1,721,008 research outputs found
Phytochemical profiling of iranian plants, and ECD calculation as tool for establishing the absolute configuration of new natural products
Get PDFBiosynthesis of secondary metabolites occurs by concerted multistep reactions in a biological (chiral) environment. Therefore, many natural products (NPs) are chiral molecules having one or several stereocenters. The biological activity of NPs and drug like molecules is generally dependent on the stereochemistry of a molecule. Thus NPs are uniquely predestined to interact with biomacromolecules, and this explains their importance as drug leads.
Chiroptical methods such as electronic circular dichroism (ECD) have been used for assignment of absolute configuration since several decades, but were limited in their applicability. The rapidly developing computer technologies and a broad diversity of quantum chemical methods available now permit to study virtually any molecule by selecting the most appropriate method for each particular case, with regard to the desired accuracy, time consumption, and available computer resources. The progress in the areas of conformational analysis and quantum chemical calculation of molecular properties has widened the applicability of ECD in unambiguous determination of chiral molecules. This is especially valuable for the analysis of new molecular entities when chemical synthesis of the compound is not an option. The good agreements between the experimental and simulated ECD curves of these compounds provided the unambiguous configurational establishment.
The aim of the present work was phytochemical investigation of Iranian medicinal plants, in order to identify bioactive compounds responsible for inhibition of Plasmodium falciparum. About 120 plant extracts were prepared from 40 plants traditionally used in Iranian traditional medicine (ITM) to treat malaria and screened for in vitro activity against P. falciparum.
In a preliminary screen, the lipophilic extracts of Artemisia persica, Salvia hydrangea, and Salvia sahendica roots potently inhibited the growth of P. falciparum K1 strain. HPLC-based activity profiling led to localizing and identification of the active constituents of these plant extracts. Their structures were elucidated by a combination of powerful analytical methods such as HPLC-PDA-TOF-MS, and microprobe NMR. In order to determine the absolute configurations of isolated chiral compounds, quantum chemical calculation of ECD spectra in combination with experimental ECD studies were used. This methodology successfully applied to establish the ACs of structurally diverse and conformationally rigid or flexible molecules including sesquiterpene coumarins, bisabolol sesquiterpenes, diterpenoids and complex isoprenoids with novel scaffolds.
Activity profiling of the active n-hexane extract from the roots of Salvia sahendica against malaria resulted in the identification of eight abietane-type diterpenoids. In vitro biological activities of isolated pure compounds were determined against P. falciparum L& strain and Trypanosoma brucei rhodesiense STIB 900 strain, and cytotoxicity in rat myoblast (L6) cells was determined. The IC50 values of the compounds ranged from 0.8 µM to over 8.8 µM against P. falciparum, and from 1.8 µM to over 32.3 µM against T. brucei rhodesiense. The cytotoxic IC50 values ranged from 0.5-15.5 µM. Selectivity indices for P. falciparum were from 0.1 to 18.2, and 0.1 to 1.2 for T. brucei rhodesiense. The absolute configuration of sahandol (3) and sahandone (4) were assigned by comparison of experimental and calculated ECD spectra and optical rotation values.
HPLC based activity profiling of the EtOAc extract of the aerial parts of Artemisia persica resulted in the isolation of a series of bisabolol oxide esters. Relative configurations of cyclohexenone/cyclohexene and tetrahydropyran moieties of 5–9 were established on the basis of 3JH–H coupling constants and NOE difference spectra. Absolute configurations of 5–9 were established by comparison of experimental ECD spectra with simulated ECD data for possible stereoisomers, by TDDFT. Assignment of AC by ECD calculation is possible even though relative stereochemistry cannot establish by NMR techniques due to the flexibility of the molecule. Bisaboloids 5–8 exhibited in vitro antimalarial activity against Plasmodium falciparum, with IC50 values ranging from 2.8 to 20.1 µM, and selectivity indices (SI) in L-6 cells of 3.7–11.9.
Hydrangenone, perovskone and salvadione three new triterpenoids with rare carbon skeletons were isolated from aerial parts and flowers of Salvia hydrangea endemic plant to Iran. These compounds indicated significance in vitro activity against P. falciparum with IC50 values 1.40, 0.18 and 1.43 µM, respectively and acceptable selectivity index in rat myoblast L-6 cells
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
Volatile constituent distribution of<i>Prangos coryombosa</i>Boiss at two stages of growth
No full textEssential oil compositions of different accessions of<i>Coriandrum sativum</i>L. from Iran
No full textVariations 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
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
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