Small-angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR) have been carried out to investigate the structure of the self-aggregates of two phenothiazine drugs, chlorpromazine (CPZ) and trifluoperazine (TFP), in aqueous solution. In the SAXS studies, drug solutions of 20 and 60 mM, at pH 4.0 and 7.0, were investigated and the best data fittings were achieved assuming several different particle form factors with a homogeneous electron density distribution in respect to the water environment. Because of the limitation of scattering intensity in the q range above 0.15 angstrom(-1), precise determination of the aggregate shape was not possible and all of the tested models for ellipsoids, cylinders, or parallelepipeds fitted the experimental data equally well. The SAXS data allows inferring, however, that CPZ molecules might self-assemble in a basis set of an orthorhombic cell, remaining as nanocrystallites in solution. Such nanocrystals are composed of a small number of unit cells (up to 10, in c-direction), with CPZ aggregation numbers of 60-80. EPR spectra of 5- and 16-doxyl stearic acids bound to the aggregates were analyzed through simulation, and the dynamic and magnetic parameters were obtained. The phenothiazine concentration in EPR experiments was in the range of 5-60 mM. Critical aggregation concentration of TFP is lower than that for CPZ...
O aumento das preocupações ambientais tem proporcionado a busca crescente por alternativas para reduzir os impactos decorrentes de resíduos perigosos oriundos de processos industriais. Dentre estes resíduos, pode-se destacar o fenol, por sua alta toxicidade e dificuldade de tratamento. O fenol é um dos principais poluentes encontrado em efluentes de indústrias de resinas fenólicas, automotivas, farmacêuticas e refinarias de petróleo. Compostos fenólicos são absorvidos facilmente por animais e seres humanos através da pele e são extremamente tóxicos para a vida aquática. Nesta busca por formas de tratamento de resíduos, a absorção é considerada uma das mais importantes técnicas de uso industrial utilizada na purificação de emissões gasosas, além de diversas aplicações em processos industriais. O princípio desta operação baseia-se no transporte de massa de pelo menos um componente de uma mistura gasosa para uma fase líquida, através da interface entre ambas. Este trabalho é parte integrante de um projeto global intitulado "Estudo da Recuperação de Poluentes Prioritários de Soluções Aquosas por Extração Liquido-Liquido com Tratamento Simultâneo de Gases Ácidos". Na primeira etapa há a remoção do fenol de soluções aquosas...
Neste trabalho, investigamos o microambiente da amilopectina na ausência e presença de tensoativos não-iônicos como o éter dodecil (7 e 23)-polioxietilênico (Unitol L-70 e L-230) e o nonilfenol (9,5)-polioxietilênico (Renex 95), por meio das propriedades físico-químicas de sondas de polaridade: pireno, xantona e Reichardt. Os estudos foram realizados através de técnicas espectroscópicas em estado estacionário (absorção de luz ultravioleta-visível e fluorescência) e resolvidas no tempo (baseadas na contagem de fótons únicos da emissão de fluorescência e na absorção triplete-triplete (T-T) e de intermediários reativos formados após a fotólise da amostra por pulso de laser). Estas técnicas forneceram os valores de: concentração de agregação crítica (cac), concentração micelar crítica (cmc), número de agregação (Nag) e polaridade (escala py e ET30) para os sistemas avaliados. Os dados obtidos foram comparados com as soluções contendo a presença ou não dos tensoativos não-iônicos e a carboximetil celulose (CMC) e 2-hidroxietilamido (2-HEAM). Por fim, a estabilidade do cátion 2-fenilbenzopirílio foi avaliada em diferentes solventes orgânicos, nas micelas dos tensoativos estudados, nos biopolímeros e nos complexos biopolímero-tensoativo. Dois procedimentos experimentais diferentes foram adotados para o preparo das soluções de amilopectina. As diferenças na preparação das soluções de amilopectina tornaram evidente que este biopolímero possui diferentes ambientes para a localização das sondas. Estas diferenças não foram observadas na presença de CMC e de 2-HEAM. Os resultados experimentais confirmaram a interação cooperativa entre a amilopectina e os tensoativos Unitol L-70 e L-230. Esta interação é menos pronunciada para os sistemas formados entre os tensoativos e 2-HEAM e desfavorecidos na presença de CMC. Nos experimentos onde foi avaliado o equilíbrio monômero-excímero do pireno...
No presente estudo, a capacidade da zeólita sintetizada a partir de cinzas de carvão na remoção do corante remazol vermelho RB de solução aquosa foi investigada por meio de processo descontínuo. O equilíbrio foi alcançado após 360 min de tempo de contato. A velocidade de adsorção seguiu o modelo cinético de pseudo-segunda-ordem. Os dados de equilíbrio obtidos se ajustaram à isoterma de adsorção de Langmuir apresentando capacidade de adsorção máxima de 1,20 mg g-1. A eficiência de adsorção estava entre 75 a 91 % no tempo de equilíbrio. Visando obter as melhores condições de remoção do corante, verificou-se a influência dos seguintes parâmetros: concentração inicial do corante, pH da solução aquosa, dose do adsorvente e temperatura. Os parâmetros termodinâmicos foram avaliados indicando que o processo de adsorção do remazol vermelho sobre a zeólita é de natureza espontânea. Experimentos adicionando-se NaCl e Na2SO4 foram realizados com o objetivo de simular as reais condições dos efluentes de banhos de tingimento e avaliar a influência destes compostos quimicos no fenômeno de adsorção. Os dados de equilíbrio de adsorção do remazol vermelho sobre a zeólita foram alcançados em um tempo menor na presença de concentrações crescentes dos sais em solução e houve um aumento na capacidade de adsorção. A eficiência do estudo como tratamento foi avaliada quanto à toxicidade aguda utilizando o microcrustáceo Daphnia similis.; In this study...
A presença de produtos farmacêuticos no meio ambiente é uma questão emergente, devido à crescente resistência bacteriana. As tecnologias utilizadas em instalações de tratamento de água não são eficientes para remover todos os resíduos farmacêuticos e os efeitos dessas substâncias não são bem conhecidos. No presente trabalho, estudou-se a degradação do antibiótico sulfametoxazol (SMX) por fotólise. O SMX é uma sulfonamida, um dos grupos de antibióticos mais utilizados. A fotodegradação de SMX em solução aquosa foi realizada por radiação UVC, sendo o composto transformado por meio de absorção de fótons de comprimento de onda igual a 254 nm. Os experimentos foram conduzidos em um reator fotoquímico anular tubular feito de vidro Pirex (volume irradiado de 3,9 L). A irradiação foi feita por uma lâmpada de mercúrio de baixa pressão de 36 W posicionada ao longo do eixo do reator. Utilizaram-se 5,5 L de solução aquosa do antibiótico (10-50 mg/L). Os efeitos das concentrações iniciais de SMX e do pH (5, 7 ou 9) foram estudados a partir de um projeto experimental Doehlert. Os resultados indicaram remoções de SMX superiores a 99% em até 30 minutos de exposição à radiação UVC. A análise estatística dos resultados em termos do tempo necessário para redução de 50% da concentração inicial de SMX e da taxa inicial de degradação confirmou que para maior quantidade inicial do antibiótico é possível observar que o pH interfere na resposta...
The organo-clay used in this work was prepared from a Na-montmorillonite (Wyoming-USA deposit) by treatment with water solution of hexadecyltrimethylammonium cations. As organo-clays exhibit strong sorptive capabilities for organic molecules, 2-mercapto-5-amino-1,3,4-thiadiazole organofunctional groups, with potential usefulness in chemical analysis, were incorporated on its solid surface. The physically adsorbed reagent did not present any restrictions in coordinating with several metal ions on the surface. The resultant organo-clay complex exhibited strong sorptive capability for removing mercury ions from water in which other metals and ions were also present. The purpose of this work is to study the selective separation of mercury(II) from aqueous solution using the organo-clay complex, measured by batch and chromatographic column techniques, and its application as preconcentration agent in a chemically modified carbon paste electrode for determination of mercury(II) in aqueous solution.
2-Mercaptobenzothiazole loaded on previously polystyrene treated clay was prepared, characterized and used for sorption and preconcentration of Hg(II) Pb(II), Zn(II) and Cd(II) from an aqueous solution. The support used was a natural clay previously treated with sulphuric acid solution. Adsorptiou isotherms of metal ions from aqueous solutions as function of pH were studied at 298 K. Conditions for quantitative retention and elution were established for each metal by batch and column methods. The chemically treated clay was very selective to Hg(II) in solution in which Zn(II), Cd(II), Pb(II) and some transition metal ions were also present.
The adsorption of benzo(a)pyrene (BaP) on to three types of asbestos (chrysotile antophyllite, and amosite) and three types of manmade mineral fibres (MMMF) (rock wool, slag wool, and glass wool) in a physiological water solution was studied. Adsorption was determined from the decrease in the liquid concentration of BaP on the addition of the solid material. Results show that all the fibres weakly adsorb BaP, approximately within the same order of magnitude. The combined adsorption of BaP and phosphatidylcholine (PC) on to chrysotile and amosite asbestos and on to rock wool in aqueous solution was also studied. PC, one of the major constituents in lung surfactant, forms a separate lipid phase in water consisting of micellar liposomes or lipid bilayers. A decrease in the liquid concentration of PC was found when any of the three materials was added, indicating adsorption of the lipid phase on to the fibres. A coincident decrease in the liquid concentration of BaP was also found indicating that BaP is readily solubilised in PC and will accompany the adsorption of this compound on to the fibres. Owing to the high lipid aqueous partition coefficient of BaP, it is concluded that the direct adsorption of BaP on to the fibres will be negligible when PC is present in the system even at low concentrations. Phospholipid adsorption by the fibres and not their direct adsorption of aromatic hydrocarbons should therefore be the crucial parameter for this indirect interaction between fibres and aromatic hydrocarbons.
Much uncertainty and controversy exist regarding the estimation of the enthalpy, entropy, and free energy of overall translational and rotational motions of solute molecules in aqueous solutions, quantities that are crucial to the understanding of molecular association/recognition processes and structure-based drug design. A critique of the literature on this topic is given that leads to a classification of the various views. The major stumbling block to experimentally determining the translational/rotational enthalpy and entropy is the elimination of vibrational perturbations from the measured effects. A solution to this problem, based on a combination of energy equi-partition and enthalpy-entropy compensation, is proposed and subjected to verification. This method is then applied to analyze experimental data on the dissociation/unfolding of dimeric proteins. For one translational/rotational unit at 1 M standard state in aqueous solution, the results for enthalpy (H degrees (tr)), entropy (S degrees (tr)), and free energy (G degrees (tr)) are H (degrees) (tr) = 4.5 +/- 1.5RT, S (degrees) (tr) = 5 +/- 4R, and G (degrees) (tr) = 0 +/- 5RT. Therefore, the overall translational and rotational motions make negligible contribution to binding affinity (free energy) in aqueous solutions at 1 M standard state.
The purpose of this research was to form stable suspensions of submicron particles of cyclosporine A, a water-insoluble drug, by rapid expansion from supercritical to aqueous solution (RESAS). A solution of cyclosporine A in CO2 was expanded into an aqueous solution containing phospholipid vesicles mixed with nonionic surfactants to provide stabilization against particle growth resulting from collisions in the expanding jet. The products were evaluated by measuring drug loading with high performance liquid chromatography (HPLC), particle sizing by dynamic light scattering (DLS), and particle morphology by transmission electron microscopy (TEM) and x-ray diffraction. The ability of the surfactant molecules to orient at the surface of the particles and provide steric stabilization could be manipulated by changing process variables including temperature and suspension concentration. Suspensions with high payloads (up to 54 mg/mL) could be achieved with a mean diameter of 500 nm and particle size distribution ranging from 40 to 920 nm. This size range is several hundred nanometers smaller than that produced by RESAS for particles stabilized by Tween 80 alone. The high drug payloads (≈10 times greater than the equilibrium solubility)...
Copper K-edge EXAFS and MXAN analyses were combined to evaluate the structure of the copper(II)-imidazole complex ion in liquid aqueous solution. Both methods converged to the same square pyramidal inner coordination sphere [Cu(Im)4Lax]2+, (Lax indeterminate) with four equatorial nitrogens at: EXAFS, 2.02±0.01 Å, and; MXAN, 1.99±0.03 Å. A short axial N/O scatterer, (Lax), was found at 2.12±0.02 (EXAFS) or 2.14±0.06 Å (MXAN). A second but very weak axial Cu-N/O interaction was found at 2.9±0.1 Å (EXAFS) or 3.0±0.1 Å (MXAN). In the MXAN fits, only a square pyramidal structural model successfully reproduced the doubled maximum of the rising K-edge XAS, specifically excluding an octahedral model. Both EXAFS and MXAN also found eight outlying oxygen scatterers at 4.2±0.3 Å that contributed significant intensity over the entire XAS energy range. Two prominent rising K-edge shoulders at 8987.1 eV and 8990.5 eV were found to reflect multiple scattering from the 3.0 Å axial scatterer and the imidazole rings, respectively. In the MXAN fits, the imidazole rings took in-plane rotationally staggered positions about copper. The combined (EXAFS and MXAN) model for the unconstrained cupric-imidazole complex ion in liquid aqueous solution is an axially elongated square pyramidal core...
Recently, ZnO has garnered widespread attention in the semiconductor community for its large set of useful properties, which include a wide bandgap and its resulting optical transparency, a large exciton binding energy, a significant piezoelectric response, and good electrical conductivity. In many ways, it shares many properties with a widely used and technologically important semiconductor GaN, which is widely used for blue LEDs and lasers. However, ZnO cannot substitute for GaN in most optoelectronic applications, because it cannot be doped p-type. On the other hand, unlike many traditional, covalently bonded semiconductors like GaN, ZnO can be easily formed aqueous solutions at close to room temperature and pressure in the form of large crystals or a variety of nanostructures, making possible applications that are normally very difficult with traditional semiconductors. In this light, we aimed to take advantage of aqueous solution-based, ZnO growth techniques and incorporated ZnO structures novel optoelectronic and photonic structures. By controlling the morphology of ZnO, we studied the effects of nanowire-based (ZnO/Cu_2O) solar cells. Carrier collection was increased using a nanowire-based device architecture. The main result...
O-Carboxymethylchitosan (OCMCS) is a kind of biocompatible derivatives of chitosan whose water solubility is strongly dependent on the degree of carboxymethylation. The OCMCS with 100 carboxymethyl groups and 75 amino groups per 100 anhydroglucosamine units of OCMCS was synthesized by the reaction of chitosan and monochloroacetic. When OCMCS was dissolved in water, its solution was neutral and OCMCS behaved like a weak polyanionic polyeclectrolyte because most of carboxylic groups were not dissociated in neutral aqueous solution. The aggregation behavior of OCMCS in aqueous solution was studied by surface tensiometry, steady-state fluorescence spectroscopy and viscometry. The critical aggregation concentration (cac) of OCMCS was determined to be between 0.042 mg/ml and 0.050 mg/ml. The possible aggregation mechanism of OCMCS in water was elucidated.; Aiping Zhu, Mary. B. Chan-Park, Sheng Dai and Lin Li
Reversible deactivation radical polymerization (RDRP) of 2-hydroxyethyl acrylate in D2O was studied using Cu(0) wire and Me6TREN, with different target chain lengths (TCL), amount of initial Cu(II)Br2, and the addition sequence of ligand. Gel formation occurred under most conditions, with the amount of gel formation reduced with short target chain lengths, increased concentration of initial Cu(II)Br2, and when ligand was added with the Cu(II)Br2. This result was explained by the reduced concentration of adsorbed active polymer species on the Cu(0) wire surface through increased desorption rate and deactivation rate on the Cu(0) wire surface, respectively.
Gel formation was eliminated using a two-step Cu(0) in situ mediation process, with experiments focusing on the effects of chain length, initial Cu(I)Br, excess NaBr, temperature and residual O2 (brought by syringe for monomer and initiator transferring) on the kinetics and molecular weight (MW) control of the system. There is no visible gel formation with the TCL range from 20 to 800 using this procedure, a result mainly attributed to the lowered number of adsorbed active species per Cu(0) particle, which are highly dispersed, greatly reducing the probability of crosslinking. The concentration of adsorbed active species on Cu(0) particle surface is the key factor controlling polymerization control and the formation of a high molecular weight (MW) shoulder seen under many conditions. Thus...
When dissolved in N,N-dimethylformamide and then dialyzed against phosphate-buffered saline, A-B-A block copolymers composed of poly [N5-(2-hydroxyethyl)-L-glutamine]-block-poly(gamma-benzyl-L-glutamate)- block-poly [N5-(2-hydroxyethyl)-L-glutamine] form particles. The particles are cage-like structures with average diameters of 300 nm (average polydispersity, 0.3-0.5). They are stable in aqueous solution at 4 degrees C for up to 3 weeks, at which time flocculation becomes apparent. Negative staining and freeze-fracture electron microscopy suggest that cage-like particles are formed by selective association of segregated micelle populations. A model of particle formation is presented in which B blocks form micelles in dimethylformamide. On dialysis against an aqueous solution, the extended A blocks then associate intermolecularly to form rod-shaped micelles, which connect the B block micelles. The result is a meshed cage-like particle. The implications of these observations on the aggregation behavior of polymeric surfactants in dilute solution are discussed.
The synthesis, X-ray structure, solution stability, and photophysical properties of several trivalent lanthanide complexes of Yb(III) and Nd(III) using both tetradentate and octadentate ligand design strategies and incorporating the 1-methyl-3-hydroxy-pyridin-2-one (Me-3,2-HOPO) chelate group are reported. Both the Yb(III) and Nd(III) complexes have emission bands in the Near Infra-Red (NIR) region, and this luminescence is retained in aqueous solution (ΦtotYb~0.09−0.22%). Furthermore, the complexes demonstrate very high stability (pYb ~ 18.8 – 21.9) in aqueous solution, making them good candidates for further development as probes for NIR imaging. Analysis of the low temperature (77 K) photophysical measurements for a model Gd(III) complex were used to gain an insight into the electronic structure, and were found to agree well with corresponding TD-DFT calculations at the B3LYP/6-311G++(d,p) level of theory for a simplified model monovalent sodium complex.
Grainless stalk of corn (GLSC) was tested for removal of Cr(VI) and Cr(III) from aqueous solution at different pH, contact time, temperature, and chromium/adsorbent ratio. The results show that the optimum pH for removal of Cr(VI) is 0.84, while the optimum pH for removal of Cr(III) is 4.6. The adsorption processes of both Cr(VI) and Cr(III) onto GLSC were found to follow first-order kinetics. Values of kads of 0.037 and 0.018 min(-1) were obtained for Cr(VI) and Cr(III), respectively. The adsorption capacity of GLSC was calculated from the Langmuir isotherm as 7.1 mg g(-1) at pH 0.84 for Cr(VI), and as 7.3 mg g(-1) at pH 4.6 for Cr(III), at 20 degrees C. At the optimum pH for Cr(VI) removal, Cr(VI) reduces to Cr(III). EPR spectroscopy shows the presence of Cr(V) + Cr(III)-bound-GLSC at short contact times and adsorbed Cr(III) as the final oxidation state of Cr(VI)-treated GLSC. The results indicate that, at pH1, GLSC can completely remove Cr(VI) from aqueous solution through an adsorption-coupled reduction mechanism to yield adsorbed Cr(III) and the less toxic aqueous Cr(III), which can be further removed at pH 4.6.
Artículo de publicación ISI; A new supramolecular sensitizer for nickel(II) ion in aqueous solution based on a pyridyltriazolopyridine-cyclodextrin inclusion complex is proposed. The inclusion complexation behavior, characterization andbinding ability of pyridyltriazolopyridine (PTP) with dimethyl- -cyclodextrin (DM CD) has been inves-tigated both in solution and solid state by means of absorption, fluorescence,1H NMR, DSC, and molecularmodeling methods. The stoichiometry of the inclusion complex is 1:1, and the thermodynamic studiesindicate that the inclusion of PTP is mainly an entropic driven process. The 2D NMR studies revealed thatthe pyridyl-triazolopyridine is included by both sides of cyclodextrin which are in good agreement withthe docking results. The fluorescence changes upon addition of divalent cations to the inclusion complexindicate a high selectivity and sensitivity for Ni2+by fluorescence quenching in neutral aqueous solution.; Fondecyt 1120142 and to CEPEDEQ from theChemical and Pharmaceutical Science Faculty of the University ofChile for the use of NMR. Ministerio de Ciencia e Innovación (Spain) (Project Consolider-Ingenio Supramed CSD 2010-00065) and to Generalitat Valenciana (Valencia, Spain)(Project PROMETEO 2011/008).
We have linked the structural and dynamic properties in aqueous solution of
amphiphilic charged diblock copolymers poly(butyl acrylate)-b-poly(acrylic
acid), PBA-b-PAA, synthesized by controlled radical polymerization, with the
physico-chemical characteristics of the samples. Despite product imperfections,
the samples self-assemble in melt and aqueous solutions as predicted by
monodisperse microphase separation theory. However, the PBA core are abnormally
large; the swelling of PBA cores is not due to AA (the Flory parameter
chiPBA/PAA, determined at 0.25, means strong segregation), but to h-PBA
homopolymers (content determined by Liquid Chromatography at the Point of
Exclusion and Adsorption Transition LC-PEAT). Beside the dominant population of
micelles detected by scattering experiments, capillary electrophoresis CE
analysis permitted detection of two other populations, one of h-PAA, and the
other of free PBA-b-PAA chains, that have very short PBA blocks and never
self-assemble. Despite the presence of these free unimers, the self-assembly in
solution was found out of equilibrium: the aggregation state is history
dependant and no unimer exchange between micelles occurs over months
(time-evolution SANS). The high PBA/water interfacial tension...
The degradation of cephalexin in aqueous solution under ultrasound irradiation was investigated. Biodegradability of the solution was evaluated by the BOD5/COD ratio, which was raised from zero to 0.36 after ultrasound treatment, indicating that the ultrasound irradiation process is a successful pre-treatment step to improve the biodegradability of cephalexin solution. The influences of ultrasound power and pH value on the degradation of cephalexin were studied. It was found that the optimal ultrasound power for cephalexin degradation in the system was 200 W and the rate of cephalexin degradation was maximal in the pH range of 6.5 to 8.5. The degradation kinetics of cephalexin in aqueous solution under various operational conditions was also investigated. It was found that the degradation of cephalexin follows a pseudo-first order kinetics.