Página 9 dos resultados de 7330 itens digitais encontrados em 0.009 segundos

Interactions between hairy rod anionic conjugated polyelectrolytes and nonionic alkyloxyethylene surfactants in aqueous solution: Observations from cloud point behaviour

Fonseca, Sofia M.; Eusébio, M. Ermelinda; Castro, Ricardo; Burrows, Hugh D.; Tapia, Maria José; Olsson, Ulf
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
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The effect of three anionic, hairy-rod fluorene based conjugated polyelectrolytes on the cloud points of the alkyloxyethylene surfactants C10E3, C12E4, C12E5, and C12E6 has been studied in aqueous solution. Although the association behaviour of these rigid polymers with surfactants is different from that of more flexible polyelectrolytes, both types of polymers are seen to increase the cloud points, probably as a consequence of associative interactions. The possible importance of Coulombic interactions is suggested by the decrease in cloud points with these systems in the presence of NaCl. With the conjugated polyelectrolytes, the effect appears to be most pronounced with poly[9,9-bis(4-phenoxybutylsulfonate)fluorene-co-2,5-thienylene], which may result from specific interactions between oxyethylene groups and the thiophene ring. The value of cloud point behaviour in designing water based formulations for preparation of devices of these conjugated polyelectrolytes is discussed.; http://www.sciencedirect.com/science/article/B6WHR-4P59X93-C/1/734f080f25b8d7b0de35dd6c030d23e1

Electron-Transfer Oxidation of Chlorophenols by Uranyl Ion Excited State in Aqueous Solution. Steady-State and Nanosecond Flash Photolysis Studies

Sarakha, Mohamed; Bolte, Michèle; Burrows, Hugh D.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
ENG
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The oxidation of chlorophenols by photoexcited uranyl ion was studied in aqueous solution at concentrations where the ground-state interactions were negligible. Nanosecond flash photolysis showed that a clean electron-transfer process from the chlorophenols to the excited uranyl ion is involved. This is suggested to lead to the formation of a U(V)/chlorophenoxyl radical pair complex. The efficiency of this charge-transfer process is unity for the three chlorophenols. However, low product yields suggest that in the absence of oxygen, back electron transfer, both within the radical pair and from separated uranium(V) to phenoxyl radicals, appears to be the major reaction pathway. In the presence of oxygen the quantum yields of disappearance of chlorophenol and of photoproduct formation increased. This leads to the conclusion that oxygen favors reaction with uranium(V) and/or the uranium(V)−phenoxyl radical pair, leading to the formation of the superoxide anion and its conjugate acid, HO2•, which then regenerate UO22+. Based on this, a catalytic cycle for chlorophenol photooxidation involving uranyl ion and molecular oxygen is proposed.; http://dx.doi.org/10.1021/jp993676t

Changes in Hydration of Lanthanide Ions on Binding to DNA in Aqueous Solution

Costa, Diana; Burrows, Hugh D.; Miguel, M. da Graça
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
ENG
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The interaction of the trivalent lanthanides Ce(III), Eu(III), and Tb(III) with sodium deoxyribonucleic acid (DNA) in aqueous solution has been studied using their luminescence spectra and decays. Complexation with DNA is indicated by changes in luminescence intensity. In the system terbium(III)−DNA, changes in luminescence with pH are suggested to be due to the protonation of phosphate groups. The degree of hydration of Tb(III) on binding to DNA is followed by luminescence lifetime measurements in water and deuterium oxide solutions, and it is found that the lanthanide ion loses at least one hydration water on binding to long double stranded DNA at pH 4.7 and pH 7. Rather different behavior is observed on binding to long or short single stranded DNA, where six water molecules are lost, independent of pH. It is suggested that in this case the lanthanide probably binds to the bases of the DNA backbone. The DNA conformation seems to be an important factor in the binding. In addition, the isotopic effect on terbium luminescence lifetime may provide a useful method to distinguish between single and double stranded DNA. DSC results are consistent with cleavage of the double helix of DNA at pH 9 in the presence of terbium.; http://dx.doi.org/10.1021/la051493u

Interaction between the Conjugated Polyelectrolyte Poly{1,4-phenylene[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} Copolymer and the Lecithin Mimic 1-O-(l-Arginyl)-2,3-O-dilauroyl-sn-glycerol in Aqueous Solution

Tapia, María J.; Burrows, Hugh D.; Knaapila, Matti; Monkman, Andrew P.; Arroyo, Antonio; Pradhan, Swapna; Scherf, Ullrich; Pinazo, Aurora; Pérez, Lourdes; Morán, Carmen
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
ENG
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In this paper, the interaction between the water-soluble conjugated polyelectrolyte poly{1,4-phenylene[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} copolymer and the amino acid glyceride conjugate 1-O-(l-arginyl)-2,3-O-dilauroyl-sn-glycerol dichlorohydrate (a mimic for the phospholipid lecithin) has been studied in aqueous solution by electronic spectroscopy (absorption and fluorescence) and small-angle neutron scattering (SANS). A significant increase in the polymer fluorescence and blue shift in its emission are observed on association with the surfactant. This is suggested to be due to breakup of polymer aggregates. In addition, the spectroscopic and photophysical data suggest this is followed by the vesicle to ribbon transition characteristic of this surfactant, leading to incorporation of single chains of the polymer within mixed polymer−surfactant aggregates. Support for this comes from preliminary SANS measurements, from which evidence for polymer dissolution and formation of two-dimensional structures has been obtained.; http://dx.doi.org/10.1021/la0612217

Multinuclear NMR study of the interaction of the shift reagent lanthanide(III) bis(triphosphate) with alkali-metal ions in aqueous solution and in the solid state

Ramasamy, Ravichandran; Freitas, Duarte Mota de; Geraldes, Carlos F. G. C.; Peters, Joop A.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
ENG
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The paramagnetic ion-induced relaxation rate enhancements of 6Li in adducts of Li+ and Ln(PPP)J- complexes (Ln = Dy, Tm) in aqueous solution show that up to seven monovalent counterions can coordinate in the second coordination sphere of the Ln(II1) ion to the outer oxygens of the triphosphate ligands. However, the pseudocontact ’Li NMR shift data suggest that in the second coordination sphere some preference of the counterions for the axial region opposite the water ligand may exist. The estimated Ln3+-Li+ distances range from 5.1 to 5.9 A for [Li+]/[Ln(PPP)J-] ratios of 0.2-7. This is supported by a two-dimensional nutation spectrum of a polycrystalline sample of Na,La(PPP),, which indicates coordination of all Na+ ions to phosphate oxygens.; http://dx.doi.org/10.1021/ic00016a016

First evidence of crystalline KHSO(4):Mn grown by an aqueous solution method and the investigation of the effect of ionizing radiation exposure

Ayta, Walter Elias Feria; Dantas, Noelio Oliveira; Silva, Anielle Christine Almeida; Mamani, Nilo Francisco Cano
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
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In this work, KHSO(4):Mn crystals doped with Mn and K(2)SO(4) were synthesized using an aqueous solution method. The samples were exposed to ionizing radiation in order to observe the effects on their physical properties. Raman spectroscopy was used to identify the structure of the crystals by detecting the vibrational frequencies of the crystalline lattice. Electron paramagnetic resonance (EPR) was used to study the creation of paramagnetic centers arising from exposure to ionizing radiation. This new synthesis method produces high quality K(2)SO(4) and KHSO(4):Mn crystals and allows control of structural, morphological, optical and magnetic properties. (C) 2009 Elsevier B.V. All rights reserved,; Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG); FAPEMIG; MCT/CNPq; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Phototransformation of hematoporphyrin in aqueous solution: Anomalous behavior at low oxygen concentration

PRATAVIEIRA, S.; SANTOS, P. L. A.; MENEZES, P. F. C.; KURACHI, Cristina; SIBATA, C. H.; JARVI, M. T.; WILSON, B. C.; BAGNATO, Vanderlei Salvador
Fonte: MAIK NAUKA/INTERPERIODICA/SPRINGER Publicador: MAIK NAUKA/INTERPERIODICA/SPRINGER
Tipo: Artigo de Revista Científica
ENG
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The photoactivation of a photosensitizer is the initial step in photodynamic therapy (PDT) where photochemical reactions result in the production of reactive oxygen species and eventually cell death. In addition to oxidizing biomolecules, some of these photochemical reactions lead to photosensitizer degradation at a rate dependent on the oxygen concentration among other factors. We investigated photodegradation of Photogem A (R) (28 mu M), a hematoporphyrin derivative, at different oxygen concentrations (9.4 to 625.0 mu M) in aqueous solution. The degradation was monitored by fluorescence spectroscopy. The degradation rate (M/s) increases as the oxygen concentration increases when the molar ratio of oxygen to PhotogemA (R) is greater than 1. At lower oxygen concentrations (< 25 mu M) an inversion of this behavior was observed. The data do not fit a simple kinetic model of first-order dependence on oxygen concentration. This inversion of the degradation rate at low oxygen concentration has not previously been demonstrated and highlights the relationship between photosensitizer and oxygen concentrations in determining the photobleaching mechanism(s). The findings demonstrate that current models for photobleaching are insufficient to explain completely the effects at low oxygen concentration.; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); CEPID; FAPESP; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); CAPES; Canadian Cancer Society/NCIC; Canadian Cancer Society/NCIC

Conformational Properties of Angiotensin II and Its Active and Inactive TOAC-Labeled Analogs in the Presence of Micelles. Electron Paramagnetic Resonance, Fluorescence, and Circular Dichroism Studies

VIEIRA, Renata F. F.; CASALLANOVO, Fabio; MARIN, Nelida; PAIVA, Antonio C. M.; SCHREIER, Shirley; NAKAIE, Clovis R.
Fonte: JOHN WILEY & SONS INC Publicador: JOHN WILEY & SONS INC
Tipo: Artigo de Revista Científica
ENG
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The interaction between angiotensin II (AII, DRVYIHPF) and its analogs carrying 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC) and detergents-negatively charged sodium dodecyl sulfate (SDS) and zwitterionic N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS)-was examined by means of EPR, CD, and fluorescence. EPR spectra of partially active TOAC(1)-AII and inactive TOAC(3)-AII in aqueous solution indicated fast tumbling, the freedom of motion being greater at the N-terminus. Line broadening occurred upon interaction with micelles. Below SDS critical micelle concentration, broader lines indicated complex formation with tighter molecular packing than in micelles. Small changes in hyperfine splittings evinced TOAC location at the micelle-water interface. The interaction with anionic micelles was more effective than with zwitterionic micelles. Peptide-micelle interaction caused fluorescence increase. The TOAC-promoted intramolecular fluorescence quenching was more, pronounced for TOAC(3)-AII because of the proximity between the nitroxide and Tyr(4). CD spectra showed that although both AII and TOAC(1)-AII presented flexible conformations in water, TOAC(3)-AII displayed conformational restriction because of the TOAC-imposed bend (Schreier et al....

Kinetic and mechanistic investigation of the ozonolysis of 2,4-xylidine (2,4-dimethyl-aniline) in acidic aqueous solution

MACHULEK JR., Amilcar; GOGRITCHIANI, Eliso; MORAES, Jose E. F.; QUINA, Frank H.; BRAUN, Andre M.; OLIVEROS, Esther
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
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The ozonolysis of 2,4-xylidine (2,4-dimethyl-aniline) in acidic aqueous solution was investigated by determining the major reaction products and their evolution as a function of the reaction time and their dependence on the pH of the reaction system. 2,4-Dimethyl-nitrobenzene and 2,4-dimethyl-phenol were found to be primary reaction products; their formation might be explained by electron transfer and substitution reactions. 2,4-Dimethyl-phenol was further oxidized yielding 2,4-dimethyl- and/or 4,6-dimethyl-resorcinol by electrophilic addition of HO(center dot) radicals. The best fitting phenomenological kinetic model and the good convergence of calculated and experimentally determined rate constants imply two additional competitive pathways of substrate oxidation: (i) electrophilic addition of HO(center dot) radicals and fast subsequent substitution would also yield the resorcinol derivatives. (ii) Substrate and isolated products are thought to be oxidized by hydrogen abstraction at the benzylic sites, but the corresponding products (alcohols, aldehydes, and carboxylic acids) could not be identified. Fe(II) was added to probe for the presence of H(2)O(2), but had no or only a minor effect on the kinetics of the ozonolysis. (c) 2009 Elsevier B.V. All rights reserved.

Reaction of a model siderophore with Ni(II), Co(II) and Zn(II) in aqueous solution: Kinetics and spectroscopy

BARRETO, Wagner J.; ANDO, Rornulo A.; SANTOS, Paulo S.; SILVA, Waleria P.
Fonte: ELSEVIER SCIENCE INC Publicador: ELSEVIER SCIENCE INC
Tipo: Artigo de Revista Científica
ENG
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A spectroscopic study was performed showing that the [Fe(III)(L(2-))(2)](1-) (L(2-) = dopacatecholate) complex reacts with Ni(II), Co(II) and Zn(II) in an aqueous solution containing S(2)O(3)(2-) resulting in the soluble [M(L(1-))(3)](1-) (L(1-) = dopasemiquinone; M = Ni(II), Co(II) or Zn(II) complex species. The Raman and IR spectra of the [CTA][M(L(1-))(3)] complexes, CTA hexadecyltrimethylammonium cation, in the solid state were obtained. The kinetic constants for the metal substitution reactions were determined at four different temperatures, providing values for Delta W(not equal) Delta S(not equal) and Delta G(not equal). The reactions were slow (k = 10(-1)1 M s(-1)) and endothermic. The system investigated can be considered as a simplified model to explain some aspects of siderophore chemistry. (c) 2007 Elsevier Inc. All rights reserved.

Adsorption of phosphate from aqueous solution by hydrous zirconium oxide

Rodrigues, Liana Alvares; Maschio, Leandro Jose; Cividanes Coppio, Luciana de Simone; Thim, Gilmar Patrocinio; Caetano Pinto da Silva, Maria Lucia
Fonte: TAYLOR & FRANCIS LTD; ABINGDON Publicador: TAYLOR & FRANCIS LTD; ABINGDON
Tipo: Artigo de Revista Científica
ENG
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Synthetic ZrO2 center dot nH(2)O was used for phosphate removal from aqueous solution. The optimum adsorbent dose obtained for phosphate adsorption on to hydrous zirconium oxide was 0.1 g. The kinetic process was described very well by a pseudo-second-order rate model. The phosphate adsorption tended to increase with the decrease in pH. The adsorption capacity increased from 61 to 66 mg g(-1) when the temperature was increased from 298 to 338 K. A phosphate desorption of approximately 74% was obtained using water at pH 12.

Synthesis of high-surface-area gamma-Al2O3 from aluminum scrap and its use for the adsorption of metals: Pb(II), Cd(II) and Zn(II)

Asencios, Yvan J. O.; Sun-Kou, Maria R.
Fonte: ELSEVIER SCIENCE BV; AMSTERDAM Publicador: ELSEVIER SCIENCE BV; AMSTERDAM
Tipo: Artigo de Revista Científica
ENG
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Several types of alumina were synthesized from sodium aluminate (NaAlO2) by precipitation with sulfuric acid (H2SO4) and subsequently calcination at 500 degrees C to obtain gamma-Al2O3. The precursor aluminate was derived from aluminum scrap. The various gamma-Al2O3 synthesized were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), adsorption-desorption of N-2 (S-BET) and scanning electron microscopy (SEM). XRD revealed that distinct phases of Al2O3 were formed during thermal treatment. Moreover, it was observed that conditions of synthesis (pH, aging time and temperature) strongly affect the physicochemical properties of the alumina. A high-surface-area alumina (371 m(2) g(-1)) was synthesized under mild conditions, from inexpensive raw materials. These aluminas were tested for the adsorption of Cd(II), Zn(II) and Pb(II) from aqueous solution at toxic metal concentrations, and isotherms were determined. (C) 2012 Elsevier B.V. All rights reserved.; Brazilian National Council for Scientific Development (CNPq)

A fluorescence probe study of gemini surfactants in aqueous solution: a comparison between n-2-n and n-6-n series of the alkanediyl-a,w-bis (dimethylalkylammonium bromides)

Junior, P. B.S.; Tiera, V. A.O.; Tiera, M. J.
Fonte: Editora Unesp Publicador: Editora Unesp
Tipo: Artigo de Revista Científica Formato: 47-54
ENG
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Two series of alkanediyl-a,w-bis (dimethylalkylammonium bromide (n-2-n and n-6-n; n=8, 10,12, and 16) have been synthesized and their micelles properties studied in aqueous solution using pyrene, pyrenecarboxaldehyde (PCA) and 1,8 anilinonaphtalene sulfonic acid sodium salt (ANS) as fluorescent probes. The micelles from these surfactants have been characterized on the basis of the information provided by micelle-solubilized fluorescent probes. The obtained results indicated that the surfactant concentration at which a marked decrease in l max parameter of pyrenecarboxaldehyde (PCA) occurs corresponds to the CMC determined by conductimetric measurements. Changes in the emission spectra of ANS and PCA observed in the submicellar range for both surfactants series (n-2-n and n-6-n) were interpreted as formation of pre-aggregates. It was found that the dimeric surfactants with long spacer (s= 6) form more hydrated aggregates when compared with those formed by the n-2-n and CnTAB surfactants series. This was attributed to a more difficult packing of n-6-n surfactant molecules to form micelles.

Structural organization of cetyltrimethylammonium sulfate in aqueous solution: the effect of Na2SO4

Feitosa, E.; Brazolin, MRS; Naal, RMZG; Del Lama, MPFDD; Lopes, JR; Loh, W.; Vasilescu, M.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 883-889
ENG
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We used dynamic light scattering (DLS), a steady-state fluorescence, time resolved fluorescence quenching (TRFQ), tensiometry, conductimetry, and isothermal titration calorimetry (ITC) to investigate the self-assembly of the cationic surfactant cetyltrimethylammonium sulfate (CTAS) in aqueous solution, which has SO42- as divalent counterion. We obtained the critical micelled concentration (cmc), aggregation number (N-agg), area per monomer (a(0)), hydrodynamic radius (R-H), and degree of counterion dissociation (alpha) of CTAS micelles in the absence and presence of up to 1 M Na2SO4 and at temperatures of 25 and 40 degrees C. Between 0.01 and 0.3 M salt the hydrodynamic radius of CTAS micelle R-H approximate to 16 angstrom is roughly independent on Na2SO4 concentration; below and above this concentration range R-H increases steeply with the salt concentration, indicating micelle structure transition, from spherical to rod-like structures. R-H increases only slightly as temperature increases from 25 to 40 degrees C, and the cmc decreases initially very steeply with Na2SO4 concentration up to about 10 mM, and thereafter it is constant. The area per surfactant at the water/air interface, a(0), initially increases steeply with Na2SO4 concentration...

Environmental coordination chemistry: Binary systems comprising some bivalent cations and monocarboxylates in aqueous solution. Ionic medium effects on equilibrium constants

Pezza, Leonardo; Molina, M.; Melios, C. B.; Moraes, M. de; Tognolli, J. O.; Gomes, H. M.
Fonte: Gordon Breach Sci Publ Ltd Publicador: Gordon Breach Sci Publ Ltd
Tipo: Artigo de Revista Científica Formato: 295-311
ENG
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The molar single activity coefficients associated with propionate ion (Pr) have been determined at 25 degrees C and ionic strengths comprised between 0.300 and 3.00 M, adjusted with NaClO4, as background electrolyte. The investigation was carried out potentiometrically by using a second class Hg/Hg2Pr2 electrode. It was found that the dependence of propionate activity coefficients as a function of ionic strength (I) can be assessed through the following empirical equation: log y(Pr) = -0.185 I-3/2 + 0.104 I-2. Next, simple equations relating stoichiometric protonation constants of several monocarboxylates and formation constants associated with 1:1 complexes involving some bivalent cations and selected monocarboxylates, in aqueous solution, at 25 degrees C, as a function of ionic strength were derived, allowing the interconversion of parameters from one ionic strength to another, up to I = 3.00 M. In addition, thermodynamic formation constants as well as parameters associated with activity coefficients of the complex species in the equilibria are estimated. The body of results shows that the proposed calculation procedure is very consistent with critically selected experimental data.

Hypertonic glucose solution 10% - 25% on the mesenterium and peritoneum of the rat: macroscopic and microscopic study

Carvalho,José Cícero Ferreira de; Leal,Antenor Teixeira; Sousa,Luis Ferreira de; Herani Filho,Benedito
Fonte: Sociedade Brasileira para o Desenvolvimento da Pesquisa em Cirurgia Publicador: Sociedade Brasileira para o Desenvolvimento da Pesquisa em Cirurgia
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2005 EN
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PURPOSE: The objective of the experimental study is to detect the macroscopic and microscopic alterations of the mesenterium and parietal peritoneum when hypertonic glucose aqueous solution 10%-25% is administrated into the peritoneal cavity of the rat. METHODS: 90 Wistar females young rats adults were used weighin between 180-250 g, numbered 1 to 90, establishing unique group and divided in three groups (A, B, C) of 30 animals chosen aleatory manner. 0,9% saline solution was used called control group, or group A, 10% glucose solution named group B, and in the others 30 was used 25% glucose solution named group C, differing in the observation period, (06h, 24h and 48h), but with the same procedure. A midline abdominal wall laparotomy was made and in the animals of the control group was injected 2 ml of a 0,9% saline solution into the peritoneal cavity. After, we made a suture in mass without to include the peritoneum. For the others groups (B, C) the rats received 10% glucose solution and 25% glucose solution injected into the peritoneal cavity respectively. All groups were kept under observation and the results were submitted to statistical analysis by a longitudinal and transversal comparative study. RESULTS: A new surgery was done in 6h...

The coordination chemistry of the pentadentate 2,2,6,6-tetrakis(aminomethyl)-4-azaheptane (ditame)

Hegetschweiler, Kaspar; Maas, Oliver; Zimmer, Anja; Geue, Rodney; Sargeson, Alan; Harmer, Jeffrey; Schweiger, Arthur; Buder, Irmgard; Schwitzgebel, Gunter; Reiland, Vera; Frank, Walter
Fonte: Wiley-VCH Verlag GMBH Publicador: Wiley-VCH Verlag GMBH
Tipo: Artigo de Revista Científica
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The protonation and metal complex formation of the branched pentaamine ligand 2,2,6,6-tetrakis(aminomethyl)-4-azaheptane (ditame, L) with CoII, CoIII, NII, CuII, ZnII, and CDII have been studied. The crystal structures of [Ni(ditame)(EtOH)] Br2, [CO2(ditame)2(O2)Cl4 ·4H2O, and [Co2-(ditame)2(O2)]Cl2 [ZnCl4][ZnCl3(H2O)]·H2O were determined by X-ray diffraction analyses. The metal complexes showed octahedral coordination geometries with exclusive formation of six-membered chelate rings, the four primary amino groups being in equatorial positions and the secondary amino group (Nsec) apical. This geometry enforces a relatively short M-Nsec bond. Complex formation in aqueous solution was evaluated by potentiometric titration. The ditame ligand forms a surprisingly stable NiII complex with logKNiL = 17.8 (25 °C, 0.1 M KNO3), and formation of protonated species [Ni(Hnditame)](n+2)+ (n = 1, 2) is not significant. Different behavior is evident for ZnII and CdII, with which protonated species are extensively formed, while the stability of [ML]2+ is relatively low. Complex formation between ditame and CuII in the range 3 < pH < 7 resulted in the formation of [Cu(H2ditame)]4+. In slightly alkaline solution, the dinuclear [Cu2(ditame)2]4+ appears to be formed. The structural assignment of this dimer is based on its UV/Vis and EPR characteristics...

Cyclodextrin Molecular Reactors

Barr, Lorna; Dumanski, Paul; Easton, Christopher; Harper, Jason B; Lee, Kitty; Lincoln, Stephen F; Meyer, Adam G; Simpson, Jamie S
Fonte: Kluwer Academic Publishers Publicador: Kluwer Academic Publishers
Tipo: Artigo de Revista Científica
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The ability of cyclodextrins to form inclusion complexes with hydrophobic species in aqueous solution makes them well-suited to the development of molecular reactors, to be used as miniature reaction vessels in order to control the outcomes of chemical transformations at the molecular level. In this manner, reaction rates can be increased and products may be obtained that are different to those normally accessible from reactions in free solution. Examples used to illustrate these effects include: the application of cyclodextrins to control the regioselectivity of bromination of aromatic substrates with pyridinium dichlorobromate; the use of a metallocyclodextrin to increase the rate of hydrolysis of a phosphate triester by almost five orders of magnitude; the development of modified cyclodextrins to increase the rates and reverse the regioselectivity of nitrile oxide cycloadditions; and the use of a cyclodextrin dimer to change the ratio of formation of indigoid dyes by a factor of more than 3500.

Removal of copper(II) ion from aqueous solution by high-porosity activated carbon

Milenković,Dragan D; Milosavljević,Milutin M; Marinković,Aleksandar D; Ðokić,Veljko R; Mitrović,Jelena Z; Bojić,Aleksandar Lj
Fonte: Water SA Publicador: Water SA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2013 EN
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The removal of copper(II) ion from aqueous solution by the granular activated carbon, obtained from hazelnut shells (ACHS) (Corylus avellana L. var. lunga istriana), was investigated. The ACHS was prepared from ground dried hazelnut shells by specific method carbonisation and water steam activation at 950ºC for 2 h. The granular activated carbon produced from hazelnut shells has a high specific surface area (1 452 m²·g-1) and highly developed microporous structure (micropore volume: 0.615 cm³·g-1). In batch tests, the influences of solution pH, contact time, initial metal ion concentration and temperature on the sorption of copper(II) ion on ACHS were studied. The results indicate that sorption of copper(II) ion on ACHS strongly depends on pH values. The adsorption data can be well described by the Langmuir isotherm and Redlich-Peterson model. The monolayer adsorption capacity of the ACHS-copper(II) ion, calculated from the Langmuir isotherms, is 3.07 mmol·g-1. The time-dependent adsorption of copper(II) ion could be described by the pseudo second-order and Elovich kinetics, indicating that the rate-limiting step might be a chemical reaction. The intra-particle diffusion model indicates that adsorption of copper(II) ions on ACHS was diffusion controlled.

Adsorption of Rhodamine B dye from aqueous solution on Irvingia gabonensis biomass: Kinetics and thermodynamics studies

Inyinbor,Adejumoke A.; Adekola,Folahan A.; Olatunji,Gabriel A.
Fonte: South African Journal of Chemistry Publicador: South African Journal of Chemistry
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2015 EN
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Raw Irvingia gabonenses (dika nut) (DN) and its acid-treated form (ADN) were used for the uptake of rhodamine B (RhB) dye from aqueous solution. The adsorbents were characterized by Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis and scanning electron microscopy (SEM). The adsorbents were found to have characteristic functional groups such as -OH, C-N and C=O. SEM revealed that acid treatment resulted in the development of several pore sizes. Sorption data fitted the Freundlich adsorption isotherm better than the Langmuir isotherm. The maximum sorption capacities, q max, obtained from the Langmuir adsorption isotherm were 212.77 and 232 mg g-1 for DN and ADN, respectively. The pseudo-second-order kinetics model was observed to fit the adsorption data. Solution pH and temperature significantly influenced the adsorption process and negative values of DG° suggest that the sorption process was spontaneous and feasible. Intraparticle diffusion mainly controlled the uptake of RhB onto DN and ADN; however, boundary layer diffusion also occurred in the RhB-ADN system. The desorption efficiency of RhB from the adsorbents was tested with a number of eluents. The eluents were found to follow the order: H2O>CH3COOH>HCl and CH3COOH>HCl>H2O for DN and ADN...