1,721,001 research outputs found
Substitution reactions between bis-chelate ligands in palladium(II) alkenyl complexes: an unusual way to form unstable trans-P complexes. A study on the isomerization mechanism
No full textThe substitution reactions between asymmetric bis-chelate ligands and alkenyl chloro derivatives of
palladium(II) of the type [Pd(L–L¢)(Rx)Cl] (L–L¢ = 2-phenylsulfanylmethyl-pyridine (HN–SPh),
2-methyl-6-phenylsulfanylmethyl-pyridine (MeN–SPh), 2,2¢-bipyridinyl (BiPy), Rx =
–CCOOMe=CMeCOOMe (Ra), –CCOOEt=CMeCOOEt (Rb), –CCOOt-Bu=CMeCOOt-Bu (Rc),
–(CCOOMe=CCOOMe)2Me (Rd)) with phosphoquinoline moieties (8-diphenylphosphanyl-quinoline
(DPPQ), 8-diphenylphosphanyl-2-methyl-quinoline (DPPQ-Me)) usually leads to the formation of the
stable geometrical isomer bearing these groups in the cis position thanks to the mutual trans influence
of the alkenyl and phosphine groups. However, when the leaving group MeN–SPh and the entering
ligand DPPQ are involved, the fast and quantitative substitution reaction leads to the formation of a
couple of geometrical isomers [Pd(DPPQ)(Rx)Cl]-trans P and [Pd(DPPQ)(Rx)Cl]-cis P (Rx = Ra, Rb,
Rc, Rd) in which the alkenyl and the phosphine groups are in mutual trans or cis position. The substrate
[Pd(DPPQ)(Rx)Cl]-trans P (Rx = Ra, Rb, Rc) slowly interconverts into its thermodynamically stable
-cis P counterpart while the bulky [Pd(DPPQ)(Rd)Cl]-trans P displays no tendency to isomerize, thereby
allowing separation of the two geometrical forms. Also, the ligand DPPQ-Me induces the formation of
the -trans P geometrical isomer which is only detectable at low temperature since it rapidly interconverts
into the -cis P derivative at RT. The kinetics of the interconversion process, a reasonable explanation of
the observed phenomenon based on theoretical calculations, and eventually an unequivocal structure
determination of the stable [Pd(DPPQ)(Rx)Cl]-cis P substrate are reported in the present pape
Dihydrofolate reductase: a new molecular target for gold(I) drugs?
No full textDehydrofolate reductasi : a new molecular target for gold(I) drugs?
R. Galassi,a A. Burini,a D. Micozzi,a A. Dolmella,b S. Pucciarellic
a School of Science and Technology, Chemistry Division, University of Camerino, 62032 Camerino (Italy);
b Department of Pharmaceutical Sciences, University of Padova, 35131 Padova (Italy);
c School of Biosciences and Biotechnology, University of Camerino, 62032 Camerino (Italy).
[email protected]
DHFR is an important enzyme mainly involved in the synthesis of pyrimidine and thymine basilar for the DNA replication and hence the cell proliferation. To perform its functions the DHFR enzyme needs the presence of a substrate and a cofactor such as NADPH and H2F.[1] Despite its fundamental importance in the cell’s metabolism this enzyme has never been tested as molecular target for gold(I) compounds which anti-proliferative action was ascertained. In fact, it is generally accepted that gold compounds act as multi-target drug and the proposed mechanisms mainly involve enzymes. Moreover, their action is function of their overall structure and of the nature of the ligands around the central metal atom.
Some pyrazolyl and imidazolyl gold(I) phosphane complexes synthesized by us have shown anticancer properties and they successfully inhibit some seleno-dependent enzymes such as thioredoxina reductase and glutathione peroxidase.[2] To investigate in depth their action on the regards of enzyme, inhibitory studies on DHFR have been carried out. Moreover, appropriate modifications in their structure have been performed in order to get information about the structure/properties relationship.
DTNB assays, stability studies in solution and affinity constant determinations have been performed too. Some conclusions about the possible mechanism of action may be taken accordingly.
Acknowledgements
Authors are grateful to CIRCSMB for Daniela Micozzi fellowship.
References
[1] M. Brandsch, I. Knütter, E. Bosse-Doenecke, J. Pharm. Pharmacol. 2008, 60, 543.
[2] R. Galassi, A. Burini, S. Ricci, M. Pellei, M. P. Rigobello, A. Citta, A. Dolmella, V. Gandin, C Marzano. Dalton Trans., 2012, 41, 530
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
Synthesis and biological activity of functionalized imidazolium salts and related water-soluble coinage metal N‐heterocyclic carbene complexes
No full textN-heterocyclic carbenes (NHCs) are an interesting class of ligands with donor properties similar to phosphines. Their chemical versatility not only implies a wide variety of structural diversity and coordination modes, but also a capability to form stable complexes with a large number of transition metals with different oxidation states. An attractive feature of NHCs chemistry is the ease with which a series of structurally similar complexes with varying lipophilicity can be synthesized simply by changing the substituents on the imidazolium salt precursor. As potential anticancer drugs, metal-NHCs constitute a recent and very rapidly growing field of research: in fact NHCs have similar donor properties to phosphines and their imidazolium salt precursors are often more easily synthesized than similarly-functionalized phosphines. To explore the possible use of NHC ligands as alternatives to phosphines in the synthesis of biologically active group 11 metal complexes, here we report the synthesis and use of N-heterocyclic pre-carbene ligands functionalized with hydrophilic groups (such as esters, amides or sulfonates) in coinage metal chemistry. In particular N-heterocyclic carbene ligand precursors HImACl (1,3-bis(2-ethoxy-2-oxoethyl)-1H-imidazol-3-ium chloride), HImBCl (1,3-bis[2-(diethylamino)-2-oxoethyl]-1H-imidazol-3-ium chloride) and NaHImPrSO3 (sodium 3,3'-(1H-imidazole-3-ium-1,3-diyl)dipropane-1-sulfonate) have been synthesized and used in the preparation of Cu(I), Ag(I) and Au(I) adducts. The cytotoxic properties of the newly synthesized NHC complexes were investigated in various human cancer cell lines, including cisplatin sensitive and resistant cells. Growth inhibitory effects were compared with those induced in human non-transformed cells. Moreover, gold(I) and silver(I) carbene complexes were evaluated for their ability to in vitro inhibit the selenoenzyme TrxR, that is recognized as the most relevant molecular target for gold(I,III) species and recently proposed as potential protein target also for silver derivatives
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