132,460 research outputs found
Molecular fields to assess recognition forces and property spaces
No full textSince the emergence of combinatorial chemistry and chemical libraries, great attention is being paid to the concepts of chemical diversity and chemical space. This approach is based on the assumption that molecular properties are invariant ones. But a growing computational power shows that a molecule cannot be considered as a static object but as an animated subject whose conformational changes may significantly affect the profile of any of its computable property. The ensemble of all conformers of a given compound is often taken as defining a conformational space. In a similar manner, many molecular properties can be shown to vary with the 3D-geometry of the molecule.
In particular, powerful computational methods based on molecular fields now allow some physicochemical properties to be computed for each conformer, as discussed in the first part of the chapter. Such methods include MEPs (Molecular Electrostatic Potentials), MLPs (Molecular Lipophilicity Potentials), which allows to back-calculate a partition coefficient of a given conformer, and the recent MHBPs (Molecular Hydrogen-Bonding Potentials). A range of property values corresponding to all realistic conformations must be examined and taken into account. The range of these values defines a property space whose form and extent will depend on both the solute and the relevant environment.
In a second part, the chapter focuses on the property spaces of the acetylcholine in a variety of polar and hydrophobic solvents. The effect of the solvent on the conformational behaviour of acetylcholine is analyzed together with the corresponding effects on the property spaces. Moreover, attention is being paid to the cross-correlation among the profiles of these spaces (both physicochemical and structural). These interrelations lead to a definition of the concept of molecular sensitivity which describes the ability of a molecule to modify its physicochemical properties as its geometry changes, as presented in the third part of the chapter. The receptor selectivity of alpha-adrenergic ligands offers an illustration of the interest and limits of molecular sensitivity and property space range in dynamic QSAR analyse
Musings on ADME predictions and molecular structure
No full textIn this overview, we first examine Structure-Activity Relations (SARs) and their components from a general point of view. Four types of interpretation emerging from statistically valid relations are considered, namely causal (mechanistic), contextual (empirical), fortuitous and tautological correlations. Implications for ADME predictions arise when discussing the diversity of interactions between active compounds (e.g. drugs) and biological systems.
In a second part, we share our views on the differences between pharmacodynamic targets (namely the sites of action of bioactive compounds, e.g. receptors and ion channels) and pharmacokinetic agents (namely the biological components that act on drugs to transport, metabolize, retain and excrete xenobiotics). While the former are usually characterized by a high (i.e., narrow) specificity towards their ligands, the latter have evolved to recognize chemically diverse compounds and thus to display a low (i.e., broad) specificity.
In a last part, we discuss the concept of molecular structure and focus on the fluctuations undergone by molecular form and functions. As a result, a molecule can exist in a large number of distinct microstates, the ensemble of which constitutes the property space of the molecul
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
Heavy quark masses
No full textIn the large quark mass limit, an argument which identifies the mass of the heavy-light pseudoscalar or scalar bound state with the renormalized mass of the heavy quark is given. The following equation is discussed: m(sub Q) = m(sub B), where m(sub Q) and m(sub B) are respectively the mass of the heavy quark and the mass of the pseudoscalar bound state
An Example of Innovative University Teaching and Learning: the Fashion-Tech Model of Integration
No full text[EN] The aim of the paper is to investigate the relationship between higher education institutions and companies in the field of Fashion-Tech educational system, in order to test the effectiveness of the integration of heterogeneous skills and disciplines. The paper firstly analyses how design, pervaded by the results of technological progress, has become over time an increasingly complex and multidisciplinary field, determining the need and development of new professional figures. Secondly, it focuses on the fashion-tech sector, the resulting area obtained from the intersection of fashion design and digital technologies, highlighting the need for a reviewed educational approach to form hybrid professional figures. To this aim the paper examines data obtained through interviews and desk research conducted within the framework of XXX European project, outlining the state of the art in fashion-tech and investigating the transversal dynamics between the academic world and companies. Next, a case study is reported: an international and multidisciplinary workshop carried out in the field of academic training with the collaboration of a company. What emerged from the experience is that in the Fashion-Tech, the close and continuous relationship with companies acquires a fundamental role.Rossato, B.; Tenuta, L.; Testa, S. (2021). An Example of Innovative University Teaching and Learning: the Fashion-Tech Model of Integration. En 7th International Conference on Higher Education Advances (HEAd'21). Editorial Universitat Politècnica de València. 817-825. https://doi.org/10.4995/HEAd21.2021.13113OCS81782
Organic stereochemistry. Part 1. Symmetry elements and operations, classification of stereoisomers
No full textThis review initiates a general presentation of the principles of stereochemistry with special reference to medicinal compounds. The general focus of this and the following Parts is twofold, namely a) broad statements of stereochemical principles, and b) illustration of these with special reference to the biochemistry and pharmacology of medicinal compounds. As for the graphical format of this work, its readers will find it essentially identical with that of a previous series of seven reviews on the Metabolism of Drugs and Other Xenobiotics published between October 2006 and October 2009 by B. T. and Stefanie Krämer in Chemistry and Biodiversity [1], and also published in book form in 2008 (Vol. 1) and 2010 (Vol. 2) [2]. The present Part 1 introduces this new series by presenting and illustrating basic concepts on which the edifice of stereochemistry is built. At the most basic level of such foundations, we find symmetry as presented here in terms of its elements, operations, and point groups. This is followed by a classification of isomeric molecular structures, as well as a classification of steric relationships between molecular fragments
Presence of Testa and Shell Maintains Oil Stability in Almond and Canarium Nuts
No full text(1) Background: The oil stability of tree nuts during storage can be influenced by storage conditions such as temperature, humidity, and moisture concentration. However, few studies have assessed how the presence of testa and shell affects the oil stability of tree nuts during storage. We aimed to determine how storage conditions affect oil stability in almond and canarium, in particular, the presence of testa and storage time of nut-in-shell (NIS). (2) Methods: We measured peroxide value (PV), free fatty acid (FFA) and hexanal concentrations of almond and canarium (blanched vs. kernel-in-testa) stored at 45 °C for 24 days. We also measured PV, FFA and fatty acid composition of canarium samples at days 0 and 140 stored as NIS under ambient conditions. (3) Results: The presence of testa in almond and canarium decreased hexanal and PV concentrations at day 24 of incubation. Canarium PV and FFA concentrations increased over 140 days of storage in the shell compared to day 0. However, both PV and FFA concentrations remained within the acceptable threshold during storage. No changes in fatty acid composition were found during NIS storage. (4) Conclusions: Testa and shell could act as a natural coating, slowing down oxidation rates. Hence, long-term storage on nuts in testa or nuts in shell are recommended for tree nuts
Path-based methods for the determination of nondispersive drainage directions in grid-based digital elevation models
No full textPath-based methods for the determination of nondispersive drainage directions ingrid-based digital elevation models are presented. These methods extend the descriptivecapabilities of the classical D8 method by cumulating the deviations between selected andtheoretical drainage directions along the drainage paths. It is shown that either angular ortransversal deviations can be employed. Accordingly, two classes of methods designatedD8-LAD (eight drainage directions, least angular deviation) and D8-LTD (eight drainagedirections, least transversal deviation) are developed. Detailed tests on four syntheticdrainage systems of known geometry and on the Liro catchment (central Italian Alps)indicate that the proposed methods provide significant improvement over the D8 methodfor the determination of drainage directions and drainage areas
L’accertamento della Etiologia nella Ipoacusia da Trauma Sonoro Cronico. Possibilità e Limiti
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