Internal Solute Concentrations Research Articles

Simulation Guided Coaxial Electrospinning of Polyvinylidene Fluoride Hollow Fibers with Tailored Piezoelectric Performance.

Electrospun polyvinylidene fluoride (PVDF) piezoelectric fibers have high potential applicability in mechanical energy harvesting and self-powered sensing owing to their high electromechanical coupling capabilities. Strategies for tailoring fiber morphology have been the primary focus for realizing enhanced piezoelectric output. However, the relationship between piezoelectric performance and fiber structure remains unclear. This study fabricates PVDF hollow fibers through coaxial electrospinning, whose wall thickness can be tuned by changing the internal solution concentration. Simulation analysis demonstrates an increased effective deformation of the hollow fiber as enlarging inner diameter, resulting in enhanced piezoelectric output, which is in excellent agreement with the experimental results. This study is the first to unravel the influence mechanism of morphology regulation of a PVDF hollow fiber on its piezoelectric performance from both simulation and experimental aspects. The optimal PVDF hollow fiber piezoelectric energy harvester (PEH) delivers a piezoelectric output voltage of 32.6V, ≈3 times that of the solid PVDF fiber PEH. Furthermore, the electrical output of hollow fiber PEH can be stably stored in secondary energy storage systems to power microelectronics. This study highlights an efficient approach for reconciling the simulation and tailoring the fiber PEH morphology for enhanced performances for future self-powered systems.

Influence of Membrane Fouling and Reverse Salt Flux on Membrane Impedance of Forward Osmosis Microbial Fuel Cell.

The forward osmosis membrane (FO membrane) is an emerging wastewater treatment technology in bioelectricity generation, organic substrate removal and wastewater reclamation. Compared with traditional membrane materials, the FO membrane has a more uniform water content distribution and internal solution concentration distribution. In the past, it was believed that one of the important factors restricting power generation was membrane fouling. This study innovatively constructed a mass transfer model of a fouling membrane. Through the analysis of the hydraulic resistance coefficient and the salt mass transfer resistance coefficient, the driving force and the tendency of reverse salt flux during membrane fouling were determined by the model. A surprising discovery was that the fouling membrane can also achieve efficient power generation. The results showed that the hydraulic resistance coefficient of the fouling membrane increased to 4.97 times the initial value, while the salt mass transfer resistance coefficient did not change significantly. Meanwhile, membrane fouling caused concentration polarization in the FO membrane, which enhanced the reverse trend of salt, and the enhancement effect was significantly higher than the impact of the water flux decline caused by membrane pollution. This will make an important contribution to research on FO membrane technology as sustainable membrane technology in wastewater treatment.

Research on Measuring Pure Membrane Electrical Resistance under the Effects of Salinity Gradients and Diffusion Boundary Layer and Double Layer Resistances.

Forward osmosis membranes are an emerging technology with great potential applicability in energy-efficient wastewater treatments and the differentiation between two solutions. Such solutions often differ in their concentrations or compositions. In this study, the membrane electrical resistances of three different membranes, including cation or anion-exchange membranes and forward osmosis membranes, were analyzed by Luggin capillary coupled with AC impedance spectroscopy (EIS) so as to obtain the real membrane and ion transfer impedance values near the membrane interface. The results reveal that the membrane impedance obtained by both the DC and AC approaches decreased as the lowest external solution concentration increased. Furthermore, the relationship between the membrane conductivity and the internal salt solution concentration was also investigated. It can be seen that the external ion concentration is directly proportional to the free ion concentration in the membrane, and the free ion concentration in the membrane is closely related to the membrane electrical resistance.

The effect of salinity on osmotic regulation and respiratory rate of the prawn Macrobrachium tenellum Smith, 1871 (Decapoda: Caridea: Palaemonidae)

Abstract The effect of salinity on oxygen consumption rate and hemolymph osmolarity of the palaemonid prawn Macrobrachium tenellum (Smith, 1871) maintained at 0, 5, 10, 15, 20 and 25 psu was analyzed. Oxygen consumption rate was measured in respiratory chambers and osmolality from samples of hemolymph. Oxygen consumption rose significantly beyond 15 psu, with individuals showing hyper regulatory behavior from 0 to 10 psu, being able to maintain its internal solutes concentration (426–504 mmol kg–1) higher than that of the water (153–348 mmol kg–1). They acted as hypo-regulators from 15 to 25 psu as their internal solute concentration (454–562 mmol kg–1) was lower than that of the water (459–744 mmol kg–1). The isosmotic point was 505 mmol kg–1 at 16 psu, and survival was high in all salinities. The osmotic behavior of M. tenellum allows it to successfully invade fresh water by keeping constant the ionic and osmotic concentrations of both extra- and intra-cellular solute concentrations, always above fresh water, but varying its O2 consumption as salinity changes. The implications of such adaptations for the dispersal of the species into freshwater habitats is discussed.

Design and Characterization of Electrochemical Sensor for the Determination of Mercury(II) Ion in Real Samples Based upon a New Schiff Base Derivative as an Ionophore.

The present paper provides a description of the design, characterization, and use of a Hg2+ selective electrode (Hg2+–SE) for the determination of Hg2+ at ultra-traces levels in a variety of real samples. The ionophore in the proposed electrode is a new Schiff base, namely 4-bromo-2-[(4-methoxyphenylimino)methyl]phenol (BMPMP). All factors affecting electrode response including polymeric membrane composition, concentration of internal solution, pH sample solution, and response time were optimized. The optimum response of our electrode was obtained with the following polymeric membrane composition (% w/w): PVC, 32; o-NPOE, 64.5; BMPMP, 2 and NaTPB, 1.5. The potentiometric response of Hg2+–SE towards Hg2+ ion was linear in the wide range of concentrations (9.33 × 10–8−3.98 × 10–3 molL–1), while, the limit of detection of the proposed electrode was 3.98 × 10–8 molL–1 (8.00 μg L–1). The Hg2+–SE responds quickly to Hg2+ ions as the response time of less than 10 s. On the other hand, the slope value obtained for the developed electrode was 29.74 ± 0.1 mV/decade in the pH range of 2.0−9.0 in good agreement with the Nernstian response (29.50 mV/decade). The Hg2+–SE has relatively less interference with other metal ions. The Hg2+–SE was used as an indicator electrode in potentiometric titrations to estimate Hg2+ ions in waters, compact fluorescent lamp, and dental amalgam alloy and the accuracy of the developed electrode was compared with ICP–OES measurement values. Moreover, the new Schiff base (BMPMP) was synthesized and characterized using ATR–FTIR, elemental analysis, 1H NMR, and 13C NMR. The PVC membranes containing BMPMP as an ionophore unloaded and loaded with Hg(II) are reported by scanning electron microscope images (SEM) along with energy-dispersive X-ray spectroscopy (EDX) spectra.

Bacterial Evolution in High-Osmolarity Environments.

Bacteria must maintain a cytosolic osmolarity higher than that of their environment in order to take up water. High-osmolarity environments therefore present formidable stress to bacteria. To explore the evolutionary mechanisms by which bacteria adapt to high-osmolarity environments, we selected Escherichia coli in media with a variety of osmolytes and concentrations for 250 generations. Adaptation was osmolyte dependent, with sorbitol stress generally resulting in increased fitness under conditions with higher osmolarity, while selection in high concentrations of proline resulted in increased fitness specifically on proline. Consistent with these phenotypes, sequencing of the evolved populations showed that passaging in proline resulted in specific mutations in an associated metabolic pathway that increased the ability to utilize proline for growth, while evolution in sorbitol resulted in mutations in many different genes that generally resulted in improved growth under high-osmolarity conditions at the expense of growth at low osmolarity. High osmolarity decreased the growth rate but increased the mean cell volume compared with growth on proline as the sole carbon source, demonstrating that osmolarity-induced changes in growth rate and cell size follow an orthogonal relationship from the classical Growth Law relating cell size and nutrient quality. Isolates from a sorbitol-evolved population that captured the likely temporal sequence of mutations revealed by metagenomic sequencing demonstrated a trade-off between growth at high osmolarity and growth at low osmolarity. Our report highlights the utility of experimental evolution for dissecting complex cellular networks and environmental interactions, particularly in the case of behaviors that can involve both specific and general metabolic stressors.IMPORTANCE For bacteria, maintaining higher internal solute concentrations than those present in the environment allows cells to take up water. As a result, survival is challenging in high-osmolarity environments. To investigate how bacteria adapt to high-osmolarity environments, we maintained Escherichia coli in a variety of high-osmolarity solutions for hundreds of generations. We found that the evolved populations adopted different strategies to improve their growth rates depending on the osmotic passaging condition, either generally adapting to high-osmolarity conditions or better metabolizing the osmolyte as a carbon source. Single-cell imaging demonstrated that enhanced fitness was coupled to faster growth, and metagenomic sequencing revealed mutations that reflected growth trade-offs across osmolarities. Our study demonstrated the utility of long-term evolution experiments for probing adaptation occurring during environmental stress.

Probing Protein Folding and Interaction in Live Cells using Osmotic Perturbations

Cells rapidly change their volume in both optimal conditions and under duress, causing changes to their internal solute concentrations. Proteins are known to respond to such fluctuations in solution concentrations even faster, well before the cell can initiate regulatory response. We take advantage of this response to probe protein conformation and interactions in live cells, under biologically relevant conditions. We induce a cellular volume change in cells by subjecting them to a jump in media osmotic pressure. Protein dynamics are observed by FRET signal collected on an epifluorescent microscope from adherent cells expressing mCherry/GFP tagged proteins. Our experiments reveal protein conformational changes, as well as binding of weakly bound protein complexes, depending on the labeling scheme used. We observe that proteins can bind and unbind, and structures can expand and contract reversibly when the cell volume increases or decreases. Our results indicate that some proteins structures are more sensitive than others to cellular volume change, and that altering the internal concentrations within the cell can alter protein processes, including folding and binding.

THE EFFECTS OF CHANGING MEMBRANE COMPOSITIONS AND INTERNAL ELECTROLYTES ON THE RESPON OF POTASSIUM ION SENSOR

A study on the changing of membrane compositions and internal solution towards the response potassium ion sensor was carried out. Potassium ion sensor based on photocured cross linking poly(n-butyl acrylate) membranes with varying composition of valinomycin (val), sodium tetrakis [3.5-bis(trifluoro-methyl) phenyl] borat (NaTFPB), types ion of internal solution were investigated. Effects of varying composition of val, NaTFPB, types and concentration of internal solution were observed on potassium ion sensor. The effect of higher val composition was lower LOD, wider linear range, lower sensitivity but increase selectivity. Higher NaTFPB compositions lead to lower LOD, higher sensitivity and selectivity. The effect of changing internal electrolyte lead to lower LOD, wider linear response range and higher selectivity according to internal electrolyte consisting Na + , Ca 2+ and K + , and sensitivity increase following internal electrolyte with Ca 2+ , K + and Na + . Key words: ion sensor, ion selective membrane, ionofor, lipofilik salt

Highly Selective Detection of Titanium (III) in Industrial Waste Water Samples Using Meso-octamethylcalix[4]pyrrole-Doped PVC Membrane Ion-Selective Electrode

A novel Ti3+ selective membrane electrode based on meso-octamethylcalix[4]pyrrole (OMCP) as an ionophore was successfully fabricated. The developed sensor revealed high selectivity towards Ti3+ ion over alkali, alkaline earth and transition metal cations. Among all of the membranes examined, the membrane with a composition of 4:33:62.8:0.2mg of I:PVC:DOP:NaTFPB showed the best Nernstian slope of 29.49±0.16 (mV per decade of activity) over the pH range from 1 to 3 with a satisfactory concentration range of 1.0×10−6M to 1.0×10−2M and detection limit of 8.0×10−7M. The effects of various parameters such as composition of the membrane, different cation interferences and concentration of internal solution were investigated. The developed sensor exhibited a good reproducibility over a useful life time of about 3 months with a fast response time of 25seconds. It demonstrated good analytical performance for accurate determination of Ti3+ trace amount in the presence of considerable concentration of common interfering ions. The fabricated sensor was used successfully as an indicator electrode for potentiometric titration of a titanium solution with EDTA and moreover it applied for direct determination of Ti3+ content of industrial waste water samples. The obtained results from optimized membranes were evaluated by comparing them with the data received from instrumental methods such as UV–Vis, AAS, ICP and SEM. By using density functional theory (DFT) calculations, several special adsorption sites of TiOH2+ close to OMCP are fully optimized and the best one selected. Furthermore, NBO and QTAIM analysis carried out to study the bonding strength in formed complex and deep understanding of the nature of interaction between TiOH2+ and OMCP.

Experimental design as an optimization approach for fabrication a new selective sensor for thallium(I) based on calix[6]arene

The performance of a new membrane sensor based on polyvinyl chloride (PVC) for Tl(I) assay was investigated using the statistical design as an optimization strategy. The Plackett-Burman and Box-Behnken designs, respectively, were utilized to find out the influencing variables and optimization of conditions. In order to evaluate the relationship between the responses of electrode (slope) and significant variables along with their interactions, a mathematical model was presented. The interactions between significant variables were intuitively illustrated according to the response surface plots. Apart from that, the optimum conditions as a result of response surface methodology for both membrane ingredients and measuring conditions such as pH, PVC, internal solution concentration, calix[6]arene, 2-nitrophenyloctylether, potassium tetrakis-(p-chlorophenyl)borate and time conditioning, respectively, were found to be: 6, 0.028 g, 0.001 M, 0.0035 g, 0.065 g, 0.0015 g and 20 h. The optimized sensor exhibits a Nernstian response for thallium(I) over a wide linear range from 2.0 × 10−6 to 2.0 × 10−2 M and the slope of 57.9 ± 0.1 mV/decade of the activity and limit of detection (LOD) 1.9 × 10−5 M. The relative standard deviations (RSD) for six replicates of the measurement at 1 × 10−5 and 1 × 10−5 M of Tl(I) were 2.7 and 3.0%, respectively. The favorable results were given through the direct determination of Tl(I) in spiked wastewater and artificial spiked urine sample with Tl(I). The electrode was also successfully applied to the titration of a Tl(I) solution with KI.

Yttrium (III) Selective Electrode Based On Zirconium (IV) Phosphoborate

Zirconium phosphoborate based heterogeneous membrane electrode has been used as a sensor for yttrium ions in aqueous medium. The electrode shows reproducible and Nernstian behavior for yttrium ions in the oncentration range 10-4M to 10-1M with an RSD of 2%. The electrode does not show any change in response within a pH range of 5-9. The effect of internal solution concentration on the calibration curve was also studied. The electrode performance was also studied in partially non-aqueous medium (5% - 20%) of acetone and ethanol. The system was used successfully as an indicator electrode in potentiometric titration of yttrium ions with EDTA.

Heteroaggregation of water-in-oil droplets: the effects of relative internal solute concentrations and size

An attractive interaction between disparately-sized aqueous droplets dispersed in oil has been observed: small salty water droplets tend to stick to and withdraw water from larger droplets that have the same or lower salinity (if <100 mM). The attractive interaction, however, is not observed if small droplets are mixed with droplets that are both larger and saltier. In the latter case, provided there is insufficient salt present in the small droplets to prevent it, the larger droplets grow by a compositional ripening mechanism.

Nanovectors for drug delivery: Long-lived pore dynamics for swelling liposomes

A liposome is a spherical, bilayer vesicle separating the interior volume containing an aqueous solution, from an exterior suspension. A fundamental practical application provides the liposome used as vehicles for drug delivery. In this case, liposomes are designed to contain a specific drug or a gene needed to fight the disease. If a vesicle containing high internal solute concentration is placed inside a dilute solution, the osmotic flux of solvent into the interior can lead to its rupture or a formation of pores. Such pores can be long-lived pores or short-lived pores suddenly closing after their formations. Long-lived pores lead to a well controlled drug delivery. In this paper, we show that the existence of long-lived pores is completely conditioned only by the pore dynamics, and that the long-lived pore dynamics is highly stable because sustained by a limit cycle. Moreover, we calculate analytically the frequency of a long-lived pore making use of the He's variational method.

Optimization of a new polymeric chromium (III) membrane electrode based on methyl violet by using experimental design

Plackett-Burman and Box-Behnken designs were applied as experimental design strategies to screen and optimize the influence of membrane ingredients on the electrode performance. A new poly(vinyl chloride) membrane sensor for Cr(III) based on methyl violet as an ionophore was planned. The major variables to find a model for achieving the best Nernstian slope as response were: PVC, plasticizers, methyl violet, KpClTPB, pH, conditioning time and internal solution concentration. Plackett-Burman design was used to screen the main factors and Box-Behnken response surface was led to find a model for optimizing the response. The optimized membrane electrode shows a Nernstian slope for chromium (III) ions over a wide linear range from 1.99x10(-6) to 3.16x10(-2)molL(-1) and a slope of 19.5+/-0.1mVdecade(-1) of activity. It would be successfully applied in the pH range from 3.5 to 6.5 with detection limit of 1.77x10(-6)molL(-1) (0.092mgL(-1)). The response time of the sensor is about 8s and the membrane can be used for more than 6 weeks without any deviation. The relative standard deviations (R.S.D.) for six replicate the measurements of 1.0x10(-4) and 1.0x10(-3)molL(-1) of Cr(III) were 3.2 and 3%, respectively. The electrode revealed comparatively good selectivity with respect to many cations including alkali earth, transition and heavy metal ions. The electrode was successfully used as an indicator in the potentiometric titration of Cr(III) with EDTA and was also applied to the direct determination chromium (III) content of spiked water and soil samples.

Cerium(III)‐Selective Membrane Electrode Based on Dibenzo‐24‐crown‐8 as a Neutral Carrier

Cerium(III)‐selective membrane electrodes have been prepared using dibenzo‐24‐crown‐8 (DB24C8) as an electroactive material. A membrane having a composition: DB24C8 (4.5%), plasticizer (NPOE, 62.5%) and PVC (33%) gives the best performance. It works well over a wide Ce(III) ion‐concentration range of 1x10-5 M to 1x10-1 M with a Nernstian slope of 19.0 mV/decade and a detection limit of 3x10-5 M. It has a fast response time of 20 seconds and has an average lifetime of four months. The internal solution concentration does not have a significant effect on the response of the electrode except for a change in intercept of the calibration curves. The working pH range for Ce(III) solutions (1x10-2 M and 1x10-3 M) is 3.5‐8.0. The proposed sensor shows a good selectivity for cerium(III) with respect to alkali, alkaline earth, some transition and rare earth metal ions that are normally present along with cerium in its ores. The proposed sensor was investigated in partially non‐aqueous media using acetone, methanol and DMSO mixtures with water. The electrode was further used as an indicator electrode for the potentiometric titration of Ce(III) solution against oxalic acid solution.

Modeling of Thermophysical Processes in Liquid Ceramic Precursor Droplets Heated by Monochromatic Irradiation

A transient heat and mass transfer model is formulated to describe radiative heating of ceramic precursor droplets in a nonconvective environment. Heating causes vaporization of solvent from the droplet and concentration of the solute within the droplet leading to precipitation of the solute. It is found that the temperatures within the droplets are fairly uniform, but show different spatial profiles depending on the characteristics of solute absorptivity and duration of radiative heating. Incident laser irradiance and wavelength were found to play a significant role in the temperature profiles within droplets due to the absorption characteristics of the solute and the solvent. Lower levels of incident laser irradiation allows longer times for mass diffusion within a droplet leading to a gradual increase of the solute concentration from its center to its surface. Based on an equilibrium homogeneous precipitation hypothesis, it is found that the droplets heated with low laser irradiance tend to form thick precipitate shells as compared to those exposed to higher irradiances and consequently faster rates of vaporization. Large droplets form thin shells through surface precipitation, while small droplets may precipitate into shells of varying thickness depending on the magnitude of irradiance. Comparisons with convective heating in a high temperature plasma indicate that, with proper tuning of the laser irradiance, similar internal temperatures and solute concentration distributions are achievable. These modeling results suggest that different particle morphologies can be obtained from processing of liquid ceramic precursor containing droplets by proper tailoring of radiation parameters (wavelength and irradiance level).

Determination of membrane permeability to water from osmotically induced light-scattering changes of membrane vesicles: Analysis of the method

The kinetics of osmotically induced changes in vesicular volume and internal solute concentration were analyzed for membrane vesicles containing fixed quantity of impermeable osmoticum in the lumen. The kinetic curves of the concentration and volume changes were shown to be dissimilar. The average durations of these two processes may differ by several tens of percents, depending on the extent and polarity of the initially imposed osmotic gradient. For vesicles containing identical solutes in the internal and external solutions, the problem is analyzed of how the concentration and volume changes are manifested in changes of the effective scattering cross-section of the vesicle. The light scattering changes, directed oppositely to volume changes, were found to coincide roughly with the kinetics of volume changes. The analysis shows that calculations of water permeability coefficient should be based on average duration of volume changes rather than the duration of concentration changes. The replacement in calculations of the first parameter with the second one may result in overestimation of water permeability by a factor of 1.5. This might be relevant to the reported discrepancies in water permeability values determined by the osmotic and isotope methods. Although the allowance for 1.5-fold overestimation cannot fully account for the differences observed, it significantly lowers the discrepancy between these estimates in some cases. The opposite signs of light scattering and volume changes originate from the presence of two components in the optical path of the vesicle, i.e., the membrane and the lumenal solution.

Neutral carriers based polymeric membrane electrodes for selective determination of mercury (II)

The potentiometric response characteristics of mercury ion-selective membrane electrodes based on 2-amino-6-purinethiol ( I 1 ) and 5-amino-1, 3, 4-thiadiazole-2-thiol ( I 2 ) were described. Ion selectivities were tested for various plasticizers, which were used as solvent mediators to incorporate the ionophores into the membrane. Effects of experimental parameters such as membrane composition, nature and amount of plasticizers and additives, pH and concentration of internal solution on the potential response of Hg 2+ electrodes were investigated. The best performance was obtained with the electrode having a membrane composition (w/w) of ( I 1 ) (3.17%): PVC (31.7%): DOP (dioctylpthalate) (63.4%): NaTPB (sodium tetraphenylborate) (1.58%). The proposed electrode reveals a Nernstian response over Hg 2+ ion in the concentration range of 7.0 × 10 −8–1.0 × 10 −1 M with limit of detection 4.4 × 10 −8 M. The electrode shows good discrimination toward Hg 2+ ion with respect to most common cations. It shows a short response time (10 s) for whole concentration range and can be used for 2 months without any considerable divergence in potentials. For evaluation of the analytical applicability, the electrode was used in the determination of Hg 2+ ion in different environmental and biological samples. The practical utility of the membrane electrode has also been observed in the presence of surfactants.

Potentiometric membrane sensor based on 6-(4-nitrophenyl)-2,4-diphenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene for detection of Sn(II) in real samples

A Sn 2+ ion-selective electrode which was prepared with a polymeric membrane based on 6-(4-nitrophenyl)-2,4-diphenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene (NDDBH) as a ionophore. Effects of experimental parameters such as membrane composition, nature and amount of plasticizer, the amount of additive and concentration of internal solution on the potential response of Sn 2+ sensor were investigated. The electrode exhibited a Nernstian slope of 28.8 ± 1.1 mV/decade of Sn 2+ over a concentration range of 1.0 × 10 −5 to 1.0 × 10 −1 M of Sn 2+ in an acidic solution (pH 1). The limit of detection was 4.0 × 10 −6 M. The results show that this electrode can be used in ethanol media until 20% (v/v) concentration without interference. It can be used for more than 6 weeks without any considerable divergence in the potentials. The proposed membrane electrode revealed very good selectivity for Sn(II) ions over a wide variety of other cations and could be used in acidic media. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the electrode. The stability constant (log K s) of the Sn(II)–ionophore complex was determined at 25 °C by potentiometric titration in mixed aqueous solution. It was used as indicator electrode in potentiometric determination of Sn(II) ion in real samples.

Highlights from the Literature

Highlights from the Literature