Structure and dynamics of aqueous 2-propanol: A THz-TDS, NMR and neutron diffraction study

Aqueous liquid mixtures, in particular, those involving amphiphilic species, play an important role in many physical, chemical and biological processes. Of particular interest are alcohol/water mixtures; however, the structural dynamics of such systems are still not fully understood. Herein, a combination of terahertz time-domain spectroscopy (THz-TDS) and NMR relaxation time analysis has been applied to investigate 2-propanol/water mixtures across the entire composition range; while neutron diffraction studies have been carried out at two specific concentrations. Excellent agreement is seen between the techniques with a maximum in both the relative absorption coefficient and the activation energy to molecular motion occurring at ∼90 mol% H₂O. Furthermore, this is the same value at which well-established excess thermodynamic functions exhibit a maximum/minimum. Additionally, both neutron diffraction and THz-TDS have been used to provide estimates of the size of the hydration shell around 2-propanol in solution. Both methods determine that between 4 and 5 H₂O molecules per 2-propanol are found in the 2-propanol/water clusters at 90 mol% H₂O. Based on the acquired data, a description of the structure of 2-propanol/water across the composition range is presented.

Portuguese georesources suitability for medical hydrology applications

In Portugal, there is an old tradition in using clayey materials for therapeutic purposes. They are applied in pelotherapy, at several beaches of the Atlantic coast in the form of clay-sea water mixtures (peloids) to treat skin and rheumatic diseases. During many generations, peloids have been applied without scienti c studies that prove their therapeutic validity. In the last decade, the Portuguese scienti c community has become increasingly more interested in assessing the properties that make clayey materials suitable for therapeutic purposes. The abundance of clayey formations and the established practices of medical hydrology in our country turned this interest into a new perspective of application. The studied materials include di erent clays (in age and origin) mainly collected from well-known Mesozoic-Cenozoic formations, in some cases outcropping at beaches where empirical applications occur. This thesis focus in the study of silt-clay fraction (< 63 m).To determine their suitability for therapy, compositional, physicochemical, technological, thermal and rheological properties were assessed. Conventional techniques (XRD, XRF and Sedigraph) were used to assess compositional features of silt-clay fraction. Electron microscopy (SEM, VPSEM, HREM) was used to study the micromorphology and composition of clay fraction (< 2 m). Physicochemical properties (cation exchange and speci c surface) were assessed using the Ammonium Acetate and BET methods. Technological properties (plasticity and abrasivity indices) were assessed using the Atterberg limits and Einlehner abrasion tests. Thermal properties (speci c heat and cooling kinetics) were estimated by DSC analysis and cooling tests. Pharmacotechnical tests (compressibility index, sediment volume and Brook eld viscosity) were used to assess the powder owability as well as the physical stability and viscosity of clay-water dispersions. We selected as suitable Portuguese clays for health applications the samples A-Pe, A-Be2, A-Sd, J-Fr , M-To, C-Lu1, C-Lu2, Pl-Ba, M-Ga and J-Ab because they represent safe materials, with an adequate composition, good technological, physicochemical and thermal properties for application, also presenting an adequate rheology when dispersed in water. Their most relevant characteristics are the high clay minerals content, abundant smectite, illite and kaolinite, and safe hazardous concentrations. They also showed moderate capacity to exchange Ca 2+, high plasticity, low abrasivity, high speci c heat and slow cooling kinetics. They evidenced fair powder owability and good potential to formulate viscous dispersions when stabilized. Because the majority of the assessed characteristics are in accordance with those presented by clays applied in European spas for pelotherapy, we considered this group of clays also suitable for medical hydrology treatments in Portuguese spas.

Pervaporation dehydration of isopropyl alcohol with NaY zeolite incorvorated hybrid membranes

With a solution technique, NaY zeolite incorporated, tetraethylorthosilicate-crosslinked poly(vinyl alcohol) membranes were prepared. The resulting membranes were tested for their ability to separate isopropyl alcohol/water mixtures by pervaporation in the temperature range of 30-50 degrees C. The effects of the zeolite content and feed composition on the pervaporation performance of the membranes were investigated. The experimental results demonstrated that both flux and selectivity increased simultaneously with increasing zeolite content in the membranes. This was explained on the basis of the enhancement of hydrophilicity, selective adsorption, and establishment of a molecular sieving action attributed to the creation of pores in the membrane matrix. The membrane containing 15 mass % zeolite exhibited the highest separation selectivity of 3991 with a flux of 5.39 X 10(-2) kg/m(2) h with 10 mass % water in the feed at 30 degrees C. The total flux and flux of water were close to each other for almost all the studied membranes, and this suggested that the membranes could be used effectively to break the azeotropic point of water/isopropyl alcohol mixtures to remove a small amount of water from isopropyl alcohol. From the temperature-dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The activation energy values obtained for water were significantly lower than those for isopropyl alcohol, and this suggested that the developed membranes had a higher separation efficiency for water/isopropyl alcohol systems. The activation energy values for total permeation and water permeation were found to be almost the same for all the membranes, and this signified that coupled transport was minimal because of the highly selective nature of the membranes. Positive heat of sorption values were observed in all the membranes, and this suggested that Henry's mode of sorption was predominant. (c) 2008 Wiley Periodicals, lnc.

Study of the mechanism of action of anoplin, a helical antimicrobial decapeptide with ion channel-like activity, and the role of the amidated C-terminus

Anoplin, an antimicrobial, helical decapeptide from wasp venom, looses its biological activities by mere deamidation of its C-terminus. Secondary structure determination, by circular dichroism spectroscopy in amphipathic environments, and lytic activity in zwitterionic and anionic vesicles showed quite similar results for the amidated and the carboxylated forms of the peptide. The deamidation of the C-terminus introduced a negative charge at an all-positive charged peptide, causing a loss of amphipathicity, as indicated by molecular dynamics simulations in TFE/water mixtures and this subtle modification in a peptide`s primary structure disturbed the interaction with bilayers and biological membranes. Although being poorly lytic, the amidated form, but not the carboxylated, presented ion channel-like activity on anionic bilayers with a well-defined conductance step; at approximately the same concentration it showed antimicrobial activity. The pores remain open at trans-negative potentials, preferentially conducting cations, and this situation is equivalent to the interaction of the peptide with bacterial membranes that also maintain a high negative potential inside. Copyright (C) 2007 European Peptide Society and John Wiley & Sons, Ltd.

Study of the mechanism of action of anoplin, a helical antimicrobial decapeptide with ion channel-like activity, and the role of the amidated C-terminus

Anoplin, an antimicrobial, helical decapeptide from wasp venom, looses its biological activities by mere deamidation of its C-terminus. Secondary structure determination, by circular dichroism spectroscopy in amphipathic environments, and lytic activity in zwitterionic and anionic vesicles showed quite similar results for the amidated and the carboxylated forms of the peptide. The deamidation of the C-terminus introduced a negative charge at an all-positive charged peptide, causing a loss of amphipathicity, as indicated by molecular dynamics simulations in TFE/water mixtures and this subtle modification in a peptide's primary structure disturbed the interaction with bilayers and biological membranes. Although being poorly lytic, the amidated form, but not the carboxylated, presented ion channel-like activity on anionic bilayers with a well-defined conductance step; at approximately the same concentration it showed antimicrobial activity. The pores remain open at trans-negative potentials, preferentially conducting cations, and this situation is equivalent to the interaction of the peptide with bacterial membranes that also maintain a high negative potential inside. Copyright (C) 2007 European Peptide Society and John Wiley & Sons, Ltd.

Determination of sugar cane herbicides in soil and soil treated with sugar cane vinasse by solid-phase extraction and HPLC-UV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Hydrolysis rates of TMOS catalyzed by oxalic acid and stimulated by ultrasound

A simple calorimetric method was employed to study the kinetics of the hydrolysis of the solventless TMOS-water mixtures, under ultrasound stimulation, as a function of the concentration of oxalic acid. The reaction rates were obtained, in relative units, from the measured thermal peak of the reaction as a non-separated function of both the sonication time and the instantaneous temperature of the medium. For concentrations of oxalic acid below 0.01 M, polycondensation reaction starts before complete hydrolysis. For concentrations of oxalic acid above 0.01 M, hydrolysis is complete and, in addition, the inverse of the time, as measured from the starting of ultrasound action until the maximum hydrolysis heat release, was found to be a reasonable relative measure of the average hydrolysis rate constant. The average hydrolysis rate constant was found to be proportional to the square root of the molar concentration of the oxalic acid. This result is in agreement with the literature if we assume small dissociation degree for the catalyst in such a solventless alkoxyde-water medium.

Design, construction, and performance of a real-time holographic refractometry prototype for liquid analysis

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Effects of HCl on the ultrasound catalyzed TEOS hydrolysis as determined by a calorimetric study

The acid catalyzed and ultrasound stimulated hydrolysis of solventless tetraethoxysilane-water mixtures was studied at 39°C as a function of HCl added to the mixtures (log[HCl]-1 ranged from 0.8 to 2.0), The reaction was carried out in a specially designed device, in which a steady state heat flow is maintained, while sonication is taking place, if no reaction is expected to occur. The exothermal hydrolysis reaction causes an increasing temperature (ΔTt) as a function of the reaction time, t. The isothermal hydrolysis rate constant, k, has been evaluated from the experimental ΔTt versus t data, after corrections for the increasing temperature effects, by using a method resulting from our theoretical modeling based on a dissolution and reaction mechanism. The hydrolysis rate constant fits closely a k α [H+] law as expected for this kind of hydrogen-ion catalyzed reaction.

Análise conformacional dos petídeos protonectina e protonectina (1-6), isolados e em associação, em mistura TFE-água

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudos da pré-hidrólise ácida do bagaço de cana-de-açúcar e fermentação alcóolica do mosto de xilose por Pachysolen tannophilus

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo do comportamento do eletrodo de vidro combinado em etanol anidro e misturas etanol-água

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Espectroscopia de impedância em soluções iônicas e mistura de etanol/água

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Determinação da entropia de mistura amônia e água para aplicações em processos de refrigeração por absorção

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

Evaluation of solvent effect on the extraction of phenolic compounds and antioxidant capacities from the berries: application of principal component analysis

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)