1,721,023 research outputs found
Molecular-level characterization of the interaction between monolayer-protected Au nanoparticles and model lipid membranes and proteins
No full textIn this thesis we study the interactions of monolayer-protected gold nanoparticles with proteins and model lipid membranes. Gold nanoparticles are a paradigm in biological applications of nanomaterials, thanks to their peculiar physico-chemical properties; among these, the possibility to bind different kinds of molecules (ligands) to gold atoms in clusters via thiol bonds is particularly important for biomedical use of nanoparticles. In fact, the ligand shell is what nanoparticles expose to the biological environment in which they are used. In in vivo applications, nanoparticles come in contact with many biological molecules before being delivered to cells, which are the target of most of biological applications of nanoparticles. Among them, proteins are particularly relevant since they can irreversibly bind to nanoparticles, thus changing the surface they expose to the biological environment.
In this thesis we use molecular dynamics simulations to study how different ligands can influence the interaction of nanoparticles with the most abundant protein in blood, human serum albumin. We test two zwitterionic ligands with
different hydrophobic content and we find that ligand conformation, which is affected by hydrophobicity, promotes different adhesion strengths between nanoparticles and albumin. We then study the interaction of nanoparticles with a model cell membrane, the first barrier they encounter in cell-targeted applications. We use molecular dynamics simulations to study the mechanism of interaction between a negatively charged nanoparticle and a neutral lipid membrane. We find that the process develops in three stages which involves the adsorption on the membrane surface and the progressive penetration in
the membrane core of the nanoparticle. Finally, we study the influence of the sign of the charge on nanoparticles on their interaction with a model membrane.
We use experiments of fluorescent dye-leakage from neutral liposomes to probe the effect of positively and negatively charged nanoparticles on the model membrane of the lipid vesicles. In particular, we find that both anionic and cationic nanoparticles behave similarly in the interaction with a zwitterionic lipid membrane. We use molecular dynamics simulations to support
the experimental findings and observe that anionic and cationic nanoparticles share similar interaction processes and energetics
Local Enhancement of Lipid Membrane Permeability Induced by Irradiated Gold Nanoparticles
No full textPhotothermal therapies are based on the optical excitation of plasmonic nanoparticles in the biological environment. The effects of the irradiation on the biological medium depend critically on the heat transfer process at the nanoparticle interface, on the temperature reached by the tissues, as well as on the spatial extent of temperature gradients. Unfortunately, both the temperature and its biological effects are difficult to be probed experimentally at the molecular scale. Here, we approach this problem using nonequilibrium molecular dynamics simulations. We focus on photoporation, a photothermal application based on the irradiation of gold nanoparticles by single, short-duration laser pulses. The nanoparticles, stably bound to cell membranes, convert the radiation into heat, inducing transient changes of membrane permeability. We make a quantitative prediction of the temperature gradient around the nanoparticle upon irradiation by typical experimental laser fluences. Water permeability is locally enhanced around the nanoparticle, in an annular region that extends only a few nanometers from the nanoparticle interface. We correlate the local enhancement of permeability at the nanoparticle-lipid interface to the temperature inhomogeneities of the membrane and to the consequent availability of free volume pockets within the membrane core
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
Monolayer-Protected Anionic Au Nanoparticles Walk into Lipid Membranes Step by Step
No full textThe
design of ligand-protected metal nanoparticles (NPs) with biomedical
applications relies on the understanding, at the molecular level,
of their interactions with cell membranes. Here we study, via unbiased
coarse grained molecular dynamics simulations, the kinetics and the
thermodynamics of the interaction between anionic ligand-protected
gold NPs and model lipid membranes. The NP–membrane interaction
is a three-step process: electrostatics-driven adhesion to the membrane
surface, hydrophobic contact and final embedding in the membrane core
via anchoring of the charged ligands to both membrane leaflets. Our
free energy calculations show that anchoring is highly favorable and
not reversible. Furthermore, we show that the interaction pathway
of NPs with random surface arrangement of anionic and hydrophobic
ligands is characterized by two metastable configurations: adsorbed
at the membrane surface, and membrane-embedded. Patched ligand arrangements,
instead, lead to the stabilization of a third, intermediate metastable
configuration, resulting in a much slower kinetics of interaction
with the membrane
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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