Charged Organic Solutes Research Articles

On the Use of Permselectivity to Describe the Selective Transfer of Organic Acids in Electrodialysis.

The increasing number of investigations on the use of electrodialysis (ED) in bio-refinery requires a better understanding and tools to evaluate and describe the transfer of charged organic solutes. This study focuses, as an example, on the selective transfer of acetate, butyrate, and chloride (used as a reference), characterized by using permselectivity. It is shown that permselectivity between two anions does not depend on the total ion concentration, neither on the ion proportions, current intensity, or time nor on the presence of an additional compound. Therefore, it is demonstrated that permselectivity can be used to model the evolution of the stream composition during ED, even at high demineralization rates. Indeed, a very good agreement is found between experimental and calculated values. This study and the application of permselectivity as a tool, as developed in this paper, could be highly valuable for a wide range of applications in electrodialysis.

Unravelling the fouling behavior of anion-exchange membrane (AEM) by organic solute of varying characteristics

Organic fouling is a major obstacle in various ion-exchange membrane based electrochemical systems. Particularly, the correlation between the main characteristics of organic solute and fouling of anion-exchange membrane (AEM) is still controversial. Herein, AEM fouling by four target charged organic solutes of distinct charge, hydrophobicity, molecular weight and solute size was explored in electrodialysis, evaluated using three fouling indicators (i.e., transition time, transmembrane migration, and membrane resistance). Sodium dodecyl sulfate (SDS) compared to the other three much larger organic solutes induced immediate rising of transmembrane electrical potential (TMEP), i.e., transition time approximating zero. Surprisingly, all organic solutes penetrated across the nano-scaled membrane, supported by the total organic carbon (TOC) content of concentrate. Then, in each fouling case, membrane impedance analysis highlighted that the resistance of membrane bulk (Rm) was dominant compared to those of the interfaces and external fouling layer, thus suggesting occurrence of severe internal fouling. Finally, correlation analysis using R language demonstrated that the electronegativity and hydrophobicity of organic solutes were highly responsible for AEM fouling (contribution >70%) under each evaluation regime, thus being more important than molecule weight and size. These results bring an insight about the relative importance of and can be useful for developing future more appropriate anti-fouling strategies for ion-exchange membranes subjected to organic fouling.

Desalination of effluents with highly concentrated salt by nanofiltration: From laboratory to pilot-plant

Nanofiltration (NF) has been widely used for treatment of industrial effluents, but very few work concerns NF process in concentrated saline solution, especially for NF-desalination aiming at permeation of monovalent salts and retention of organic solutes. In this study, NF270 membrane was chosen to treat model solutions and three industrial effluents with highly concentrated salt (crude iron dextran solution, iminodiacetic acid mother liquor, and raw soy sauce), showing that with increase of salt concentration, the retention of all the solutes decreased while concentration polarization was increased. In the presence of charged organic solutes, inorganic salt retention would decline, even negative retention of monovalent salt was found. Increasing pH would induce membrane swelling in saline solution, which might be caused by the higher local salt concentration around the membrane polymers at higher pH. As NF-desalination of industrial effluents with highly concentrated salt was scaled up from laboratory to pilot-plant, the dead-end stirred filtration at constant flux could provide some important information for pilot-plant tests, such as membrane selection, optimum operating parameters and mechanism analysis, but it was necessary to re-optimize operating mode and method for crossflow filtration at constant pressure, in order to control the concentration polarization at high salt concentration.

Construction and validation of a full-scale model for rejection of organic micropollutants by NF membranes

A transport model for the rejection of charged and uncharged organic solutes was derived and validated in this paper. The rejection of 21 pharmaceuticals and 6 pesticides was determined on a pilot plant, operating at 75%, 82.5% and 90% recovery. For the neutral organic solutes, a solute transport model was constructed, based on a convection–diffusion model. The partition coefficient of the solutes in the membrane phase was determined with a steric model, and then compared with a fitted partition coefficient, incorporating solute–membrane affinity. For the charged solutes, the “charge concentration polarisation” concept was used to model the rejection. Both models for charged and uncharged organic solutes were then incorporated into a general model, and the influence of hydrodynamic concentration polarisation was introduced into the model. Afterwards, the general model was translated to a full-scale rejection model, which was then validated. The rejection model seemed to fit/predict the experimentally determined rejection values for neutral, as well as charged organic solutes quite well, at all the different feed water recoveries used in this study. The use of the steric model for the partition coefficient led to an overestimation of rejection values, because solute–membrane affinity was not incorporated.

Catanionic surfactant vesicles for electrostatic molecular sequestration and separation

Mixtures of oppositely charged surfactants, commonly called catanionic mixtures, are one of the most interesting and promising areas of colloidal chemistry. In this paper we review our previous work and report new results on electrostatic adsorption of organic solutes and DNA to the exterior surfaces of catanionic, unilamellar vesicles which form spontaneously in mixtures of sodium dodecylbenzenesulfonate (SDBS) and cetyltrimethylammonium tosylate (CTAT). Our group, along with others, has shown that organic ions and polyelectrolytes will bind to the exterior surface of oppositely charged catanionic vesicles through interactions with unpaired ionic surfactants present in the vesicle bilayer. The electrostatic sequestration of organic ions with catanionic vesicles is extremely efficient with excellent long-term stability and can be used to perform separations on mixtures of charged organic solutes. Using regular solution theory extended to vesicle-forming surfactant mixtures, we can understand how the composition of the bilayer changes with surfactant dilution, and we study this effect using fluorescence correlation spectroscopy (FCS). We employ FCS to make sensitive measurements of bilayer adsorption and compare the adsorption of a small molecular probe with that of a single-stranded, dye-labeled DNA molecule. From these FCS studies, adsorption isotherms can be obtained that report on the relative binding strengths of the two systems. The results show that DNA binds much more strongly to the exterior surface of positively charged catanionic vesicles, and can even stabilize vesicles at very low surfactant concentrations near the critical aggregation concentration (cac).

Design of new enzyme stabilizers inspired by glycosides of hyperthermophilic microorganisms

In response to stressful conditions like supra-optimal salinity in the growth medium or temperature, many microorganisms accumulate low-molecular-mass organic compounds known as compatible solutes. In contrast with mesophiles that accumulate neutral or zwitterionic compounds, the solutes of hyperthermophiles are typically negatively charged. (2 R)-2-(α- d-Mannopyranosyl)glycerate (herein abbreviated as mannosylglycerate) is one of the most widespread solutes among thermophilic and hyperthermophilic prokaryotes. In this work, several molecules chemically related to mannosylglycerate were synthesized, namely (2 S)-2-(1- O-α- d-mannopyranosyl)propionate, 2-(1- O-α- d-mannopyranosyl)acetate, (2 R)-2-(1- O-α- d-glucopyranosyl)glycerate and 1- O-(2-glyceryl)-α- d-mannopyranoside. The effectiveness of the newly synthesized compounds for the protection of model enzymes against heat-induced denaturation, aggregation and inactivation was evaluated, using differential scanning calorimetry, light scattering and measurements of residual activity. For comparison, the protection induced by natural compatible solutes, either neutral (e.g., trehalose, glycerol, ectoine) or negatively charged (di- myo-inositol-1,3′-phosphate and diglycerol phosphate), was assessed. Phosphate, sulfate, acetate and KCl were also included in the assays to rank the solutes and new compounds in the Hofmeister series. The data demonstrate the superiority of charged organic solutes as thermo-stabilizers of enzymes and strongly support the view that the extent of protein stabilization rendered by those solutes depends clearly on the specific solute/enzyme examined. The relevance of these findings to our knowledge on the mode of action of charged solutes is discussed.

The role of electrostatic interactions on the rejection of organic solutes in aqueous solutions with nanofiltration

The effects of electrostatic interactions on the rejection of organic solutes with nanofiltration membranes were investigated. For two different membranes, the rejection of selected organic acids, positively and negatively charged pharmaceuticals and neutral pharmaceuticals was investigated at different feed water chemistries (different ionic strengths and pH conditions, with and without the presence of NOM and divalent cations). It was concluded that for negatively charged membranes, electrostatic repulsion leads to an increase of the rejection of negatively charged solutes and electrostatic attraction leads to a decrease of the rejection of positively charged solutes, compared to neutral solutes. Neutral and positively charged solutes engage in hydrophobic interactions with negatively charged membranes, whereas negatively charged solutes do not engage in hydrophobic interactions since they cannot approach the membrane surface. This provides proof for the theory of an increased concentration of positively charged organic solutes and a decreased concentration of negatively charged organic solutes at the membrane surface compared to the bulk fluid. This concept may be denoted as “charge concentration polarisation”. The concept was further used as a modelling tool to predict the effects of electrostatic interactions on the rejection of trace organic solutes.

Rejection of trace organic pollutants with high pressure membranes (NF/RO)

AbstractThis article presents a modeling approach for the rejection of trace organic pollutants in high‐pressure membranes. The rejection values of uncharged organic solutes with a wide range of solute size and hydrophobicity are determined. Sigmoidal rejection curves are constructed and modeled for solutes of different hydrophobicity. The model is based on a log‐normal pore size distribution model. A model is also presented to model the rejection of charged organic solutes, based on the rejection of uncharged solutes and the concept of a “charge concentration polarization.” Moreover, scale‐up issues arising when translating results from bench‐scale units to full‐scale plants are addressed, by assessing the viability of a full‐scale rejection model. The full‐scale model is based on a convection‐diffusion model for the transport of organic solutes through the high‐pressure membranes and the use of mass balances in the system. © 2008 American Institute of Chemical Engineers Environ Prog, 2008

Di-myo-inositol phosphate and novel UDP-sugars accumulate in the extreme hyperthermophile Pyrolobus fumarii

The archaeon Pyrolobus fumarii, one of the most extreme members of hyperthermophiles known thus far, is able to grow at temperatures up to 113 degrees C. Over a decade after the description of this organism our knowledge about the structures and strategies underlying its remarkable thermal resistance remains incipient. The accumulation of a restricted number of charged organic solutes is a common response to heat stress in hyperthermophilic organisms and accordingly their role in thermoprotection has been often postulated. In this work, the organic solute pool of P. fumarii was characterized using 1H, 13C, and 31P NMR. Di-myo-inositol phosphate was the major solute (0.21 micromol/mg protein), reinforcing the correlation between the occurrence of this solute and hyperthermophily; in addition, UDP-sugars (total concentration 0.11 micromol/mg protein) were present. The structures of the two major UDP-sugars were identified as UDP-alpha-GlcNAc3NAc and UDP-alpha-GlcNAc3NAc-(4<--1)-beta-GlcpNAc3NAc. Interestingly, the latter compound appears to be derived from the first one by addition of a 2,3-N-acetylglucoronic acid unit, suggesting that these UDP-sugars are intermediates of an N-linked glycosylation pathway. To our knowledge the UDP-disaccharide has not been reported elsewhere. The physiological roles of these organic solutes are discussed.

Polarization Effects in Aqueous and Nonaqueous Solutions.

Polarization effects in aqueous and nonaqueous solutions were analyzed for nine neutral and three charged organic solutes by the SM8 universal implicit solvation model and class IV partial atomic charges based on Charge Model 4M (CM4M) with the M06-2X density functional. The CM4M partial atomic charges in neutral and ionic solutes and in the corresponding clustered solutes (supersolutes), which included one solute molecule and one or two solvent molecules, were modeled in three solvents (benzene, methylene chloride, and water) and compared to those in the gas phase. The use of the supersolute approach (microsolvation) allows one to account for charge transfer from the solute to the solvent, and we find charge transfers as large as 0.06 atomic units for neutral solutes (pyridine in water) and 0.32 atomic units for ions (methoxide anion in water). Relaxation of the electronic structure of the solute in the presence of solvent increases the polarization free energy of the neutral solutes studied here, on average, by 16% in benzene, 30% in methylene chloride, and 43% in water. The increase for the ions in water averaged 43%.

Surfactant Vesicles for High-Efficiency Capture and Separation of Charged Organic Solutes

We demonstrate the unique ability of catanionic vesicles, formed by mixing single-tailed cationic and anionic surfactants, to capture ionic solutes with remarkable efficiency. In an initial study (Wang, X.; Danoff, E. J.; Sinkov, N. A.; Lee, J.-H.; Raghavan, S. R.; English, D. S. Langmuir 2006, 22, 6461) with vesicles formed from cetyl trimethylammonium tosylate (CTAT) and sodium dodecylbenzenesulfonate (SDBS), we showed that CTAT-rich (cationic) vesicles could capture the anionic solute carboxyfluorescein with high efficiency (22%) and that the solute was retained by the vesicles for very long times (t1/2 = 84 days). Here we expand on these findings by investigating the interactions of both anionic and cationic solutes, including the chemotherapeutic agent doxorubicin, with both CTAT-rich and SDBS-rich vesicles. The ability of these vesicles to capture and hold dyes is extremely efficient (>20%) when the excess charge of the vesicle bilayer is opposite that of the solute (i.e., for anionic solutes in CTAT-rich vesicles and for cationic solutes in SDBS-rich vesicles). This charge-dependent effect is strong enough to enable the use of vesicles to selectively capture and separate an oppositely charged solute from a mixture of solutes. Our results suggest that catanionic surfactant vesicles could be useful for a variety of separation and drug delivery applications because of their unique properties and long-term stability.

A study on the removal of organic acids from wastewaters using nanofiltration membranes

This study aimed to evaluate the application potential of nanofiltration (NF) membranes for the rejection of organic acids in wastewaters. The rejection tests at different feed water chemistries, including pH and concentration, were performed on a laboratory scale using five different organic acids. The rejection of selected organic acids by the ES10 and NF270 membranes increased with increasing pH, depending on the degree of dissociation. The rejection of succinic and citric acids, which have molecular weights ( M Ws) larger than or closer to the molecular weight cutoffs (MWCOs) of employed NF membranes, was over 90% irrespective of operating pressure. Contrarily, the rejection of organic acids with M Ws much smaller than MWCOs of the NF membranes increased gradually with increasing the applied pressure. The degree of organic acid rejection, except for formic acid, by the NF membranes was not significantly changed when altered in feed concentrations of 50–500 mg L −1. The rejection degree of charged organic solutes with M W much smaller than MWCO of a NF membrane can be negatively affected by the presence of salts. Results of the short-term filtration test using an actual anaerobic effluent revealed that the NF270 efficiently removed organic acids from the wastewater. The increase of DOC rejection with filtration time could be explained by increase of electrostatic repulsion between membrane and dissociated organic acid and by membrane fouling. NF process showed considerable potential as an advanced wastewater treatment process for removing organic acids in wastewaters.

The role of membrane surface charge and solute physico-chemical properties in the rejection of organic acids by NF membranes

The objective of this study was to investigate the contribution of electrostatic interactions to the rejection of selected organic acids by nanofiltration membranes. Effective membrane surface charge (determined by two methods of zeta potential measurements) of two commercial nanofiltration membranes was examined at different pH values and feed water chemistries. Six different organic acids were selected for this study representing typical physico-chemical properties of emerging organic trace pollutants. Findings of this study indicated that the rejection of negatively charged organic acids was larger than expected based on steric exclusion and was primarily driven by the surface charge of the membrane and correlated with the degree of ionization of the solute. Increasing feed water pH resulted in an increased negative surface charge, an increased percentage of solutes in the deprotonated state and an increased rejection through electrostatic repulsion. The rejection of the pharmaceutical residue ibuprofen, an organic acid with hydrophobic properties, was also pH dependent, but at pH values below the p K a ibuprofen adsorbed and partitioned through the membrane. At pH above the p K a, adsorption of ibuprofen was minimal due to an increased solubility and the dominant role of electrostatic repulsion. The presence of calcium in the feed water lowered the effective membrane surface charge (as determined by electrophoretic mobility measurements) of both membranes tested, however, rejection of negatively charged organic solutes decreased only for membranes with a molecular weight cut-off larger than the solute molecular weight.

Bonded Reverse Phase Ion Exchange Columns for the Liquid Chromatographic Separations of Neutral and Ionic Organic Compounds

Octadecylsilane was chemically bonded in situ on cation and anion exchange packings. The columns were tested for the liquid chromatographic separations of neutral and charged organic solutes which included nucleotides, polynuclear aromatic hydrocarbons, amines, carboxylic acids, and organometallic compounds. While some separations were effected predominantly by either the ion exchange sites or the reverse phase moieties, most separations appeared to be the combined effects of both stationary phases. The reverse phase partitioning, apparently induced by the solvophobic interaction, can make the elution volume and order of a charged solute significantly different from that found in a conventional ion exchange column. The mixed mode of ion exchange and reverse phase solvophobic interactions are illustrated.