124,732 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Structural analysis of Cu(II) ligation to the 5'-GMP nucleotide by pulse EPR spectroscopy
Get PDFSimple copper salts are known to denature poly d(GC). On the other hand, copper complexes of substituted 1,4,7,10,13-pentaazacyclohexadecane-14,16-dione are able to convert the right-handed B form of the same DNA sequence to the corresponding left-handed Z form. A research program was started in order to understand why Cu(II) as an aquated ion melts DNA and induces the conformational change to Z-DNA in the form of an azamacrocyclic complex. In this paper, we present a continuous wave and pulse electron paramagnetic resonance study of the mononucleotide model system Cu(II)-guanosine 5'-monophosphate . Pulse EPR methods like electron-nuclear double resonance and hyperfine sublevel correlation spectroscopy provide unique information about the electronic and geometric structure of this model system through an elaborate mapping of the hyperfine and nuclear quadrupole interactions between the unpaired electron of the Cu(II) ion and the magnetic nuclei of the nucleotide ligand. It was found that the Cu(II) ion is directly bound to N7 of guanosine 5'-monophosphate and indirectly bound via a water of hydration to a phosphate group. This set of experiments opens the way to more detailed structural characterization of specifically bound metal ions in a variety of nucleic acids of biological interest, in particular to understand the role of the metal-(poly)nucleotide interaction
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
Cu(II) complex with poly(dG-dC): structure determination with the help of pulse EPR spectroscopy
No full textPulse EPR spectroscopy is used to investigate possible structural features of the copper(II) ion coordinated to poly(dG-dC).poly(dG-dC) in a frozen aqueous solution, and the structural changes of the polynucleotide induced by the presence of the metal ion. Two different copper species were identified and their geometry explained by a molecular model. According to this model, one species is exclusively coordinated to a single guanine with the N7 nitrogen atom forming a coordinative bond with the copper. In the other species, a guanine and a cytosine form a ternary complex together with the copper ion. A copper crosslink between the N7 of guanine and N3 of cytosine is proposed as the most probable coordination site. Moreover, no evidence was found for an interaction of either copper species with a phosphate group or equatorial water molecules. In addition, circular dichroism (CD) spectroscopy showed that the DNA of the CuII-poly(dG-dC)•poly(dG-dC) adducts resembles the left-handed Z-form. These results suggest that metal-mediated Hoogsteen base pairing, as previously proposed for a right-handed DNA duplex, can also occur in a double-stranded left-handed DNA (Santangelo et al. [1])
Can copper(II) mediate Hoogsteen base-pairing in a left-handed DNA duplex? A pulse EPR study
No full textPulse EPR spectroscopy is sued to investigate possible structural features of the copper(II) ion coordinated to poly(dG-dC) poly(dG-dC) in a frozen aqueous solution, and the structural change of the polynucleotide induced by the presence of the metal ion. Two different copper species were identified and their geometry explained by a molecular model. According to this model, one species is exclusively coordinated to a single guanine with the N7 nitrogen atom forming a coordinative bond with the copper. In the other species, a guanine and a cytosine form a ternary complex together with the copper ion. A copper crosslink between the N7 of guanine and N3 of cytosine is proposed as the most probable coordination site. Moreover, no evidence was found for an interaction of either copper species with a phosphate group or equatorial water molecules. In addition, circular dichroism (CD) spectroscopy showed that the DNA of the Cu-II-poly(dG-dC)center dot poly(dG-dC) adducts resembles the left-handed Z-form. These results suggest that metal-mediated Hoogsteen base pairing, as previously proposed for a right-handed DNA duplex, can also occur in a double-stranded left-handed DNA
N,N,O and N,O,N Meridional cis Coordination of Two Guanines to Copper(II) by d(CGCGCG)<sub>2</sub>
No full textMany
research groups study the generation of supramolecular n-dimensional arrays by combining metals with DNA building
blocks. Most of the time, the natural nucleobases are modified to
obtain higher-affinity metal binding sites. Using unmodified nucleobases
avoids a potentially difficult synthesis; however, they have the possible
disadvantage of a less defined and/or weaker coordination mode of
the metal. Structural studies on the behavior of copper(II) as a linking
metal and guanine as the natural ligand for metals in unmodified DNA
are reported. Previously, the ability of mono- and dinuclear metal
complexes to induce Z-DNA has been explored [Medina-Molner, A.; Spingler,
B. Chem. Commun. 2012, 48, 1961; Medina-Molner,
A.; Rohner, M.; Pandiarajan, D.; Spingler, B. Dalton Trans. 2015, 44, 3664]. Herein, X-ray crystallographic studies
of the structures resulting from the combination of copper(II) ions
with DNA hexamers of the general sequence d(CG)3 are presented.
Three different packing motifs were observed in three crystal structures
with resolutions ranging from 2.15 to 1.45 Å. The motifs are
dependent upon other cations being present and/or the crystallization
conditions. The first examples of intramolecular O6,N7-chelates of
a neutral purine nucleobase to copper(II) were obtained as well as
the first meridional N,N,O and N,O,N coordination modes of two guanines
to copper(II). The fascinating coordination chemistry of copper(II)
complexes generated by the Z-DNA oligonucleotides and the differences
to simple nucleobases complexes with copper(II) are discussed in detail
N,N,O and N,O,N Meridional cis Coordination of Two Guanines to Copper(II) by d(CGCGCG)2
Get PDFMany research groups study the generation of supramolecular n-dimensional arrays by combining metals with DNA building blocks. Most of the time, the natural nucleobases are modified to obtain higher-affinity metal binding sites. Using unmodified nucleobases avoids a potentially difficult synthesis; however, they have the possible disadvantage of a less defined and/or weaker coordination mode of the metal. Structural studies on the behavior of copper(II) as a linking metal and guanine as the natural ligand for metals in unmodified DNA are reported. Previously, the ability of mono- and dinuclear metal complexes to induce Z-DNA has been explored [Medina-Molner, A.; Spingler, B. Chem. Commun. 2012, 48, 1961; Medina-Molner, A.; Rohner, M.; Pandiarajan, D.; Spingler, B. Dalton Trans. 2015, 44, 3664]. Herein, X-ray crystallographic studies of the structures resulting from the combination of copper(II) ions with DNA hexamers of the general sequence d(CG)3 are presented. Three different packing motifs were observed in three crystal structures with resolutions ranging from 2.15 to 1.45 Å. The motifs are dependent upon other cations being present and/or the crystallization conditions. The first examples of intramolecular O6,N7-chelates of a neutral purine nucleobase to copper(II) were obtained as well as the first meridional N,N,O and N,O,N coordination modes of two guanines to copper(II). The fascinating coordination chemistry of copper(II) complexes generated by the Z-DNA oligonucleotides and the differences to simple nucleobases complexes with copper(II) are discussed in detail
Induction of DNA-double-strand breaks by auger electrons from 99mTc complexes with DNA-binding ligands.
No full textThe potential of certain Auger electron emitting nuclides for systemic radiotherapeutic applications has recently gained much attention. In particular, the ability of several nuclides, including 111In, 125I, and 123I, to induce DNA double-strand breaks (dsb), a good indicator of cytotoxicity, has been extensively studied. However, this ability has never previously been shown experimentally for 99mTc, which, besides the well-known gamma radiation that is used for diagnostic applications, also emits an average of 1.1 conversion electrons and 4 Auger or Coster-Kronig electrons per decay. Owing to the short range of Auger electrons, the radionuclide needs to be located very close to the DNA for dsb to occur. We synthesized two cationic 99mTcI-tricarbonyl complexes with pendant DNA binders, pyrene and anthraquinone. The X-ray crystal structures of the two complexes could be elucidated. Linear dichroism and UV/Vis spectroscopy revealed that the complex with pyrene intercalates DNA with a stability constant, K, of 1.1 x 10(6) M(-1), while the analogous complex with anthraquinone interacts with DNA in a groove-binding mode and has an affinity value of K=8.9 x 10(4) M(-1). We showed with phiX174 double-stranded DNA that the corresponding 99mTc complexes induce a significant amount of dsb, whereas non-DNA-binding [TcO4]- and nonradioactive Re compounds did not. These results indicate that the Auger electron emitter 99mTc can induce dsb in DNA when decaying in its direct vicinity and this implies potential for systemic radiotherapy with 99mTc complexes
Interaction of Novel Metal Complexes with DNA: Synthetic and Structural Aspects
Get PDFMetal ions bind to nucleic acids at various positions. This binding can be modulated by using metal complexes with appropriate ligands. Novel mono- and especially dinuclear metal complexes could be a powerful tool to detect rare, but still physiologically relevant, forms of DNA, e.g. the left-handed Z-DNA. In this review, our recent research activities in this area of bioinorganic chemistry are summarized. A special emphasis is laid on the synthetic challenges that arose upon the synthesis of the polyamine ligands. Further, some rather unusual approaches to elucidate the solution structure of copper bound to guanosine monophosphate with the help of pulsed EPR techniques like ENDOR and HYSCORE are described
Pragmatic Case Studies as a Source of Unity in Applied Psychology
No full textTo unify or not to unify applied psychology: that is the question. In this article we review pendulum swings in the historical efforts to answer this question—from a comprehensive, positivist, “top-down,” deductive yes between the 1930s and the early 60s, to a postmodern no since then. A rationale and proposal for a limited, “bottom-up,” inductive yes in applied psychology is then presented, employing a case-based paradigm that integrates both positivist and postmodern themes and components. This paradigm is labeled “pragmatic psychology” and, its specific use of case studies, the “Pragmatic Case Study Method” (“PCS Method”). We call for the creation of peer-reviewed journal-databases of pragmatic case studies as a foundational source of unifying applied knowledge in our discipline. As one example, the potential of the PCS Method for unifying different angles of theoretical regard is illustrated in an area of applied psychology, psychotherapy, via the case of Mrs. B. The article then turns to the broader historical and epistemological arguments for the unifying nature of the PCS Method in both applied and basic psychology.Peer reviewe
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