1,721,173 research outputs found
Effect of solution conductivity on the volatile constituents of Origanum dictamnus L. in nutrient film culture
No full textThe chemical composition of the essential oils obtained from leaves and bracts of hydroponically cultivated Origanum dictamnus L. (Cretan dittany), growing under various electrical conductivity (EC) levels (2.0, 4.0, and 6.0 mS/cm), was studied, using the nutrient film technique (NFT). The analysis of the essential oil content was achieved by GC-MS technique, and totals of 41 and 38 different compounds were identified in both cases of large-leaved and narrow-leaved samples of leaves and bracts, respectively. Differences in the composition content and of the percentage of each of the constituents in the two studied samples (i.e., large-leaved and narrow-leaved) and within the essential oils of leaves and bracts in both samples were observed. Carvacrol and p-cymene were identified as the main constituents in all essential oils, whereas thymoquinone was found in higher percentage in the essential oils of large-leaved than in narrow-leaved plants. The results obtained from GC-MS analysis were submitted to chemometric analysis, and a phenotypic similarity of the essential oils of narrow-leaved O. dictamnus was observed, whereas the essential oils of large-leaved O. dictamnus showed two separate subgroups © 2005 American Chemical Society
Sesquiterpene lactones from Centaurea spinosa and their antibacterial and cytotoxic activities
No full textTen sesquiterpene lactones, 8α-O-(3,4-dihydroxy-2- methylenebutanoyloxy)sonchucarpolide (4-epi-malacitanolide) (1), 8α-O-(4-acetoxy-2-hydroxymethylbuten-2-oyloxy)-4-epi-sonchucarpolide (2), malacitanolide (3), its 4′-acetyl derivative (4), 8α-O-(3,4- dihydroxy-2-metnylenebutanoyloxy)dehydromelitensine (5), 8α-O-(3,4- dihydroxy-2-methylenebutanoyloxy)-15-oxo-5,7αH,6βH-eleman-1,3,11(13) -trien-6,12-olide (6), the germacranolides 8α-O-(4-acetoxy-2- hydroxymethylbuten-2-oyloxy)salonitenolide (7), cnicin (8), and 4′-acetylcnicin (9), and the sesquiterpene methyl 8α-O-(3,4- dihydroxy-2-methylenebutanoyloxy)-6α,15-dihydroxyelema-1,3,11(13) -trien-12-oate (10), were isolated from the aerial parts of Centaurea spinosa. Nine known flavonoids were also isolated. The structures and the stereochemistry of the new compounds 1 and 2 were deduced by spectroscopic methods. The in vitro activity of 1-10 against three Gram-positive and three Gram-negative bacteria was evaluated using a microdilution method, and their in vitro cytotoxic activity was determined against a panel of human tumor cell lines. © 2005 American Chemical Society and American Society of Pharmacognosy
Bioactive sesquiterpene lactones from Centaurea species and their cytotoxic/cytostatic activity against human cell lines in vitro
No full textSesquiterpene lactones isolated from the aerial parts of various species of the genus Centaurea were examined for their in vitro cytotoxic/cytostatic activity against five human cell lines (i.e., DLD1, SF268, MCF7, H460 and OVCAR3). Compounds 1-4 were isolated from C. zuccariniana, 5 and 6 from C. achaia, 7 from C. thessala ssp. drakiensis and compounds 8 and 9 from C. deusta. Compound 1, 8α-O-(3,4-dihydroxy-2-methylenebutanoyloxy)-dehydromelitensine was found to be the most active, exhibited a considerable growth inhibiting activity against three of the cell lines tested, while compound 5 8α-O-(3-hydroxy-2-methylenepropanoyl)dehydromelitensin exhibited a growth inhibiting effect against most of the tested cell lines. A new eudesmanolide (8α-hydroxysonchucarpolide, 4) was isolated from C. zuccariniana and its structure was elucidated by spectroscopic methods
Liquid crystalline nanoparticles for drug delivery: The role of gradient and block copolymers on the morphology, internal organisation and release profile
No full textAmphiphilic polymers represent one of the main class of stabilizers for non-lamellar lyotropic liquid crystalline nanoparticles, being essential for their formation and stability. In the present study, poly(ethylene oxide)-block-poly(ε-caprolactone) (PEO-b-PCL) block copolymers and poly(2-methyl-2-oxazoline)-grad-poly(2-phenyl-2-oxazoline) (MPOx) gradient copolymers were incorporated as stabilizers in liquid crystalline nanoparticles prepared from glyceryl monooleate. The polymers were chosen according to their high biocompatibility and promising stealth properties, in order to develop safe and efficient drug delivery nanosystems. The physicochemical characteristics and fractal dimension of the resultant nanosystems were obtained from light scattering techniques, while their micropolarity and microfluidity from fluorescence spectroscopy. The effect of temperature, serum proteins and ionic strength on the physicochemical behavior was monitored. Their morphology was assessed by cryo-TEM, while their thermal behavior by microcalorimetry and high-resolution ultrasound spectroscopy. Their properties were dependent on the stabilizer chemistry and topology (block/gradient copolymer) and its concentration. Subsequently, resveratrol, as model hydrophobic drug, was loaded into the nanosystems, the entrapment efficiency was calculated and in vitro release studies were carried out, highlighting how the different stabilizer can differentiate the drug release profile. In conclusion, the proposed copolymers broaden the toolbox of polymeric stabilizers for the development of liquid crystalline nanoparticles intended for drug delivery applications
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
Effect of Nitrogen Concentration of the Nutrient Solution on the Volatile Constituents of Leaves of Salvia fruticosa Mill. in Solution Culture
No full textEssential oils from hydroponically cultivated Salvia fruticosa were analyzed by GC-MS techniques. Three different levels of nitrogen (100, 150, and 200 mg/L) were used in the nutrient solution for the cultivation, using the nutrient film technique. A total of 79 compounds were identified, and qualitative and quantitative differences have been observed between the samples collected at full bloom (flowering stage) and at the end of the seed formation stage. 1,8-Cineole, β-caryophyllene, and viridiflorol were the predominant constituents in most cases. 13-epi-Manool was identified by using GC parameters and mass spectrum fragmentation pattern, whereas labd-7,13-dien-15-ol, a labdane type diterpene, was identified for the first time in the genus Salvia, using GC parameters and an authentic sample. The results obtained from GC-MS analyses were submitted to chemometric analysis
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
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