Diffusion Of Aqueous Solutions Research Articles

Synergistically Constructed Lamination-like Network of Redox-active Polyimide and MXene via π-π interactions for Aqueous Storage

As a nonmetallic charge carrier, ammonium ion () has garnered significant attention in the construction of aqueous batteries due to its advantages of low molar mass, small hydration size and rapid diffusion in aqueous solutions. Polymers are a kind of potential electro-active materials for aqueous storage. However, traditional polymer electrodes are typically created by covering the bulky collectors with excessive additives, which could lead to low volume capacity and unsatisfactory stability. Herein, a nanoparticle-like polyimide (PI) was synthesized and then combined with MXene nanosheets to synergistically construct an additive-free and self-standing PI@MXene composite electrode. Significantly, the redox-active PI nanoparticles are enclosed between conductive MXene flakes to create a 3D lamination-like network that promotes electron transmission, while the π-π interactions existing between PI and MXene contribute to the enhanced structural integrity and stability within the composite electrode. As such, it delivers superior aqueous storage behaviors in terms of a notable specific capacity of 110.7 mAh cm–3 and a long lifespan with only 0.0064% drop each cycle. Furthermore, in-situ Raman and UV-vis examinations provide evidence of reversible and stable redox mechanism of the PI@MXene composite electrode during uptake/removal, highlighting its significance in the area of electrochemical energy storage.

Chitosan Membranes Stabilized with Varying Acyl Lengths Release Cis-2-Decenoic Acid and Bupivacaine at Controlled Rates and Inhibit Pathogenic Biofilm.

Adherence of complex bacterial biofilm communities to burned tissue creates a challenge for treatment, with infection causing 51% of burn victim deaths. This study evaluated the release of therapeutics from wound care biomaterials and their antimicrobial activity against pathogens Staphylococcus aureus, Acinetobacter baumannii, and Pseudomonas aeruginosa. Electrospun chitosan membranes (ESCMs) were fabricated and acylated with chain lengths ranging from 6-10 carbons then loaded with 0.15 mg of anti-biofilm agent, cis-2-decenoic acid (C2DA), and 0.5 mg of local anesthetic, bupivacaine. Combinations of therapeutics released from modified ESCMs at a cumulative amount of 45-70% of bupivacaine and less than 20% of C2DA. Results from bacterial studies suggest that this combination reduced biofilm 10-fold for S. aureus, 2-fold for Acinetobacter baumannii, and 2-3-fold for Pseudomonas aeruginosa by 24 hours. Additionally, dual loaded groups reduced planktonic Staphylococcus aureus ~4-fold by 24 hours as well as Acinetobacter baumannii ~3-fold by 48 hours. The combination of therapeutics used has a significant role in biofilm prevention for selected strains via direct contact or diffusion in aqueous solutions.

Isotope fractionation of alkaline and alkaline-earth elements (Li, K, Rb, Mg, Ca, Sr, Ba) during diffusion in aqueous solutions

In this study, we used an improved “diffusion cell” method to precisely determine the diffusion-driven kinetic isotope fractionation factors of the Li, K, Rb, Mg, Ca, Sr, and Ba cations in aqueous solutions under room temperature. The obtained isotope fractionation factors (±2σ errors) are, α7/6Li = 0.996139 ± 0.000140, α41/39K = 0.998572 ± 0.000072, α87/85Rb = 0.999333 ± 0.000020, α26/24Mg = 0.999877 ± 0.000010, α44/42Ca = 0.999704 ± 0.000010, α88/86Sr = 0.999781 ± 0.000014, α138/135Ba = 0.999716 ± 0.000018. The results show that the charge of the cation and the ion-water bond length for the aquo ions are the two predominant factors affecting the mass dependence of isotope fractionation (β factor) during cation diffusion in aqueous solutions. Cations with higher charge numbers and shorter ion-water bond lengths exhibit less kinetic isotope fractionation during diffusion. Therefore, the isotope separation effect during diffusion (or β factor) in fluids is fundamentally controlled by the intensity of ion-water interaction. Weaker ion-water interaction (e.g., lower charge number, longer ion-water bond length) leads to less prominent hydrodynamic behavior for diffusing ions at the molecular level, thus more significant isotope fractionation in bulk solutions, and vice versa. Ions of larger radius would show stronger mass dependence of isotope fractionation (β factor), which can cancel the effect of decreasing relative isotope mass difference for heavier elements, thus kinetic isotope fractionation during diffusion in aqueous solutions remains prominent even for heavy elements such as Rb, Sr, and Ba. The diffusion-driven kinetic isotope fractionation factors measured in this study could provide a useful basis for interpreting specific natural isotopic variability of alkaline and alkaline-earth elements in supergene environments where chemical diffusion takes place.

Transport Properties of Carbohydrates: Towards the Minimization Toxicological Risks of Cobalt and Chromium Ions

The influence of oligosaccharides (α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin), and a polysaccharide, sodium hyaluronate (NaHy), on the diffusion of aqueous solutions of cobalt and chromium chlorides has been investigated. Cobalt and chromium are constituents of metal alloys for biomedical use, including dental prostheses. Thus, the release of these ions in the human body can lead to harmful biological effects. The interaction of metal ions with saccharides might have information on the role of mouthwashes in preventing these effects. This interaction has been assessed by measuring multicomponent intermolecular diffusion coefficients at 298.15 K. It has been found that β-cyclodextrin has the highest interaction towards cobalt and chromium ions. This work will contribute to unveiling the mechanisms responsible for transport by diffusion in aqueous solutions, and, therefore, mitigating the potential toxicity inherent to those metal ions.

High-Strength, High-Water-Retention Hemicellulose-Based Hydrogel and Its Application in Urea Slow Release.

The use of fertilizer is closely related to crop growth and environmental protection in agricultural production. It is of great significance to develop environmentally friendly and biodegradable bio-based slow-release fertilizers. In this work, porous hemicellulose-based hydrogels were created, which had excellent mechanical properties, water retention properties (the water retention ratio in soil was 93.8% after 5 d), antioxidant properties (76.76%), and UV resistance (92.2%). This improves the efficiency and potential of its application in soil. In addition, electrostatic interaction and coating with sodium alginate produced a stable core-shell structure. The slow release of urea was realized. The cumulative release ratio of urea after 12 h was 27.42% and 11.38%, and the release kinetic constants were 0.0973 and 0.0288, in aqueous solution and soil, respectively. The sustained release results demonstrated that urea diffusion in aqueous solution followed the Korsmeyer-Peppas model, indicating the Fick diffusion mechanism, whereas diffusion in soil adhered to the Higuchi model. The outcomes show that urea release ratio may be successfully slowed down by hemicellulose hydrogels with high water retention ability. This provides a new method for the application of lignocellulosic biomass in agricultural slow-release fertilizer.

ЭКСПЕРИМЕНТАЛЬНАЯ ОЦЕНКА КОЭФФИЦИЕНТА ДИФФУЗИИ В ЖИДКИХ РАСТВОРАХ

The paper describes a method for experimental evaluation of molecular diffusion in aqueous solutions. The method is based on solving the equation of non-stationary molecular diffusion in dimensionless form

The Roles of Carbonic Anhydrases in Carbon Concentrating Mechanisms of Aquatic Photoautotrophs

The article surveys the role of carbonic anhydrases (CAs) in inorganic carbon (Ci) acquisition by cyanobacteria, microalgae, and macrophytes under Ci limiting conditions. Slow Ci diffusion in aquatic environments imposes the need for carbon concentrating mechanisms (also named CO2 concentrating mechanisms, CCMs) in aquatic photoautotrophs, to transport Ci against the gradient and ensure a CO2 supply for photosynthesis. There are common requirements for efficient CCM functioning in cyanobacteria, algae, and aquatic angiosperms, including active transport of HCO3- to the Ci-concentrating compartment and CO2 generation from the HCO3- pool in the Rubisco-enriched subcompartment. Facilitating Ci diffusion in aqueous solutions and across lipid bilayers, CAs play essential roles in CCMs that are best studied in cyanobacteria, green algae, and diatoms. Roles of CAs in CCMs depend on their localization and include facilitation of active transmembrane Ci uptake by supplying C1 at the outer surface (Role 1) whilst removing it at the inner surface (Role 2), as well as accelerating CO2 production from HCO3- near Rubisco (Role 3) in a specialised CO2-tight compartment, known as the carboxysome in cyanobacteria or pyrenoid in microalgae. The compartmentalization of CAs is also critical because, if activated in the HCO3- -concentrating compartment, they can easily eliminate the Ci gradient created by the CCMs.

Роль карбоангідраз у механізмах концентрування карбону водних фотоавтотрофів

The article surveys multiple roles of carbonic anhydrases (CAs) in inorganic carbon (Ci) acquisition by cyanobacteria, microalgae, and macrophytes under Ci limiting conditions. Slow Ci diffusion in aquatic environments imposes the need for carbon concentrating mechanisms (also named CO2 concentrating mechanisms, CCMs) in aquatic photoautotrophs to transport Ci against the gradient and ensure CO2 supply to photosynthesis. There are common requirements for efficient CCM functioning in cyanobacteria, algae, and aquatic angiosperms, including active transport of HCO3- to the Ci-concentrating compartment and CO2 generation from the HCO3- pool in the Rubisco-enriched subcompartment. Facilitating Ci diffusion in aqueous solutions and across lipid bilayers, CAs play essential roles in CCMs that are best studied in cyanobacteria, green algae, and diatoms. Roles of CAs in CCMs depend on their localization and include facilitation of active transmembrane Ci uptake by its supplying at the outer surface (Role 1) and removal at the inner surface (Role 2), as well as the acceleration of CO2 production from HCO3- near Rubisco (Role 3) in a special CO2-tight compartment, carboxysome in cyanobacteria or pyrenoid in microalgae. The compartmentalization of CAs is also critical because, if activated in the HCO3- –concentrating compartment, they can easily eliminate the Ci gradient created by CCMs.

Improved indicator algorithms for tracking a hydrated proton as a local structural defect in Grotthuss diffusion in aqueous solutions

Keeping track of a hydrated proton in dynamics simulations is important and nontrivial. Here, we report two revised algorithms for the proton indicator, a pseudo-atom whose position approximates the location of an excess proton diffusing via the Grotthuss mechanism in aqueous solution. The new methods describe the delocalized proton as a structural defect. Encouragingly, in test simulations of a hydrated proton in bulk water, the new algorithms substantially outperform the original scheme by significantly reducing large displacements in the indicator positions upon donor switch, yielding smoother trajectories that effectively track the movement of the solvated proton.

Three-dimensional feedback-driven trapping of a single nanoparticle or molecule in aqueous solution with a confocal fluorescence microscope.

Control of electroosmotic flows in a two-layer microfluidic device with crossed channels is used to counteract Brownian diffusion in aqueous solution for three-dimensional trapping of a single nanoparticle or molecule within the probe volume of a confocal fluorescence microscope. A field programmable gate array sorts and counts photons into four channels synchronous with laser pulses in four beams focused to waists slightly offset from the center of the confocal volume and uses the counts to update voltages between the four fluidic inlets every 13.5 µs. Trapping is demonstrated for 40 nm nanoparticles for up to 240 s, 20 nm nanoparticles for up to 25 s, and single molecules of streptavidin-Alexa 647 for up to 1.2 s.

Hydrogen bond dynamics and vibrational spectral diffusion in aqueous solution of formaldehyde: a first principles molecular dynamics study

Water spectacle extraordinary ability to form a variety of hydrogen bonded structure when confronted with hydrophilic solutes. We present the comparative analysis of structural and dynamical features of deuterated formaldehyde in heavy water (D2O) using density functional theory (DFT) and dispersion corrected DFT. Ab initio molecular dynamics calculation is performed by Car–Parrinello method and frequency-time calculations using time series analysis method at ambient conditions. We find that the higher frequency of OD modes of water present inside the first solvation shell of formaldehyde is a result of weak interaction compared to bulk water. We also find that the inclusion of dispersion (i.e., BLYP-D) alters the dynamical features like diffusion, frequency correlation with enhancement of momentum; therefore, molecules experience lower barrier toward their motion and show relatively faster dynamics.

Diffusion in ternary aqueous {L-dopa + (NaSO3) -β-cyclodextrin} solutions using the pseudo-binary approximation

Mass transport in (drug + cyclodextrin) solutions is investigated by using Taylor dispersion technique, monitored by differential refractometry, to measure ternary mutual diffusion in aqueous solutions of {L-dopa + (NaSO3)n-β-CD} (the sodium salt of sulfated β-cyclodextrin). The values of the binary mutual diffusion coefficients of both aqueous L-dopa and aqueous (NaSO3)n-β-CD solutions are close to each other differing only by a few per cent units. As a result, the eigenvalues for the matrix of the ternary Dik diffusion coefficients for aqueous {L-dopa(1) + (NaSO3)n-β-CD(2)} solutions are nearly identical, and the numerical analysis of the Taylor dispersion data may be ill-conditioned in view of the unreliable data obtained from their analysis. To overcome these difficulties, the pseudo-binary diffusion approximation is used to evaluate in a simple way this ternary system. The pseudo-binary diffusion coefficient values found, Dp1 and Dp2, are very close to the binary diffusion ones, being the cross-coefficients approached zero, within the experimental error. From the obtained results, and under the circumstances of this study, we may deduct that no interaction between L-dopa and NaSO3ßCD was determined.

Preferential solvation, ion pairing, and dynamics of concentrated aqueous solutions of divalent metal nitrate salts.

We have investigated the characteristics of preferential solvation of ions, structure of solvation shells, ion pairing, and dynamics of aqueous solutions of divalent alkaline-earth metal nitrate salts at varying concentration by means of molecular dynamics simulations. Hydration shell structures and the extent of preferential solvation of the metal and nitrate ions in the solutions are investigated through calculations of radial distribution functions, tetrahedral ordering, and also spatial distribution functions. The Mg2+ ions are found to form solvent separated ion-pairs while the Ca2+ and Sr2+ ions form contact ion pairs with the nitrate ions. These findings are further corroborated by excess coordination numbers calculated through Kirkwood-Buff G factors for different ion-ion and ion-water pairs. The ion-pairing propensity is found to be in the order of Mg(NO3)2 < Ca(NO3)2 < Sr(NO3)2, and it follows the trend given by experimental activity coefficients. It is found that proper modeling of these solutions requires the inclusion of electronic polarization of the ions which is achieved in the current study through electronic continuum correction force fields. A detailed analysis of the effects of ion-pairs on the structure and dynamics of water around the hydrated ions is done through classification of water into different subspecies based on their locations around the cations or anions only or bridged between them. We have looked at the diffusion coefficients, relaxation of orientational correlation functions, and also the residence times of different subspecies of water to explore the dynamics of water in different structural environments in the solutions. The current results show that the water molecules are incorporated into fairly well-structured hydration shells of the ions, thus decreasing the single-particle diffusivities and increasing the orientational relaxation times of water with an increase in salt concentration. The different structural motifs also lead to the presence of substantial dynamical heterogeneity in these solutions of strongly interacting ions. The current study helps us to understand the molecular details of hydration structure, ion pairing, and dynamics of water in the solvation shells and also of ion diffusion in aqueous solutions of divalent metal nitrate salts.

Role of solvation structure in the shuttling of the hydrated excess proton

The classic Marcus electron transfer reaction model demonstrated that a barrierless electron transfer reaction can occur when both the reactant and product have almost similar solvation environment. In our recently developed proton model, we have incorporated the pre-solvation concept and showed that it indeed facilitates the proton diffusion in aqueous solution. In this work, we further quantify the degree of pre-solvation using different structural parameters, e.g., tetrahedral order parameter, average numbers of hydrogen bonds. All the above said parameters exhibit a very strong correlation with the proton share parameter. The more Zundel-like configurations have almost identical solvation environment for both the water molecules and support the pre-solvation concept. However, in the case of Eigen-like configurations, the central hydronium and “special pair” water have distinctly different solvation structures. Synopsis Hydrated excess proton transfer events in liquid water are highly coupled with local solvent orientations than previously thought. The weak hydrogen bond accepting nature of the hydronium helps to create water-like solvation environment around hydronium. This pre-solvated configuration facilitates the proton transfer process in liquid water. Proton sharing parameter-dependent radial distribution function shows the tiny intensity at 2.0 Å, which arises from the $$4^{\mathrm{th}}$$ water molecule solvating the hydronium moiety.

Evaluation of the antibacterial activity of a cationic polymer in aqueous solution with a convenient electrochemical method.

Quaternized chitosan is a cationic biopolymer with good antibacterial activity, biocompatibility, and biodegradability, and it has been widely applied in many fields. We have developed a convenient method to evaluate the antibacterial activity of hydroxypropyltrimethylammonium chloride chitosan (HACC) with a nonionic surfactant poloxamer in aqueous solution by monitoring the change of the oxidation peak current in cyclic voltammetry. Increasing values of the oxidation peak current were positively correlated with the antibacterial activity of HACC-poloxamer solutions. Optical microscope images, the zeta potential, and fluorescence spectroscopy showed that the aggregation state of HACC-poloxamer was related to the ratio of the two polymers and also to the antibacterial activity and oxidation peak current. At an HACC-to-poloxamer ratio of 1:0.75, the maximum surface charge density and the smooth edge of HACC-poloxamer aggregates can accelerate diffusion in aqueous solution. It is expected that this convenient method can be applied for a quick evaluation of the antibacterial activity of cationic biopolymers in aqueous solution. Graphical Abstract The cyclic voltammograms of MB in HACC/poloxamer solution, and the antibacterial efficiency against S. aureus after incubated with HACC (a) and 1/0.75 of HACC/poloxamer (b).

Sucrose diffusion in aqueous solution.

The diffusion of sugar in aqueous solution is important both in nature and in technological applications, yet measurements of diffusion coefficients at low water content are scarce. We report directly measured sucrose diffusion coefficients in aqueous solution. Our technique utilises a Raman isotope tracer method to monitor the diffusion of non-deuterated and deuterated sucrose across a boundary between the two aqueous solutions. At a water activity of 0.4 (equivalent to 90 wt% sucrose) at room temperature, the diffusion coefficient of sucrose was determined to be approximately four orders of magnitude smaller than that of water in the same material. Using literature viscosity data, we show that, although inappropriate for the prediction of water diffusion, the Stokes-Einstein equation works well for predicting sucrose diffusion under the conditions studied. As well as providing information of importance to the fundamental understanding of diffusion in binary solutions, these data have technological, pharmaceutical and medical implications, for example in cryopreservation. Moreover, in the atmosphere, slow organic diffusion may have important implications for aerosol growth, chemistry and evaporation, where processes may be limited by the inability of a molecule to diffuse between the bulk and the surface of a particle.

Molecular Simulation of Structure and Diffusion at Smectite–Water Interfaces: Using Expanded Clay Interlayers as Model Nanopores

In geologic settings relevant to a number of extraction and potential sequestration processes, nanopores bounded by clay mineral surfaces play a critical role in the transport of aqueous species. Solution structure and dynamics at clay–water interfaces are quite different from their bulk values, and the spatial extent of this disruption remains a topic of current interest. We have used molecular dynamics simulations to investigate the structure and diffusion of aqueous solutions in clay nanopores approximately 6 nm thick, comparing the effect of clay composition with model Na-hectorite and Na-montmorillonite surfaces. In addition to structural properties at the interface, water and ion diffusion coefficients were calculated within each aqueous layer at the interface, as well as in the central bulk-like region of the nanopore. The results show similar solution structure and diffusion properties at each surface, with subtle differences in sodium adsorption complexes and water structure in the first adsorbed...

Wanted: scalable tracers for diffusion measurements.

Scalable tracers are potentially a useful tool to examine diffusion mechanisms and to predict diffusion coefficients, particularly for hindered diffusion in complex, heterogeneous, or crowded systems. Scalable tracers are defined as a series of tracers varying in size but with the same shape, structure, surface chemistry, deformability, and diffusion mechanism. Both chemical homology and constant dynamics are required. In particular, branching must not vary with size, and there must be no transition between ordinary diffusion and reptation. Measurements using scalable tracers yield the mean diffusion coefficient as a function of size alone; measurements using nonscalable tracers yield the variation due to differences in the other properties. Candidate scalable tracers are discussed for two-dimensional (2D) diffusion in membranes and three-dimensional diffusion in aqueous solutions. Correlations to predict the mean diffusion coefficient of globular biomolecules from molecular mass are reviewed briefly. Specific suggestions for the 3D case include the use of synthetic dendrimers or random hyperbranched polymers instead of dextran and the use of core–shell quantum dots. Another useful tool would be a series of scalable tracers varying in deformability alone, prepared by varying the density of crosslinking in a polymer to make say “reinforced Ficoll” or “reinforced hyperbranched polyglycerol.”

Structure of facial brick and lyophilic of his surface

The dependence of the kinetics of water saturation and capillary suction of ceramic material on the lyophily of its surface and porosity, connected with the chemical and mineralogical composition of the feedstock, the degree of sintering during firing and phase composition is shown. Based on the analysis of experimental data, it was concluded that the interaction of ceramic material with water can be determined by the ratio between its composition, structure, degree of defectiveness, energy state of the surface. This is confirmed by quantitative parameters of such indicators as porosity and its nature, water absorption, wetting angle. These properties of the brick material play a crucial role in the processes of diffusion of aqueous solutions and the formation of efflorescence on the surface. In practical terms, these are two interrelated processes, which can proceed in the following sequence: water absorption by the ceramic material → its interaction with water-soluble salts → formation of saline water solutions → diffusion of the latter as a result of the change in gradients of concentration, humidity, temperature.

Direct Measurement of Diffusion in Olfactory Cilia Using a Modified FRAP Approach

The diffusion coefficient of fluorescein in detached cilia of Xenopus laevis olfactory receptor neurons was measured using spatially-resolved FRAP, where the dye along half of the ciliary length was photobleached and its spatiotemporal fluorescence redistribution recorded. Fitting a one-dimensional numerical simulation of diffusion and photobleaching for 35 cilia resulted in a mean value of the diffusion coefficient and thus a reduction by a factor of compared to free diffusion in aqueous solution.