1,721,044 research outputs found
The effect of the thiolate group on the complex formation processes of peptides containing different donor groups in side chains
Full text linkA biológiai rendszerekben előforduló fehérjék legfontosabb fémionkötő helyei a hisztidin imidazol nitrogénje, az aszparaginsav vagy glutaminsav karboxilátcsoportja, illetve a cisztein tiolátcsoportja. A fémionok ezen oldalláncokhoz kötődve tudják betölteni enzimatikus vagy szerkezetalakító funkcióikat vagy éppen szerepet játszhatnak bizonyos neurodegeneratív betegségekben. Ezen funkciók pontos megértéséhez ugyanakkor elengedhetetlen olyan kistagszámú peptidek vizsgálata, amelyek elkülönülten tartalmazzák a fémionok legfontosabb kötőhelyeit. Munkánk első felében célul tűztük ki nikkel(II)-komplexek elméleti kémiai vizsgálatát sűrűségfunkcionál-elmélet alkalmazásával, annak érdekében, hogy választ adjunk arra, hogy egy adott rendszer mennyire jól vizsgálható ezen módszerrel, illetve TD-DFT segítségével kívántuk egyes komplexek UV-látható spektrumát számolni. Munkánk második felében különböző, C-terminuson ciszteint tartalmazó peptidek komplexképző sajátságait vizsgáltuk átmenetifémionokkal. Ennek során arra kerestük a választ, hogy hogyan szabályozható a peptid C-terminális régiójához való kötődés abban az esetben, ha a peptid N-terminális régiója is erős fémkötő domént tartalmaz.The imidazole nitrogen of histidine, the carboxylate group of aspartic or glutamic acids and the thiolate group of cysteine are the most important metal binding sites for proteins in biological systems. The metal ions bounded to these side chains are able to operate their enzymatic or structural functions and may play role in neurodegenerative disorders. For better understanding of these interactions it is indispensable to investigate small modelpeptides containing separately these metal binding domains. Our first goal was to investigate the complex formation processes between nickel(II) and peptides using DFT methods. TD-DFT studies have also been performed to predict the electronic absorption spectra of the complexes formed in the systems. In the second part of our work the complex formation processes of different peptides containing cysteine on C-termini have been investigated with several transition metal ions. We were interested in how the metal binding ability can be modified if the N-terminal part of the peptides contains strongly coordinating domain.d
Complex formation between [(η6-p-cym)Ru(H2O)3]2+ and oligopeptides containing three histidyl moieties
No full textIn order to model the metal ion binding capabilities of high molecular mass components of blood the interaction between [(η6-p-cym)Ru(H2O)3]2+ and terminally protected oligopeptides containing three histidyl moieties (Ac-HHH-NH2, Ac-HAHH-NH2, Ac-HAHAH-NH2 and Ac-H*AH*AH*-NH2, where A = L-alanyl, H = L-histidyl, H* = N3-methyl-L-histidyl) were studied by pH-potentiometric, ESI-TOF-MS, circular dichroism and NMR methods at an ionic strength of 0.20 M KCl or KNO3 as well as using density functional theory (DFT) calculations. Protonation constants of the novel peptides are reported. Although for Ac-HHH-NH2 the immediate formation of precipitation with [(η6-p-cym)Ru(H2O)3]2+ hindered any further solution investigations results of the detailed NMR and MS studies revealed that the other three ligands coordinate to the metal ion in rather slow processes via the imidazole moieties forming [(η6-p-cym)RuL]2+ (L = oligopeptide) type species in the slightly acidic, neutral pH-range. At pH ∼7.5 identical binding mode of Ac-HAHH-NH2 and Ac-HAHAH-NH2 in the [(η6-p-cym)RuL]2+ via three imidazole nitrogens was found hindering completely the hydrolysis of the metal ion even at 1:1 metal ion to ligand ratio. At elevated pH MS evidences support the involvement of amide-N donor(s) in metal ion binding too beside partial hydrolysis. 0.20 M KCl medium was found to hinder effectively the hydrolytic processes of the metal ion in the basic pH-range without altering the coordination of the imidazole side chains. Both NMR and DFT results support the imidazole-N1 (“far” or “τ”) over the N3 (“near” or “π”) coordination of the histidyl side chains of all these oligopeptides to the organometallic ruthenium(II) cation
Introducing the penicillamine moiety into a metallopeptide mimicking the NiSOD enzyme: electronic and kinetic effects
No full textAccurate prediction of vertical electronic transitions of Ni(II) coordination compounds via time dependent density functional theory
Full text linkTime dependent d. functional theory calcns. are completed for five Ni(II) complexes formed by polydentate peptides to predict the electronic absorption spectrum. The ligands examd. were glycyl-glycyl-glycine (GGG), glycyl-glycyl-glycyl-glycine (GGGG), glycyl-glycyl-histidine (GGH), glycyl-glycyl-cysteine (GGC), and triethylenetetramine (trien). Fifteen functionals and two basis sets were tested. On the basis of the mean abs. percent deviation (MAPD), the ranking among the functionals is: HSE06 ∼ MPW1PW91 ∼ PBE0 > ω-B97x-D ∼ B3P86 ∼ B3LYP ∼ CAM-B3LYP > PBE ∼ BLYP ∼ BP86 > TPSS > TPSSh > BHandHLYP > M06 » M06-2X. Concerning the basis sets, the triple-ζ def2-TZVP performs better than the double-ζ LANL2DZ. With the functional HSE06 and basis set def2-TZVP the MAPD with respect to the exptl. λmax is 1.65% with a std. deviation of 1.26%. The absorption electronic spectra were interpreted in terms of vertical excitations between occupied and virtual MOs based on Ni-d AOs. The electronic structure of the Ni(II) species is also discussed. [on SciFinder(R)
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
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