1,720,995 research outputs found
Role of Metal Ions in Dopamine Oxidation
No full textThis is an easy and cheap experiment where chemistry Masters students can evaluate the role of some metal ions (i.e., CuII and MnII) in dopamine oxidation, related to Parkinsonism. The required prior knowledge is being familiar with the basis of UV-vis spectroscopy. Details of the activity, including procedure and experimental data, are provided
Freshening up Old Methods for New Students: A Colorful Laboratory Experiment to Measure the Formation Constants of Ni(II) Complexes Containing Ethane-1,2-Diamine
No full textThis is an easy and inexpensive laboratory experiment in which undergraduate students at the Bachelor's degree level in Chemistry can measure formation constants of complexes [Ni(en)n(OH2)6-2n]2+(n = 1, 2 or 3; en = ethylenediamine) through an acid-base titration. The background information necessary to understand the activity involves familiarity with equilibria and basic coordination chemistry, and the lab experience uses only common glassware and a pH meter. The mathematical treatment of the results is based on Bjerrum's formation function. Details of the activity, including full procedural and experimental data, are provided. The experiment can be augmented with additional work based on Job's method to analyze the stoichiometry of the complexes under investigation
Microwave-Assisted Synthesis: Can Transition Metal Complexes Take Advantage of This “Green” Method?
No full textMicrowave-assisted synthesis is considered environmental-friendly and, therefore, in agreement with the principles of green chemistry. This form of energy has been employed extensively and successfully in organic synthesis also in the case of metal-catalyzed synthetic procedures. However, it has been less widely exploited in the synthesis of metal complexes. As microwave irradiation has been proving its utility as both a time-saving procedure and an alternative way to carry on tricky transformations, its use can help inorganic chemists, too. This review focuses on the use of microwave irradiation in the preparation of transition metal complexes and organometallic compounds and also includes new, unpublished results. The syntheses of the compounds are described following the group of the periodic table to which the contained metal belongs. A general overview of the results from over 150 papers points out that microwaves can be a useful synthetic tool for inorganic chemists, reducing dramatically the reaction times with respect to traditional heating. This is often accompanied by a more limited risk of decomposition of reagents or products by an increase in yield, purity, and (sometimes) selectivity. In any case, thermal control is operative, whereas nonthermal or specific microwave effects seem to be absent
Tumor Niche Influences the Activity and Delivery of Anticancer Drugs: Pharmacology Meets Chemistry
Full text linkCellular and molecular characteristics of the tumor microenvironment are fundamental for the formation of niches. These structures include both cellular and matrix components and have been shown to protect and promote cancer formation and progression. The peculiarities of tumor niches have been suggested by many authors as targets with high therapeutic potential. This narrative review analyzes the chemical characteristics of the tumor microenvironment and describes experimental and clinical approaches to influence its contribution to cancer promotion and the spread of metastases. In particular, the possible chemical differences, like pH, oxygen levels, and cell composition, to be used for the design of drugs or the delivery of antiproliferative moieties for a more precise oncology approach, will be discussed. The literature proposes a vast number of molecules, but this review focuses on hypoxia-activated molecules, pH-sensitive nanocarriers, metal-based drugs, and gasotransmitters targeting selectively the tumor microenvironment as possible negative modulators of the contribution of niches to tumor promotion. The chemical peculiarities of the tumor niche are discussed for possible pharmacological developments
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
Protonation of Pt(IV) Anticancer Complexes Assayed by Vibrational Ion Spectroscopy
No full textPlatinum(IV) complexes are being studied as potential alternatives to traditional platinum(II)-based chemotherapy drugs. They promise reduced side effects and potential for oral administration. In fact, a preliminary reduction in the cellular medium is recognized as a crucial step for activation. However, a deeper understanding of the protonation sites and substitution behavior of Pt(IV) complexes is needed, considering that ligand hydrolysis may compete with reduction-mediated activation, particularly in acidic environments such as the stomach. In this study, we investigated protonated Pt(IV) complexes with equatorial ligands common to widely used Pt(II) drugs containing square planar geometry, such as cisplatin and carboplatin. The additional axial substituents in the octahedral coordination sphere of Pt(IV) include different combinations of hydroxido and acetato ligands. Mass spectrometry-based methods, including collision-induced dissociation (CID) and infrared multiple photon dissociation (IRMPD) spectroscopy, supported by density functional theory (DFT) calculations, were employed. Structural characterization revealed that protonation preferences are influenced by the type and position of the ligands. Notably, protonation is generally favored on the carboxylato ligands; however, the carboplatin-derived complex exhibited a mixed population of protomers, highlighting the significance of both axial and equatorial ligand configurations in shaping the prototropic equilibria happening in solution
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
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