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Towards the development of alternative platinum-based anticancer drugs: a kinetic and mechanistic study of mono and dinuclear trans-platinum(II) complexes.
Get PDFDoctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.Abstract available in PDF
Correction to: A kinetic investigation of mononuclear trans-platinum(II) complexes with mixed amine ligands
No full textThe article “A kinetic investigation of mononuclear trans-platinum(II) complexes with mixed amine ligands”, written by “Moses Ariyo Olusegun, Desigan Reddy and Deogratius Jaganyi”, was originally published electronically on the publisher’s internet portal https://link.springer.com/article/10.1007/s11243-020-00381-0 on 12 March 2020 with open access. With the author(s)’ decision to step back from Open Choice, the copyright of the article changed on 20 April 2020 to ©Springer Nature Switzerland AG 2020 and the article is forthwith distributed under the terms of copyright
Understanding the role of flexible alkyl-α,ω-diamine linkers on the substitution behaviour of dinuclear trans-platinum(II) complexes: A kinetic and mechanistic study
No full textAn investigation of the role of flexible alkyl-α,ω-diamine linkers on the substitution behaviour of dinuclear trans-platinum(II) complexes. The substitution reactions of four dinuclear trans-platinum(II) complexes viz. [PtNH3Cl2]2-µ-NH2(CH2)2NH2] (P12), [PtNH3Cl2]2-µ-NH2(CH2)3NH2] (P13), [PtNH3Cl2]2-µ-NH2(CH2)4NH2] (P14) and [PtNH3Cl2]2-µ-NH2(CH2)5NH2] (P15) with three neutral thiourea-based nucleophiles specifically: thiourea (TU), N-methyl-2-thiourea (MTU) and N,N-dimethyl-2-thiourea (DMTU) were studied quantitatively under pseudo-first-order condition as function of concentration and temperature by conventional UV–Visible and stopped-flow spectrophotometers. The ligand substitution reaction of the complexes proceeds in veritably three consecutive steps. Each step follows first-order kinetics with the respective complex and nucleophile. The pseudo first order rate constants, kobs(1/2/3), for sequential substitution of the chlorido ligands, the ammine, and subsequent displacement of the linker obeyed the rate law: kobs(1/2/3) = k(1/2/3)[NU]. The ligand substitution reactions were driven by both electronic and steric factors. However, our findings revealed that upon the substitution of the chlorido ligands by the nucleophiles at the platinum centres, the σ-donor capacity via inductive effect of these electron-rich nucleophiles over compensate the steric strain imposed by the nucleophiles and by the alkanediamine linker at the substitution sites. Consequently, electronic factors governed the overall reaction pattern of these complexes. 195Pt NMR results confirmed the simultaneous substitution of all the chlorido ligands by thiourea-based nucleophiles, followed by the subsequent but successive displacement of the ammine groups and the flexible alkanediamine linker from the metal centres. The order of reactivity of the nucleophiles with the complexes decreases with the increase in steric bulk in the nucleophiles: TU > MTU > DMTU. The small positive enthalpy and the large but negative entropy confirm the associative mode of activation for all the studied complexes. Computational modelling using density functional theory (DFT) calculations was employed to rationalise the kinetic trends
A kinetic and mechanistic study of analogous bifunctional dialkylamine platinum(ii) complexes
No full textThis study was aimed at investigating the comparative substitution behaviour of analogous cis/trans-Pt(II) complexes with inert dialkylamine ligands. The rate of substitution of the aqua ligands by three nucleophiles, viz. thiourea (TU), 1,3-dimethylthiourea (DMTU) and 1,1,3,3-tetramethylthiourea (TMTU), for the complexes: [cis-Pt(OH2)2(NH3)2](ClO4)2 (cPt), [cis-Pt(OH2)2(NH2CH3)2](ClO4)2 (cPtM), [cis-Pt(OH2)2{NH2CH(CH3)2}2](ClO4)2 (cPtR), [trans-Pt(OH2)2(NH3)2](ClO4)2 (tPt), [trans-Pt(OH2)2(NH2CH3)2](ClO4)2 (tPtM) and [trans-Pt(OH2)2{NH2CH(CH3)2}2](ClO4)2 (tPtR) was investigated under pseudo first-order conditions as a function of concentration and temperature by stopped-flow and UV/visible spectrophotometry. The reactions of the cis-complexes proceed in two concerted steps whereas those of the trans-complexes followed a stepwise mechanism involving rate determining substitution of the first chloride followed by a fast second substitution step, with no intermediates being detected. The pseudo first-order rate constants, kobs obeyed the rate law: kobs = k2[nucleophile]. The trans-complexes were observed to be approximately 103 times more reactive than their corresponding cis-analogues. The electronic and the steric hindrance due to the geometries of the complexes controlled the overall reaction pattern. The order of reactivity of the complexes is tPt > tPtM > tPtR > cPt > cPtM > cPtR. The reactivity of the nucleophiles with the complexes decreases with an increase in steric demand in the order: TU > DMTU > TMTU. The trans-dialkylamine complexes formed distinctly different kinetic products relative to their cis-analogues. 195Pt NMR spectroscopic results confirmed the final kinetic products of each of the cis- and trans-complexes. The negative entropy of activation (ΔS≠) values in all the complexes investigated assert an associative substitution mechanism, with the mechanism being more pronounced in the cis-complexes than in their trans-analogues
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
Variations on the Author
Get PDF“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
Get PDFWe 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
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
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