Networks In Aqueous Solutions Research Articles

Mixed Network of Hydrogen Bonds in Aqueous Solutions of 3-Amino-1-propanol: Results of Molecular Dynamic Modeling

The H2O–3-amino-1-propanol (3AP) system at 300 K was studied by molecular dynamics, graph theory, and Delaunay simplex methods. All the molecules were shown to be bound into a three-dimensional network of hydrogen bonds over the entire range of concentrations in the system. The characteristics of the networks and their concentration dependences were determined. The frequency at which the environment of molecules changes is discussed. The results were compared with those for mixed networks in aqueous solutions of 1,3-propanediol and monoethanolamine.

Self-assembly of thyminyl l-tryptophanamide (TrpT) building blocks for the potential development of drug delivery nanosystems

The design, synthesis and characterization of a novel nucleoamino acid derivative based on an l-tryptophanamide functionalised with a thymine nucleobase (named TrpT) is here described. The novel construct’s tendency to self-assemble into supramolecular networks in aqueous solution was demonstrated by dynamic light scattering (DLS), circular dichroism (CD), fluorescence and UV spectroscopic measurements. TrpT nanoaggregates showed good stability (up to 5 h) at 140 µM and proved to comprise species of mean hydrodynamic diameter 330 nm and a homogeneous size distribution; scanning electron microscopy (SEM) analysis further revealed these to be spherical-shaped assemblies. The ability of TrpT nanoaggregates to bind curcumin, selected as a model anticancer drug, was also evaluated and its release was monitored over time by confocal microscopy. Molecular docking studies were performed on both TrpT self-assembly and curcumin-loaded nanoaggregates suggesting that the phytomolecule can be accommodated in the interior of the supramolecular network via hydrophobic (π−π and π-alkyl) interactions; the formation of TrpT-curcumin adducts may improve the polarity of the highly-hydrophobic curcumin with a resulting logP closer to the optimal values expected for a good drug bioavailability, as estimated by the ADMETlab software. Finally, the high stability of TrpT nanoassembly in human serum, and the absence of significant toxic effects on human model cells in a cell viability assay, were also demonstrated. Despite its thymine-based scaffold, TrpT was shown not to bind adenine-bearing nucleic acids, suggesting that this interaction is hindered by its intrinsic propensity to self-assemble in preference to forming A-T base pairings. Instead, TrpT was able to interact with a serum protein such as bovine serum albumin (BSA), known to improve the bloodstream transportation and bioavailability of its cargo. Collectively, our findings support the potential use of TrpT for the development of new drug delivery systems.Graphical abstract

Thermosensitive Hydrogels of BAB Triblock Copolymers Exhibiting Gradually Slower Exchange Dynamics and an Unexpected Critical Reorganization Temperature Upon Heating

BAB amphiphilic triblock copolymers comprising poly(methoxyethyl acrylate) (PMEA) B blocks of variable degrees of polymerization (x = 50, 100, or 200) and a central poly(dimethyl acrylamide) (PDMAc) hydrophilic A block with a degree of polymerization y = 400 were synthesized by reversible addition fragmentation chain transfer polymerization, and their self-assembly in water was studied by light scattering and rheology. The BAB triblocks form a transient network in aqueous solution consisting of hydrophobic B cores bridged by hydrophilic A blocks. The exchange of B blocks is fast at low temperature (10 °C) and/or low x values because PMEA is not too hydrophobic. However, the PMEA blocks become more hydrophobic with increasing temperature, leading to a decrease of the exchange rate of the B blocks and to tunable thermo-thickening properties, opposite to the classical Arrhenius behavior. In contrast to many thermosensitive BAB triblocks that undergo an abrupt sol–gel transition above the critical solubility temperature of the B blocks, the hydrophobicity of PMEA gradually increases with T, leading to a progressive increase of the viscosity of the polymer dispersion. In addition, an unprecedented reorganization of the network was observed by rheology at a critical temperature, leading to a further decrease of the exchange rate of the B blocks that is not fully reversible. These features were attributed to the progressive variation of the hydrophobic character and hydration of PMEA with temperature.

Hierarchical clustering analysis of hydrogen bond networks in aqueous solutions.

To understand the relation between the macroscopic properties and microscopic structure of hydrogen bond networks in solutions, we introduced a hierarchical clustering method to analyze the typical configurations of water clusters in this type of network. Regarding hydrogen bonds as frames, the rings, fragments and clusters are defined and analyzed to provide a comprehensive perspective for the distributional and dynamic characteristics of the hydrogen-bonding network in NaCl solution at different concentrations. The properties of the radial distribution function and hydrogen bonds are first analyzed. Destruction and shorter lifetimes of hydrogen bonds are observed in solutions. In further analysis of the two-dimensional configuration, i.e., ring, and three-dimensional configuration, i.e., fragment, the average number, size and lifetime of these structures consistently decrease as the concentration increases. Ionic effects on disrupting rings and fragments are significant in the first hydration shell, especially with sodium cations, and these effects weaken beyond the first hydration shell. Regarding the clusters obtained using the Louvain algorithm, our results indicate that clusters break and become smaller as the NaCl concentration increases. The presence of ions also leads to the isolation of clusters and therefore the inhibition of changes. The lifetime of clusters increases with NaCl concentration, indicating the slowed breakage and reformation of clusters in NaCl solutions. This method can be further applied to quantitatively characterize hydrogen bond networks to elucidate more properties of aqueous solutions.

Ion association in hydrothermal aqueous NaCl solutions: implications for the microscopic structure of supercritical water.

Knowledge of the microscopic structure of fluids and changes thereof with pressure and temperature is important for the understanding of chemistry and geochemical processes. In this work we investigate the influence of sodium chloride on the hydrogen-bond network in aqueous solution up to supercritical conditions. A combination of in situ X-ray Raman scattering and ab initio molecular dynamics simulations is used to probe the oxygen K-edge of the alkali halide aqueous solution in order to obtain unique information about the oxygen's local coordination around the ions, e.g. solvation-shell structure and the influence of ion pairing. The measured spectra exhibit systematic temperature dependent changes, which are entirely reproduced by calculations on the basis of structural snapshots obtained via ab initio molecular dynamics simulations. Analysis of the simulated trajectories allowed us to extract detailed structural information. This combined analysis reveals a net destabilizing effect of the dissolved ions which is reduced with rising temperature. The observed increased formation of contact ion pairs and occurrence of larger polyatomic clusters at higher temperatures can be identified as a driving force behind the increasing structural similarity between the salt solution and pure water at elevated temperatures and pressures with drawback on the role of hydrogen bonding in the hot fluid. We discuss our findings in view of recent results on hot NaOH and HCl aqueous fluids and emphasize the importance of ion pairing in the interpretation of the microscopic structure of water.

Aggregation and weak gel formation by pectic polysaccharide homogalacturonan

This study presents a novel model of homogalacturonan (HG) based on the dissipative particle dynamics (DPD). The model was applied to investigate the mechanism of self-aggregation of low-methoxylated homogalacturonan in aqueous solutions in the absence of cations. The coarse-grained model provided new insights into the structural features of HG aggregates and networks in aqueous solutions. Depending on the properties and concentration of polysaccharides, two major patterns of self-assembly were observed for HG - ellipsoidal aggregates and a continuous three-dimensional network. Simulations showed that a decrease in the degree of dissociation of HG results in a higher rate of self-aggregation, as well as facilitating the formation of larger assemblies or thicker nanofilaments depending on the type of final self-assembly. Simulations of polysaccharides of different chain lengths suggested the existence of a structural threshold for the formation of a spatial network for HG consisting of less than 35 GalA units.

Swelling of Cellulose-Based Fibrillar and Polymeric Networks Driven by Ion-Induced Osmotic Pressure

Cellulose-based model materials in the form of fibrillar networks and macromolecular hydrogels were used to investigate the ion-induced swelling in relation to the elasticity and structure of the network. Both networks were charged by the introduction of carboxyl groups onto the cellulose surface, and the dimensions of the networks in aqueous solution were measured as a function of pH. The use of cellulose-model materials that contained either noncrystalline cellulose or cellulose I fibrils made it possible to model the effect of the ion-induced osmotic pressure of a delignified wood fiber wall. The noncrystalline hydrogels represented the noncrystalline domains of the fiber wall and the fibrillar network represented the supramolecular network of cellulose I fibrils of the fiber wall. The experimental results were compared to swelling potentials computed using the Donnan theory, and it was found that the ion-induced water uptake within the cellulose networks followed the theoretical predictions to a large extent. However, fibrillar networks were found to plastically deform upon swelling and deviated from the ideal Donnan theory for polyelectrolyte gel networks. Upon addition of salt to the aqueous phase surrounding the cellulose materials, both hydrogels and fibrillar networks deviated from the Donnan theory predictions, suggesting that structural differences between the networks impact their swelling.

Nanometric Water Channels in Water-in-Salt Lithium Ion Battery Electrolyte.

Lithium-ion batteries (LIBs) have been deployed in a wide range of energy-storage applications and helped to revolutionize technological development. Recently, a lithium ion battery that uses superconcentrated salt water as its electrolyte has been developed. However, the role of water in facilitating fast ion transport in such highly concentrated electrolyte solutions is not fully understood yet. Here, femtosecond IR spectroscopy and molecular dynamics simulations are used to show that bulk-like water coexists with interfacial water on ion aggregates. We found that dissolved ions form intricate three-dimensional ion-ion networks that are spontaneously intertwined with nanometric water hydrogen-bonding networks. Then, hydrated lithium ions move through bulk-like water channels acting like conducting wires for lithium ion transport. Our experimental and simulation results indicate that water structure-breaking chaotropic anion salts with a high propensity to form ion networks in aqueous solutions would be excellent candidates for water-based LIB electrolytes. We anticipate that the present work will provide guiding principles for developing aqueous LIB electrolytes.

Ultra-strong polyethyleneimine-graphene oxide nanocomposite film via synergistic interactions and its use for humidity sensing

The ternary roles of polyethyleneimine (PEI) as a polymer matirx, a reducing agent and a surface modifier have been presented to fabricate graphene oxide (GO) reinforced polymer nanocomposite films. GO is modified with PEI-glycerol diglycidyl ether (GDE) cross-linking networks in aqueous solution and in situ reduced by PEI simultaneously. Synergistic reinforcement of mechanical interlocking and hydrogen bonding leads to dramatic increases in tensile strength and Young’s modulus by 98.3% and 87% respectively, at 7.5 wt% GO loading of PEI. The partial reduced GO sheets serve as moisture barriers for water-soluble PEI, and the nanocomposite films are shown to be structurally robust humidity sensors over the relative humidity (RH) range of 40–90%.

New insights into the sol-gel condensation of silica by reactive molecular dynamics simulations.

The sol-gel method is an attractive technique to synthesize homogeneous silicate glasses with high purity while relying on a lower synthesis temperature than in the melt-quench method. However, the mechanism and kinetics of the condensation of the silicate network in aqueous solution remain unclear. Here, based on reactive molecular dynamics simulations (ReaxFF), we investigate the sol-gel condensation kinetics of a silica glass. The influence of the potential parametrization and system size is assessed. Our simulation methodology is found to offer good agreement with experiments. We show that the aqueous concentration of the Si(OH)4 precursors and the local degree of polymerization of the Si atoms play a crucial role in controlling the condensation activation energy. Based on our simulations, we demonstrate that the gelation reaction is driven by the existence of some local atomic stress that gets released upon condensation.

Capsaicin-Inspired Thiol-Ene Terpolymer Networks Designed for Antibiofouling Coatings.

Novel photocurable ternary polymer networks were prepared by incorporating N-(4-hydroxy-3-methoxybenzyl)-acrylamide (HMBA) into a cross-linked thiol-ene network based on poly(ethylene glycol)diacrylate (PEGDA) and (mercaptopropyl)methylsiloxane homopolymers (MSHP). The ternary network materials displayed bactericidal activity against Escherichia coli and Staphylococcus aureus and reduced the attachment of marine organism Phaeodactylum tricornutum. Extensive soaking of the polymer networks in aqueous solution indicated that no active antibacterial component leached out of the materials, and thus the ternary thiol-ene coating killed the bacteria by surface contact. The surface structures of the polymer networks with varied content ratios were studied by sum frequency generation (SFG) vibrational spectroscopy. The results demonstrated that the PDMS Si-CH3 groups and mimic-capsaicine groups are predominantly present at the polymer-air interface of the coatings. Surface reorganization was apparent after polymers were placed in contact with D2O: the hydrophobic PDMS Si-CH3 groups left the surface and returned to the bulk of the polymer networks, and the hydrophilic PEG chains cover the polymer surfaces in D2O. The capasaicine methoxy groups are able to segregate to the surface in an aqueous environment, depending upon the ratio of HMBA/PEGDA. SFG measurements in situ showed that the antibacterial HMBA chains, rather than the nonfouling PEG, played a dominant role in mediating the antibiofouling performance in this particular polymer system.

DNA-Wrapped Single-Walled Carbon Nanotube Assemblies

Here, we report the assembly of single-walled carbon nanotubes (SWCNTs) into two-dimensional structures and networks in aqueous solution. The assembly of SWCNTs was controlled via side-to-side interactions: we found that changes in the reaction conditions led to changes in the structures obtained. Moreover, by dispersing our SWCNT-based assemblies into a polymer matrix, we found that the mechanical properties of thin films can be modified in relation to the kind of SWCNT assemblies employed.

Enhanced Dewatering of Waste Sludge With Polyacrylamide/Montmorillonite Composite and Its Conditioning Mechanism

In order to improve the waste sludge dewaterability of polyacrylamide (PAM), the composite conditioner of PAM/montmorillonite (MMT) was prepared. The structure and intermolecular hydrogen bonding of the composite were studied, and the effects of PAM/MMT weight ratio and dosage on the dewaterability of the waste sludge were systematically investigated. The results revealed that the MMT platelets were in an exfoliated state in the PAM matrix, and hydrogen bonding between –OH groups of MMT and –NH groups of PAM led to relatively high elastic modulii (G') values and low tan δ values, indicating the possible formation of a physically cross-linked network in aqueous solution. The addition of MMT significantly reduced the specific resistance to filtration (SRF) of the waste sludge, with a minimum value being achieved at a 1:1 PAM/MMT weight ratio. The UV transmittance and the turbidity of the supernatant of the waste sludge were also improved at a proper PAM/MMT weight ratio. The synergistic effect of the two components in the composite through the charge neutrality and bridging action of PAM as well as the adsorption capacity of MMT resulted in an enhanced dewaterability of waste sludge.

Altering associations of doxorubicin‐loaded alginate esters micelles in presence of β‐cyclodextrin

ABSTRACTThe aim of this article was to evaluate the effects of β‐cyclodextrin (β‐CD) on doxorubicin (DOX)‐loaded alginate esters (SA‐C16) micelles (DOX/SA‐C16) in aqueous solution. DOX was physically loaded into SA‐C16 micelles by an o/w emulsion method with a substantial encapsulation efficiency (EE) level (36.12%), and DOX/SA‐C16 was distributed in size diameters of approximately 254 nm. SA‐C16 as carriers for the DOX can lead to the formation of associative networks in aqueous solutions between the hydrophobic tails of SA‐C16 and DOX, and the dried morphology of DOX/SA‐C16 aggregate was spherical shape. Addition of β‐CD to the system of DOX/SA‐C16 facilitated decoupling of these associations via inclusion complex formation between β‐CD cavities and the polymer hydrophobic tails that produced the release of DOX immediately, and the EE level was dropped to 0.08%, and at the same time the size distribution of aggregate was increased to about 413 nm, moreover, the aggregate was relatively large and becoming irregular spherical shape. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40702.

Quantum-Dot-Induced Self-Assembly of Cricoid Protein for Light Harvesting

Stable protein one (SP1) has been demonstrated as an appealing building block to design highly ordered architectures, despite the hybrid assembly with other nano-objects still being a challenge. Herein, we developed a strategy to construct high-ordered protein nanostructures by electrostatic self-assembly of cricoid protein nanorings and globular quantum dots (QDs). Using multielectrostatic interactions between 12mer protein nanoring SP1 and oppositely charged CdTe QDs, highly ordered nanowires with sandwich structure were achieved by hybridized self-assembly. QDs with different sizes (QD1, 3-4 nm; QD2, 5-6 nm; QD3, ∼10 nm) would induce the self-assembly protein rings into various nanowires, subsequent bundles, and irregular networks in aqueous solution. Atomic force microscopy, transmission electron microscopy, and dynamic light scattering characterizations confirmed that the size of QDs and the structural topology of the nanoring play critical functions in the formation of the superstructures. Furthermore, an ordered arrangement of QDs provides an ideal scaffold for designing the light-harvesting antenna. Most importantly, when different sized QDs (e.g., QD1 and QD3) self-assembled with SP1, an extremely efficient Förster resonance energy transfer was observed on these protein nanowires. The self-assembled protein nanostructures were demonstrated as a promising scaffold for the development of an artificial light-harvesting system.

In situ polymerization of cationic polyacrylamide/montmorillonite composites and its flocculation characteristics

In order to improve the waste sludge dewaterability of polyacrylamide (PAM), composite conditioner of cationic PAM/montmorillonite (CPAM/MMT) was synthesized by in situ polymerization. The structure and property of the composite were studied in terms of intermolecular hydrogen bonding, melting behavior, intercalation behavior, and dewaterability of the waste sludge. The results revealed that the molecular weight and cationic degree of CPAM/MMT composites decreased with the increase of MMT content. The hydrogen bonding between –OH groups of MMT and –NH groups of CPAM was confirmed by Fourier transform infrared spectroscopic analysis, which led to a relatively high elastic modulus values and low tan δ values at 5 wt% MMT content, indicating the possible formation of a physically cross-linked network in aqueous solution for the composite. The melting temperature of the composites presented decreasing trend first and then became higher as the content of MMT increased. The MMT platelets dispersed well with an intercalated state in CPAM matrix as indicated by x-ray diffraction analysis and transmission electron microscopic observation. The addition of MMT reduced the specific resistance to filtration of the waste sludge, with a minimum value being achieved at 5 wt% MMT content, while the ultraviolet transmittance of the supernatant of the waste sludge was also improved, and the turbidity was reduced. This synergistic effect of the two components in the composite through charge neutrality and bridging action of CPAM as well as the adsorption capacity of MMT resulted in an enhanced dewaterability of waste sludge.

Homogeneous dispersion of SiO2 nanoparticles in an hydrosoluble polymeric network

The main difficulty still encountered in the elaboration of polymer/silica nanocomposites is the control of the nanoparticles dispersion homogeneity and the stability of the nanoparticle dispersion in the surrounding substance. The innovative point of this work is the elaboration of hybrid networks in aqueous solution performed with ASE (alkali swellable emulsion) thickeners grafted with silica nanoparticles. The thickening ability of the polymer should favour silica nanoparticles dispersion in fluid matrices. Two ASE copolymers were realised by copolymerisation in emulsion of MA (methacrylic acid) and EA (ethyl acrylate) and/or TFEM (trifluoroethyl methacrylate). The substitution of a part of EA by TFEM gave fluorinated ASE copolymers. Their free acid functions were then coupled with different ratio of amine functionalized silica nanoparticles to afford nanocomposites. The amounts of silica nanoparticles in the copolymers were determined by thermogravimetric experiments. Depending on the silica nanoparticles/copolymer ratio in basic aqueous solutions we achieved stable translucent gel like aqueous suspensions of silica nanoparticles containing 1wt.% of the polymer/SiO2 nanocomposite.

High Strength of Physical Hydrogels Based on Poly(acrylic acid)-g-poly(ethylene glycol) Methyl Ether: Role of Chain Architecture on Hydrogel Properties

This investigation was to study the connections between polymer branch architecture of physical hydrogels and their properties. The bottle-brush-like polymer chains of poly(acrylic acid)-g-poly(ethylene glycol) methyl ether (PAA-g-mPEG) with PAA as backbones and mPEG as branch architecture were synthesized and in situ grafted from silica nanoparticles (SNs) to construct hydrogels cross-linked networks in aqueous solutions. The structural variables to be discussed included molecular weight and molar ratio of branch chains, and new aspects of the formation mechanism of physical hydrogels with branch structure in the absence of organic cross-links were present. The results indicated that the differences of polymer chain architecture could be distinguished via their different interactions that are present by gelation process and mature gel properties, such as gel strength and swelling ratio. The gelation occurred at the critical polymer concentration and molecular weight, respectively, and the inorganic/organic (SNs/PAA-g-mPEG) nanoparticles began to entangle and construct the cross-linking networks afterward. The gel-to-sol transition temperature (T(g-s)) and radii of SNs that were encapsulated by polymer chains as a function of time for chains' disentanglement were monitored according to the observation of the dissolution process, and the molecular weight between two consecutive entanglements (M(e)) was calculated thereafter. This study showed that the introduction of branch chain onto the linear backbone significantly promoted the chain interactions and increased entanglement density, which contributed to the hydrogels' network integrity and rigidity, thus illustrating greater elongation at break and tensile strength than the hydrogels formulated with linear polymer chains.

Polypeptide grafted hyaluronan: A self-assembling comb-branched polymer constructed from biological components.

Rheological evidence is provided demonstrating that covalent grafting of monodisperse isotactic poly(L-leucine) branches onto linear hyaluronan (HA) polysaccharide chains yields comb-branched HA chains that self-assemble into long-lived physical networks in aqueous solutions driven by hydrophobic interactions between poly(L-leucine) chains. This is in stark contrast to native (unmodified) HA solutions which exhibit no tendency to form long-lived physical networks.

Kinetics and Equilibrium Swelling Properties of Hydrophilic Polymethacrylate Networks

AbstractSummary: Hydrogels were synthesized by polymerization of 2‐Hydroxy ethylmethacrylate (HEMA) in the presence of ethyleneglycoldimethacrylate (EGDMA) as a crosslinking agent. Structural information and thermophysical properties of the hydrogels were analyzed using Fourier‐Transform Infrared spectroscopy, thermogravimetrical analysis, and differential scanning calorimetry. The swelling behaviour of the obtained chemically crosslinked P(HEMA‐EGDMA) networks in aqueous solution was investigated as a function of the pH value and concentration of crosslinking agent. Plateau values were found at equilibrium swelling for a low pH value after one day swelling, whereas increasing water uptake was obtained for pH = 6.32 even at swelling times of more than five days. For short swelling times, a linear relationship between swelling ratio and time was found. Experimental data were rationalized using Fick's second law of diffusion. For early and moderate times of diffusion, threshold values were found in all cases considered here, indicating a Fickian behaviour below and a non‐Fickian diffusion mechanism above the threshold.