Browse
Submit Data
Databases
API
Help

Dataset Information

0 Views

0 Connections

0 Citations

0 Reanalyses

0 Downloads

Omics score: 0

Supramolecular Magnetic Brushes: The Impact of Dipolar Interactions on the Equilibrium Structure.

ABSTRACT: The equilibrium structure of supramolecular magnetic filament brushes is analyzed at two different scales. First, we study the density and height distributions for brushes with various grafting densities and chain lengths. We use Langevin dynamics simulations with a bead-spring model that takes into account the cross-links between the surface of the ferromagnetic particles, whose magnetization is characterized by a point dipole. Magnetic filament brushes are shown to be more compact near the substrate than nonmagnetic ones, with a bimodal height distribution for large grafting densities. This latter feature makes them also different from brushes with electric dipoles. Next, in order to explain the observed behavior at the filament scale, we introduce a graph theory analysis to elucidate for the first time the structure of the brush at the scale of individual beads. It turns out that, in contrast to nonmagnetic brushes, in which the internal structure is determined by random density fluctuations, magnetic forces introduce a certain order in the system. Because of their highly directional nature, magnetic dipolar interactions prevent some of the random connections to be formed. On the other hand, they favor a higher connectivity of the chains' free and grafted ends. We show that this complex dipolar brush microstructure has a strong impact on the magnetic response of the brush, as any weak applied field has to compete with the dipole-dipole interactions within the crowded environment.

SUBMITTER: Sanchez PA

PROVIDER: S-EPMC4625168 | biostudies-other | 2015 Oct

REPOSITORIES: biostudies-other

ACCESS DATA

Json Xml

Similar Datasets

The J-triplet Cooper pairing with magnetic dipolar interactions.

Project description:Recently, cold atomic Fermi gases with the large magnetic dipolar interaction have been laser cooled down to quantum degeneracy. Different from electric-dipoles which are classic vectors, atomic magnetic dipoles are quantum-mechanical matrix operators proportional to the hyperfine-spin of atoms, thus provide rich opportunities to investigate exotic many-body physics. Furthermore, unlike anisotropic electric dipolar gases, unpolarized magnetic dipolar systems are isotropic under simultaneous spin-orbit rotation. These features give rise to a robust mechanism for a novel pairing symmetry: orbital p-wave (L = 1) spin triplet (S = 1) pairing with total angular momentum of the Cooper pair J = 1. This pairing is markedly different from both the (3)He-B phase in which J = 0 and the (3)He-A phase in which J is not conserved. It is also different from the p-wave pairing in the single-component electric dipolar systems in which the spin degree of freedom is frozen.

| S-EPMC3340607 | biostudies-other

Change in the magnetic configurations of tubular nanostructures by tuning dipolar interactions.

Project description:We have investigated the equilibrium states of ferromagnetic single wall nanotubes by means of atomistic Monte Carlo simulations of a zig-zag lattice of Heisenberg spins on the surface of a cylinder. The main focus of our study is to determine how the competition between short-range exchange (J) and long-range dipolar (D) interactions influences the low temperature magnetic order of the nanotubes as well as the thermal-driven transitions involved. Apart from the uniform and vortex states occurring for dominant J or D, we find that helical states become stable for a range of intermediate values of γ = D/J that depends on the radius and length of the nanotube. Introducing a vorticity order parameter to better characterize helical and vortex states, we find the pseudo-critical temperatures for the transitions between these states and we establish the magnetic phase diagrams of their stability regions as a function of the nanotube aspect ratio. Comparison of the energy of the states obtained by simulation with those of simpler theoretical structures that interpolate continuously between them, reveals a high degree of metastability of the helical structures that might be relevant for their reversal modes.

| S-EPMC6035215 | biostudies-literature

Equilibrium Model for Supramolecular Copolymerizations.

Project description:The coassembly of different building blocks into supramolecular copolymers provides a promising avenue to control their properties and to thereby expand the potential of supramolecular polymers in applications. However, contrary to covalent copolymerization which nowadays can be well controlled, the control over sequence, polymer length, and morphology in supramolecular copolymers is to date less developed, and their structures are more determined by the delicate balance in binding free energies between the distinct building blocks than by kinetics. Consequently, to rationalize the structures of supramolecular copolymers, a thorough understanding of their thermodynamic behavior is needed. Though this is well established for single-component assemblies and over the past years several models have been proposed for specific copolymerization cases, a generally applicable model for supramolecular cooperative copolymers is still lacking. Here, we provide a generalization of our earlier mass-balance models for supramolecular copolymerizations that encompasses all our earlier models. In this model, the binding free energies of each pair of monomer types in each aggregate type can be set independently. We provide scripts to solve the model numerically for any (co)polymerization of one or two types of monomer into an arbitrary number of distinct aggregate types. We illustrate the applicability of the model on data from literature as well as on new experimental data of triarylamine triamide-based copolymers in three distinct solvents. We show that apart from common properties such as the degree of polymerization and length distributions, our approach also allows us to investigate properties such as the copolymer microstructure, that is, the internal ordering of monomers within the copolymers. Moreover, we show that in some cases, also intriguing analytical approximations can be derived from the mass balances.

| S-EPMC6681264 | biostudies-literature

Sorption Characteristics of Polymer Brushes in Equilibrium with Solvent Vapors.

Project description:While polymer brushes in contact with liquids have been researched intensively, the characteristics of brushes in equilibrium with vapors have been largely unexplored, despite their relevance for many applications, including sensors and smart adhesives. Here, we use molecular dynamics simulations to show that solvent and polymer density distributions for brushes exposed to vapors are qualitatively different from those of brushes exposed to liquids. Polymer density profiles for vapor-solvated brushes decay more sharply than for liquid-solvated brushes. Moreover, adsorption layers of enhanced solvent density are formed at the brush-vapor interface. Interestingly and despite all of these effects, we find that solvent sorption in the brush is described rather well with a simple mean-field Flory-Huggins model that incorporates an entropic penalty for stretching of the brush polymers, provided that parameters such as the polymer-solvent interaction parameter, grafting density, and relative vapor pressure are varied individually.

| S-EPMC7558291 | biostudies-literature

Effect of magnetic dipolar interactions on nanoparticle heating efficiency: implications for cancer hyperthermia.

Project description:Nanostructured magnetic systems have many applications, including potential use in cancer therapy deriving from their ability to heat in alternating magnetic fields. In this work we explore the influence of particle chain formation on the normalized heating properties, or specific loss power (SLP) of both low- (spherical) and high- (parallelepiped) anisotropy ferrite-based magnetic fluids. Analysis of ferromagnetic resonance (FMR) data shows that high particle concentrations correlate with increasing chain length producing decreasing SLP. Monte Carlo simulations corroborate the FMR results. We propose a theoretical model describing dipole interactions valid for the linear response regime to explain the observed trends. This model predicts optimum particle sizes for hyperthermia to about 30% smaller than those previously predicted, depending on the nanoparticle parameters and chain size. Also, optimum chain lengths depended on nanoparticle surface-to-surface distance. Our results might have important implications to cancer treatment and could motivate new strategies to optimize magnetic hyperthermia.

| S-EPMC3791447 | biostudies-literature

Conformational equilibrium in supramolecular chemistry: Dibutyltriuret case.

Project description:The association of substituted benzoates and naphthyridine dianions was used to study the complexation of dibutyltriuret. The title molecule is the simplest molecule able to form two intramolecular hydrogen bonds. The naphthyridine salt was used to break two intramolecular hydrogen bonds at a time while with the use of substituted benzoates the systematic approach to study association was achieved. Both, titrations and variable temperature measurements shed the light on the importance of conformational equilibrium and its influence on association in solution. Moreover, the associates were observed by mass spectrometry. The DFT-based computations for complexes and single bond rotational barriers supports experimental data and helps understanding the properties of multiply hydrogen bonded complexes.

| S-EPMC4660960 | biostudies-literature

Non-equilibrium steady states in supramolecular polymerization.

Project description:Living systems use fuel-driven supramolecular polymers such as actin to control important cell functions. Fuel molecules like ATP are used to control when and where such polymers should assemble and disassemble. The cell supplies fresh ATP to the cytosol and removes waste products to sustain steady states. Artificial fuel-driven polymers have been developed recently, but keeping them in sustained non-equilibrium steady states (NESS) has proven challenging. Here we show a supramolecular polymer that can be kept in NESS, inside a membrane reactor where ATP is added and waste removed continuously. Assembly and disassembly of our polymer is regulated by phosphorylation and dephosphorylation, respectively. Waste products lead to inhibition, causing the reaction cycle to stop. Inside the membrane reactor, however, waste can be removed leading to long-lived NESS conditions. We anticipate that our approach to obtain NESS can be applied to other stimuli-responsive materials to achieve more life-like behaviour.

| S-EPMC5481825 | biostudies-literature

Sensing Magnetic Field and Intermolecular Interactions in Diamagnetic Solution Using Residual Dipolar Couplings of Zephycandidine.

Project description:An unusual residual dipolar coupling of methylene protons was recorded in NMR spectra because aromatic zephycandidine has preferential orientation at the external magnetic field. The observed splitting contains contribution from the dipole-dipole D-coupling and the anisotropic component of J-coupling. Absolute values of the anisotropy of magnetic susceptibility |Δχax| are larger for protic solvents because of the hydrogen-bonding compared to aprotic solvents for which polar and dispersion forces are more important. The energy barrier for the reorientation due to hydrogen-bonding is 1.22 kJ/mol in methanol-d4, 0.85 kJ/mol in ethanol-d6 and 0.87 kJ/mol in acetic acid-d6. In dimethyl sulfoxide-d6, 1.08 kJ/mol corresponds to the interaction of solvent lone pair electrons with π-electrons of zephycandidine. This energy barrier decreases for acetone-d6 which has smaller electric dipole moment. In acetonitrile-d3, there is no energy barrier which suggests solvent ordering around the solute due to the solvent-solvent interactions. The largest absolute values of the magnetic anisotropy are observed for aromatic benezene-d6 and tolune-d8 which have their own preferential orientation and enhance the order in the solution. The magnetic anisotropy of "isolated" zephycandidine, not hindered by intermolecular interaction could be estimated from the correlation between Δχax and cohesion energy density.

| S-EPMC9737189 | biostudies-literature

Effect of the peptide secondary structure on the peptide amphiphile supramolecular structure and interactions.

Project description:Bottom-up fabrication of self-assembled nanomaterials requires control over forces and interactions between building blocks. We report here on the formation and architecture of supramolecular structures constructed from two different peptide amphiphiles. Inclusion of four alanines between a 16-mer peptide and a 16 carbon long aliphatic tail resulted in a secondary structure shift of the peptide headgroups from ? helices to ? sheets. A concomitant shift in self-assembled morphology from nanoribbons to core-shell worm-like micelles was observed by cryogenic transmission electron microscopy (cryo-TEM) and atomic force microscopy (AFM). In the presence of divalent magnesium ions, these a priori formed supramolecular structures interacted in distinct manners, highlighting the importance of peptide amphiphile design in self-assembly.

| S-EPMC3103120 | biostudies-literature

Cucurbit[8]uril directed stimuli-responsive supramolecular polymer brushes for dynamic surface engineering.

Project description:In situ modification of surfaces with thin layers of polymers is of growing interest as adjustment of surface properties can be made on demand. We present herein a supramolecular 'grafting to' polymer brush via the recognition of surface-bound cucurbit[8]uril (CB[8]) rotaxanes towards end-functionalised polyethylene glycol (PEG). This dynamic supramolecular method represents advantages over traditional approaches, which employ covalent bond formation in the 'grafting to' process. Brush properties can be easily modified post-preparation by exchanging the polymers with small molecules in a controlled, reversible manner. Including both redox- and light-responsive guests in a single rotaxane entity, the CB[8]-mediated preparation of the polymer brush offers unique opportunities to switch the brush composition efficiently. While the PEG brushes are well hydrated in a good solvent (water) and stretch away from the surface, they collapse in a poor solvent (toluene), leading to the formation of a dense layer on the surface. This collapsed conformation protects the heteroternary complexes of CB[8]-rotaxane from dissociation and maintains the attachment of polymers on the surface.

| S-EPMC5504464 | biostudies-literature

OmicsDI is part of the ELIXIR infrastructure

OmicsDI is an Elixir interoperability service. Learn more ›

Tweets

OmicsDI Databases

PRIDE
PeptideAtlas
MassIVE
JPOST Repository
Physiome Model Repository

EGA
EVA
ENA
LINCS
PAXDB
Cell Collective

MetaboLights
Metabolomics Workbench
MetabolomeExpress
GNPS
BioModels
FAIRDOMHub

ArrayExpress
dbGaP
ExpressionAtlas
GEO
NODE

Information

Databases
Help
API
Contact us
Code on GitHub
Terms of use
Submit Data