1,720,959 research outputs found
Dehydration without Heating: Use of Polymer-Assisted Grinding for Understanding the Stability of Hydrates in the Presence of Polymeric Excipients
Full text linkHydrates are ubiquitous
multicomponent solids of particular interest
in the pharmaceutical field. As such, there is a practical need of
monitoring the stability of this class of solids, especially when
formulated with one or more excipients. In this paper, we propose
an innovative solid state method, namely, polymer-assisted grinding
(POLAG), for exploring the stability of carbamazepine dihydrate under
the simultaneous effects of manufacturing-induced stress (milling)
and the presence of polymeric excipients. We demonstrate that, while
milling alone did not cause any dehydration, the presence of specific
polymers induced partial or total dehydration of the selected model
drug carbamazepine dihydrate. Through detailed experimental evidence,
it is concluded that the polymer chain length plays a main role in
the kinetics of the solid state reaction, while a combination of the
amount of polymer and the milling time allowed the isolation of different
polymorphic forms of the resulting dehydrated carbamazepine solid.
Additional POLAG experiments suggested that polymers of a high molecular
weight are less likely to cause dehydration due to their lower affinity
for water. POLAG may therefore be used both as a screening method
for determining the dehydration propensity of a specific hydrated
form in the presence of polymers and for isolating highly metastable
forms of the resulting anhydrous product
Mechanochemical Synthesis of Multicomponent Crystals: One Liquid for One Polymorph? A Myth to Dispel
Full text linkIdentifying as many polymorphs as possible for a molecular compound is important in the design of materials with desired properties. In this paper we demonstrate, using a simple experimental procedure, how the amount of liquid present during liquid-assisted mechanochemical reactions can be used to rapidly explore polymorph diversity. Through detailed experimental evidence it is concluded that for the specific (multicomponent) crystal system investigated (caffeine–anthranilic acid) the commonly accepted rule “one liquid for one specific polymorph” is not correct. Additionally we demonstrate that through modification of the amount of added liquid it is possible to form a polymorph previously obtained only by a desolvation reaction. We believe that while the results raise many mechanistic questions the approach is advantageous as a means of rapidly screening for polymorph diversity as well as being a simple screening methodology. While we focus here on a cocrystal system, we believe a similar approach will be advantageous for single component systems
Nanostructured drugs embedded into a polymeric matrix: Vinpocetine/PVP hybrids investigated by Debye function analysis
No full textMicrocrystalline vinpocetine, coground with cross-linked polyvinylpyrrolidone, affords hybrids containing nanosized drug nanocrystals, the size and size distributions of which depend on milling times and drug-to-polymer weight ratios. Using an innovative approach to microstructural characterization, we analyzed wide-angle X-ray total scattering data by the Debye function analysis and demonstrated the possibility to characterize pharmaceutical solid dispersions obtaining a reliable quantitative view of the physicochemical status of the drug dispersed in an amorphous carrier. The microstructural properties derived therefrom have been successfully employed in reconciling the enigmatic difference in behavior between in vitro and in vivo solubility
tests performed on nanosized vinpocetine embedded in a polymeric matrix
Polymer-Assisted Grinding, a Versatile Method for Polymorph Control of Cocrystallization
No full textDespite the great interest that cocrystals
are currently gaining
for their application to the design of new supramolecular structures
with desired functional properties, studies concerning new experimental
strategies capable of controlling polymorphism phenomena of a given
system are scarcely reported. We propose herein the use of polymer-assisted
grinding (POLAG) as a new method for the selective control of the
product polymorphic form in a mechanochemical cocrystallization reaction.
Specifically, to the model system selected in this study formed by
caffeine and glutaric acid, we demonstrate that the polymorphic outcome
can be controlled by modifying the number of monomer units of the
catalyst from the shortest dimer to a polymer with chains of approximately
1000 units. The characteristics of each polymorphic form were investigated
by low-dose high-resolution TEM, and the mechanistic aspects of the
cocrystal formation were studied through a series of ex situ and interconversion
experiments. The results suggest that for this system the modification
of the catalyst chain length and, consequently, modification of polarity
drives cocrystal formation toward the more stable polymorph. The approach
proposed in this paper can be readily applied to each system, where
polarity is the main issue for polymorph control without the risk
of solvate formation
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
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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