1,720,966 research outputs found
Chemical composition, seasonal variation and a new sesquiterpene alcohol from the essential oil of Lippia integrifolia
Get PDFChemical investigations on the essential oil of Lippia integrifolia performed by column chromatography, HPLC, GC-MS, 1H- and 13C-NMR spectroscopy led to the identification of 78 components. A new sesquiterpene alcohol, trans-africanan-1α-ol (4), was characterized as a significant component of the oil. Additionally, six samples obtained at monthly intervals through the annual cycle of the shrub (November-April) were studied. The oil was characterized by large amounts of oxygenated sesquiterpenes (53.3-69.4%) and sesquiterpene hydrocarbons (14.3-27.9%), along with small amounts of monoterpenoids (1.4-2.9%). Lippifoli-1(6)-en-5-one (2), african-5-en-1α-ol (3), β-caryophyllene oxide, 4,5-seco-africanan-4,5-dione (10), trans-africanan-1α-ol (4), humulene epoxide II, integrifolian-1,5-dione (1) and lippifoli-1(6)-en4β-ol-5-one (7) were the main oxygenated constituents. Although the qualitative composition appeared to be constant, there were large quantitative variations in the content of most components through the studied period. Copyright © 2006 John Wiley & Sons, Ltd.Fil: Coronel, Angelina del Carmen. Universidad Nacional de Tucumán; ArgentinaFil: Cerda García-Rojas, Carlos M.. CENTRO DE INVESTIGACIÓN Y DE ESTUDIOS AVANZADOS ; INSTITUTO POLITÉCNICO NACIONAL;Fil: Joseph Nathan, Pedro. CENTRO DE INVESTIGACIÓN Y DE ESTUDIOS AVANZADOS ; INSTITUTO POLITÉCNICO NACIONAL;Fil: Catalan, Cesar Atilio Nazareno. Universidad Nacional de Tucumán; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; Argentin
Vibrational circular dichroism of africanane and lippifoliane sesquiterpenes from Lippia integrifolia
Get PDFThe agreement between theoretical and experimental vibrational circular dichroism curves of (4R,9R,10R)-(+)-african-l(5)-ene-2,6-dione (1) and (4R,9S,10R)-lippifoli-l(6)-en-5-one (2), isolated from the widely used plant Lippia integrifolia, allowed the determination of the conformation and absolute configuration of 1 and confirmed both structural features for 2. Molecular modeling of 1 and 2 was carried out by means of a systematic and a Monte Carlo search protocol followed by geometry optimization employing density functional theory calculations with the B3LYP/6-31G(d), B3LYP/ DGDZVP, and/or B3PW91/DGDZVP2 functionals/basis sets. Validation of the minimum energy conformations for both tricyclic substances was achieved by comparison of the experimental and theoretical vicinal 1H-1H NMR coupling constants obtained by DFT-GIAO calculations.Fil: Cerda García Rojas, Carlos M.. Instituto Politécnico Nacional. Centro de Estudios Avanzados; MéxicoFil: Catalan, Cesar Atilio Nazareno. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; ArgentinaFil: Muro, Ana Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; ArgentinaFil: Joseph Nathan, Pedro. Instituto Politécnico Nacional. Centro de Estudios Avanzados; Méxic
1H and 13C NMR study of copteroside E derivatives
Get PDFThe triterpenoid saponin copteroside E (1) was isolated from the flowers and leaves of Verbesina suncho. Detailed 1H and 13C NMR assignment of its acetyl derivatives 2 and 3 was achieved by 2D NMR techniques including COSY, TOCSY, NOESY, HMQC and HMBC. The presence of a glucuronolactone moiety in 2 is supported by the calculated vs observed 1H–1H coupling constants. Molecular mechanics calculations on 1 were useful for understanding the formation of glucuronolactone 2 and decaacetate 3.Fil: Cerda García Rojas, Carlos M.. Instituto Politécnico Nacional; MéxicoFil: Zamorano, Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; ArgentinaFil: Chávez Oribe, María Isabel. Universidad Nacional Autónoma de México; MéxicoFil: Catalan, Cesar Atilio Nazareno. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; ArgentinaFil: Joseph Nathan, Pedro. Instituto Politécnico Nacional; Méxic
Absolute configuration of trixanolides from Trixis pallida
Get PDFThe aerial parts of Trixis pallida afforded seven known trixanolides (18-24) together with 17 new trixanolides (1-17). Their structures were determined by 1D and 2D NMR techniques, while the absolute configuration of the trixane skeleton was determined using the Mosher method and turned out to be enantiomeric to that reported using the Horeau method. This result is further discussed from the biosynthetic point of view.Fil: Kotowicz, Claudia. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química Orgánica; ArgentinaFil: Hernández, Luis R.. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química Orgánica; ArgentinaFil: Cerda García Rojas, Carlos M.. Instituto Politécnico Nacional; MéxicoFil: Villecco, Margarita Beatriz. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química Orgánica; ArgentinaFil: Catalan, Cesar Atilio Nazareno. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; ArgentinaFil: Joseph Nathan, Pedro. Instituto Politécnico Nacional; Méxic
Absolute configuration of lippifoliane and africanane derivatives
Get PDFThe absolute configuration of naturally occurring lippifoliane derivatives isolated from the widely used plant Lippia integrifolia was assigned by analysis of the circular dichroism data in combination with density functional theory minimum energy molecular models of (1S,4A,6S,9S,10R)-lippifolian-1-ol-5-one (1), (4R,9S,10R)-lippifoli-1(6)-en-5-one (2), and (4S,9S,10R)-lippifoli-1(6)-en-4- ol-5-one (3) and application of the octant rule for saturated ketone 1 and the helicity rules for α,β-unsaturated ketones 2 and 3. The results were reinforced by the anomalous dispersion effect observed in the X-ray diffraction analysis of (4S,9S,10R)-4,10,11-tribromo-10,11-seco-lippifoli-1(6)-en-5-one (4) prepared from 2. The biogenetic relationships between lippifolianes 1-3 and africanane derivatives 7-9 and 13 isolated from the same species, together with chiroptical data for africananes isolated from the Hepaticae family, complete a stereochemical scenario in relation to the absolute configuration of africananes from L. integrifolia.Fil: Cerda García Rojas, Carlos M.. Instituto Politécnico Nacional; MéxicoFil: Coronel, Angelina del Carmen. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química Orgánica; ArgentinaFil: Perotti, Marina Elvira. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química Orgánica; ArgentinaFil: Catalan, Cesar Atilio Nazareno. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química Orgánica; ArgentinaFil: Joseph Nathan, Pedro. Instituto Politécnico Nacional; Méxic
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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