1,721,011 research outputs found
Ενεργοποίηση του οξυγόνου από αμφίφιλα σύμπλοκα του βαναδίου V(ΙV) και V( V) στα έλαια.
No full textOxygen can be activated in the presence of transition metals and produce reactive oxygen species. Reactive oxygen species (ROS) in low concentrations are necessary for the defence of human health against damaging agents such as bacteria and viruses. However, ROS are strong oxidative agents and large amounts of reactive oxygen species can be a weapon against the human body, because ROS can interact with biological targets such as DNA, proteins and lipids. As a result of this interaction, humans suffer from various chronic and degenerative diseases such as cancer, Parkinson, Alzheimer disease, aging and others. The human organism in order to protect itself from such diseases has developed a system that controls the balance between oxidative agents (ROS) and antioxidants (reduction molecules). One of the most important antioxidant sources is edible oils (mainly olive oils), which contain large amounts of polyphenols. Besides polyphenols, edible oils also contain lipids. Because of the edible oil’s composition, that is similar with cellular wall composition, edible oils can be used as useful biomimetic media of cellular walls. The present master thesis studies the reaction of oxygen activation which is catalyzed by amphiphilic vanadium complexes such as VOC18DEA and VOC18DPA, synthesized in the bioinorganic laboratory of Dr. Anastasios Keramidas. The study has been focused on various parameters that affect the oxygen activation in vegetable oils, such as the presence or the absence of vanadium complexes, oxygen, polyphenols, tyrosol and tocopherol. This study aims to help clarify the mechanism of cellular wall oxidation by ROS and to the characterization of vegetable oils according to their antioxidant content. In this study we used electrochemical techniques (cyclic voltammetry, linear sweep), spectroscopic techniques (EPR, NMR, UV-Vis) and analytical techniques (iodometric titration). The result from this research was that oxygen can be activated by vanadium. Also, the research shows that phenols, such as tocopherol and tyrosol, can trap the radicals that are generated from oxygen activation and that polyphenols can act as prooxidants that accelerate oxygen activation.Epaminontas Leontidis
Anastasios Keramidas
Anastasios TasiopoulosComplete
Σύνθεση και Χαρακτηρισμός Βιολογικά Ενεργών Οξειδοαναγωγικών μορίων Βαναδίου με Πολυφαινικούς υποκαταστάτες
No full textIn this work, we introduce new transition metal complexes with phenolic ligands which are models for the study of metabolic pathways in food matrixes and biological systems. In addition, there was a study upon the mechanism of radicals that created with the interaction of the phenols with metal ions. That possibility was in great interest because of the use of those kinds of systems as anticancer drugs. Finally, we developed an analytical method in order to be able to evaluate these phenol molecules in biological systems. In particular, hydroquinones and tocopherols were fluoro-labelled and vanadium labelled to be easily observed and evaluated with 19F and 51V NMR, EPR and UV-Vis spectroscopy. The quantification of the molecules using the 19F NMR took place in olive oil environment which is very like the cell membrane environment. The antioxidant action of the metal-organic molecules with the metal ions, in addition with the radical induced mechanisms were evaluated with spectroscopy, crystallography and electrochemically. Antioxidants are components of foods and there are biomolecules that are necessary for the ordinary function of human body. They used as conservatives in food matrixes against oxidation. Hydroquinones are model molecules for antioxidants and tocopherols containing a saturated phytyl chain and a different placement of methyl groups on the chromanol ring. Tocotrienol isoforms have an unsaturated side chain. Vitamin E is a generic term that represents a family of compounds composed of various tocopherol and tocotrienol isoforms. Tocopherols display potent anti-angiogenic and antiproliferative activities. Redox silent tocopherol analogues also display potent anticancer activity. Polyphenolic compounds in biological systems could easily interact with metal ions producing free radical species causing several diseases in human body. The true is that controlled production of free radicals could induce apoptosis of cancer cells. Especially vitamin E and its analogues are very active in mitochondria of cells and they are potential drugs acting against cancer cells. It is also well known that tocopherol analogues are targeting only cancer cells because they are very high redox active. Even though the above reactions are very useful there are are some drawbacks in their study. There is a lack of well-known metal -organic molecules with notable mechanism of action. In this work, we are introducing new analytical methods for the determination of those models in order to be able to monitor their metabolic pathways in biological systems and we have studied the redox mechanisms behind this action and their interaction with vanadium metal ions for possible use as anticancer drugs.Keramidas Anastasios
Drouza Chryssoula
Theocharis Charis
Kapnissi-Christodoulou ConstantinaComplete
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
Reductive Dioxygen Activation by biomimetic vanadium complexes
No full textThe high importance of the peroxido-vanadium complexes in many oxidative catalytic reactions has enhanced the research interest in investigating molecular oxygen activation by ligation of O2 on vanadium metal ions. Dioxygen (O2) is a benign, cheap and economically viable oxidant. The activation of O2 by metal ions is a key challenge for modeling biological processes and in applications such as the homogeneous oxidative alkane functionalization, the production of hydrogen peroxide and emerging energy technologies. The activation of O2 by vanadium complexes may involve either coordination and partial reduction of O2 or, in rare cases, the attack of O2 on the organic ligand activated by ligation to metal ion. In this chapter, the advances of dioxygen activation by simple functional vanadium complexes will be reviewed
Solid state and aqueous solution characterization of rectangular tetranuclear VIV/V-p-semiquinonate/hydroquinonate complexes exhibiting a proton induced electron transfer
No full textReaction of the non-innocent dinucleating ligand 2,5-bis[N,N- bis(carboxymethyl) arninomethyl]hydroquinone (H6bicah) with VO 2+ and VO43- salts in water in the pH range 2 to 4.5 provides a series of novel tetranuclear VIV and/or V V macrocycles with the main core consisting of the anions [V V4O4(a-0)2(μ-bicah)2] 4- isolated at pH = 2.5 and [VIV2V V2O4(μ-O)2(μ-bicas)(μ- bicah)]5- and [VIV4O4(μ-O) 2(μ-bicas)2]6- isolated at pH = 4.5 (bicas•5- = 2,5-bis[N,N-bis(carboxymethyl) aminomethyl]-p- semiquinonate), whereas at pH = 2 the dinuclear [(VIVO) 2(OH2)2(μ-bicah)]2- was obtained. All vanadium compounds have been characterized, and the charge of the ligand has been assigned in solid state by X-ray crystallography and infrared spectroscopy. The structures of the tetranuclear anions consist of four vanadium atoms arranged at the corners of a rectangle with the two bridging bicas •5- and/or bicah6- ligands on the long and the two VIV/V-O-VIV/V bridges on the short sides of the rectangle. UV-vis, 51V and 1H NMR spectroscopy and electrochemistry showed that these complexes interconvert to each other by varying the pH. This pH induced redox transformation of the tetranuclear anions has been attributed to the shift of the reduction potential of the bicas•5- to higher values by decreasing the pH. The electron is transferred intramolecularly from the metal ion to the electron accepting semiquinones resulting in reduction of bicas•5- to bicah6- and concurrent oxidation of the VIV to VV. The resulting complexes are further oxidized by atmospheric oxygen. This system as a model for the H + coupled redox reactions in metalloenzymes and its relevance is discussed briefl
Charge distribution in vanadium p-(hydro/semi) quinonate complexes
No full textThe known crystal structures of co-ordination compounds containing p-dioxolene ligands in the form of hydroquinone, semiquinone or quinone have been examined. A simple method is proposed to correlate the oxidation state of these ligands with the structural distortion based on crystallographic data. The results fit well with the literature oxidation-state assignments for ligands ligated either to one or to two bridged through the ligand metal ions including the vanadium(IV/V) (hydro/semi)quinonate complexe
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
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