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1.
PLoS Pathog ; 19(3): e1011259, 2023 03.
Artigo em Inglês | MEDLINE | ID: mdl-36940224

RESUMO

BACKGROUND: The TprK protein of the syphilis agent, Treponema pallidum subsp. pallidum (T. pallidum), undergoes antigenic variation in seven discrete variable (V) regions via non-reciprocal segmental gene conversion. These recombination events transfer information from a repertoire of 53 silent chromosomal donor cassettes (DCs) into the single tprK expression site to continually generate TprK variants. Several lines of research developed over the last two decades support the theory that this mechanism is central to T. pallidum's ability for immune avoidance and persistence in the host. Structural and modeling data, for example, identify TprK as an integral outer membrane porin with the V regions exposed on the pathogen's surface. Furthermore, infection-induced antibodies preferentially target the V regions rather than the predicted ß-barrel scaffolding, and sequence variation abrogates the binding of antibodies elicited by antigenically different V regions. Here, we engineered a T. pallidum strain to impair its ability to vary TprK and assessed its virulence in the rabbit model of syphilis. PRINCIPAL FINDINGS: A suicide vector was transformed into the wild-type (WT) SS14 T. pallidum isolate to eliminate 96% of its tprK DCs. The resulting SS14-DCKO strain exhibited an in vitro growth rate identical to the untransformed strain, supporting that the elimination of the DCs did not affect strain viability in absence of immune pressure. In rabbits injected intradermally with the SS14-DCKO strain, generation of new TprK sequences was impaired, and the animals developed attenuated lesions with a significantly reduced treponemal burden compared to control animals. During infection, clearance of V region variants originally in the inoculum mirrored the generation of antibodies to these variants, although no new variants were generated in the SS14-DCKO strain to overcome immune pressure. Naïve rabbits that received lymph node extracts from animals infected with the SS14-DCKO strain remained uninfected. CONCLUSION: These data further support the critical role of TprK in T. pallidum virulence and persistence during infection.


Assuntos
Sífilis , Animais , Coelhos , Treponema pallidum , Treponema , Variação Antigênica/genética , Anticorpos
2.
J Infect Dis ; 229(2): 403-412, 2024 Feb 14.
Artigo em Inglês | MEDLINE | ID: mdl-37486790

RESUMO

BACKGROUND: Rhinovirus (RV) infections can progress from the upper (URT) to lower (LRT) respiratory tract in immunocompromised individuals, causing high rates of fatal pneumonia. Little is known about how RV evolves within hosts during infection. METHODS: We sequenced RV complete genomes from 12 hematopoietic cell transplant patients with infection for up to 190 days from both URT (nasal wash, NW) and LRT (bronchoalveolar lavage, BAL). Metagenomic and amplicon next-generation sequencing were used to track the emergence and evolution of intrahost single nucleotide variants (iSNVs). RESULTS: Identical RV intrahost populations in matched NW and BAL specimens indicated no genetic adaptation is required for RV to progress from URT to LRT. Coding iSNVs were 2.3-fold more prevalent in capsid over nonstructural genes. iSNVs modeled were significantly more likely to be found in capsid surface residues, but were not preferentially located in known RV-neutralizing antibody epitopes. Newly emergent, genotype-matched iSNV haplotypes from immunocompromised individuals in 2008-2010 could be detected in Seattle-area community RV sequences in 2020-2021. CONCLUSIONS: RV infections in immunocompromised hosts can progress from URT to LRT with no specific evolutionary requirement. Capsid proteins carry the highest variability and emergent mutations can be detected in other, including future, RV sequences.


Assuntos
Infecções por Enterovirus , Transplante de Células-Tronco Hematopoéticas , Humanos , Proteínas do Capsídeo/genética , Capsídeo , Rhinovirus/genética , Mutação
3.
J Infect Dis ; 229(3): 866-875, 2024 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-37769216

RESUMO

BACKGROUND: The incidence of syphilis continues to increase in the United States, yet little is known about Treponema pallidum genomic epidemiology within American metropolitan areas. METHODS: We performed whole-genome sequencing and tprK deep sequencing of 28 T. pallidum-containing specimens, collected mostly from remnant Aptima swab specimens from 24 individuals from Seattle Sexual Health Clinic during 2021-2022. RESULTS: All 12 individuals infected with Nichols-lineage strains were men who have sex with men, while a specific SS14 cluster (mean, 0.33 single-nucleotide variant) included 1 man who has sex with women and 5 women. All T. pallidum strains sequenced were azithromycin resistant via 23S ribosomal RNA A2058G mutation. Identical T. pallidum genomic sequences were found in pharyngeal and rectal swab specimens taken concurrently from the same individuals. The tprK sequences were less variable between patient-matched specimens and between epidemiologically linked clusters. We detected a 528-base pair deletion in the tprK donor site locus, eliminating 9 donor sites, in T. pallidum genomes of 3 individuals with secondary syphilis, associated with diminution of TprK diversity. CONCLUSIONS: We developed an end-to-end workflow for public health genomic surveillance of T. pallidum from remnant Aptima swab specimens. tprK sequencing may assist in linking cases beyond routine T. pallidum genome sequencing. T. pallidum strains with deletions in tprK donor sites currently circulate and are associated with diminished TprK antigenic diversity.


Assuntos
Minorias Sexuais e de Gênero , Sífilis , Masculino , Feminino , Humanos , Treponema pallidum/genética , Homossexualidade Masculina , Sequência de Aminoácidos , Sífilis/epidemiologia , Variação Antigênica , Genômica
4.
J Chem Phys ; 160(16)2024 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-38661197

RESUMO

The focus of our study is an in-depth investigation of the quantum effects associated with the surface tension and other thermodynamic properties of nanoscopic liquid drops. The behavior of drops of quantum Lennard-Jones fluids is investigated with path-integral Monte Carlo simulations, and the test-area method is used to determine the surface tension of the spherical vapor-liquid interface. As the thermal de Broglie wavelength, λB, becomes more significant, the average density of the liquid drop decreases, with the drop becoming mechanically unstable at large wavelengths. As a consequence, the surface tension is found to decrease monotonically with λB, vanishing altogether for dominant quantum interactions. Quantum effects can be significant, leading to values that are notably lower than the classical thermodynamic limit, particularly for smaller drops. For planar interfaces (with infinite periodicity in the direction parallel to the interface), quantum effects are much less significant with the same values of λB but are, nevertheless, consequential for values representative of hydrogen or helium-4 at low temperatures corresponding to vapor-liquid coexistence. Large quantum effects are found for small drops of molecules with quantum interactions corresponding to water, ethane, methanol, and carbon dioxide, even at ambient conditions. The notable decrease in the density and tension has important consequences in reducing the Gibbs free-energy barrier of a nucleating cluster, enhancing the nucleation kinetics of liquid drops and of bubble formation. This implies that drops would form at a much greater rate than is predicted by classical nucleation theory.

5.
J Chem Phys ; 159(2)2023 Jul 14.
Artigo em Inglês | MEDLINE | ID: mdl-37435943

RESUMO

The ability to predict transport properties of fluids, such as the self-diffusion coefficient and viscosity, has been an ongoing effort in the field of molecular modeling. While there are theoretical approaches to predict the transport properties of simple systems, they are typically applied in the dilute gas regime and are not directly applicable to more complex systems. Other attempts to predict transport properties are performed by fitting available experimental or molecular simulation data to empirical or semi-empirical correlations. Recently, there have been attempts to improve the accuracy of these fittings through the use of Machine-Learning (ML) methods. In this work, the application of ML algorithms to represent the transport properties of systems comprising spherical particles interacting via the Mie potential is investigated. To this end, the self-diffusion coefficient and shear viscosity of 54 potentials are obtained at different regions of the fluid-phase diagram. This data set is used together with three ML algorithms, namely, k-Nearest Neighbors (KNN), Artificial Neural Network (ANN), and Symbolic Regression (SR), to find correlations between the parameters of each potential and the transport properties at different densities and temperatures. It is shown that ANN and KNN perform to a similar extent, followed by SR, which exhibits larger deviations. Finally, the application of the three ML models to predict the self-diffusion coefficient of small molecular systems, such as krypton, methane, and carbon dioxide, is demonstrated using molecular parameters derived from the so-called SAFT-VR Mie equation of state [T. Lafitte et al. J. Chem. Phys. 139, 154504 (2013)] and available experimental vapor-liquid coexistence data.

6.
J Chem Phys ; 159(19)2023 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-37982487

RESUMO

There is an ever increasing use of local density dependent potentials in the mesoscale modeling of complex fluids. Questions remain, though, about the dependence of the thermodynamic and structural properties of such systems on the cutoff distance used to calculate these local densities. These questions are particularly acute when it comes to the stability and structure of the vapor/liquid interface. In this article, we consider local density dependent potentials derived from an underlying van der Waals equation of state. We use simulation and density functional theory to examine how the bulk thermodynamic and interfacial properties vary with the cutoff distance, rc, used to calculate the local densities. We show quantitatively how the simulation results for bulk thermodynamic properties and vapor-liquid equilibrium approach the van der Waals limit as rc increases and demonstrate a scaling law for the radial distribution function in the large rc limit. We show that the vapor-liquid interface is stable with a well-defined surface tension and that the interfacial density profile is oscillatory, except for temperatures close to critical. Finally, we show that in the large rc limit, the interfacial tension is proportional to rc and, therefore, unlike the bulk thermodynamic properties, does not approach a constant value as rc increases. We believe that these results give new insights into the properties of local density dependent potentials, in particular their unusual interfacial behavior, which is relevant for modeling complex fluids in soft matter.

7.
J Chem Phys ; 159(5)2023 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-37526165

RESUMO

For industrial applications of self-assembled wormlike micelles, measurement and characterization of a micellar material's microstructure and rheology are paramount for the development and deployment of new high-performing and cost-effective formulations. Within this workflow, there are significant bottlenecks associated with experimental delays and a lack of transferability of results from one chemistry to another. In this work, we outline a process to predict microscopic and thermodynamic characteristics of wormlike micelles directly from rheological data by combining a more robust and efficient fitting algorithm with a recently published constitutive model called the Toy Shuffling model [J. D. Peterson and M. E. Cates, J. Rheol. 64, 1465-1496 (2020) and J. D. Peterson and M. E. Cates, J. Rheol. 65, 633-662 (2021)]. To support this work, linear rheology measurements were taken for 143 samples comprising a common base formulation of commercial sodium lauryl ether sulfate, cocamidopropyl betaine, and salt (NaCl). The steady state zero shear viscosity evident in linear rheology was measured in duplicate via direct steady and oscillatory shear experiments. Fitting the collected data to the model, we found trends in the microstructural and thermodynamic characteristics that agree with molecular dynamics simulations. These trends validate our new perspective on the parameters that inform the study of the relationship between chemical formulation and rheology. This work, when implemented at scale, can potentially be used to inform and test strategies for predicting self-assembled micellar structures based on chemical formulation.

8.
Int J Mol Sci ; 22(9)2021 Apr 27.
Artigo em Inglês | MEDLINE | ID: mdl-33925417

RESUMO

Craniofacial neuropathic pain affects millions of people worldwide and is often difficult to treat. Two key mechanisms underlying this condition are a loss of the negative control exerted by inhibitory interneurons and an early microglial reaction. Basic features of these mechanisms, however, are still poorly understood. Using the chronic constriction injury of the infraorbital nerve (CCI-IoN) model of neuropathic pain in mice, we have examined the changes in the expression of GAD, the synthetic enzyme of GABA, and GlyT2, the membrane transporter of glycine, as well as the microgliosis that occur at early (5 days) and late (21 days) stages post-CCI in the medullary and upper spinal dorsal horn. Our results show that CCI-IoN induces a down-regulation of GAD at both postinjury survival times, uniformly across the superficial laminae. The expression of GlyT2 showed a more discrete and heterogeneous reduction due to the basal presence in lamina III of 'patches' of higher expression, interspersed within a less immunoreactive 'matrix', which showed a more substantial reduction in the expression of GlyT2. These patches coincided with foci lacking any perceptible microglial reaction, which stood out against a more diffuse area of strong microgliosis. These findings may provide clues to better understand the neural mechanisms underlying allodynia in neuropathic pain syndromes.


Assuntos
Microglia/metabolismo , Neuralgia/etiologia , Corno Dorsal da Medula Espinal/metabolismo , Animais , Comportamento Animal , Proteínas de Ligação ao Cálcio/metabolismo , Densitometria , Modelos Animais de Doenças , Proteínas da Membrana Plasmática de Transporte de Glicina/metabolismo , Hiperalgesia/etiologia , Masculino , Nervo Maxilar/lesões , Camundongos Endogâmicos C57BL , Proteínas dos Microfilamentos/metabolismo , Microglia/patologia , Corno Dorsal da Medula Espinal/patologia , Núcleo Inferior Caudal do Nervo Trigêmeo/metabolismo , Núcleo Inferior Caudal do Nervo Trigêmeo/patologia
9.
J Chem Phys ; 153(23): 234901, 2020 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-33353329

RESUMO

The Ewald method has been the cornerstone in molecular simulations for modeling electrostatic interactions of charge-stabilized many-body systems. In the late 1990s, Wolf and collaborators developed an alternative route to describe the long-range nature of electrostatic interactions; from a computational perspective, this method provides a more efficient and straightforward way to implement long-range electrostatic interactions than the Ewald method. Despite these advantages, the validity of the Wolf potential to account for the electrostatic contribution in charged fluids remains controversial. To alleviate this situation, in this contribution, we implement the Wolf summation method to both electrolyte solutions and charged colloids with moderate size and charge asymmetries in order to assess the accuracy and validity of the method. To this end, we verify that the proper selection of parameters within the Wolf method leads to results that are in good agreement with those obtained through the standard Ewald method and the theory of integral equations of simple liquids within the so-called hypernetted chain approximation. Furthermore, we show that the results obtained with the original Wolf method do satisfy the moment conditions described by the Stillinger-Lovett sum rules, which are directly related to the local electroneutrality condition and the electrostatic screening in the Debye-Hückel regime. Hence, the fact that the solution provided by the Wolf method satisfies the first and second moments of Stillinger-Lovett proves, for the first time, the reliability of the method to correctly incorporate the electrostatic contribution in charge-stabilized fluids. This makes the Wolf method a powerful alternative compared to more demanding computational approaches.

10.
J Headache Pain ; 21(1): 96, 2020 Aug 06.
Artigo em Inglês | MEDLINE | ID: mdl-32762640

RESUMO

BACKGROUND: Stimulation of the occipital or trigeminal nerves has been successfully used to treat chronic refractory neurovascular headaches such as migraine or cluster headache, and painful neuropathies. Convergence of trigeminal and occipital sensory afferents in the 'trigeminocervical complex' (TCC) from cutaneous, muscular, dural, and visceral sources is a key mechanism for the input-induced central sensitization that may underlie the altered nociception. Both excitatory (glutamatergic) and inhibitory (GABAergic and glycinergic) mechanisms are involved in modulating nociception in the spinal and medullary dorsal horn neurons, but the mechanisms by which nerve stimulation effects occur are unclear. This study was aimed at investigating the acute effects of electrical stimulation of the greater occipital nerve (GON) on the responses of neurons in the TCC to the mechanical stimulation of the vibrissal pad. METHODS: Adult male Wistar rats were used. Neuronal recordings were obtained in laminae II-IV in the TCC in control, sham and infraorbital chronic constriction injury (CCI-IoN) animals. The GON was isolated and electrically stimulated. Responses to the stimulation of vibrissae by brief air pulses were analyzed before and after GON stimulation. In order to understand the role of the neurotransmitters involved, specific receptor blockers of NMDA (AP-5), GABAA (bicuculline, Bic) and Glycine (strychnine, Str) were applied locally. RESULTS: GON stimulation produced a facilitation of the response to light facial mechanical stimuli in controls, and an inhibition in CCI-IoN cases. AP-5 reduced responses to GON and vibrissal stimulation and blocked the facilitation of GON on vibrissal responses found in controls. The application of Bic or Str significantly reduced the facilitatory effect of GON stimulation on the response to vibrissal stimulation in controls. However, the opposite effect was found when GABAergic or Glycinergic transmission was prevented in CCI-IoN cases. CONCLUSIONS: GON stimulation modulates the responses of TCC neurons to light mechanical input from the face in opposite directions in controls and under CCI-IoN. This modulation is mediated by GABAergic and Glycinergic mechanisms. These results will help to elucidate the neural mechanisms underlying the effectiveness of nerve stimulation in controlling painful craniofacial disorders, and may be instrumental in identifying new therapeutic targets for their prevention and treatment.


Assuntos
Nervos Espinhais/fisiopatologia , Nervo Trigêmeo/fisiopatologia , Neuralgia do Trigêmeo/fisiopatologia , Vibrissas , Animais , Cefaleia Histamínica , Estimulação Elétrica , Cabeça , Transtornos da Cefaleia , Masculino , Transtornos de Enxaqueca , Neurônios/fisiologia , Nociceptividade , Ratos , Ratos Sprague-Dawley , Ratos Wistar
11.
Cereb Cortex ; 28(8): 2846-2853, 2018 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-29106544

RESUMO

Androgenization in adult natal women, as in transsexual men (TM), affects brain cortical thickness and the volume of subcortical structures. In order to understand the mechanism underlying these changes we have developed an adult female rat model of androgenization. Magnetic resonance imaging and spectroscopy were used to monitor brain volume changes, white matter microstructure and ex vivo metabolic profiles over 32 days in androgenized and control subjects. Supraphysiological doses of testosterone prevents aging decrease of fractional anisotropy values, decreased general cortical volume and the relative concentrations of glutamine (Gln) and myo-Inositol (mI). An increase in the N-acetylaspartate (NAA)/mI ratio was detected d. Since mI and Gln are astrocyte markers and osmolytes, we suspect that the anabolic effects of testosterone change astrocyte osmolarity so as to extrude Mi and Gln from these cells in order to maintain osmotic homeostasis. This mechanism could explain the brain changes observed in TM and other individuals receiving androgenic anabolic steroids.


Assuntos
Encéfalo/metabolismo , Encéfalo/patologia , Metaboloma/fisiologia , Virilismo/patologia , Animais , Anisotropia , Encéfalo/diagnóstico por imagem , Encéfalo/efeitos dos fármacos , Feminino , Lateralidade Funcional , Ácido Glutâmico/metabolismo , Glicina/metabolismo , Inositol/metabolismo , Imageamento por Ressonância Magnética , Ratos , Ratos Wistar , Testosterona/sangue , Propionato de Testosterona/farmacologia , Trítio/metabolismo , Virilismo/sangue , Virilismo/diagnóstico por imagem , Substância Branca/patologia
12.
Proc Natl Acad Sci U S A ; 113(35): 9699-703, 2016 08 30.
Artigo em Inglês | MEDLINE | ID: mdl-27540114

RESUMO

Materials comprising porous structures, often in the form of interconnected concave cavities, are typically assembled from convex molecular building blocks. The use of nanoparticles with a characteristic nonconvex shape provides a promising strategy to create new porous materials, an approach that has been recently used with cagelike molecules to form remarkable liquids with "scrabbled" porous cavities. Nonconvex mesogenic building blocks can be engineered to form unique self-assembled open structures with tunable porosity and long-range order that is intermediate between that of isotropic liquids and of crystalline solids. Here we propose the design of highly open liquid-crystalline structures from rigid nanorings with ellipsoidal and polygonal geometry. By exploiting the entropic ordering characteristics of athermal colloidal particles, we demonstrate that high-symmetry nonconvex rings with large internal cavities interlock within a 2D layered structure leading to the formation of distinctive liquid-crystalline smectic phases. We show that these smectic phases possess uniquely high free volumes of up to ∼95%, a value significantly larger than the 50% that is typically achievable with smectic phases formed by more conventional convex rod- or disklike mesogenic particles.

13.
Stroke ; 49(9): 2163-2172, 2018 09.
Artigo em Inglês | MEDLINE | ID: mdl-30018160

RESUMO

Background and Purpose- Recanalization with tPA (tissue-type plasminogen activator) is the only pharmacological therapy available for patients with ischemic stroke. However, the percentage of patients who may receive this therapy is limited by the risk of hemorrhagic transformation (HT)-the main complication of ischemic stroke. Our aim is to establish whether iron overload affects HT risk, to identify mechanisms that could help to select patients and to prevent this devastating complication. Methods- Mice fed with control or high-iron diet were subjected to thromboembolic stroke, with or without tPA therapy at different times after occlusion. Blood samples were collected for determination of malondialdehyde, matrix metalloproteinases, and fibronectin. Brain samples were collected 24 hours after occlusion to determine brain infarct and edema size, hemorrhage extension, IgG extravasation, and inflammatory and oxidative markers (neutrophil infiltration, 4-hydroxynonenal, and matrix metalloproteinase-9 staining). Results- Despite an increased rate of recanalization, iron-overload mice showed less neuroprotection after tPA administration. Importantly, iron overload exacerbated the risk of HT after early tPA administration, accelerated ischemia-induced serum matrix metalloproteinase-9 increase, and enhanced basal serum lipid peroxidation. High iron increased brain lipid peroxidation at most times and neutrophil infiltration at the latest time studied. Conclusions- Our data showing that iron overload increases the death of the compromised tissues, accelerates the time of tPA-induced reperfusion, and exacerbates the risk of HT may have relevant clinical implications for a safer thrombolysis. Patients with stroke with iron overload might be at high risk of HT after fibrinolysis, and, therefore, clinical studies must be performed to confirm our results.


Assuntos
Fibrinolíticos/efeitos adversos , Infarto da Artéria Cerebral Média/tratamento farmacológico , Hemorragias Intracranianas/induzido quimicamente , Sobrecarga de Ferro/metabolismo , Tromboembolia/tratamento farmacológico , Ativador de Plasminogênio Tecidual/efeitos adversos , Aldeídos/metabolismo , Animais , Barreira Hematoencefálica/metabolismo , Modelos Animais de Doenças , Imunoglobulina G/metabolismo , Infarto da Artéria Cerebral Média/complicações , Hemorragias Intracranianas/etiologia , Sobrecarga de Ferro/complicações , Ferro da Dieta , Peroxidação de Lipídeos , Metaloproteinase 9 da Matriz/metabolismo , Camundongos , Infiltração de Neutrófilos , Estresse Oxidativo , Acidente Vascular Cerebral/complicações , Acidente Vascular Cerebral/tratamento farmacológico , Tromboembolia/complicações
14.
J Chem Phys ; 148(16): 164701, 2018 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-29716204

RESUMO

A molecular simulation study of binary mixtures of hard spherocylinders (HSCs) and hard spheres (HSs) confined between two structureless hard walls is presented. The principal aim of the work is to understand the effect of the presence of hard spheres on the entropically driven surface nematization of hard rod-like particles at surfaces. The mixtures are studied using a constant normal-pressure Monte Carlo algorithm. The surface adsorption at different compositions is examined in detail. At moderate hard-sphere concentrations, preferential adsorption of the spheres at the wall is found. However, at moderate to high pressure (density), we observe a crossover in the adsorption behavior with nematic layers of the rods forming at the walls leading to local demixing of the system. The presence of the spherical particles is seen to destabilize the surface nematization of the rods, and the degree of demixing increases on increasing the hard-sphere concentration.

15.
Appl Opt ; 57(12): 3119-3125, 2018 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-29714345

RESUMO

We consider the propagation of electromagnetic waves throughout a nanocomposite structurally chiral medium consisting of metallic nanoballs randomly dispersed in a structurally chiral material whose dielectric properties can be represented by a resonant effective uniaxial tensor. It is found that an omnidirectional narrow pass band and two omnidirectional narrow band gaps are created in the blue optical spectrum for right and left circularly polarized light, as well as narrow reflection bands for right circularly polarized light that can be controlled by varying the light incidence angle and the filling fraction of metallic inclusions.

16.
Langmuir ; 33(42): 11257-11263, 2017 10 24.
Artigo em Inglês | MEDLINE | ID: mdl-28862872

RESUMO

ReaxFF-based molecular dynamics simulations are used in this work to study the effect of the polarity of adsorbed molecules in the liquid phase on the structure and polarization of hematite (α-Fe2O3). We compared the adsorption of organic molecules with different polarities on a rigid hematite surface and on a flexible and polarizable surface. We show that the displacements of surface atoms and surface polarization in a flexible hematite model are proportional to the adsorbed molecule's polarity. The increase in electrostatic interactions resulting from charge transfer in the outermost solid atoms in a flexible hematite model results in better-defined adsorbed layers that are less ordered than those obtained assuming a rigid solid. These results suggest that care must be taken when parametrizing empirical transferable force fields because the calculated charges on a solid slab in vacuum may not be representative of a real system, especially when the solid is in contact with a polar liquid.

17.
Soft Matter ; 13(10): 2085-2098, 2017 Mar 08.
Artigo em Inglês | MEDLINE | ID: mdl-28225134

RESUMO

We investigate the phase behaviour and self-assembly of convex spherical caps using Monte Carlo simulations. This model is used to represent the main features observed in experimental colloidal particles with mushroom-cap shape [Riley et al., Langmuir, 2010, 26, 1648]. The geometry of this non-centrosymmetric convex model is fully characterized by the aspect ratio χ* defined as the spherical cap height to diameter ratio. We use NPT Monte Carlo simulations combined with free energy calculations to determine the most stable crystal structures and the phase behaviour of convex spherical caps with different aspect ratios. We find a variety of crystal structures at each aspect ratio, including plastic and dimer-based crystals; small differences in chemical potential between the structures with similar morphology suggest that convex spherical caps have the tendency to form polycrystalline phases rather than crystallising into a single uniform structure. With the exception of plastic crystals observed at large aspect ratios (χ* > 0.75), crystallisation kinetics seem to be too slow, hindering the spontaneous formation of ordered structures. As an alternative, we also present a study of directing the self-assembly of convex spherical caps via sedimentation onto solid substrates. This study contributes to show how small changes to particle shape can significantly alter the self-assembly of crystal structures, and how a simple gravity field and a template can substantially enhance the process.

18.
Soft Matter ; 13(45): 8618-8624, 2017 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-29114688

RESUMO

The fabrication of chiral structures using achiral building blocks is a fundamental problem that remains a challenge in materials science. In this work we present a molecular dynamics simulation study of nonconvex polygonal platelets, interacting via soft-repulsive interactions, that are confined in two-dimensional space. These particle models are designed to promote, even at moderate densities, a natural offset displacement between the edges of neighbouring particles. In particular we demonstrate that nonconvex platelets exhibit macroscopic chiral symmetry breaking when the symmetry of the particles equals (or is multiple of) the number of nearest neighbours in the condensed crystalline phase, corresponding to the situation of platelets with 4-, 6-, and 12-fold symmetries.

19.
Int J Mol Sci ; 19(1)2017 Dec 27.
Artigo em Inglês | MEDLINE | ID: mdl-29280965

RESUMO

Glutamate is the most common neurotransmitter in both the central and the peripheral nervous system. Glutamate is present in all types of neurons in sensory ganglia, and is released not only from their peripheral and central axon terminals but also from their cell bodies. Consistently, these neurons express ionotropic and metabotropic receptors, as well as other molecules involved in the synthesis, transport and release of the neurotransmitter. Primary sensory neurons are the first neurons in the sensory channels, which receive information from the periphery, and are thus key players in the sensory transduction and in the transmission of this information to higher centers in the pathway. These neurons are tightly enclosed by satellite glial cells, which also express several ionotropic and metabotropic glutamate receptors, and display increases in intracellular calcium accompanying the release of glutamate. One of the main interests in our group has been the study of the implication of the peripheral nervous system in sensory-dependent plasticity. Recently, we have provided novel evidence in favor of morphological changes in first- and second-order neurons of the trigeminal system after sustained alterations of the sensory input. Moreover, these anatomical changes are paralleled by several molecular changes, among which those related to glutamatergic neurotransmission are particularly relevant. In this review, we will describe the state of the art of the glutamatergic system in sensory ganglia and its involvement in input-dependent plasticity, a fundamental ground for advancing our knowledge of the neural mechanisms of learning and adaptation, reaction to injury, and chronic pain.


Assuntos
Gânglios Sensitivos/fisiologia , Ácido Glutâmico/metabolismo , Plasticidade Neuronal , Células Receptoras Sensoriais/metabolismo , Animais , Humanos , Ácido Caínico/metabolismo , N-Metilaspartato/metabolismo , Neuralgia/metabolismo , Receptores de AMPA/metabolismo , Receptores de Ácido Caínico/metabolismo , Receptores de Glutamato Metabotrópico/metabolismo , Transmissão Sináptica , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiônico/metabolismo
20.
Langmuir ; 32(16): 3907-16, 2016 04 26.
Artigo em Inglês | MEDLINE | ID: mdl-27052957

RESUMO

A mild and simple way to prepare stable aqueous colloidal suspensions of composite particles made of a cellulosic material (Sigmacell cellulose) and multiwalled carbon nanotubes (MWCNTs) is reported. These suspensions can be dried and redispersed in water at pH 10.5. Starting with rather crude initial materials, commercial Sigmacell cellulose and MWCNTs, a significant fraction of composite dispersed in water could be obtained. The solid composites and their colloidal suspensions were characterized by electronic microscopy, thermal analyses, FTIR and Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and light scattering. The composite particles consist of tenuous aggregates of CNTs and cellulose, several hundred nanometers large, and are composed of 55 wt % cellulose and 45 wt % CNTs. Such particles were shown to stabilize cyclohexane-in-water emulsions. The adsorption and the elasticity of the layer they form at interface were characterized by the pendant drop method. The stability of the oil-in-water emulsions was attributed to the formation of an elastic network of composite particles at interface. Cyclohexane droplet diameters could be tuned from 20 to 100 µm by adjusting the concentration of composite particles. This behavior was attributed to the limited coalescence phenomenon, just as expected for Pickering emulsions. Interestingly, cyclohexane droplets were stable over time and sustained pH modifications over a wide range, although acidic pH induced accelerated creaming. This study points out the possibility of combining crude cellulose and MWCNTs through a simple process to obtain colloidal systems of interest for the design of functional conductive materials.

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