carbon nanotubes with different oxygen contents

Yu, Fei; Ma, Jie; Han, Sheng
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
367.45566%

## Infleunce of pH on the partition of glucose-6-phosphate dehydrogenase and hexokinase in aqueous two-phase system

Silva,Daniel Pereira da; Pontes,Marcela Zanella Ribeiro; Souza,Maria Aparecida de; Vitolo,Michele; Silva,João Batista de Almeida e; Pessoa-Junior,Adalberto
Tipo: Artigo de Revista Científica Formato: text/html
Relevância na Pesquisa
367.45566%
Glucose-6-phosphate dehydrogenase (G6PDH) and hexokinase (HK) are important enzymes used in biochemical and medical studies and in several analytical methods. Aqueous two-phase system (ATPS) formed by a polymer solution and an electrolyte solution provides a method for the separation and purification of enzymes with several advantages, including biocompatibility and easy scale up of the process. In this work, the effects of different pH values on the storage stability and partitioning behavior (K, partition coefficient) of the enzymes G6PDH and HK from baker's yeast extract were investigated in ATPS. The results, obtained from the 17.5% PEG 400 : 15.0% phosphate system, showed that when the pH was increased from 5.0 to 8.8, the K HK increased 26-fold and the K G6PDH 2.2-fold. In the 20.0% PEG 1500 : 17.5% phosphate system, the K HK and K G6PDH increased 13 and 1.2-fold, when the pH value was increased from 3.8 to 8.8, respectively. This leads to the conclusion that the partition coefficient for both enzymes is favored by high pH values. A statistical analysis of the results was conducted to confirm this conclusion.

## Thermal conductivity of TiO₂ nanoparticles based aqueous nanofluids with an addition of a modified silver particle; Thermal conductivity of TiO(2) nanoparticles based aqueous nanofluids with an addition of a modified silver particle

Batmunkh, M.; Tanshen, M.R.; Nine, M.J.; Myekhlai, M.; Choi, H.; Chung, H.; Jeong, H.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
367.45566%
Nanofluid is a colloidal suspension which has received great attention over the past two decades, but its limited heat transfer enhancement is a matter of concern for industrial applications. We demonstrate an improvement in the thermal conductivity of TiO2 nanofluids with an addition of negligible amounts of modified silver “Ag” nanoparticles. In this work, the surface/shape of newly synthesized “Ag” nanoparticles is modified by planetary ball milling. Then, to enhance the thermal conductivity of TiO2 nanofluids, the flattened “Ag” particles are incorporated with the combination of small (15 nm) and large (300 nm) TiO2 nanoparticles in an aqueous solution. The thermal conductivities of Ag/TiO2−water nanofluids with various weight concentrations are measured at temperatures ranging from 15 to 40 °C. As a result, the present study confirms that the thermal conductivity of TiO2 based solution can be improved by introducing the flattened “Ag” particles.; Munkhbayar Batmunkh, Md. R. Tanshen, Md. J. Nine, Munkhshur Myekhlai, Heekyu Choi, Hanshik Chung, and Hyomin Jeong

## Measurement of Interaction Forces between Lignin and Cellulose as a Function of Aqueous Electrolyte Solution Conditions

Notley, Shannon; Norgren, Magnus
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
367.45566%
The interaction between a lignin film and a cellulose sphere has been measured using the colloidal probe force technique as a function of aqueous electrolyte solution conditions. The lignin film was first studied for its roughness and stability using atom

## Film Growth and Surface Roughness with Fluctuating Covalent Bonds in Evaporating Aqueous Solution of Reactive Hydrophobic and Polar Groups: A Computer Simulation Model

Yang, Shihai; Seyfarth, Adam; Bateman, Sam; Pandey, Ras B.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
367.45566%
A computer simulation model is proposed to study film growth and surface roughness in aqueous ($A$) solution of hydrophobic ($H$) and hydrophilic ($P$) groups on a simple three dimensional lattice of size $L_x \times L_y \times L_z$ with an adsorbing substrate. Each group is represented by a particle with appropriate characteristics occupying a unit cube (i.e., eight sites). The Metropolis algorithm is used to move each particle stochastically. The aqueous constituents are allowed to evaporate while the concentration of $H$ and $P$ is constant. Reactions proceed from the substrate and bonded particles can hop within a fluctuating bond length. The film thickness ($h$) and its interface width ($W$) are examined for hard-core and interacting particles for a range of temperature ($T$). Simulation data show a rapid increase in $h$ and $W$ is followed by its non-monotonic growth and decay before reaching steady-state equilibrium ($h_s, W_s$) in asymptotic time step limit. The growth can be described by power-laws, e.g., $h \propto t^{\gamma}, W \propto t^{\beta}$ with a typical value of $\gamma \approx 2, \beta \approx 1$ in initial time regime followed by $\gamma \approx 1.5, \beta \approx 0.8$ at $T = 0.5$. For hard-core system, the equilibrium film thickness ($h_s$) and surface roughness ($w_s$) seem to scale linearly with the temperature...

## Bi_xTi_(1−x)O_z Functionalized Heterojunction Anode with an Enhanced Reactive Chlorine Generation Efficiency in Dilute Aqueous Solutions

Cho, Kangwoo; Hoffmann, Michael R.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Article; PeerReviewed Formato: application/pdf
Relevância na Pesquisa
367.45566%
Ir_(0.7)Ta_(0.3)O_y/Bi_xTi_(1–x)O_z heterojunction anodes have been developed and characterized for reactive chlorine species (RCS) generation in dilute aqueous solution (50 mM NaCl). The primary objective of the research was to control the electro-stationary speciation of hydrous metal oxides between hydroxyl radical (>MO_x(·OH)) and higher valence-state oxides (>MO_(x+1)). An underlying layer of the mixed-metal oxide, Ir_(0.7)Ta_(0.3)O_y, was synthesized to serve as a primary Ohmic contact and electron shuttle. Binary thin films of Bi_xTi_(1–x)O_z were prepared from the thermal decomposition of an aqueous solution mixture of Ti/Bi complexes. With these core components, the measured current efficiency for RCS generation (η_(RCS)) was enhanced where the values observed for x = 0.1 or 0.3 were twice of the η_(RCS) of the Ir_(0.7)Ta_(0.3)O_y anode. At the same time, the rates of RCS generation were enhanced by factors of 20–30%. Partial substitution of Ti with Bi results in a positive shift in surface charge allowing for stronger interaction with anions, as confirmed by FTIR-ATR analysis. A kinetic model to describe the formate ion degradation showed that an increasing fraction of Bi in the composite promotes a redox transition of >MO_x(·OH) to >MO_(x+1). In accelerated life tests under conditions corresponding to a service life of 2 years under an operational current density of 300 A m^(–2)...

## Corrosion Inhibition by an Aqueous Extract of Phyllanthus Amarus

Sangeetha,M.; Rajendran,S.; Sathiyabama,J.; Krishnaveni,A.; Shanthy,P.; Manimaran,N.; Shyamaladevi,B.
Tipo: Artigo de Revista Científica Formato: text/html
Relevância na Pesquisa
367.45566%
The inhibition efficiency (IE) of phyllanthus amarus extract (PAE)-Zn2+ system, in controlling corrosion of carbon steel in an aqueous solution containing 60 ppm of Cl-, has been evaluated by weight loss method. Weight loss study reveals that the formulation consisting of 2 mL of PAE and 25 ppm of Zn2+ has 98% inhibition efficiency in controlling corrosion of carbon steel immersed in an aqueous solution containing 60 ppm of Cl-. Synergistic parameters suggest that a synergistic effect exists between PAE and Zn2+. Polarization study reveals that this system functions as mixed type of inhibitor controlling the cathodic reaction and anodic reaction to an equal extend. AC impedance spectra reveal that a protective film is formed on the metal surface. The FTIR spectra reveal that the protective film consists of Fe2+-phyllanthus complex.

## Comparative study of polypyrrole films electrosynthesized on zinc surfaces from organic and aqueous solutions

Martins,J. I.; Bazzaoui,M.
Fonte: LNEG - Laboratório Nacional de Energia e Geologia, I.P. Publicador: LNEG - Laboratório Nacional de Energia e Geologia, I.P.
Tipo: Artigo de Revista Científica Formato: text/html