1,720,955 research outputs found
Extração de antioxidantes com sistemas aquosos bifásicos
Full text linkMestrado em Bioquímica - Bioquímica ClínicaNowadays, antioxidants present a great relevance in a variety of applications used by the pharmaceutical and the cosmetic industries. The antioxidants are able to inhibit or to retard the oxidation of other compounds, and mainly the oxidation caused by free radicals, and that is the reason of their importance in the industry and their incorporation into a variety of products. For the utilization of antioxidants in effective quantities, it is necessary to either chemically synthesize them, what is expensive and may causes problems due to their non-natural origin, or to extract them from their natural sources (biomass). Conventional methods for the extraction of antioxidants and the following purification are normally expensive and time-consuming. Therefore, other extraction methods, like the liquid-liquid extraction using aqueous biphasic systems (ABS), have been studied. In this work, the use of ABS based on ionic liquids (ILs) and polymers is proposed as an alternative for the conventional systems that are mostly composed of polymers and inorganic salts. The use of ILs allows the tuning of the properties of the extraction systems by variation of their ions and so to increase the extraction efficiencies.
In this work, it is shown, for the first time, that poly(vinyl pyrrolidone) (PVP) and poly(vinyl alcohol) (PVA) of different molecular weights form ABS with phosphonium-based and imidazolium-based ILs. The respective phase diagrams were determined at 25 °C to define the minimum concentrations that are necessary for the formation of two aqueous phases. Finally, the ability of these systems as liquid-liquid extraction systems was evaluated. To this end, the partition coefficients and extraction efficiencies of several antioxidants (gallic acid, vanillin, vanillic acid and syringic acid) using the studied systems were determined. Extraction efficiencies ranging from 75% to 95 % were obtained for the different systems, thus demonstrating their capability for extracting purposes.
In general, the most efficient system for the extraction of antioxidants was that composed of the IL 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([C4mim][CF3SO3]) and the PVA of 9,000-10,000 g.mol-1 (PVA9) for the extraction of all the studied antioxidants.Atualmente os antioxidantes apresentam uma relevância elevada numa vasta gama de aplicações utilizadas pela indústria farmacêutica e de cosmética. Os antioxidantes são capazes de inibir ou de retardar a oxidação de outros compostos, principalmente a oxidação causada por radicais livres, e daí o seu destaque na indústria e da sua incorporação nos produtos mais variados. No entanto, para a utilização de antioxidantes em quantidades eficazes, é necessário sintetizá-los quimicamente, o que é dispendioso e pode acarretar problemas devido à sua origem não natural, ou extraí-los das suas fontes naturais (biomassa). Os métodos convencionais para a extração e posterior purificação de antioxidantes são normalmente dispendiosos e morosos. Neste sentido, têm vindo a ser estudados outros métodos de extração, e mais recentemente, a extração líquido-líquido recorrendo a sistemas aquosos bifásicos (SAB). Neste trabalho propõe-se a utilização de SAB constituídos por líquidos iónicos (LIs) e polímeros como alternativa aos sistemas convencionais maioritariamente formados por polímeros e sais inorgânicos. A utilização de LIs permite afinar as propriedades dos sistemas extrativos por variação dos iões que os compõem, e portanto, aumentar as eficiências de extração.
Neste trabalho foi demostrada, pela primeira vez, a formação de SAB constituídos por polivinilpirrolidona (PVP) e álcool polivinílico (PVA) de várias massas moleculares e LIs das famílias dos fosfónios e dos imidazólios. Os respetivos diagramas de fase foram determinados a 25 ºC de modo a inferir sobre as concentrações mínimas necessárias para a formação de duas fases aquosas. Por fim, estes sistemas foram avaliados quanto à sua capacidade como sistemas de extração do tipo líquido-líquido. Para tal, determinaram-se os coeficientes de partição e as eficiências de extração para vários antioxidantes (ácido gálico, vanilina, ácido vanílico e ácido siríngico) utilizando os diversos sistemas estudados. Obtiveram-se eficiências de extração que variaram entre 75 % e 95 %, o que demonstra a viabilidade destes sistemas na extração de antioxidantes. De um modo geral, o sistema mais eficiente para extrair antioxidantes é composto pelo LI 1-butil-3-metilimidazólio trifluorometanosulfonato ([C4mim][CF3SO3]) juntamente com o PVA de 9.000-10.000 g.mol-1 (PVA9) para todos antioxidantes estudados
Sistemas aquosos bifásicos com líquidos iónicos e polissacarídeos
Full text linkMestrado em Biotecnologia - Biotecnologia MolecularAiming at finding more biocompatible and environmentally-benign separation processes, aqueous biphasic systems composed of ionic liquids can be envisaged as an alternative and advantageous approach for the extraction and purification of the most diverse biomolecules.
In this work, the main goal consisted on the study of the ability of polysaccharides, as a benign alternative over inorganic salts typically used, to form aqueous biphasic systems with ionic liquids. To this aim, the phase diagrams and respective compositions of the two phases in equilibrium for ternary systems consisting of several ionic liquids, water, and polysaccharides were determined at 298 K. By the combination of different families of ionic liquids, achieved by a representative variety of cations and anions, with dextrans and maltodextrins, it was possible to infer on the effect of the IL structural characteristics, as well as on the polysaccharides molecular weight through the formation ability of aqueous two-phase systems. Finally, and to ascertain on the potential application of these new systems such as extraction techniques, some of them were also used and evaluated regarding their aptitude to extract amino acids.
The use of polysaccharides, namely dextran and maltodextrin, as salting-out molecules to form aqueous biphasic systems with ionic liquids was the main focus of this work. It was demonstrated here, for the first time, that a new class of aqueous biphasic systems composed of ionic liquids and polysaccharides can be formed while contributing to the development of more efficient and sustainable separation and purification techniques. These systems can be also seen as promising routes in the improvement of biotechnological processes which increasingly tend to be decisive in industry.No âmbito da procura de processos de separação mais biocompatíveis e amigos do ambiente, os sistemas aquosos bifásicos com líquidos iónicos constituem uma abordagem alternativa e vantajosa para a extração e purificação das mais diversas biomoléculas.
Neste trabalho pretendeu-se estudar especificamente a capacidade de polissacarídeos, como uma alternativa mais benigna face aos sais normalmente utilizados, para formar sistemas aquosos bifásicos com líquidos iónicos. Para tal, determinaram-se os diagramas de fase e composições das duas fases em equilíbrio para diversos sistemas ternários formados por líquidos iónicos, água e polissacarídeos a 298 K. O estudo destes novos sistemas, combinando diferentes famílias de líquidos iónicos representados por uma variedade alargada de catiões e aniões, com dextranas e maltodextrinas, permitiu avaliar o efeito das características estruturais dos líquidos iónicos, bem como da massa molecular dos polissacarídeos, na capacidade de formação de sistemas de duas fases aquosas. Por fim, e para suportar a sua aplicação como novas técnicas de extração, alguns destes sistemas foram também avaliados no que respeita à sua capacidade para extrair aminoácidos.
A utilização de polissacarídeos, nomeadamente de dextrano e maltodextrina, enquanto moléculas indutoras de salting-out para formar sistemas aquosos bifásicos com líquidos iónicos, constituiu o foco principal deste trabalho. Pela primeira vez foi mostrado que existe uma nova classe de sistemas aquosos bifásicos constituídos por líquidos iónicos e polissacarídeos contribuindo assim para o desenvolvimento de técnicas de separação e purificação de uma forma mais eficiente, sustentável e ecológica. Estes sistemas poderão ainda ser vistos como vias promissoras no melhoramento de processos biotecnológicos que tendem a ser cada vez mais decisivos na indústria
Interacção de substâncias húmicas estuarinas com os iões hidrogénio, cobre(II) e chumbo(II)
No full textDoutoramento em QuímicaNeste trabalho foi estudado o comportamento ácido-base de substâncias
húmicas de águas estuarinas, bem como a sua interacção com iões de metais
vestigiários, nomeadamente os iões cobre(l1) e chumbo(ll).
As substâncias húmicas foram extraídas e isoladas da água de um estuário, por
adsorção a resina XAD-8, segundo o método adoptado pela Intemational Humic
Substances Society (IHSS). Os ácidos fúlvicos e os ácidos húmicos obtidos foram
posteriormente fraccionados segundo a carga, por eluição com solventes de pH
crescente, após a adsorção na resina X4D-8. As substâncias húmicas recolhidas foram
caracterizadas por análise elementar e espectroscopias de infravemelho e de
ressonância magnética nuclear de "C. A composição das substâncias obtidas é típica
das amostras estuarinas, verificando-se, como é usual, uma maior aromaticidade dos
ácidos húmicos relativamente aos ácidos fúlvicos. O fraccionamento segundo a carga
separa as fracções obtidas essencialmente no que respeita ao teor em grupos
carboxílicos, verificando-se que este diminui com o pH do solvente utilizado na eluição.
O grau de aromaticidade, pelo contrário, aumenta com o pH da eluição.
A quantificação e a caracterização dos grupos funcionais, muito heterogéneos,
das substâncias húmicas foi efectuada através de titulações com base, seguidas
potenciometricamente. A determinação da concentração hidrogeniónica é o passo
decisivo nos estudos de protonação e foi efectuada com o máximo rigor. Nesse sentido,
foi proposto e utilizado um método de calibração inovador, em que os parâmetros da
resposta do eléctrodo são retirados da própria titulação das substâncias húmicas.
Os parâmetros de protonação, nomeadamente as concentrações e afinidades
hidrogeniónicas, foram estimados utilizando modelos de distribuição discreta e de
distribuição contínua para as afinidades, tendo-se concluído que a heterogeneidade das
substâncias húmicas pode ser modelada satisfatoriamente dos dois modos, desde que
seja utilizado um número suficientemente elevado de parâmetros. (etc.)The aim of this work was to study the proton and metal ion interactions with
estuanne humic matter.
The humic substances were isolated from an estuanne water by adsorption onto
an XAD-8 resin, accordingly to the procedure proposed by the Intemational Humic
Substances Society. The fulvic and humic acids thus obtained were further fraccionated
on a charge base, by desorption from XAD-8 resin with solvents of sequencially higher
pH values. The substances were characterized by elemental analysis, IR and %-NMR
spectroscopies, and were found to be typical of estuanne humic matter. The carboxylic
content was higher for fulvic than for hurnic acids, and for the aromaticity the reverse
was true. The charge fraccionation separated the substances mainly for their carboxylic
content, which varied inversely with the pH of extraction.
The acid-base behaviour of the substances was studied by potentiometnc
titrations. A new method of electrode calibration was developed to determine the proton
conmtration, that withdraws the electrode parameters directly from the humic
substances titrations. The method proved to be both consistent and reliable.
Base titrations were periormed at three electrolyte concentrations, as well as
electrolyte titrations at constant pH. The dissociation of the functional groups is
enhanced when raising ionic strength values, and their heterogeneity is diminished. The
electrostatic effect was modelled using both a Donnan rnodel and a thermodynamic
double layer model. After correcting the base titrations data for this efíect, an intrinsic
distnbution for proton affinities was obtained. The estimated parameten for the
rnolecular size show that the humic molecules radius is about twice the fulvic one.
Hysteresis was observed for proton binding to the humic substances, probabiy
due to confomational changes of the particles, since revenibility of hysteresis was
dependent on ionic strength. .
The binding of copper to the hurnic and fulvic acids was studied by potentiornetric
titrations using a copper ion selective electrode. The binding of the fulvic acids was the
sarne for pH values 4, 6 and 8, but for the hurnic acids it was higher for the highest pH.
The affinity of copper(l1) was slightly stronger for phenolic than for carboxylic groups.
The cornplexation of lead with the humic substances was studied by voltarnrnetric
techniques. The experiments were perfomed at high ligandlrnetal ion ratios as usually
found in the aquatic environrnent, and so a sensitive technique such as anodic stripping
voltamrnetry was used to determine the complexing pararneters. The binding of lead to
the hurnic substances was mainly due to carboxylic goups, and was stronger for the
lowest ionic stregth. The influente of secondary phenomena, such adsorption and
surface electrode concentrations, was studied and proved to affect voltamrnetric
determinations. The conforrnation of hurnic substances particles in solution was found to
be dependent on the procedure followed for the solution preparation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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