1,720,959 research outputs found
Charge and hydrophobicity effects at nano-bio interfaces
No full textGold nanoparticles coated with bio-compatible ligands are promising tools for biomedical applications due their water solubility, bio-compatibility and efficient light-to-heat conversion. In in vivo applications, nanoparticles come in contact with many biological molecules before being delivered to cells. The understanding of the physical and chemical nature of these different nano-bio interfaces is crucial to the rational design of nanoparticles with biomedical applications. The aim of this thesis is to understand, by molecular dynamics, how the composition, hydrophobicity and charge of the ligand shell of a small gold nanoparticle can influence its interaction with i. the solvent, ii. model biological membranes and iii. serum proteins. For each of these relevant interfaces we address a specific case of study.
In our first case study, we address the role of ligands during the transfer of heat from a hot irradiated gold nanoparticle to the surrounding solvent (water). Indeed, in photothermal therapies laser-irradiated resonant nanoparticles convert light into heat, which is then released to the surrounding biological tissues. Nevertheless, no clear physical interpretation is currently available to explain thermal transport at the nanoparticle surface, where a solid-liquid (metal--ligand) interface is coupled to a liquid-liquid (ligand--solvent) interface. We use computer simulations to show that thermal transport at the nanoparticle surface depends on solvent diffusivity at the ligand--solvent interface. Furthermore, using physical indicators of water confinement around hydrophobic and hydrophilic ligands, we develop a predictive model to allow engineering of nanoparticle coatings with the desired thermal conductivities at the nanoscale.
The second case study is the interaction between an anionic, monolayer-protected gold nanoparticle and a model neutral lipid membrane. The cell membrane is the first barrier that gold nanoparticles meet in cell-targeted applications. Here we show how the nanoparticle surface functionalization, and in particular its charge state, can drive the mechanism of interaction with a zwitterionic lipid membrane.
Our third case study is the interaction between a monolayer-protected gold nanoparticle and a serum protein, ubiquitin. Indeed, when nanoparticles circulate in the bloodstream, they come in contact with many serum proteins, which can irreversibly bind to nanoparticles, thus changing the surface they expose to the biological environment. We combine computer simulations and experimental results to study how the ligand charge and composition influence the interaction between nanoparticles and ubiquitin. We find that interfacial water molecules are more bound to the nanoparticles with the largest negative charge and this reflects in an increase of their hydrodynamic radius and in a slower kinetics of binding to the protein during unbiased simulations
Water dynamics affects thermal transport at the surface of hydrophobic and hydrophilic irradiated nanoparticles
Get PDFPlasmonic nanoparticles, such as Au nanoparticles (NPs) coated with bio-compatible ligands, are largely studied and tested in nanomedicine for photothermal therapies. Nevertheless, no clear physical interpretation is currently available to explain thermal transport at the nanoparticle surface, where a solid–liquid (core–ligand) interface is coupled to a liquid–liquid (ligand–solvent) interface. This lack of understanding makes it difficult to control the temperature increase imposed by the irradiated NPs to the surrounding biological environment, and it has so far hindered the rational design of the NP surface chemistry. Here, atomistic molecular dynamics simulations are used to show that thermal transport at the nanoparticle surface depends dramatically on solvent diffusivity at the ligand–solvent interface. Furthermore, using physical indicators of water confinement around hydrophobic and hydrophilic ligands, a predictive model is developed to allow the engineering of NP coatings with the desired thermal conductivities at the nanoscale
Membrane Phase Drives the Assembly of Gold Nanoparticles on Biomimetic Lipid Bilayers
No full textIn recent years, many efforts have been devoted to investigating the interaction of nanoparticles (NPs) with lipid biomimetic interfaces, both from a fundamental perspective aimed at understanding relevant phenomena occurring at the nanobio interface and from an application standpoint for the design of novel lipid-nanoparticle hybrid materials. In this area, recent reports have revealed that citrate-capped gold nanoparticles (AuNPs) spontaneously associate with synthetic phospholipid liposomes and, in some cases, self-assemble on the lipid bilayer. However, the mechanistic and kinetic aspects of this phenomenon are not yet completely understood. In this study, we address the kinetics of interaction of citrate-capped AuNP with lipid vesicles of different rigidities (gel-phase rigid membranes on one side and liquid-crystalline-phase soft membranes on the other). The formation of AuNP-lipid vesicle hybrids was monitored over different time and length scales, combining experiments and simulation. The very first AuNP-membrane contact was addressed through molecular dynamics simulations, while the structure, morphology, and physicochemical features of the final colloidal objects were studied through UV-visible spectroscopy, small-angle X-ray scattering, dynamic light scattering, and cryogenic electron microscopy. Our results highlight that the physical state of the membrane triggers a series of events at the colloidal length scale, which regulate the final morphology of the AuNP-lipid vesicle adducts. For lipid vesicles with soft membranes, the hybrids appear as single vesicles decorated by AuNPs, while more rigid membranes lead to flocculation with AuNPs acting as bridges between vesicles. Overall, these results contribute to a mechanistic understanding of the adhesion or self-assembly of AuNPs onto biomimetic membranes, which is relevant for phenomena occurring at the nano-bio interfaces and provide design principles to control the morphology of lipid vesicle-inorganic NP hybrid systems
Au Nanoparticles in Lipid Bilayers: A Comparison between Atomistic and Coarse-Grained Models
No full textThe
computational study of the interaction between charged, ligand-protected
metal nanoparticles and model lipid membranes has been recently addressed
at both atomistic and coarse-grained levels. Here we compare the performance
of three versions of the coarse-grained Martini force field at describing
the nanoparticle–membrane interaction. The three coarse-grained
models differ in terms of treatment of long-range electrostatic interactions
and water polarizability. The NP–membrane interaction consists
of the transition from a metastable NP–membrane complex, in
which the NP is only partially embedded in the membrane, to a configuration
in which the NP is anchored to both membrane leaflets. All three of
the coarse-grained models provide a description of the metastable
NP–membrane complex that is consistent with that obtained using
an atomistic force field. As for the anchoring transition, the polarizable-water
Martini correctly describes the molecular mechanisms and the energetics
of the transition. The standard version of the Martini model, instead,
underestimates the free-energy barriers for anchoring and does not
completely capture the membrane deformations involved in the transition
process
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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