Diffusion Coefficient Of Acid Research Articles

Determining the molecular diffusion coefficient of naphthenic acid in water as a heavy oil pollutant by experimental method

ABSTRACT Naphthenic acids are the most significant environmental pollutants created by the extraction of oil from oil sand deposits. Since the diffusion coefficient of naphthenic acid has a direct effect on the modeling of diffusion and advection and determining its behavior and movement in water, this number is needed for modeling work and future studies. In this study, the diffusion coefficient of this substance in water was determined experimentally and in a laboratory. The researchers used the device of the Armfield company, known as the device for determining the diffusion coefficient in liquids, In this research, after examining different methods of determining the concentration of naphthenic acid in the water, including UV–vis, chemical oxygen demand (COD), crystal violet, oxidation reduction potential, pH meter, and electrical conductivity meter, the COD method was the best method in determining the concentration at different times, which provided a suitable numerical range for the concentrations and a device was built for heavy oil pollutants with poor solubility in water to specify the diffusion coefficient, and for the first time, the diffusion coefficient of naphthenic acid in water was obtained with experiments and experimental equations as 0.69 × 10−9 m2/s which this number indicates the weak diffusion of this substance in water.

Miscible Polymer Blend Membranes Bearing Pyrrolidone for Fractioning Sulfuric Acid and Sulfates

ABSTRACTIon exchange membranes of new chemistry based on polymer blends are proposed through a convenient solution‐blending process using the hydrophobic commodity polymer polyvinyl chloride (PVC) and the hydrophilic polyvinylpyrrolidone (PVP), which are completely miscible. The pyrrolidone groups can be protonated to form oxonium ions, functioning as transient fixed positive charges for fractioning sulfuric acid and sulfates via diffusion. The influence of PVC molecular weight and the membrane composition on the physical, chemical properties, and mass transfer performance of PVC‐PVP blend membranes was systematically investigated. After equilibrium in 2.68 mol/L sulfuric acid, the sulfuric acid, and water contents in the blend membranes increase with the increase of the membrane PVP contents (20–75 wt%). The permeability coefficients of sulfuric acid and ferrous sulfate for the blend membranes also exhibit a gradual increase. Membranes of mass transfer properties comparable to commercial ones can be easily obtained by tuning the membrane PVP contents. It is proved that the larger sulfuric acid permeability over sulfates (FeSO4 as an example) is due to both larger solubility and diffusion coefficient of sulfuric acid in the membrane phase. The optimal PVC‐PVP blend membranes have shown nice performance in fractioning sulfuric acid from sulfates, when treating titania waste acid. This study provides valuable guidance for the design of high‐performance yet low‐cost ion exchange membranes with pyrrolidone chemistry from commodity polymers for resource recovery.

Transport and Kinetic Property of the Butyric Acid in Water: A Simulation Study

Microbiota is defined as a class of all microorganisms which includes fungi, protozoa, bacteria and viruses. About 90 % of all microbiota in our body are found in our gut that regulates host immunity. The gut-brain axis is a bidirectional communication system that allows gut microbiota to communicate with the brain and vice versa. Studies suggest that the gut dysbiosis may enhance neurotoxic substances such as short-chain fatty-acids (SCFAs which are acetate, propionate, and butyrate) to the blood circulation and even to the brain through damaged blood brain barrier (BBB) and may cause protein aggregation which are implicated in the pathogenesis of several neurodegenerative diseases like Alzheimer’s disease (AD), Parkinson’s disease (PD), prion disease, motor neuron disease, Huntington’s disease (HD), Amyotrophic lateral sclerosis (ALS). Specifically, butyric acid are the main SCFA product that may impact on gut health. Therefore, this article aims to investigate the transport and kinetic properties such as diffusion coefficient, activation energy and radial distribution function of butyric acid in water at different temperatures through molecular dynamics simulations. The self and binary diffusion coefficient of butyric acid in water obtained from our MD simulation are found to be 0.8699×10−9m2s−1 and 0.8714×10−9m2s−1, respectively at 300 K and the activation energy for self-diffusion coefficient of water estimated from the slope of ln(D) versus 1/T is equal to 16.07 kJ/mol. Our results are in accordance with those obtained from the experimental values. This study offers an alternate approach to researching the diffusion of butyric acid in living organisms. This knowledge contributes to advancements in various fields, including nutrition, gastroenterology, microbiology, and pharmacology.

NMR study of the electrolyte diffusion in bituminous coal

The transfer of the electrolyte molecules (H2SO4 or H3PO4) into bituminous coal was studied by the method of solid-state NMR spectroscopy. The kinetic dependences of the electrolytes transfer into a coal membrane from an aqueous solution have been obtained. It was shown that the transfer of H2SO4 molecules into a coal thin layer is determined by the solid phase diffusion. The process was investigated in the framework of a mathematical model of diffusion in layered media. When the flow of electrolyte is directed perpendicular to the surface of the layer the diffusion coefficient of sulfuric acid in the coal equals 1∙10-13 m2/s. The diffusion coefficient of H2SO4 in the bituminous coal is four order of less than the self-diffusion coefficient of proton in aqueous solution. The diffusion process of the electrolyte delivery may be the rate-limiting stage preceding chemical transformations with the H2SO4 participation in bituminous coal.

Highly Cross-Linked butene grafted poly (Vinyl Alcohol)–co-Vinyl pyridine based anion exchange membrane for improved acid recovery and desalination efficiency

Water treatment and waste acid reclamation are important in present situation due to huge industrialization. Different processes are available for the water treatment and waste treatment. Ion exchange membranes based electrodialysis (ED) and diffusion dialysis (DD) are attracted by the researchers since last decade due to its simplicity and economical operation. Acid reclamation by diffusion dialysis has been gained huge attention due to their absolute selectivity and energy less process. Here, we report the synthesis of efficient anion exchange membrane (AEM) by free radical co-polymerization of butene grafted poly (vinyl alcohol) and 4-vinyl pyridine followed by in-situ quaternization and cross-linking. Different amount 4-vinyl pyridine was chosen for the membrane preparation, and its impact on physiochemical and electrochemical properties has been studied. Structural and chemical characterisation of the membranes were studied using nuclear magnetic resonance (NMR), attenuated total reflectance-infrared spectroscopy (ATR-IR), while surface-phase morphology was investigated through scanning electron microscopy (SEM) and atomic force microscopy (AFM). The thermo-mechanical properties of prepared membranes were studied using thermogravimetric analysis (TGA), differential scanning colorimetry (DSC), dynamic mechanical analysis (DMA) and universal testing machine (UTM) analysis. The cross-linked PVA-x membranes showed high acidic stability as well as good antioxidation property. The synthesized membranes were studied for their salt removal performance by electrodialysis and acid recovery by diffusion dialysis. The optimised membrane (PVA-0.8) shows 0.90 kWh kg−1 energy consumption and 93.49 % current efficiency during salt removal from brackish water using electrodialysis. All cross-linked PVA-x membranes have diffusion coefficient of acid are in the range of 0.0556–0.0716 mh−1 and separation factor values are between the 79.51 to 91.33 at 25 °C, which comparable to commercial DF-120B membrane. This result shows that the prepared cross-linked AEMs may be a good candidate for the electrochemical applications.

Prebiotic Aggregates (Tissues) Emerging from Reaction-Diffusion: Formation Time, Configuration Entropy and Optimal Spatial Dimension.

For the formation of a proto-tissue, rather than a protocell, the use of reactant dynamics in a finite spatial region is considered. The framework is established on the basic concepts of replication, diversity, and heredity. Heredity, in the sense of the continuity of information and alike traits, is characterized by the number of equivalent patterns conferring viability against selection processes. In the case of structural parameters and the diffusion coefficient of ribonucleic acid, the formation time ranges between a few years to some decades, depending on the spatial dimension (fractional or not). As long as equivalent patterns exist, the configuration entropy of proto-tissues can be defined and used as a practical tool. Consequently, the maximal diversity and weak fluctuations, for which proto-tissues can develop, occur at the spatial dimension 2.5.

Turbulence leads to overestimation of the acid-diffusion coefficient at typical experimental conditions using the rotating disk apparatus

A rotating-disk apparatus (RDA) is used to determine the acid-diffusion coefficient. The equations to interpret RDA tests were previously derived assuming laminar flow to the disk, i.e. uniform accessibility with equal flux of the reactive species over the entire surface of the disk. Thus, the acid-diffusion coefficient is overestimated if the tests are run at transition or turbulent flow regimes. The present work validated laminar flow assumptions at typical RDA experimental conditions to optimize the acid-diffusion coefficient measurements. Disks of calcite marble with a diameter of 0.72, 1.11, and 1.46 in. were reacted in an RDA with hydrochloric acid at temperatures ranging from 73.4 to 100 °F and disk rotational speeds ranging from 207 to 1555 rpm. Transition to turbulent flow was observed at Reynolds numbers one order of magnitude lower than the universally accepted critical value of 3 × 105. Dissolution patterns on the disks after the experiments and the simulation results using a developed computational fluid-dynamics model confirm this conclusion.

Evaluation of ferrous benzoic methylthymol-blue gel as a dosimeter via magnetic resonance imaging.

In previous studies, methylthymol-blue and benzoic acid have been introduced as a diffuser limiter and sensitivity enhancer in the gel dosimeter composition, respectively. This work focused on analyzing a formulation of the Fricke gel dosimeter consisting of methylthymol-blue and benzoic acid through magnetic resonance imaging. The gel dosimeter samples were irradiated using 6, 10, and 15 MV photons with different levels of doses and read using a 1.5T scanner in order to evaluate the dose-response sensitivity and to study the effect of benzoic acid concentration, diffusion coefficient and temperature and to determine the temporal stability of the gel dosimeter. Inspection of radiological properties revealed that this gel dosimeter can be considered as a tissue equivalent medium. Within the dose range 0 to 1000cGy, the R1 sensitivity and R2 sensitivity of the gel dosimeter equaled 0.058±0.003 and 0.092±0.004s-1Gy-1, respectively. The diffusion coefficient was less than 0.85±0.02mm2h-1 for doses higher than 200cGy. In addition, by changing the temperature from 15C to 25, the R1 sensitivity and R2 sensitivity decreased about 5 and 11%, respectively. Further, no significant energy and dose rate dependence were observed over photon energies of 6, 10, and 15 MV and over the range 65 to 525cGymin-1. Based on our observation, the ferrous benzoic acid methylthymol-blue gel dosimeter can be suggested to measure the dose distribution. Further analysis is required to clarify its performance in clinical situations.

Study of rejuvenators dynamic diffusion behavior into aged asphalt and its effects

Recycled asphalt pavements are widely used in road maintenance and reconstruction with techniques developing. As aged asphalt would partially lose its initial properties, rejuvenators have been developed and used in recycling process to enhance properties of such aged asphalt. In this research, three rejuvenators with different composition and three markers with typical and different molecular structures were used to study the dynamic diffusion behavior of rejuvenators into aged asphalt. Diffusion tests were designed based on the viscosity and SARA test to evaluate the diffusivity. IR tests were used to study the diffusion trace of markers. Diffusion coefficients were calculated to evaluate the dynamic diffusion behavior based on Fick’s law. The main conclusions are as follows: Aromatic content promoted the diffusion of rejuvenators into aged asphalt. Molecules with larger molecular polarity and smaller molecular size were easier to diffuse. Diffusion coefficient of dodecanoic acid was the lowest, indicating that the long-chain saturated hydrocarbon structure is not conducive to diffuse, and some large functional groups will also play an obstacle role in diffusion at microscopic level.

Design and Characterization of Ethosomes for Transdermal Delivery of Caffeic Acid.

The present investigation describes a formulative study aimed at designing ethosomes for caffeic acid transdermal administration. Since caffeic acid is characterized by antioxidant potential but also high instability, its encapsulation appears to be an interesting strategy. Ethosomes were produced by adding water into a phosphatidylcholine ethanol solution under magnetic stirring. Size distribution and morphology of ethosome were investigated by photon correlation spectroscopy, small-angle X-ray spectroscopy, and cryogenic transmission electron microscopy, while the entrapment capacity of caffeic acid was evaluated by high-performance liquid chromatography. Caffeic acid stability in ethosome was compared to the stability of the molecule in water, determined by mass spectrometry. Ethosome dispersion was thickened by poloxamer 407, obtaining an ethosomal gel that was characterized for rheological behavior and deformability. Caffeic acid diffusion kinetics were determined by Franz cells, while its penetration through skin, as well as its antioxidant activity, were evaluated using a porcine skin membrane–covered biosensor based on oxygen electrode. Ethosome mean diameter was ≈200 nm and almost stable within three months. The entrapment of caffeic acid in ethosome dramatically prolonged drug stability with respect to the aqueous solution, being 77% w/w in ethosome after six months, while in water, an almost complete degradation occurred within one month. The addition of poloxamer slightly modified vesicle structure and size, while it decreased the vesicle deformability. Caffeic acid diffusion coefficients from ethosome and ethosome gel were, respectively, 137- and 33-fold lower with respect to the aqueous solution. At last, the caffeic acid permeation and antioxidant power of ethosome were more intense with respect to the simple solution.

A rapid voltammetric strategy for determination of ferulic acid using electrochemical nanostructure tool in food samples

In this project, we performed an electrochemical investigation using a reduced graphene (rG) decorated CdO nanocomposite/1-methyl-3-octylimidazolium tetrafluoroborate ionic liquid (MOITF) carbon paste electrode (rG-CdO/MOITF/CPE) for determination of ferulic acid in food samples. In preparation of rG-CdO/MOITF/CPE, 6% w/w rG-CdO nanocomposite and 20% v/v room temperature ionic liquid were used to modify the bare CPE. SEM (Scanning Electron Microscopy) and XRD (X-Ray Diffraction) methods were applied to characterize the structure of the synthesized rG-CdO nanocomposite. At all the stages of this research, phosphate buffer solution (PBS) with the pH of 5.0, as an optimized pH condition, was used. The electron transfer coefficient (α) was obtained ⁓0.68 by recorded data from cyclic voltammogram of rG-CdO/MOITF/CPE in the presence of ferulic acid. In addition, using the chronoamperometric technique, the diffusion coefficient (D) of ferulic acid at rG-CdO/MOITF/CPE was calculated 5.4 × 10−5 cm2/s. Using the square wave voltammetry method, the linear dynamic range (LDR) was calculated to be from 0.02 to 400 μM, and the limitation of detection (LOD) was obtained as 8.0 nM. Eventually, the rG-CdO/MOITF/CPE was utilized to determine the amount of ferulic acid in food samples, and statistical calculations confirmed the sensitivity, selectivity, and precision of rG-CdO/MOITF/CPE, which is an electroanalytical tool.

Conductive Gauze Based Electronic Sensor for Rapid Uric Acid Detection

Introduction Accurate real-time health monitoring with fabric-based biomedical devices is coming to the foreground with improvements in efficiency [1,2]. Cotton fabric-based wearable sensors are a soft and breathable substrate that provides comfort to patients. Flexibility, robustness and easy integration with skin or garments provide real-time updates of health issues [3]. Fast response time and low cost make the textile-based wearable sensors eye-catcher of the clinical market. Wearable sensors are used in various important clinical applications and the real status of a chronic wound is one of the critical issues. Wearable sensors for monitoring various wound parameters are reported using gauze [4,5]. These reported sensors suffered from mechanical and chemical stability with poor wireless connectivity [6,7]. In this study we have fabricated a textile woven, conformal, and conductive gauze based sensor that enables quantitative sensing of uric acid in chronic wound fluid. Sensor Design Cotton gauze was cleaned via acetone solution and kept for drying in the oven for 2 hrs. The cotton gauze surface was modified with graphene nano-platelet via dipping the treated gauze in graphene solution for 15 minutes followed by drying at room temperature. Graphene reducing agent basic L-cysteine solution was used to reduce oxidized graphene nano-platelets into neutral graphene-modified conductive gauze. Obtained conductive gauze is a flexible substrate. Screen printing technique is used for printing WE, RE and CE with silver ink (Fig. 1 A). The electrochemical response of uric acid on fabricated conductive gauze was evaluated via a multichannel electrochemical station (CHI-230B Potentiostat). Electrochemical Measurement Cyclic voltammetry was performed to evaluate the response of uric acid in a phosphate buffer saline solution (pH 7.4) over the fabricated conductive gauze. The well-defined redox peak at -0.38 V and 0.08 V in cyclic voltammogram confirms the selective and sensitive sensing of uric acid (Fig. 1 B). The linear response of scan rates and obtained current signal of uric acid confirms the diffusion-limited kinetics on conductive gauze. The diffusion-limited kinetics supports the mass transport mechanism on gauze (Fig. 1 C). This facilitates the ppm level selective sensing of uric acid and confirms the feasibility of fabricated gauze as a wound dressing. The uric acid response was evaluated for the same concentration (100 m M) on two conductive gauzes. Both gauzes were showing excellent reproducibility with RSD 1.2%. Furthermore, to evaluate the diffusion coefficient of uric acid on conductive gauze chonoamperometry measurements using different uric acid concentrations (50, 75, 100, 125 mM) in phosphate buffer saline (pH 7.4) were performed (Fig. 1 D). The mean diffusion coefficient of uric acid as per the Cottrell equation is 4.15×10−7 cm2 s-1. The result obtained from both electrochemical techniques, cyclic voltammetry and chronoamperometry confirm diffusion-limited kinetics on conductive gauze based flexible sensors. Conclusions The excellent electrochemical response of uric acid on metallic printed conductive gauze and reproducibility could open a new approach and flexible material for wound dressing. The mechanical stability in a thorough washing and flexibility test is under progress. Cheap, easily available, skin comfortable, disposable features and with the obtained electronic signal of fabricated conductive gauze, encourage us to design novel wound dressing, which can be integrated with human skin or garments and could serve as an assistant to monitor the status of chronic wounds.

Determination of Diffusion Coefficients and Antioxidant Activities of Ascorbic Acid in Guava Juice using Cyclic Voltammetry

Ascorbic acid is the most abundant antioxidant present in guava (Psidiumguajava L.). There had only been few studies concerning the determination of diffusion coefficient and antioxidant activity of ascorbic acid in guava juice using cyclic voltammetry specifically at varying temperatures. Thus, this study on the effect of temperature on diffusion coefficient and antioxidant activity on ascorbic acid found in guava was done using cyclic voltammetry. The temperatures tested were at 15°C, 25°C, 36°C, and 45°C. Electrodes used in the experiment were glassy carbon as the working electrode, platinum wire as the counter electrode, and Ag/AgCl electrode as the reference electrode. The results showed that the peak currents of ascorbic acid in guava juice at 15°C, 25°C, 36°C, and 45°C were -0.5720, -0.5380, -0.5000, and -0.4760 μA, respectively. The diffusion coefficients of the ascorbic acid were obtained using the Randles-Sevcik equation at all given temperatures and the values were 2.1489 x10−5, 2.1711 x10−5, 2.2070 x10−5, and 2.2250 x10−5 cm2/s, respectively. The antioxidant activities, in terms of concentration, at the said temperatures were found to be 0.3374, 0.3212, 0.3015, and 0.2899 mM, respectively. It is concluded that at higher temperature, ascorbic acid in guava juice has a higher diffusion coefficient but lower antioxidant activity. The present results can be used by other researchers doing similar work on fate and transport of the studied system.

A New Method To Evaluate Reaction Kinetics of Acids with Carbonate Rocks Using NMR Diffusion Measurements

In this work, a new method to evaluate the reaction kinetics of different stimulation fluids with carbonate rocks was introduced. NMR diffusion measurements were used to determine the acid diffusion coefficient and the acid tortuous path inside carbonate rocks. Reaction kinetics can also be evaluated using rotating disk apparatus (RDA) in which a disc is rotated in the bulk fluid at different rotational speeds. RDA does not represent the actual, restricted acid diffusion that takes place in the porous media because only the surface of the rock is exposed to the reaction and the acid is not confined in the porous media. NMR diffusion measurements can accurately describe and determine the acid restricted diffusion in porous media. The diffusion coefficient of the acid is a crucial term in describing the reaction kinetics of acids with carbonate rocks. It is also used to predict the optimum injection rate required during the acidizing treatment and the soaking time for different fluids required to remove scales and deposits in the wellbore. The restricted diffusion was determined for different fluids such as GLDA chelating agent, HEDTA chelating agent, and EDTA chelating agent. Core flooding experiments for each fluid were conducted to determine the optimum injection rate. NMR restricted diffusion measurements then were conducted to determine the restricted diffusion and in turn to determine the optimum injection rate. The optimum injection rate estimated from the NMR was compared to that from the core flooding experiments. The results were a good match showing that NMR is a suitable, reliable, and robust method to evaluate reaction kinetics of different fluids with carbonate rocks.

Impact of tumbling operating parameters on salt, water and acetic acid transfers during biltong-type meat processing

This study investigated the impact of tumbling on mass transfer mechanisms occurring in small beef meat pieces during biltong production, by measuring salt, water and acetic acid profiles within the meat for different experimental tumbling conditions. Tumbling conditions significantly impacted the solute concentration profiles, except for that of water. Values of both salt and acetic acid diffusion coefficients obtained clearly showed that tumbling increased solute transfers inside meat, with diffusion coefficient values ranging from 2 to 27 × 10−9 m2 s−1 and from 0.2 to 8.6 × 10−9 m2 s−1, respectively. The tumbling mechanical effect related to the device used impacted the most on mass transfers (p-value<0.01 for salt and acetic acid diffusion), followed by tumbling time (p-value<0.01 for salt and acetic acid diffusion), and to a lesser extent, the use of vacuum (p-value<0.01 for salt diffusion and p-value<0.05 for acetic acid diffusion). Further studies should define the best salt and acid concentration profiles generated when tumbling, so as to obtain the best trade-off between good sanitary protection of meat and a sufficiently tender and organoleptically acceptable end-product after the final drying operation.

Application of diffusion dialysis for reduction of acidity of real pregnant leach solutions containing Ni and Co ions

ABSTRACT Diffusion dialysis (DD) was proposed as a pretreatment step to reduce the acidity of real sulfate/chloride pregnant leach solutions containing cobalt(II) and nickel(II). Optimum DD conditions that enable reduction of acidity in the feed while maintaining a high rejection level of metal ions present in PLS were proposed, e.g. for 0.06 dm3/min flow of both aqueous phases H+ concentration in the dialysate reached 3.8 and 2.99 M for PLS1 and PLS2, respectively. Acid diffusion coefficients varied from 0.32 ∙10 −6 to 3.15∙10−6 m/s and decreased with increasing phase flow rates. Moreover, dialysate neutralization was beneficial for the H+ reduction in the feed.

Optical Fiber Sensors for the Detection of Hydrochloric Acid and Sea Water in Epoxy and Glass Fiber-Reinforced Polymer Composites.

Optical fiber sensors (OFSs), which rely on evanescent wave sensing for the early detection of the diffusion of water and hydrochloric acid through glass fiber-reinforced polymers (GFRPs), have been developed and tested. Epoxy and GFRP specimens, in which these sensors were embedded, were subjected to tests in artificial sea water and hydrochloric acid. The sensors were able to detect the diffusion of chemicals through the epoxy and GFRP samples on the basis of a drop in the reflected signal from the tip of the optical sensor probe. Water and hydrochloric acid diffusion coefficients were calculated from gravimetric measurements and compared with the experimental response of the OFSs. Furthermore, mechanical tests were carried out to assess the influence of the sensors on the structural integrity of the GFRP specimens.

Antioxidant Activity and Release Kinetics of Caffeic and p-Coumaric Acids from Hydrocolloid-Based Active Films for Healthy Packaged Food.

Sustainable hydrocolloid-based films containing natural antioxidants, caffeic and p-coumaric acids at different concentrations of 0.5%, 1%, 5%, and 10% w/w of polymers, were designed for packing fatty foods. Antioxidant activities and kinetics for all film formulations were assessed using radical scavenging activity (DPPH), reducing power, and iron chelating ability. Release kinetics of the antioxidants from the films into a food simulant (96% ethanol) were analyzed. The intermolecular interactions between antioxidants and polymers chains were assessed by Fourier transform infrared attenuated total reflectance (FTIR-ATR) and related to the film properties. Antioxidant activity of pure compounds (powder), showed that caffeic acid (IC50 = 4 μg/mL) had higher activity than p-coumaric acid (IC50 = 33 μg/mL). Films containing caffeic acid exhibited higher antioxidant activity, reducing power, and iron chelating ability than p-coumaric acid films. The antioxidant activity is concentration dependent. However, the percentage of release (PR) in ethanol (96%) is not influenced by the initial concentration. PR is 88% ± 9% and 82% ± 5%, respectively, for caffeic and p-coumaric acids. Determination of the partition ( Kp) and the apparent diffusion ( D) coefficients allowed better characterization of the release kinetic mechanisms. The partition coefficients of caffeic acid ( Kp = 454) and p-coumaric acid ( Kp = 480) are not influenced by the initial concentration. The diffusion coefficients ( D) of caffeic and p-coumaric acids were of same order, but they slightly increased with the antioxidant concentration and probably related to antioxidant activity. FTIR displayed that amide B and amide-III are involved in the interactions occurring between polymer chains and antioxidants. However, interactions are of only low energy and unable to significantly affect the structure of films and consequently the release kinetics.

Force Field Benchmark of Amino Acids: I. Hydration and Diffusion in Different Water Models.

Thermodynamic and kinetic properties are of critical importance for the applicability of computational models to biomolecules such as proteins. Here we present an extensive evaluation of the Amber ff99SB-ILDN force field for modeling of hydration and diffusion of amino acids with three-site (SPC, SPC/E, SPC/Eb, and TIP3P), four-site (TIP4P, TIP4P-Ew, and TIP4P/2005), and five-site (TIP5P and TIP5P-Ew) water models. Hydration free energies (HFEs) of neutral amino acid side chain analogues have little dependence on the water model, with a root-mean-square error (RMSE) of ∼1 kcal/mol from experimental observations. On the basis of the number of interacting sites in the water model, HFEs of charged side chains can be putatively classified into three groups, of which the group of three-site models lies between those of four- and five-site water models; for each group, the water model dependence is greatly eliminated when the solvent Galvani potential is considered. Some discrepancies in the location of the first hydration peak ( RRDF) in the ion-water radial distribution function between experimental and calculated observations were detected, such as a systematic underestimation of the acetate (Asp side chain) ion. The RMSE of calculated diffusion coefficients of amino acids from experiment increases linearly with the increasing diffusion coefficients of the solvent water models at infinite dilution. TIP3P has the fastest diffusivity, in line with literature findings, while the "FB" and "OPC" water model families as well as TIP4P/2005 perform well, within a relative error of 5%, and TIP4P/2005 yields the most accurate estimate for the water diffusion coefficient. All of the tested water models overestimate amino acid diffusion coefficients by approximately 40% (TIP4P/2005) to 200% (TIP3P). Scaling of protein-water interactions with TIP4P/2005 in the Amber ff99SBws and ff03ws force fields leads to more negative HFEs but has little influence on the diffusion of amino acids. The most recent FF/water combinations of ff14SB/OPC3, ff15ipq/SPC/Eb, and fb15/TIP3P-FB do not show obvious improvements in accuracy for the tested quantities. These findings here establish a benchmark that may aid in the development and improvement of classical force fields to accurately model protein dynamics and thermodynamics.

One-Step Fabrication of Methylthiazole-Functionalized Anion Exchange Membranes for Diffusion Dialysis

Anion exchange membranesusing brominated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) as starting material were prepared from one-step functionalization by 4-methylthiazole (MTz). The obtain membranes with high thermal stability and mechanical strength showed satisfied diffusion dialysis performance for acid recovery. Specifically, when the optimal membrane was evaluated to recover acid from the simulated iron polishing waste solution (1.0 mol·L-1 FeCl2 + 0.2 mol·L-1 HCl), its acid diffusion coefficient (UH+) was 0.019 m h-1 and separation factor was 40.1 at 25°C, both of these two parameters are much higher than the corresponding values of the commercial DF-120 membrane, suggesting the great potential in the practical application for acid recovery.