Aqueous Volume Research Articles

Voltage Dependence and Modulation of Bacterial Channel MscL

Channels carrying canonical voltage sensor domains with multiple charges respond to voltage steeply. Non-voltage-gated channels lacking specialized voltage sensors, nevertheless, can also be modulated by voltage acting on other domains. The reason is that a typical channel residing in the polarized membrane represents a non-uniform protein insert characterized by local parameters of dielectric permeability, dipole and charge whose distributions may change as the channel transitions between the states. Here we describe a strong voltage modulation of bacterial mechanosensitive channel MscL and especially its gain-of-function mutant (V23T), which is exerted through a non-specific dielectric mechanism by water present in the pore with some contribution from the dipole moment of the protein itself. Patch-clamp measurements obtained under linear pressure ramp stimulation at different voltages reveal that both versions of MscL have dipole (linear with voltage) and dielectric/capacitive (quadratic with voltage) components that contribute to the transition energy. In contrast to WT, which exhibits a larger dipole and a smaller dielectric contribution, V23T shows a dominating dielectric effect likely related to the more pronounced hydration of the mutant pore. The increasing aqueous volume of the pore and the flattening of the protein complex impart the capacitive/dielectric energy contribution that stabilizes the expanded and subconductive states of V23T MscL. To further explore the nature of the electric field effect on open probability, we have compared the V23T MscL behavior in electrically symmetric and asymmetric droplet interface bilayers where a large intrinsic electric bias was created by using lipids with different interfacial dipole potentials. The results confirm that V23T MscL senses the local intramembrane electric field in the membrane core between the interfacial layers, and thus the voltage imposed by external electrodes is sensed not directly, but rather in combination with the potential imparted by the lipids.

Enhanced phenol hydrogenation for cyclohexanone production by membrane dispersion

Continuous liquid-phase phenol hydrogenation to cyclohexanone over Pd/Al2O3 was conducted in a membrane dispersion based fixed-bed reactor system. The effects of membrane structure on the phenol hydrogenation and gas–liquid two-phase flow were investigated by experimental results coupled with computational studies. The phenol conversion and cyclohexanone yield can be effectively improved by selecting suitable pore size and channel number of membrane. Gas holdup, axial fluid velocity and gas distribution predicted by computational fluid dynamics (CFD) studies provide insights into the relationship between membrane structure and catalytic efficiency. As compared to the phenol conversion and cyclohexanone yield obtained by direct feeding of hydrogen, those are enhanced substantially in the presence of membrane dispersion at the conditions of high LHSV and low hydrogen/phenol aqueous solution volume ratio. A phenol conversion above 85.6% and a cyclohexanone selectivity at ∼98% can be achieved in a continuous phenol hydrogenation to cyclohexanone of 50 h. This work will provide guidance for the green cyclohexanone production.

Fractional Factorial Analysis for Identifying Significant Factors in Extraction of Jacalin From Jackfruit Seeds Using Anionic Reverse Micellar System

Abstract Reverse micellar extraction is emerging as one of the most reliable method for extraction and purification of various proteins and enzymes. In this study, fractional factorial design was used to identify the significant factors having the largest effects on the forward extraction process of jacalin using reverse micelles formed by an anionic surfactant, sodium bis(2-ethylhexyl) sulfosuccinate (AOT). Effect of five different factors, namely the aqueous phase pH, surfactant (AOT) concentration, salt (NaCl) concentration, contact time and volume ratio of organic to aqueous phase on the forward extraction efficiency were investigated using the 25-1 fractional factorial design. The results showed that only the aqueous phase pH, NaCl concentration and concentration of AOT had significant effects on the forward extraction efficiency of jacalin into AOT reverse micelles. Results obtained indicated that the fractional factorial design was a useful method for screening many process factors with minimum number of experiments.

Synthesis, characterization and application of a new nano-structured samarium(III) ion-imprinted polymer

This work presents the synthesis of a new nano-structured samarium ion-imprinted polymer (Sm(III)-IIP) by precipitation polymerization. The Sm(III)-IIP nanoparticles were prepared by the copolymerization of Sm(III)–acrylic acid–4-vinylpyridine ternary complex with ethylene glycol dimethacrylate and methyl methacrylate, and then, Sm(III) was leached to obtain Sm(III)-IIP leached particles. Moreover, non-imprinted polymer particles were similarly prepared without Sm(III) ions. The characterization of polymers was carried out by Fourier transform IR spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), thermogravimetric analysis–differential scanning calorimetry (TGA–DSC) and surface analysis. The effect of several parameters such as solution’s pH, sorption and desorption time, type, concentration and volume of eluent on the extraction of the polymers was investigated and optimized by one variable at the time. Optimized parameters were as follows: pH 4; mass sorbent 0.1 g; sorption time, 120 min; desorption time, 120 min; aqueous phase volume, 10 mL. Moreover, it is found that 30 mL of HCl (3 M) provided the most effective elution of Sm3+ ion from IIP beads. The maximum sorbent capacity of the IIPs is 14.91 mg g−1. The sorbent was used for purification of samarium-152 stable isotope. The samarium-152 stable isotope recovery yield was % 99.67. The detection limit of the method was evaluated to be 0.27 ng mL−1. The precision of the method (%RSD, n = 6) was % 0.47.

Purification of pregnant solution resulted from sphalerite concentrate extraction using sulfate acid for zinc oxyde production

Purification of pregnant solution from sphalerite concentrate extraction using sulfate acid to produce zinc oxide was meant to prepare zinc oxide production technology utilizing existing internal sphalerite mineral raw material. The pregnant solution used to produce zinc oxide contains 29.84% zinc (Zn), with the biggest impurities iron (Fe) 11.68%. In order to obtain high purity zinc oxide, the pregnant solution should be recovered. It was done through solvent extraction method, in two process steps: extraction and stripping. The extraction was applying ligan bis di2ethylhexyle phosphate acid (D2EHPA) in toluene solvent, through ligan concentrate variation, pH and comparison of aqueous volume with organic volume (V A :Vo) and its excess. Stripping was carried out using sulphate acid through variation of concentration, pH and Vo:V A . To obtain optimum recovery, thus extraction and stripping should be carried out in many steps. The extractions and the strippings were calculated using McCabe Thiele diagram. Furthermore, zinc oxide was resulted from deposition and calcination of pure pregnant solution at temperature 700°C. Purification results show that the best extraction occurred at concentration D2EHPA 1 M, pH 3 and Vo:Va 2:1, through 4 step processes obtained recovery 97.50% with distribution coefficient 77.9; while the best stripping was obtained at H 2 SO 4 concentration 2 M, V O :V A 2:1 through 3 step processes which obtained stripping percent 98.22% with stripping coefficient 1.51. On the other hand, zinc oxide solution resulted from purification was obtained Zn 93.31% in the form of hexagonal crystals (wurtzite).

Rheology of Water-in-Crude Oil Emulsions: Influence of Concentration and Temperature

The effect of aqueous phase content and temperature North Sea crude oil emulsion viscoelastic behavior has been studied. Heavy crude oil from the North Sea is of high viscosity and is capable of forming stable water-in-crude oil (w/o) emulsions without introducing any synthetic surfactants. The aqueous phase volume content was varied from 1 to 40%, and the temperature was varied from 0 to 30 °C. The w/o emulsion viscosity increased sharply when the aqueous phase content exceeds 20%, being more pronounced at the lower temperatures. The viscosity flow curves for emulsions containing more than 20% aqueous phase demonstrate non-Newtonian behavior, in contrast to crude oil, which is Newtonian. The coefficients in the master curve describing the viscosity-temperature dependence were determined. Oscillatory rheological tests showed that the loss modulus substantially exceeds the storage modulus which indicates the liquid-like state of the emulsions.

Investigation and prediction of retention characteristics of imidazoline and serotonin receptor ligands and their related compounds on mixed-mode stationary phase

Investigation of the retention behavior of a wide range of analytes, 43 nitrogen containing heterocyclic and guanidine derivatives such, as imidazoline and serotonin receptor ligands or their related compounds, was performed on mixed-mode stationary phase in the combined reversed-phase (RP) and hydrophilic interaction liquid chromatography (HILIC) modes.Suitability of the linear retention modelling in the HILIC and RP modes was tested including separate contributions from adsorption and partition. For the HILIC retention, the partition model was found to provide better description compared with the adsorption model. In a wider range of the aqueous eluent volume fractions, φ(aq), retention was described as a function of volume fractions and total polarity of mobile phase using the mixed-mode retention modelling. The obtained results revealed that the shift of the chromatographic mode can be calculated from the change of total polarity of mobile phase in a multi-modal relation, logarithm of retention factor vs. total polarity, with the minimum value representing the turning point between the HILIC and the RP mode.Molecular properties of the investigated compounds that influence the retention behavior and the turning point were selected using Multiple Linear Regression (MLR) and Support Vector Machine (SVM). Slightly better statistical results were found for the logkwRP(aq)/MLR, logkwHILIC(org)/MLR, logkbHILIC(aq)/MLR, and φmin (aq)/SVM (RBF) QSRR models than for the logkwRP(aq)/SVM, logkwHILIC(org)/SVM, logkbHILIC(aq)/SVM, and φmin(aq)/MLR modelling. With this insight, it is possible to precisely define and predict the retention characteristics based on physico-chemical properties of imidazoline and piperazine related compounds.

Phacoemulsifier occlusion break surge volume reduction

To compare the volumetric occlusion break surge responses of phacoemulsification units from 1 company over 3 generations under varying vacuum limits and target intraocular pressure (IOP) settings. Alcon Research, Ltd., Lake Forest, California, USA. Experimental study. Three generations of phacoemulsification units (Infiniti Vision System, Centurion Vision System, and Centurion Vision System with Active Sentry upgrades) were tested. Volumetric surge responses were measured after occlusion breaks at vacuum limits of 200mm Hg, 300mm Hg, 400mm Hg, 500mm Hg, and 600mm Hg and target IOPs of 30mm Hg, 55mm Hg, and 80mm Hg. An acrylic test chamber with a piston attached to 3 springs modeled the human eye in this study. The springs were calibrated to mimic volumetric changes in the eye over a wide range of IOPs. Occlusion break surge volumes varied from 17.4μL to 153μL, corresponding to 7% and 61%, respectively, of the aqueous volume in the average phakic eye and to 4% and 33% of the aqueous volume in the average aphakic eye. Occlusion break surge volumes decreased with increasing target IOP, decreasing vacuum limit, and each generational increment in the phacoemulsification system.

Preparation of bamboo leaf hydrosols by the steam-distillation extraction process

The best extraction characteristics and optimal parameters for the steam-distillation extraction of bamboo leaf hydrosols were investigated to provide a data foundation for the subsequent study of bamboo leaf hydrosols and their industrial applications. The colligation score (CS) of the bamboo leaf hydrosols antioxidant activity (based on its DPPH free radical scavenging ability and total antioxidant capacity) was used as an evaluation index. The extraction time, crushing degree, and solid-to-liquid ratio were selected as the extraction parameters and response surface methodology was used to optimize the extraction process. The CS and sensory evaluation were used to determine the best distilled volume of bamboo leaf hydrosols. The results showed that the prepared bamboo leaf hydrosols had a high CS of 0.9967 (the DPPH free radical scavenging capacity was 0.052 mg/mL Vc equivalent, and the total antioxidant capacity was 0.2771 mg/mL Trolox equivalent) when the bamboo leaf crushing degree was 10 mesh, the solid-to-liquid ratio was 1:25, and the extraction time was 6 h. When the distilled volume was one-quarter of the total aqueous extract volume, the bamboo leaf hydrosols were highly active, colorless, and had a pleasantly aromatic odor.

Recovery of molybdenum from alkaline leach solution of spent hydrotreating catalyst by solvent extraction using methyl tricaprylammonium hydroxide

Detailed extraction of molybdenum(VI) from alkaline sodium hydroxide solution by quaternary ammonium salt (Aliquat 336, R3CH3NOH) mixed with kerosene was investigated. The different factors affecting the extraction system such as time of shaking, alkali, extractant, metal ion concentrations, temperature and the organic to aqueous volume phase ratio were studied in order to obtain the best conditions for separating molybdenum(VI). Based on the slope analysis method, the extracted molybdenum(VI) species was suggested to be [(R3CH3N)2MoO4]. Increasing the temperature was found to slightly increase the extraction affinity indicating the endothermic character of the process. Stripping was successfully accomplished by 2.0 M NaOH solution. The extraction procedures were applied to recover molybdenum(VI) from a sample of spent hydrotreating catalyst containing a significant amount of Al(III), Cu(II) and Ni(II). The recovery yield was found to be 96% and a hydrometallurgical flowsheet was also proposed.

Mercury determination at trace levels using membrane preconcentration and benchtop total reflection X-ray fluorescence analysis

At present, there is a considerable interest in Hg monitoring in water samples due to its widespread occurrence and the high toxicity of most of its compounds. Hg determination in water samples by means of total reflection X-ray fluorescence spectrometry (TXRF) entails some difficulties due to the high vapour pressure and low boiling point of this element that produce evaporation and loss of Hg from the surface of the reflector during the drying process, commonly employed in sample preparation in TXRF analysis.In a former work we demonstrated the usefulness of PVC-based membranes functionalized with dithizone for Hg preconcentration. Limits of detection as low as 0.8 μg·L−1 Hg were obtained using a 1 kW TXRF system. The main goal of the present research was to improve the extraction system and to apply it in combination with low power TXRF instrumentation (50 W). In this sense, some extraction parameters as well as measurement conditions such as the volume of membrane deposited on the quartz reflector, the agitation speed during extraction, the aqueous sample volume and the measurement time were carefully evaluated to obtain the maximum sensitivity for Hg determination. Using the best analytical conditions, a limit of detection for Hg of 0.3 μg·L−1 was obtained which is adequate according to the limits of current legislation on the quality of water for human consumption. Additionally, a morphological study of the preconcentrated sample on the quartz reflector was performed by optical microscopy and information regarding Hg distribution along the membrane was obtained by μ-XRF analysis. It was found that Hg is not homogenously accumulated on the membrane and thus, the size of the membrane on the reflector is a critical parameter that has to be controlled to ensure the complete exposure of the loaded membrane to the X-ray beam. This fact is of special relevance when using this preconcentration approach in combination with micro-TXRF. Finally, to further prove applicability of the TXRF method for real water sample analysis, different types of spiked water samples were analysed.

Influence of an integrated quasi-reference electrode on the stability of all-solid-state AlGaN/GaN based pH sensors

An all-solid-state AlGaN/GaN based ion-sensitive heterostructure field effect transistor (ISHFET) pH sensor was fabricated by integrating a noble metal (Au) quasi-reference electrode to improve the device stability when measuring the pH value of a small aqueous volume. In this paper, the influence of the size of the quasi-reference electrode against the stability of the pH readings was investigated. Through optimizing the size of the integrated quasi-reference electrode, the all-solid-state ISHFET pH sensor can sustain stable pH measurements for aqueous solutions of micro-litre size. A sensitivity of 55 mV/pH was achieved by the pH sensor at room temperature. Thus, the device may have potential uses in biomedical applications which require small volume pH measurements.

An integrated theoretical-experimental approach to understand facilitated proton transfer-electron transfer coupled reactions at thick-film modified electrodes

The main purpose of the current work is to generalize the analytical model for the facilitated proton transfer-electron transfer coupled reactions at thick organic film-modified electrodes, including ion pairing in the organic phase and considering non-ideal electrolyte solutions in both phases. The main equations to calculate half-wave potentials developed in this model allow the simulation of different chemical systems, comprising hydrophilic and hydrophobic neutral weak bases, at different experimental conditions such as pH, organic phase to aqueous phase volume ratio, and concentration ratios between the redox probe and the transferring protonated species. The model was checked against experimental voltammetric responses measured with the transfer of Tylosin A at the water|1,2-dichloroethene interface. Consequently, we present here an integrated theoretical-experimental approach in order to compare the results of our previous model [Zanotto et al. Electrochim. Acta 258 (2017) 727–734] with experimental data from Tylosin A and predicted half-wave potentials.

Liquid–Liquid Extraction from Frozen Aqueous Phases Enhances Efficiency with Reduced Volumes of Organic Solvent

Liquid–liquid extraction is widely employed for the separation and analysis of mixtures of compounds, both in the laboratory and in industry. Although a large volume of organic solvent is required to maximize extraction efficiency, the principles of sustainability and green chemistry dictate that the consumption of organic solvents should be minimized. This paper proposes a new liquid–liquid extraction method, realizing high extraction efficiencies with only a small volume of organic solvent. Since extraction efficiency is a function of the ratio of organic and aqueous solvent volumes, attaining high extraction efficiency usually requires a large volume of the organic phase. In general, it is difficult to increase this ratio by reducing the volume of the aqueous phase, except by heating—which damages, and potentially decomposes, the solutes. However, if the aqueous phase is frozen, a freeze-concentrated solution containing the solutes is formed; the volume of the freeze-concentrated solution can be contro...

Aqueous volume loss associated with occlusion break surge in phacoemulsifiers from 4 different manufacturers

To evaluate aqueous volume losses associated with occlusion breaks at varying vacuum limits in phacoemulsification systems from 4 different manufacturers. Alcon Research Ltd., Lake Forest, California, USA. Experimental study. The anterior chamber was modeled using the spring eye model. Systems tested included the Centurion, Whitestar Signature, Stellaris PC, and EVA. Occlusion breaks were actuated at vacuum limits of 200, 300, 400, 500, and 600mm Hg and a target intraocular pressure of 55mm Hg. The model eye piston reached its measurement limit just below 600mm Hg on the EVA and just above 400mm Hg on the Stellaris PC. Higher vacuum limits could not be tested on these 2 units. Surge volumes varied from 17 to 77μL on the Centurion, 30 to 103μL on the Whitestar Signature, 67μL to 163μL on the Stellaris PC, and 47 to 165μL on the EVA. Assuming an average phakic eye aqueous volume of 250μL, these μL values correspond to percent aqueous volume losses of 7% to 31% on the Centurion, 12% to 41% on the Whitestar Signature, 27% to 65% on the Stellaris PC, and 19% to 66% on the EVA. Surge responses increased on all machines with each increment in vacuum limit. The Centurion had the lowest surge volumes across all vacuum limits. Occlusion break surge volumes vary considerably across phacoemulsification platforms. Severe chamber shallowing might occur if an occlusion break occurs under high vacuum on some systems.

Separating Extreme pH Gradients Using Amphiphilic Copolymer Membranes.

Polymeric vesicles, also called polymersomes, are highly efficient biomimetic systems. They can generate compartmentalized volumes at the nanoscale supported by synthetic amphiphilic membranes that closely mimic their biological counterparts. Membrane permeability and the ability to separate extreme pH gradients is a crucial condition a successful biomimetic system must meet. We show that polymersomes formed by non-ionic polybutadiene-b-polyethylene oxide (PBd-b-PEO) amphiphilic block copolymers engineer robust and stable membranes that are able to sustain pH gradients of 10 for a minimum of eight days. The cells' endo-lysomal compartments separate gradients between three and one, while we generated a pH gradient of threefold as great. This feature clearly is of great importance for applications as nanoreactors and drug-delivery systems where separating different aqueous volumes at the nanoscale level is an essential requirement.

Mitigation of source term in suppression pools: Large uncertainties in predictability

The Fukushima accident has revived the interest of suppression pools as a passive way to scrub radioactivity from the gas reaching the aqueous volume in case of a severe accident. However, modeling of pool scrubbing is far from being mature. This paper focuses on the scrubbing occurring at the nearby of the injection point and, by illustrating how far from observations prediction can be, it highlights the importance of developing proper models at this region of the pool. To do so, a specific simple ASTEC model has been set-up and a jet scrubbing database has been gathered from the open pool scrubbing literature by picking suitable tests in which all the key initial and boundary conditions were recorded and reported. In particular, low-submergence experiments with high injection velocity experiments have been chosen to address what is known as jet scrubbing (i.e., scrubbing at the inlet region when particles are carried in the pool by a gas submerged jet).

Challenges for the Self-Assembly of Poly(Ethylene Glycol)⁻Poly(Lactic Acid) (PEG-PLA) into Polymersomes: Beyond the Theoretical Paradigms.

Polymersomes (PL), vesicles formed by self-assembly of amphiphilic block copolymers, have been described as promising nanosystems for drug delivery, especially of biomolecules. The film hydration method (FH) is widely used for PL preparation, however, it often requires long hydration times and commonly results in broad size distribution. In this work, we describe the challenges of the self-assembly of poly (ethylene glycol)-poly(lactic acid) (PEG-PLA) into PL by FH exploring different hydrophilic volume fraction (f) values of this copolymer, stirring times, temperatures and post-FH steps in an attempt to reduce broad size distribution of the nanostructures. We demonstrate that, alongside f value, the methods employed for hydration and post-film steps influence the PEG-PLA self-assembly into PL. With initial FH, we found high PDI values (>0.4). However, post-hydration centrifugation significantly reduced PDI to 0.280. Moreover, extrusion at higher concentrations resulted in further improvement of the monodispersity of the samples and narrow size distribution. For PL prepared at concentration of 0.1% (m/v), extrusion resulted in the narrower size distributions corresponding to PDI values of 0.345, 0.144 and 0.081 for PEG45-PLA69, PEG114-PLA153 and PEG114-PLA180, respectively. Additionally, we demonstrated that copolymers with smaller f resulted in larger PL and, therefore, higher encapsulation efficiency (EE%) for proteins, since larger vesicles enclose larger aqueous volumes.

Optimization of valsartan encapsulation in biodegradables polyesters using Box-Behnken design

The aim of this study was to encapsulate an antihypertensive drug (valsartan) within polyester microparticles, namely constituted of poly (lactic acid) (PLA) and poly (ε-caprolactone) (PCL), by using the emulsion solvent evaporation method. In order to optimize the parameters of valsartan encapsulation, design of experiments was applied. Thus, a Box-Behnken matrix was carried out with three independent variables: the PLA amount (X1), the aqueous phase volume (X2) and the surfactant concentration (X3). The analysis of the variance (ANOVA) showed a significant quadratic regression model with the high coefficients of determination values. The optimum conditions were found to be: X1 = 200 mg, X2 = 40 mL and X3 = 0.2%, respectively. Under these conditions, the experimental results showed that the valsartan encapsulation efficiency was equal to 60.05 ± 1.806% with PLA, while it was equal to 69.82 ± 0.645% with PCL. The SEM analysis showed that the shape of the particles was spherical for all formulations and that their size varied between 2 μm and 44 μm. The study of the in-vitro drug release performed in phosphate-buffered saline at pH = 6.8, showed that the valsartan release was more gradual with PCL than with PLA.

A Simple Dynamic Diffusion Model of the Response of Highly Selective Electrodes: The Effect of Simulation Parameters and Boundary Conditions on the Results of Calculations

For a tetrabutylammonium-selective electrode with a ion-exchange membrane, in the real-work scenario corresponding to the determination of selectivity coefficients by the IUPAC-recommended method of separate solutions, it is shown that of the results of calculations obtained within the framework of the dynamic diffusion model based on the use of the finite-difference technique substantially depend on of the chosen boundary conditions and the values of arbitrarily set simulation parameters. The key parameter that determines the quality of simulation results is the thickness of the elementary layer in the membrane phase, especially for low diffusion coefficients. It is found that the use of thin elementary layers in membranes and thick elementary layers in the aqueous phase makes it possible to combine the high quality with the high calculation rate. In simulating the long-term experiments, account should be taken of the accumulation of the potential-determining ion in the aqueous solution volume as a result of its displacement by a foreign ion from the membrane. A good correspondence between calculation data and experimental results is demonstrated.